Paper/patches/server/0902-Add-Alternate-Current-redstone-implementation.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Space Walker <spacedoesrs@gmail.com>
Date: Wed, 8 Jun 2022 18:47:18 +0200
Subject: [PATCH] Add Alternate Current redstone implementation

Author: Space Walker <spacedoesrs@gmail.com>

Original license: MIT
Original project: https://github.com/SpaceWalkerRS/alternate-current

This patch adds Alternate Current's redstone implementation as an alternative to vanilla and Eigencraft's.
Performance of (de)powering redstone dust is many times faster than vanilla, and even exceeds Eigencraft.
Similar to Eigencraft, Alternate Current heavily changes the update order of redstone dust. This means any contraption that
is location dependent in vanilla will either work everywhere or nowhere when using Alternate Current/Eigencraft. Beyond that
parity issues should be rare for both implementations, though Alternate Current has not been tested as thoroughly, so I
cannot comment on how the two compare in that aspect.

Alternate Current is more invasive than Eigencraft, though some of the modifications can be removed with only a minor
performance penalty in a small number of cases. Alternate Current needs the following modifications:
* Level/ServerLevel: Each level has its own 'wire handler' that handles redstone dust power changes.
* RedStoneWireBlock: Replace calls to vanilla's or Eigencraft's methods for handling power changes with calls to
Alternate Current's wire handler.
* (optional) Every power emitter's block class: new methods added to these classes make it easier for Alternate Current
to check if any block is a potential power source.

The use-faster-eigencraft-redstone config has been replaced with the redstone-implementation config, which can be used to
switch between the vanilla, Eigencraft, and Alternate Current implementations.

diff --git a/src/main/java/alternate/current/wire/LevelHelper.java b/src/main/java/alternate/current/wire/LevelHelper.java
new file mode 100644
index 0000000000000000000000000000000000000000..f55c5c67b8461e9ef5614ea1a37f6e2866f39be3
--- /dev/null
+++ b/src/main/java/alternate/current/wire/LevelHelper.java
@@ -0,0 +1,65 @@
+package alternate.current.wire;
+
+import org.bukkit.event.block.BlockRedstoneEvent;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ChunkStatus;
+import net.minecraft.world.level.chunk.LevelChunkSection;
+
+public class LevelHelper {
+
+    static int doRedstoneEvent(ServerLevel level, BlockPos pos, int prevPower, int newPower) {
+        BlockRedstoneEvent event = new BlockRedstoneEvent(level.getWorld().getBlockAt(pos.getX(), pos.getY(), pos.getZ()), prevPower, newPower);
+        level.getCraftServer().getPluginManager().callEvent(event);
+
+        return event.getNewCurrent();
+    }
+
+    /**
+     * An optimized version of {@link net.minecraft.world.level.Level#setBlock
+     * Level.setBlock}. Since this method is only used to update redstone wire block
+     * states, lighting checks, height map updates, and block entity updates are
+     * omitted.
+     */
+    static boolean setWireState(ServerLevel level, BlockPos pos, BlockState state, boolean updateNeighborShapes) {
+        int y = pos.getY();
+
+        if (y < level.getMinBuildHeight() || y >= level.getMaxBuildHeight()) {
+            return false;
+        }
+
+        int x = pos.getX();
+        int z = pos.getZ();
+        int index = level.getSectionIndex(y);
+
+        ChunkAccess chunk = level.getChunk(x >> 4, z >> 4, ChunkStatus.FULL, true);
+        LevelChunkSection section = chunk.getSections()[index];
+
+        if (section == null) {
+            return false; // we should never get here
+        }
+
+        BlockState prevState = section.setBlockState(x & 15, y & 15, z & 15, state);
+
+        if (state == prevState) {
+            return false;
+        }
+
+        // notify clients of the BlockState change
+        level.getChunkSource().blockChanged(pos);
+        // mark the chunk for saving
+        chunk.setUnsaved(true);
+
+        if (updateNeighborShapes) {
+            prevState.updateIndirectNeighbourShapes(level, pos, Block.UPDATE_CLIENTS);
+            state.updateNeighbourShapes(level, pos, Block.UPDATE_CLIENTS);
+            state.updateIndirectNeighbourShapes(level, pos, Block.UPDATE_CLIENTS);
+        }
+
+        return true;
+    }
+}
diff --git a/src/main/java/alternate/current/wire/Node.java b/src/main/java/alternate/current/wire/Node.java
new file mode 100644
index 0000000000000000000000000000000000000000..3e25047fd8db65bf34bb39ae9a07fe01b5b61786
--- /dev/null
+++ b/src/main/java/alternate/current/wire/Node.java
@@ -0,0 +1,113 @@
+package alternate.current.wire;
+
+import java.util.Arrays;
+
+import alternate.current.wire.WireHandler.Directions;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+
+/**
+ * A Node represents a block in the world. It also holds a few other pieces of
+ * information that speed up the calculations in the WireHandler class.
+ * 
+ * @author Space Walker
+ */
+public class Node {
+
+    // flags that encode the Node type
+    private static final int CONDUCTOR = 0b01;
+    private static final int SOURCE    = 0b10;
+
+    final ServerLevel level;
+    final Node[] neighbors;
+
+    BlockPos pos;
+    BlockState state;
+    boolean invalid;
+
+    private int flags;
+
+    /** The previous node in the update queue. */
+    Node prev;
+    /** The next node in the update queue. */
+    Node next;
+    /** The priority with which this node was queued. */
+    int priority;
+    /** The wire that queued this node for an update. */
+    WireNode neighborWire;
+
+    Node(ServerLevel level) {
+        this.level = level;
+        this.neighbors = new Node[Directions.ALL.length];
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (!(obj instanceof Node)) {
+            return false;
+        }
+
+        Node node = (Node)obj;
+
+        return level == node.level && pos.equals(node.pos);
+    }
+
+    @Override
+    public int hashCode() {
+        return pos.hashCode();
+    }
+
+    Node update(BlockPos pos, BlockState state, boolean clearNeighbors) {
+        if (state.is(Blocks.REDSTONE_WIRE)) {
+            throw new IllegalStateException("Cannot update a regular Node to a WireNode!");
+        }
+
+        if (clearNeighbors) {
+            Arrays.fill(neighbors, null);
+        }
+
+        this.pos = pos.immutable();
+        this.state = state;
+        this.invalid = false;
+
+        this.flags = 0;
+
+        if (this.state.isRedstoneConductor(this.level, this.pos)) {
+            this.flags |= CONDUCTOR;
+        }
+        if (this.state.isSignalSource()) {
+            this.flags |= SOURCE;
+        }
+
+        return this;
+    }
+
+    /**
+     * Determine the priority with which this node should be queued.
+     */
+    int priority() {
+        return neighborWire.priority;
+    }
+
+    public boolean isWire() {
+        return false;
+    }
+
+    public boolean isConductor() {
+        return (flags & CONDUCTOR) != 0;
+    }
+
+    public boolean isSignalSource() {
+        return (flags & SOURCE) != 0;
+    }
+
+    public WireNode asWire() {
+        throw new UnsupportedOperationException("Not a WireNode!");
+    }
+}
diff --git a/src/main/java/alternate/current/wire/UpdateQueue.java b/src/main/java/alternate/current/wire/UpdateQueue.java
new file mode 100644
index 0000000000000000000000000000000000000000..3afe0ef9dfe16c2dc144b553069286b6e72eac1b
--- /dev/null
+++ b/src/main/java/alternate/current/wire/UpdateQueue.java
@@ -0,0 +1,211 @@
+package alternate.current.wire;
+
+import java.util.AbstractQueue;
+import java.util.Arrays;
+import java.util.Iterator;
+
+import net.minecraft.world.level.redstone.Redstone;
+
+public class UpdateQueue extends AbstractQueue<Node> {
+
+    private static final int OFFSET = -Redstone.SIGNAL_MIN;
+
+    /** The last node for each priority value. */
+    private final Node[] tails;
+
+    private Node head;
+    private Node tail;
+
+    private int size;
+
+    public UpdateQueue() {
+        this.tails = new Node[(Redstone.SIGNAL_MAX + OFFSET) + 1];
+    }
+
+    @Override
+    public boolean offer(Node node) {
+        if (node == null) {
+            throw new NullPointerException();
+        }
+
+        int priority = node.priority();
+
+        if (contains(node)) {
+            if (node.priority == priority) {
+                // already queued with this priority; exit
+                return false;
+            } else {
+                // already queued with different priority; move it
+                move(node, priority);
+            }
+        } else {
+            insert(node, priority);
+        }
+
+        return true;
+    }
+
+    @Override
+    public Node poll() {
+        if (head == null) {
+            return null;
+        }
+
+        Node node = head;
+        Node next = node.next;
+
+        if (next == null) {
+            clear(); // reset the tails array
+        } else {
+            if (node.priority != next.priority) {
+                // If the head is also a tail, its entry in the array
+                // can be cleared; there is no previous node with the
+                // same priority to take its place.
+                tails[node.priority + OFFSET] = null;
+            }
+
+            node.next = null;
+            next.prev = null;
+            head = next;
+
+            size--;
+        }
+
+        return node;
+    }
+
+    @Override
+    public Node peek() {
+        return head;
+    }
+
+    @Override
+    public void clear() {
+        for (Node node = head; node != null; ) {
+            Node n = node;
+            node = node.next;
+
+            n.prev = null;
+            n.next = null;
+        }
+
+        Arrays.fill(tails, null);
+
+        head = null;
+        tail = null;
+
+        size = 0;
+    }
+
+    @Override
+    public Iterator<Node> iterator() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public int size() {
+        return size;
+    }
+
+    public boolean contains(Node node) {
+        return node == head || node.prev != null;
+    }
+
+    private void move(Node node, int priority) {
+        remove(node);
+        insert(node, priority);
+    }
+
+    private void remove(Node node) {
+        Node prev = node.prev;
+        Node next = node.next;
+
+        if (node == tail || node.priority != next.priority) {
+            // assign a new tail for this node's priority
+            if (node == head || node.priority != prev.priority) {
+                // there is no other node with the same priority; clear
+                tails[node.priority + OFFSET] = null;
+            } else {
+                // the previous node in the queue becomes the tail
+                tails[node.priority + OFFSET] = prev;
+            }
+        }
+
+        if (node == head) {
+            head = next;
+        } else {
+            prev.next = next;
+        }
+        if (node == tail) {
+            tail = prev;
+        } else {
+            next.prev = prev;
+        }
+
+        node.prev = null;
+        node.next = null;
+
+        size--;
+    }
+
+    private void insert(Node node, int priority) {
+        node.priority = priority;
+
+        // nodes are sorted by priority (highest to lowest)
+        // nodes with the same priority are ordered FIFO
+        if (head == null) {
+            // first element in this queue \o/
+            head = tail = node;
+        } else if (priority > head.priority) {
+            linkHead(node);
+        } else if (priority <= tail.priority) {
+            linkTail(node);
+        } else {
+            // since the node is neither the head nor the tail
+            // findPrev is guaranteed to find a non-null element
+            linkAfter(findPrev(node), node);
+        }
+
+        tails[priority + OFFSET] = node;
+
+        size++;
+    }
+
+    private void linkHead(Node node) {
+        node.next = head;
+        head.prev = node;
+        head = node;
+    }
+
+    private void linkTail(Node node) {
+        tail.next = node;
+        node.prev = tail;
+        tail = node;
+    }
+
+    private void linkAfter(Node prev, Node node) {
+        linkBetween(prev, node, prev.next);
+    }
+
+    private void linkBetween(Node prev, Node node, Node next) {
+        prev.next = node;
+        node.prev = prev;
+
+        node.next = next;
+        next.prev = node;
+    }
+
+    private Node findPrev(Node node) {
+        Node prev = null;
+
+        for (int i = node.priority + OFFSET; i < tails.length; i++) {
+            prev = tails[i];
+
+            if (prev != null) {
+                break;
+            }
+        }
+
+        return prev;
+    }
+}
diff --git a/src/main/java/alternate/current/wire/WireConnection.java b/src/main/java/alternate/current/wire/WireConnection.java
new file mode 100644
index 0000000000000000000000000000000000000000..4fd8cb29024330397cfe4cbc1f237d285bfb7b3e
--- /dev/null
+++ b/src/main/java/alternate/current/wire/WireConnection.java
@@ -0,0 +1,30 @@
+package alternate.current.wire;
+
+/**
+ * This class represents a connection between some WireNode (the 'owner') and a
+ * neighboring WireNode. Two wires are considered to be connected if power can
+ * flow from one wire to the other (and/or vice versa).
+ * 
+ * @author Space Walker
+ */
+public class WireConnection {
+
+    /** The connected wire. */
+    final WireNode wire;
+    /** Cardinal direction to the connected wire. */
+    final int iDir;
+    /** True if the owner of the connection can provide power to the connected wire. */
+    final boolean offer;
+    /** True if the connected wire can provide power to the owner of the connection. */
+    final boolean accept;
+
+    /** The next connection in the sequence. */
+    WireConnection next;
+
+    WireConnection(WireNode wire, int iDir, boolean offer, boolean accept) {
+        this.wire = wire;
+        this.iDir = iDir;
+        this.offer = offer;
+        this.accept = accept;
+    }
+}
diff --git a/src/main/java/alternate/current/wire/WireConnectionManager.java b/src/main/java/alternate/current/wire/WireConnectionManager.java
new file mode 100644
index 0000000000000000000000000000000000000000..5a7209f05b549c222f6c9bc2af2a35790964947e
--- /dev/null
+++ b/src/main/java/alternate/current/wire/WireConnectionManager.java
@@ -0,0 +1,136 @@
+package alternate.current.wire;
+
+import java.util.Arrays;
+import java.util.function.Consumer;
+
+import alternate.current.wire.WireHandler.Directions;
+import alternate.current.wire.WireHandler.NodeProvider;
+
+public class WireConnectionManager {
+
+    /** The owner of these connections. */
+    final WireNode owner;
+
+    /** The first connection for each cardinal direction. */
+    private final WireConnection[] heads;
+
+    private WireConnection head;
+    private WireConnection tail;
+
+    /** The total number of connections. */
+    int total;
+
+    /**
+     * A 4 bit number that encodes in which direction(s) the owner has connections
+     * to other wires.
+     */
+    private int flowTotal;
+    /** The direction of flow based connections to other wires. */
+    int iFlowDir;
+
+    WireConnectionManager(WireNode owner) {
+        this.owner = owner;
+
+        this.heads = new WireConnection[Directions.HORIZONTAL.length];
+
+        this.total = 0;
+
+        this.flowTotal = 0;
+        this.iFlowDir = -1;
+    }
+
+    void set(NodeProvider nodes) {
+        if (total > 0) {
+            clear();
+        }
+
+        boolean belowIsConductor = nodes.getNeighbor(owner, Directions.DOWN).isConductor();
+        boolean aboveIsConductor = nodes.getNeighbor(owner, Directions.UP).isConductor();
+
+        for (int iDir = 0; iDir < Directions.HORIZONTAL.length; iDir++) {
+            Node neighbor = nodes.getNeighbor(owner, iDir);
+
+            if (neighbor.isWire()) {
+                add(neighbor.asWire(), iDir, true, true);
+
+                continue;
+            }
+
+            boolean sideIsConductor = neighbor.isConductor();
+
+            if (!sideIsConductor) {
+                Node node = nodes.getNeighbor(neighbor, Directions.DOWN);
+
+                if (node.isWire()) {
+                    add(node.asWire(), iDir, belowIsConductor, true);
+                }
+            }
+            if (!aboveIsConductor) {
+                Node node = nodes.getNeighbor(neighbor, Directions.UP);
+
+                if (node.isWire()) {
+                    add(node.asWire(), iDir, true, sideIsConductor);
+                }
+            }
+        }
+
+        if (total > 0) {
+            iFlowDir = WireHandler.FLOW_IN_TO_FLOW_OUT[flowTotal];
+        }
+    }
+
+    private void clear() {
+        Arrays.fill(heads, null);
+
+        head = null;
+        tail = null;
+
+        total = 0;
+
+        flowTotal = 0;
+        iFlowDir = -1;
+    }
+
+    private void add(WireNode wire, int iDir, boolean offer, boolean accept) {
+        add(new WireConnection(wire, iDir, offer, accept));
+    }
+
+    private void add(WireConnection connection) {
+        if (head == null) {
+            head = connection;
+            tail = connection;
+        } else {
+            tail.next = connection;
+            tail = connection;
+        }
+
+        total++;
+
+        if (heads[connection.iDir] == null) {
+            heads[connection.iDir] = connection;
+            flowTotal |= (1 << connection.iDir);
+        }
+    }
+
+    /**
+     * Iterate over all connections. Use this method if the iteration order is not
+     * important.
+     */
+    void forEach(Consumer<WireConnection> consumer) {
+        for (WireConnection c = head; c != null; c = c.next) {
+            consumer.accept(c);
+        }
+    }
+
+    /**
+     * Iterate over all connections. Use this method if the iteration order is
+     * important.
+     */
+    void forEach(Consumer<WireConnection> consumer, int iFlowDir) {
+        for (int iDir : WireHandler.CARDINAL_UPDATE_ORDERS[iFlowDir]) {
+            for (WireConnection c = heads[iDir]; c != null && c.iDir == iDir; c = c.next) {
+                consumer.accept(c);
+            }
+        }
+    }
+}
diff --git a/src/main/java/alternate/current/wire/WireHandler.java b/src/main/java/alternate/current/wire/WireHandler.java
new file mode 100644
index 0000000000000000000000000000000000000000..bdc4969e157de034929c8a0ffebc62075aad59f8
--- /dev/null
+++ b/src/main/java/alternate/current/wire/WireHandler.java
@@ -0,0 +1,1179 @@
+package alternate.current.wire;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Queue;
+import java.util.function.Consumer;
+
+import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectMap.Entry;
+import it.unimi.dsi.fastutil.longs.Long2ObjectMaps;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.redstone.Redstone;
+
+/**
+ * This class handles power changes for redstone wire. The algorithm was
+ * designed with the following goals in mind:
+ * <br>
+ * 1. Minimize the number of times a wire checks its surroundings to determine
+ * its power level.
+ * <br>
+ * 2. Minimize the number of block and shape updates emitted.
+ * <br>
+ * 3. Emit block and shape updates in a deterministic, non-locational order,
+ * fixing bug MC-11193.
+ * 
+ * <p>
+ * In Vanilla redstone wire is laggy because it fails on points 1 and 2.
+ * 
+ * <p>
+ * Redstone wire updates recursively and each wire calculates its power level in
+ * isolation rather than in the context of the network it is a part of. This
+ * means a wire in a grid can change its power level over half a dozen times
+ * before settling on its final value. This problem used to be worse in 1.13 and
+ * below, where a wire would only decrease its power level by 1 at a time.
+ * 
+ * <p>
+ * In addition to this, a wire emits 42 block updates and up to 22 shape updates
+ * each time it changes its power level.
+ * 
+ * <p>
+ * Of those 42 block updates, 6 are to itself, which are thus not only
+ * redundant, but a big source of lag, since those cause the wire to
+ * unnecessarily re-calculate its power level. A block only has 24 neighbors
+ * within a Manhattan distance of 2, meaning 12 of the remaining 36 block
+ * updates are duplicates and thus also redundant.
+ * 
+ * <p>
+ * Of the 22 shape updates, only 6 are strictly necessary. The other 16 are sent
+ * to blocks diagonally above and below. These are necessary if a wire changes
+ * its connections, but not when it changes its power level.
+ * 
+ * <p>
+ * Redstone wire in Vanilla also fails on point 3, though this is more of a
+ * quality-of-life issue than a lag issue. The recursive nature in which it
+ * updates, combined with the location-dependent order in which each wire
+ * updates its neighbors, makes the order in which neighbors of a wire network
+ * are updated incredibly inconsistent and seemingly random.
+ * 
+ * <p>
+ * Alternate Current fixes each of these problems as follows.
+ * 
+ * <p>
+ * 1. To make sure a wire calculates its power level as little as possible, we
+ * remove the recursive nature in which redstone wire updates in Vanilla.
+ * Instead, we build a network of connected wires, find those wires that receive
+ * redstone power from "outside" the network, and spread the power from there.
+ * This has a few advantages:
+ * <br>
+ * - Each wire checks for power from non-wire components just once, and from
+ * nearby wires just twice.
+ * <br>
+ * - Each wire only sets its power level in the world once. This is important,
+ * because calls to Level.setBlock are even more expensive than calls to
+ * Level.getBlockState.
+ * 
+ * <p>
+ * 2. There are 2 obvious ways in which we can reduce the number of block and
+ * shape updates.
+ * <br>
+ * - Get rid of the 18 redundant block updates and 16 redundant shape updates,
+ * so each wire only emits 24 block updates and 6 shape updates whenever it
+ * changes its power level.
+ * <br>
+ * - Only emit block updates and shape updates once a wire reaches its final
+ * power level, rather than at each intermediary stage.
+ * <br>
+ * For an individual wire, these two optimizations are the best you can do, but
+ * for an entire grid, you can do better!
+ * 
+ * <p>
+ * Since we calculate the power of the entire network, sending block and shape
+ * updates to the wires in it is redundant. Removing those updates can reduce
+ * the number of block and shape updates by up to 20%.
+ * 
+ * <p>
+ * 3. To make the order of block updates to neighbors of a network
+ * deterministic, the first thing we must do is to replace the location-
+ * dependent order in which a wire updates its neighbors. Instead, we base it on
+ * the direction of power flow. This part of the algorithm was heavily inspired
+ * by theosib's 'RedstoneWireTurbo', which you can read more about in theosib's
+ * comment on Mojira <a href="https://bugs.mojang.com/browse/MC-81098?focusedCommentId=420777&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-420777">here</a>
+ * or by checking out its implementation in carpet mod <a href="https://github.com/gnembon/fabric-carpet/blob/master/src/main/java/carpet/helpers/RedstoneWireTurbo.java">here</a>.
+ * 
+ * <p>
+ * The idea is to determine the direction of power flow through a wire based on
+ * the power it receives from neighboring wires. For example, if the only power
+ * a wire receives is from a neighboring wire to its west, it can be said that
+ * the direction of power flow through the wire is east.
+ * 
+ * <p>
+ * We make the order of block updates to neighbors of a wire depend on what is
+ * determined to be the direction of power flow. This not only removes
+ * locationality entirely, it even removes directionality in a large number of
+ * cases. Unlike in 'RedstoneWireTurbo', however, I have decided to keep a
+ * directional element in ambiguous cases, rather than to introduce randomness,
+ * though this is trivial to change.
+ * 
+ * <p>
+ * While this change fixes the block update order of individual wires, we must
+ * still address the overall block update order of a network. This turns out to
+ * be a simple fix, because of a change we made earlier: we search through the
+ * network for wires that receive power from outside it, and spread the power
+ * from there. If we make each wire transmit its power to neighboring wires in
+ * an order dependent on the direction of power flow, we end up with a
+ * non-locational and largely non-directional wire update order.
+ * 
+ * @author Space Walker
+ */
+public class WireHandler {
+
+    public static class Directions {
+
+        public static final Direction[] ALL        = { Direction.WEST, Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.DOWN, Direction.UP };
+        public static final Direction[] HORIZONTAL = { Direction.WEST, Direction.NORTH, Direction.EAST, Direction.SOUTH };
+
+        // Indices for the arrays above.
+        // The cardinal directions are ordered clockwise. This allows
+        // for conversion between relative and absolute directions
+        // ('left' 'right' vs 'east' 'west') with simple arithmetic:
+        // If some Direction index 'iDir' is considered 'forward', then
+        // '(iDir + 1) & 0b11' is 'right', '(iDir + 2) & 0b11' is 'backward', etc.
+        public static final int WEST  = 0b000; // 0
+        public static final int NORTH = 0b001; // 1
+        public static final int EAST  = 0b010; // 2
+        public static final int SOUTH = 0b011; // 3
+        public static final int DOWN  = 0b100; // 4
+        public static final int UP    = 0b101; // 5
+
+        public static int iOpposite(int iDir) {
+            return iDir ^ (0b10 >>> (iDir >>> 2));
+        }
+
+        /**
+         * Each array is placed at the index that encodes the direction that is missing
+         * from the array.
+         */
+        private static final int[][] I_EXCEPT = {
+            {       NORTH, EAST, SOUTH, DOWN, UP },
+            { WEST,        EAST, SOUTH, DOWN, UP },
+            { WEST, NORTH,       SOUTH, DOWN, UP },
+            { WEST, NORTH, EAST,        DOWN, UP },
+            { WEST, NORTH, EAST, SOUTH,       UP },
+            { WEST, NORTH, EAST, SOUTH, DOWN     }
+        };
+    }
+
+    /**
+     * This conversion table takes in information about incoming flow, and outputs
+     * the determined outgoing flow.
+     * 
+     * <p>
+     * The input is a 4 bit number that encodes the incoming flow. Each bit
+     * represents a cardinal direction, and when it is 'on', there is flow in that
+     * direction.
+     * 
+     * <p>
+     * The output is a single Direction index, or -1 for ambiguous cases.
+     * 
+     * <p>
+     * The outgoing flow is determined as follows:
+     * 
+     * <p>
+     * If there is just 1 direction of incoming flow, that direction will be the
+     * direction of outgoing flow.
+     * 
+     * <p>
+     * If there are 2 directions of incoming flow, and these directions are not each
+     * other's opposites, the direction that is 'more clockwise' will be the
+     * direction of outgoing flow. More precisely, the direction that is 1 clockwise
+     * turn from the other is picked.
+     * 
+     * <p>
+     * If there are 3 directions of incoming flow, the two opposing directions
+     * cancel each other out, and the remaining direction will be the direction of
+     * outgoing flow.
+     * 
+     * <p>
+     * In all other cases, the flow is completely ambiguous.
+     */
+    static final int[] FLOW_IN_TO_FLOW_OUT = {
+        -1,               // 0b0000: -                     -> x
+        Directions.WEST,  // 0b0001: west                  -> west
+        Directions.NORTH, // 0b0010: north                 -> north
+        Directions.NORTH, // 0b0011: west/north            -> north
+        Directions.EAST,  // 0b0100: east                  -> east
+        -1,               // 0b0101: west/east             -> x
+        Directions.EAST,  // 0b0110: north/east            -> east
+        Directions.NORTH, // 0b0111: west/north/east       -> north
+        Directions.SOUTH, // 0b1000: south                 -> south
+        Directions.WEST,  // 0b1001: west/south            -> west
+        -1,               // 0b1010: north/south           -> x
+        Directions.WEST,  // 0b1011: west/north/south      -> west
+        Directions.SOUTH, // 0b1100: east/south            -> south
+        Directions.SOUTH, // 0b1101: west/east/south       -> south
+        Directions.EAST,  // 0b1110: north/east/south      -> east
+        -1,               // 0b1111: west/north/east/south -> x
+    };
+    /**
+     * Update order of cardinal directions. Given that the index encodes the
+     * direction that is to be considered 'forward', the resulting update order is {
+     * front, back, right, left }.
+     */
+    static final int[][] CARDINAL_UPDATE_ORDERS = {
+        { Directions.WEST , Directions.EAST , Directions.NORTH, Directions.SOUTH },
+        { Directions.NORTH, Directions.SOUTH, Directions.EAST , Directions.WEST  },
+        { Directions.EAST , Directions.WEST , Directions.SOUTH, Directions.NORTH },
+        { Directions.SOUTH, Directions.NORTH, Directions.WEST , Directions.EAST  }
+    };
+    /**
+     * The default update order of all cardinal directions.
+     */
+    static final int[] DEFAULT_CARDINAL_UPDATE_ORDER = CARDINAL_UPDATE_ORDERS[0];
+    /**
+     * The default update order of all directions. It is equivalent to the order of
+     * shape updates in vanilla Minecraft.
+     */
+    static final int[] DEFAULT_FULL_UPDATE_ORDER = {
+        Directions.WEST,
+        Directions.EAST,
+        Directions.NORTH,
+        Directions.SOUTH,
+        Directions.DOWN,
+        Directions.UP
+    };
+
+    private static final int POWER_MAX = Redstone.SIGNAL_MAX;
+    private static final int POWER_MIN = Redstone.SIGNAL_MIN;
+    private static final int POWER_STEP = 1;
+
+    // If Vanilla will ever multi-thread the ticking of levels, there should
+    // be only one WireHandler per level, in case redstone updates in multiple
+    // levels at the same time. There are already mods that add multi-threading
+    // as well.
+    private final ServerLevel level;
+
+    /** All the wires in the network. */
+    private final List<WireNode> network;
+    /** Map of wires and neighboring blocks. */
+    private final Long2ObjectMap<Node> nodes;
+    /** The queue for updating wires and neighboring nodes. */
+    private final Queue<Node> updates;
+
+    private int rootCount;
+    // Rather than creating new nodes every time a network is updated we keep
+    // a cache of nodes that can be re-used.
+    private Node[] nodeCache;
+    private int nodeCount;
+
+    /** Is this WireHandler currently working through the update queue? */
+    private boolean updating;
+
+    public WireHandler(ServerLevel level) {
+        this.level = level;
+
+        this.network = new ArrayList<>();
+        this.nodes = new Long2ObjectOpenHashMap<>();
+        this.updates = new UpdateQueue();
+
+        this.nodeCache = new Node[16];
+        this.fillNodeCache(0, 16);
+    }
+
+    /**
+     * Retrieve the {@link alternate.current.wire.Node Node} that represents the
+     * block at the given position in the level.
+     */
+    private Node getOrAddNode(BlockPos pos) {
+        return nodes.compute(pos.asLong(), (key, node) -> {
+            if (node == null) {
+                // If there is not yet a node at this position, retrieve and
+                // update one from the cache.
+                return getNextNode(pos);
+            }
+            if (node.invalid) {
+                return revalidateNode(node);
+            }
+
+            return node;
+        });
+    }
+
+    /**
+     * Return a {@link alternate.current.wire.Node Node} that represents the block
+     * at the given position.
+     */
+    private Node getNextNode(BlockPos pos) {
+        return getNextNode(pos, level.getBlockState(pos));
+    }
+
+    /**
+     * Return a node that represents the given position and block state. If it is a
+     * wire, then create a new {@link alternate.current.wire.WireNode WireNode}.
+     * Otherwise, grab the next {@link alternate.current.wire.Node Node} from the
+     * cache and update it.
+     */
+    private Node getNextNode(BlockPos pos, BlockState state) {
+        return state.is(Blocks.REDSTONE_WIRE) ? new WireNode(level, pos, state) : getNextNode().update(pos, state, true);
+    }
+
+    /**
+     * Grab the first unused Node from the cache. If all of the cache is already in
+     * use, increase it in size first.
+     */
+    private Node getNextNode() {
+        if (nodeCount == nodeCache.length) {
+            increaseNodeCache();
+        }
+
+        return nodeCache[nodeCount++];
+    }
+
+    private void increaseNodeCache() {
+        Node[] oldCache = nodeCache;
+        nodeCache = new Node[oldCache.length << 1];
+
+        for (int index = 0; index < oldCache.length; index++) {
+            nodeCache[index] = oldCache[index];
+        }
+
+        fillNodeCache(oldCache.length, nodeCache.length);
+    }
+
+    private void fillNodeCache(int start, int end) {
+        for (int index = start; index < end; index++) {
+            nodeCache[index] = new Node(level);
+        }
+    }
+
+    private Node removeNode(BlockPos pos) {
+        return nodes.remove(pos.asLong());
+    }
+
+    /**
+     * Try to revalidate the given node by looking at the block state that is
+     * occupying its position. If the given node is a wire but the block state is
+     * not, a new node must be created/grabbed from the cache. Otherwise, the node
+     * can be quickly revalidated with the new block state;
+     */
+    private Node revalidateNode(Node node) {
+        BlockPos pos = node.pos;
+        BlockState state = level.getBlockState(pos);
+
+        boolean wasWire = node.isWire();
+        boolean isWire = state.is(Blocks.REDSTONE_WIRE);
+
+        if (wasWire != isWire) {
+            return getNextNode(pos, state);
+        }
+
+        node.invalid = false;
+
+        if (isWire) {
+            // No need to update the block state of this wire - it will grab
+            // the current block state just before setting power anyway.
+            WireNode wire = node.asWire();
+
+            wire.prepared = false;
+            wire.inNetwork = false;
+        } else {
+            node.update(pos, state, false);
+        }
+
+        return node;
+    }
+
+    /**
+     * Retrieve the neighbor of a node in the given direction and create a link
+     * between the two nodes if they are not yet linked.
+     */
+    private Node getNeighbor(Node node, int iDir) {
+        Node neighbor = node.neighbors[iDir];
+
+        if (neighbor == null || neighbor.invalid) {
+            Direction dir = Directions.ALL[iDir];
+            BlockPos pos = node.pos.relative(dir);
+
+            Node oldNeighbor = neighbor;
+            neighbor = getOrAddNode(pos);
+
+            if (neighbor != oldNeighbor) {
+                int iOpp = Directions.iOpposite(iDir);
+
+                node.neighbors[iDir] = neighbor;
+                neighbor.neighbors[iOpp] = node;
+            }
+        }
+
+        return neighbor;
+    }
+
+    /**
+     * Iterate over all neighboring nodes of the given wire. The iteration order is
+     * designed to be an extension of the default block update order, and is
+     * determined as follows:
+     * <br>
+     * 1. The direction of power flow through the wire is to be considered
+     * 'forward'. The iteration order depends on the neighbors' relative positions
+     * to the wire.
+     * <br>
+     * 2. Each neighbor is identified by the step(s) you must take, starting at the
+     * wire, to reach it. Each step is 1 block, thus the position of a neighbor is
+     * encoded by the direction(s) of the step(s), e.g. (right), (down), (up, left),
+     * etc.
+     * <br>
+     * 3. Neighbors are iterated over in pairs that lie on opposite sides of the
+     * wire.
+     * <br>
+     * 4. Neighbors are iterated over in order of their distance from the wire. This
+     * means they are iterated over in 3 groups: direct neighbors first, then
+     * diagonal neighbors, and last are the far neighbors that are 2 blocks directly
+     * out.
+     * <br>
+     * 5. The order within each group is determined using the following basic order:
+     * { front, back, right, left, down, up }. This order was chosen because it
+     * converts to the following order of absolute directions when west is said to
+     * be 'forward': { west, east, north, south, down, up } - this is the order of
+     * shape updates.
+     */
+    private void forEachNeighbor(WireNode wire, Consumer<Node> consumer) {
+        int forward   = wire.iFlowDir;
+        int rightward = (forward + 1) & 0b11;
+        int backward  = (forward + 2) & 0b11;
+        int leftward  = (forward + 3) & 0b11;
+        int downward  = Directions.DOWN;
+        int upward    = Directions.UP;
+
+        Node front = getNeighbor(wire, forward);
+        Node right = getNeighbor(wire, rightward);
+        Node back  = getNeighbor(wire, backward);
+        Node left  = getNeighbor(wire, leftward);
+        Node below = getNeighbor(wire, downward);
+        Node above = getNeighbor(wire, upward);
+
+        // direct neighbors (6)
+        consumer.accept(front);
+        consumer.accept(back);
+        consumer.accept(right);
+        consumer.accept(left);
+        consumer.accept(below);
+        consumer.accept(above);
+
+        // diagonal neighbors (12)
+        consumer.accept(getNeighbor(front, rightward));
+        consumer.accept(getNeighbor(back, leftward));
+        consumer.accept(getNeighbor(front, leftward));
+        consumer.accept(getNeighbor(back, rightward));
+        consumer.accept(getNeighbor(front, downward));
+        consumer.accept(getNeighbor(back, upward));
+        consumer.accept(getNeighbor(front, upward));
+        consumer.accept(getNeighbor(back, downward));
+        consumer.accept(getNeighbor(right, downward));
+        consumer.accept(getNeighbor(left, upward));
+        consumer.accept(getNeighbor(right, upward));
+        consumer.accept(getNeighbor(left, downward));
+
+        // far neighbors (6)
+        consumer.accept(getNeighbor(front, forward));
+        consumer.accept(getNeighbor(back, backward));
+        consumer.accept(getNeighbor(right, rightward));
+        consumer.accept(getNeighbor(left, leftward));
+        consumer.accept(getNeighbor(below, downward));
+        consumer.accept(getNeighbor(above, upward));
+    }
+
+    /**
+     * This method should be called whenever a wire receives a block update.
+     */
+    public void onWireUpdated(BlockPos pos) {
+        invalidateNodes();
+        findRoots(pos);
+        tryUpdatePower();
+    }
+
+    /**
+     * This method should be called whenever a wire is placed.
+     */
+    public void onWireAdded(BlockPos pos) {
+        Node node = getOrAddNode(pos);
+
+        if (!node.isWire()) {
+            return; // we should never get here
+        }
+
+        WireNode wire = node.asWire();
+        wire.added = true;
+
+        invalidateNodes();
+        tryAddRoot(wire);
+        tryUpdatePower();
+    }
+
+    /**
+     * This method should be called whenever a wire is removed.
+     */
+    public void onWireRemoved(BlockPos pos, BlockState state) {
+        Node node = removeNode(pos);
+        WireNode wire;
+
+        if (node == null || !node.isWire()) {
+            wire = new WireNode(level, pos, state);
+        } else {
+            wire = node.asWire();
+        }
+
+        wire.invalid = true;
+        wire.removed = true;
+
+        // If these fields are set to 'true', the removal of this wire was part of
+        // already ongoing power changes, so we can exit early here.
+        if (updating && wire.shouldBreak) {
+            return;
+        }
+
+        invalidateNodes();
+        tryAddRoot(wire);
+        tryUpdatePower();
+    }
+
+    /**
+     * The nodes map is a snapshot of the state of the world. It becomes invalid
+     * when power changes are carried out, since the block and shape updates can
+     * lead to block changes. If these block changes cause the network to be updated
+     * again every node must be invalidated, and revalidated before it is used
+     * again. This ensures the power calculations of the network are accurate.
+     */
+    private void invalidateNodes() {
+        if (updating && !nodes.isEmpty()) {
+            Iterator<Entry<Node>> it = Long2ObjectMaps.fastIterator(nodes);
+
+            while (it.hasNext()) {
+                Entry<Node> entry = it.next();
+                Node node = entry.getValue();
+
+                node.invalid = true;
+            }
+        }
+    }
+
+    /**
+     * Look for wires at and around the given position that are in an invalid state
+     * and require power changes. These wires are called 'roots' because it is only
+     * when these wires change power level that neighboring wires must adjust as
+     * well.
+     * 
+     * <p>
+     * While it is strictly only necessary to check the wire at the given position,
+     * if that wire is part of a network, it is beneficial to check its surroundings
+     * for other wires that require power changes. This is because a network can
+     * receive power at multiple points. Consider the following setup:
+     * 
+     * <p>
+     * (top-down view, W = wire, L = lever, _ = air/other)
+     * <br> {@code _ _ W _ _ }
+     * <br> {@code _ W W W _ }
+     * <br> {@code W W L W W }
+     * <br> {@code _ W W W _ }
+     * <br> {@code _ _ W _ _ }
+     * 
+     * <p>
+     * The lever powers four wires in the network at once. If this is identified
+     * correctly, the entire network can (un)power at once. While it is not
+     * practical to cover every possible situation where a network is (un)powered
+     * from multiple points at once, checking for common cases like the one
+     * described above is relatively straight-forward.
+     * 
+     * <p>
+     * While these extra checks can provide significant performance gains in some
+     * cases, in the majority of cases they will have little to no effect, but do
+     * require extra code modifications to all redstone power emitters. Removing
+     * these optimizations would limit code modifications to the RedStoneWireBlock
+     * and ServerLevel classes while leaving the performance mostly intact.
+     */
+    private void findRoots(BlockPos pos) {
+        Node node = getOrAddNode(pos);
+
+        if (!node.isWire()) {
+            return; // we should never get here
+        }
+
+        WireNode wire = node.asWire();
+        tryAddRoot(wire);
+
+        // If the wire at the given position is not in an invalid state or is not
+        // part of a larger network, we can exit early.
+        if (!wire.inNetwork || wire.connections.total == 0) {
+            return;
+        }
+
+        for (int iDir : DEFAULT_FULL_UPDATE_ORDER) {
+            Node neighbor = getNeighbor(wire, iDir);
+
+            if (neighbor.isConductor()) {
+                // Redstone components can power multiple wires through solid
+                // blocks.
+                findSignalSourcesAround(neighbor, Directions.iOpposite(iDir));
+            } else if (neighbor.state.isSignalSourceTo(level, neighbor.pos, Directions.ALL[iDir])) {
+                // Redstone components can also power multiple wires directly.
+                findRootsAroundSignalSource(neighbor, Directions.iOpposite(iDir));
+            }
+        }
+    }
+
+    /**
+     * Find signal sources around the given node that can provide direct signals to
+     * that node, and then search for wires that require power changes around those
+     * signal sources.
+     */
+    private void findSignalSourcesAround(Node node, int except) {
+        for (int iDir : Directions.I_EXCEPT[except]) {
+            Node neighbor = getNeighbor(node, iDir);
+
+            if (neighbor.state.isDirectSignalSourceTo(level, neighbor.pos, Directions.ALL[iDir])) {
+                findRootsAroundSignalSource(neighbor, iDir);
+            }
+        }
+    }
+
+    /**
+     * Find wires around the given signal source that require power changes.
+     */
+    private void findRootsAroundSignalSource(Node node, int except) {
+        for (int iDir : Directions.I_EXCEPT[except]) {
+            // Directions are backwards for redstone related methods, so we must
+            // check for power emitted in the opposite direction that we are
+            // interested in.
+            int iOpp = Directions.iOpposite(iDir);
+            Direction opp = Directions.ALL[iOpp];
+
+            boolean signal = node.state.isSignalSourceTo(level, node.pos, opp);
+            boolean directSignal = node.state.isDirectSignalSourceTo(level, node.pos, opp);
+
+            // If the signal source does not emit any power in this direction,
+            // move on to the next direction.
+            if (!signal && !directSignal) {
+                continue;
+            }
+
+            Node neighbor = getNeighbor(node, iDir);
+
+            if (signal && neighbor.isWire()) {
+                tryAddRoot(neighbor.asWire());
+            } else if (directSignal && neighbor.isConductor()) {
+                findRootsAround(neighbor, iOpp);
+            }
+        }
+    }
+
+    /**
+     * Look for wires around the given node that require power changes.
+     */
+    private void findRootsAround(Node node, int except) {
+        for (int iDir : Directions.I_EXCEPT[except]) {
+            Node neighbor = getNeighbor(node, iDir);
+
+            if (neighbor.isWire()) {
+                tryAddRoot(neighbor.asWire());
+            }
+        }
+    }
+
+    /**
+     * Check if the given wire is in an illegal state and needs power changes.
+     */
+    private void tryAddRoot(WireNode wire) {
+        // Each potential root needs to be checked only once.
+        if (wire.prepared) {
+            return;
+        }
+
+        prepare(wire);
+        findPower(wire, false);
+
+        if (needsPowerChange(wire)) {
+            addRoot(wire);
+        }
+    }
+
+    /**
+     * Add the given wire to the network as a root.
+     */
+    private void addRoot(WireNode wire) {
+        network.add(wire);
+        rootCount++;
+
+        wire.inNetwork = true;
+
+        if (wire.connections.iFlowDir >= 0) {
+            wire.iFlowDir = wire.connections.iFlowDir;
+        }
+    }
+
+    /**
+     * Before a wire can be added to the network, it must be properly prepared.
+     * This method
+     * <br>
+     * - checks if this wire should break. Rather than break the wire right away,
+     * its effects are integrated into the power calculations.
+     * <br>
+     * - determines the 'external power' this wire receives (power from non-wire
+     * components).
+     * <br>
+     * - finds connections this wire has to neighboring wires.
+     */
+    private void prepare(WireNode wire) {
+        // Each wire only needs to be prepared once.
+        if (wire.prepared) {
+            return;
+        }
+
+        wire.prepared = true;
+        wire.inNetwork = false;
+
+        if (!wire.removed && !wire.shouldBreak && !wire.state.canSurvive(level, wire.pos)) {
+            wire.shouldBreak = true;
+        }
+
+        wire.virtualPower = wire.externalPower = getInitialPower(wire);
+        wire.connections.set(this::getNeighbor);
+    }
+
+    private int getInitialPower(WireNode wire) {
+        return (wire.removed || wire.shouldBreak) ? POWER_MIN : getExternalPower(wire);
+    }
+
+    private int getExternalPower(WireNode wire) {
+        int power = POWER_MIN;
+
+        for (int iDir = 0; iDir < Directions.ALL.length; iDir++) {
+            Node neighbor = getNeighbor(wire, iDir);
+
+            // Power from wires is handled separately.
+            if (neighbor.isWire()) {
+                continue;
+            }
+
+            // Since 1.16 there is a block that is both a conductor and a signal
+            // source: the target block!
+            if (neighbor.isConductor()) {
+                power = Math.max(power, getDirectSignalTo(wire, neighbor, Directions.iOpposite(iDir)));
+            }
+            if (neighbor.isSignalSource()) {
+                power = Math.max(power, neighbor.state.getSignal(level, neighbor.pos, Directions.ALL[iDir]));
+            }
+
+            if (power >= POWER_MAX) {
+                return POWER_MAX;
+            }
+        }
+
+        return power;
+    }
+
+    /**
+     * Determine the direct signal the given wire receives from neighboring blocks
+     * through the given conductor node.
+     */
+    private int getDirectSignalTo(WireNode wire, Node node, int except) {
+        int power = POWER_MIN;
+
+        for (int iDir : Directions.I_EXCEPT[except]) {
+            Node neighbor = getNeighbor(node, iDir);
+
+            if (neighbor.isSignalSource()) {
+                power = Math.max(power, neighbor.state.getDirectSignal(level, neighbor.pos, Directions.ALL[iDir]));
+
+                if (power >= POWER_MAX) {
+                    return POWER_MAX;
+                }
+            }
+        }
+
+        return power;
+    }
+
+    /**
+     * Determine the power level the given wire receives from the blocks around it.
+     * Power from non-wire components has already been determined, so only power
+     * received from other wires needs to be checked. There are a few exceptions:
+     * <br>
+     * - If the wire is removed or going to break, its power level should always be
+     * the minimum value. This is because it (effectively) no longer exists, so
+     * cannot provide any power to neighboring wires.
+     * <br>
+     * - Power received from neighboring wires will never exceed {@code POWER_MAX - 
+     * POWER_STEP}, so if the external power is already larger than or equal to
+     * that, there is no need to check for power from neighboring wires.
+     */
+    private void findPower(WireNode wire, boolean ignoreNetwork) {
+        if (wire.removed || wire.shouldBreak || wire.externalPower >= (POWER_MAX - POWER_STEP)) {
+            return;
+        }
+
+        // The virtual power is reset to the external power, so the flow information
+        // must be reset as well.
+        wire.virtualPower = wire.externalPower;
+        wire.flowIn = 0;
+
+        findWirePower(wire, ignoreNetwork);
+    }
+
+    /**
+     * Determine the power level the given wire receives from connected wires.
+     */
+    private void findWirePower(WireNode wire, boolean ignoreNetwork) {
+        wire.connections.forEach(connection -> {
+            if (!connection.accept) {
+                return;
+            }
+
+            WireNode neighbor = connection.wire;
+
+            if (!ignoreNetwork || !neighbor.inNetwork) {
+                int power = Math.max(POWER_MIN, neighbor.virtualPower - POWER_STEP);
+                int iOpp = Directions.iOpposite(connection.iDir);
+
+                wire.offerPower(power, iOpp);
+            }
+        });
+    }
+
+    private boolean needsPowerChange(WireNode wire) {
+        return wire.removed || wire.shouldBreak || wire.virtualPower != wire.currentPower;
+    }
+
+    private void tryUpdatePower() {
+        if (rootCount > 0) {
+            updatePower();
+        }
+        if (!updating) {
+            nodes.clear();
+            nodeCount = 0;
+        }
+    }
+
+    /**
+     * Propagate power changes through the network and notify neighboring blocks of
+     * these changes.
+     * 
+     * <p>
+     * Power changes are done in the following 3 steps.
+     * 
+     * <p>
+     * <b>1. Build up the network</b>
+     * <br>
+     * Collect all the wires around the roots that need to change their power
+     * levels.
+     * 
+     * <p>
+     * <b>2. Find powered wires</b>
+     * <br>
+     * Find those wires in the network that receive power from outside the network.
+     * This can come in 2 forms:
+     * <br>
+     * - Power from non-wire components (repeaters, torches, etc.).
+     * <br>
+     * - Power from wires that are not in the network.
+     * <br>
+     * These powered wires will then queue their power changes.
+     * 
+     * <p>
+     * <b>3. Let power flow</b>
+     * <br>
+     * Work through the queue of power changes. After each wire's power change, emit
+     * shape and block updates to neighboring blocks, then queue power changes for
+     * connected wires.
+     */
+    private void updatePower() {
+        // Build a network of wires that need power changes. This includes the roots
+        // as well as any wires that will be affected by power changes to those roots.
+        buildNetwork();
+
+        // Find those wires in the network that receive power from outside it.
+        // Remember that the power changes for those wires are already queued here!
+        findPoweredWires();
+
+        // Once the powered wires have been found, the network is no longer needed. In
+        // fact, it should be cleared before block and shape updates are emitted, in
+        // case a different network is updated that needs power changes.
+        network.clear();
+        rootCount = 0;
+
+        // Carry out the power changes and emit shape and block updates.
+        try {
+            letPowerFlow();
+        } catch (Throwable t) {
+            // If anything goes wrong while carrying out power changes, this field must
+            // be reset to 'false', or the wire handler will be locked out of carrying
+            // out power changes until the world is reloaded.
+            updating = false;
+
+            throw t;
+        }
+    }
+
+    /**
+     * Build up a network of wires that need power changes. This includes the roots
+     * that were already added and any wires powered by those roots that will need
+     * power changes as a result of power changes to the roots.
+     */
+    private void buildNetwork() {
+        for (int index = 0; index < network.size(); index++) {
+            WireNode wire = network.get(index);
+
+            // The order in which wires are added to the network can influence the
+            // order in which they update their power levels.
+            wire.connections.forEach(connection -> {
+                if (!connection.offer) {
+                    return;
+                }
+
+                WireNode neighbor = connection.wire;
+
+                if (neighbor.inNetwork) {
+                    return;
+                }
+
+                prepare(neighbor);
+                findPower(neighbor, false);
+
+                if (needsPowerChange(neighbor)) {
+                    addToNetwork(neighbor, connection.iDir);
+                }
+            }, wire.iFlowDir);
+        }
+    }
+
+    /**
+     * Add the given wire to the network and set its outgoing flow to some backup
+     * value. This avoids directionality in redstone grids.
+     */
+    private void addToNetwork(WireNode wire, int iBackupFlowDir) {
+        network.add(wire);
+
+        wire.inNetwork = true;
+        // Normally the flow is not set until the power level is updated. However,
+        // in networks with multiple power sources the update order between them
+        // depends on which was discovered first. To make this less prone to
+        // directionality, each wire node is given a 'backup' flow. For roots, this
+        // is the determined flow of their connections. For non-roots this is the
+        // direction from which they were discovered.
+        wire.iFlowDir = iBackupFlowDir;
+    }
+
+    /**
+     * Find those wires in the network that receive power from outside it, either
+     * from non-wire components or from wires that are not in the network, and queue
+     * the power changes for those wires.
+     */
+    private void findPoweredWires() {
+        for (int index = 0; index < network.size(); index++) {
+            WireNode wire = network.get(index);
+            findPower(wire, true);
+
+            if (index < rootCount || wire.removed || wire.shouldBreak || wire.virtualPower > POWER_MIN) {
+                queueWire(wire);
+            } else {
+                // Wires that do not receive any power do not queue power changes
+                // until they are offered power from a neighboring wire. To ensure
+                // that they accept any power from neighboring wires and thus queue
+                // their power changes, their virtual power is set to below the
+                // minimum.
+                wire.virtualPower--;
+            }
+        }
+    }
+
+    /**
+     * Carry out power changes, setting the new power of each wire in the world,
+     * notifying neighbors of the power change, then queueing power changes of
+     * connected wires.
+     */
+    private void letPowerFlow() {
+        // If an instantaneous update chain causes updates to another network
+        // (or the same network in another place), new power changes will be
+        // integrated into the already ongoing power queue, so we can exit early
+        // here.
+        if (updating) {
+            return;
+        }
+
+        updating = true;
+
+        while (!updates.isEmpty()) {
+            Node node = updates.poll();
+
+            if (node.isWire()) {
+                WireNode wire = node.asWire();
+
+                if (!needsPowerChange(wire)) {
+                    continue;
+                }
+
+                findPowerFlow(wire);
+                transmitPower(wire);
+
+                if (wire.setPower()) {
+                    queueNeighbors(wire);
+
+                    // If the wire was newly placed or removed, shape updates have
+                    // already been emitted. However, unlike before 1.19, neighbor
+                    // updates are now queued, so to preserve behavior parity with
+                    // previous versions, we emit extra shape updates here to
+                    // notify neighboring observers.
+                    updateNeighborShapes(wire);
+                }
+            } else {
+                WireNode neighborWire = node.neighborWire;
+
+                if (neighborWire != null) {
+                    BlockPos neighborPos = neighborWire.pos;
+                    Block neighborBlock = neighborWire.state.getBlock();
+
+                    updateNeighbor(node, neighborPos, neighborBlock);
+                }
+            }
+        }
+
+        updating = false;
+    }
+
+    /**
+     * Use the information of incoming power flow to determine the direction of
+     * power flow through this wire. If that flow is ambiguous, try to use a flow
+     * direction based on connections to neighboring wires. If that is also
+     * ambiguous, use the backup value that was set when the wire was first added to
+     * the network.
+     */
+    private void findPowerFlow(WireNode wire) {
+        int flow = FLOW_IN_TO_FLOW_OUT[wire.flowIn];
+
+        if (flow >= 0) {
+            wire.iFlowDir = flow;
+        } else if (wire.connections.iFlowDir >= 0) {
+            wire.iFlowDir = wire.connections.iFlowDir;
+        }
+    }
+
+    /**
+     * Transmit power from the given wire to neighboring wires and queue updates to
+     * those wires.
+     */
+    private void transmitPower(WireNode wire) {
+        wire.connections.forEach(connection -> {
+            if (!connection.offer) {
+                return;
+            }
+
+            WireNode neighbor = connection.wire;
+
+            int power = Math.max(POWER_MIN, wire.virtualPower - POWER_STEP);
+            int iDir = connection.iDir;
+
+            if (neighbor.offerPower(power, iDir)) {
+                queueWire(neighbor);
+            }
+        }, wire.iFlowDir);
+    }
+
+    /**
+     * Emit shape updates around the given wire.
+     */
+    private void updateNeighborShapes(WireNode wire) {
+        BlockPos wirePos = wire.pos;
+        BlockState wireState = wire.state;
+
+        for (int iDir : DEFAULT_FULL_UPDATE_ORDER) {
+            Node neighbor = getNeighbor(wire, iDir);
+
+            if (!neighbor.isWire()) {
+                int iOpp = Directions.iOpposite(iDir);
+                Direction opp = Directions.ALL[iOpp];
+
+                updateNeighborShape(neighbor, opp, wirePos, wireState);
+            }
+        }
+    }
+
+    private void updateNeighborShape(Node node, Direction fromDir, BlockPos fromPos, BlockState fromState) {
+        BlockPos pos = node.pos;
+        BlockState state = level.getBlockState(pos);
+
+        // Shape updates to redstone wire are very expensive, and should never happen
+        // as a result of power changes anyway.
+        if (!state.isAir() && !state.is(Blocks.REDSTONE_WIRE)) {
+            BlockState newState = state.updateShape(fromDir, fromState, level, pos, fromPos);
+            Block.updateOrDestroy(state, newState, level, pos, Block.UPDATE_CLIENTS);
+        }
+    }
+
+    /**
+     * Queue block updates to nodes around the given wire.
+     */
+    private void queueNeighbors(WireNode wire) {
+        forEachNeighbor(wire, neighbor -> {
+            queueNeighbor(neighbor, wire);
+        });
+    }
+
+    /**
+     * Queue the given node for an update from the given neighboring wire.
+     */
+    private void queueNeighbor(Node node, WireNode neighborWire) {
+        // Updates to wires are queued when power is transmitted.
+        if (!node.isWire()) {
+            node.neighborWire = neighborWire;
+            updates.offer(node);
+        }
+    }
+
+    /**
+     * Queue the given wire for a power change. If the wire does not need a power
+     * change (perhaps because its power has already changed), transmit power to
+     * neighboring wires.
+     */
+    private void queueWire(WireNode wire) {
+        if (needsPowerChange(wire)) {
+            updates.offer(wire);
+        } else {
+            findPowerFlow(wire);
+            transmitPower(wire);
+        }
+    }
+
+    /**
+     * Emit a block update to the given node.
+     */
+    private void updateNeighbor(Node node, BlockPos fromPos, Block fromBlock) {
+        BlockPos pos = node.pos;
+        BlockState state = level.getBlockState(pos);
+
+        // While this check makes sure wires in the network are not given block
+        // updates, it also prevents block updates to wires in neighboring networks.
+        // While this should not make a difference in theory, in practice, it is
+        // possible to force a network into an invalid state without updating it, even
+        // if it is relatively obscure.
+        // While I was willing to make this compromise in return for some significant
+        // performance gains in certain setups, if you are not, you can add all the
+        // positions of the network to a set and filter out block updates to wires in
+        // the network that way.
+        if (!state.isAir() && !state.is(Blocks.REDSTONE_WIRE)) {
+            state.neighborChanged(level, pos, fromBlock, fromPos, false);
+        }
+    }
+
+    @FunctionalInterface
+    public static interface NodeProvider {
+
+        public Node getNeighbor(Node node, int iDir);
+
+    }
+}
diff --git a/src/main/java/alternate/current/wire/WireNode.java b/src/main/java/alternate/current/wire/WireNode.java
new file mode 100644
index 0000000000000000000000000000000000000000..dde98a49b0f4db023386f8e4b98c99340d51c871
--- /dev/null
+++ b/src/main/java/alternate/current/wire/WireNode.java
@@ -0,0 +1,118 @@
+package alternate.current.wire;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.util.Mth;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.RedStoneWireBlock;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.redstone.Redstone;
+
+/**
+ * A WireNode is a Node that represents a wire in the world. It stores all the
+ * information about the wire that the WireHandler needs to calculate power
+ * changes.
+ * 
+ * @author Space Walker
+ */
+public class WireNode extends Node {
+
+    final WireConnectionManager connections;
+
+    /** The power level this wire currently holds in the world. */
+    int currentPower;
+    /**
+     * While calculating power changes for a network, this field is used to keep
+     * track of the power level this wire should have.
+     */
+    int virtualPower;
+    /** The power level received from non-wire components. */
+    int externalPower;
+    /**
+     * A 4-bit number that keeps track of the power flow of the wires that give this
+     * wire its power level.
+     */
+    int flowIn;
+    /** The direction of power flow, based on the incoming flow. */
+    int iFlowDir;
+    boolean added;
+    boolean removed;
+    boolean shouldBreak;
+    boolean prepared;
+    boolean inNetwork;
+
+    WireNode(ServerLevel level, BlockPos pos, BlockState state) {
+        super(level);
+
+        this.pos = pos.immutable();
+        this.state = state;
+
+        this.connections = new WireConnectionManager(this);
+
+        this.virtualPower = this.currentPower = this.state.getValue(RedStoneWireBlock.POWER);
+        this.priority = priority();
+    }
+
+    @Override
+    Node update(BlockPos pos, BlockState state, boolean clearNeighbors) {
+        throw new UnsupportedOperationException("Cannot update a WireNode!");
+    }
+
+    @Override
+    int priority() {
+        return Mth.clamp(virtualPower, Redstone.SIGNAL_MIN, Redstone.SIGNAL_MAX);
+    }
+
+    @Override
+    public boolean isWire() {
+        return true;
+    }
+
+    @Override
+    public WireNode asWire() {
+        return this;
+    }
+
+    boolean offerPower(int power, int iDir) {
+        if (removed || shouldBreak) {
+            return false;
+        }
+        if (power == virtualPower) {
+            flowIn |= (1 << iDir);
+            return false;
+        }
+        if (power > virtualPower) {
+            virtualPower = power;
+            flowIn = (1 << iDir);
+
+            return true;
+        }
+
+        return false;
+    }
+
+    boolean setPower() {
+        if (removed) {
+            return true;
+        }
+
+        state = level.getBlockState(pos);
+
+        if (!state.is(Blocks.REDSTONE_WIRE)) {
+            return false; // we should never get here
+        }
+
+        if (shouldBreak) {
+            Block.dropResources(state, level, pos);
+            level.setBlock(pos, Blocks.AIR.defaultBlockState(), Block.UPDATE_CLIENTS);
+
+            return true;
+        }
+
+        currentPower = LevelHelper.doRedstoneEvent(level, pos, currentPower, Mth.clamp(virtualPower, Redstone.SIGNAL_MIN, Redstone.SIGNAL_MAX));
+        state = state.setValue(RedStoneWireBlock.POWER, currentPower);
+
+        return LevelHelper.setWireState(level, pos, state, added);
+    }
+}
diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 145c9fb394ec18bc18c43157d7e4ed2b9c8380fa..7dcdb9ea2f633359740b4263e7deb062851f93bc 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -88,7 +88,7 @@ public class PaperWorldConfig {
     }
 
     public enum RedstoneImplementation {
-        VANILLA, EIGENCRAFT
+        VANILLA, EIGENCRAFT, ALTERNATE_CURRENT
     }
     public RedstoneImplementation redstoneImplementation = RedstoneImplementation.VANILLA;
     private void redstoneImplementation() {
@@ -109,7 +109,7 @@ public class PaperWorldConfig {
         }
         switch (implementation) {
             default:
-                logError("Invalid redstone-implementation config " + implementation + " - must be one of: vanilla, eigencraft");
+                logError("Invalid redstone-implementation config " + implementation + " - must be one of: vanilla, eigencraft, alternate-current");
             case "vanilla":
                 redstoneImplementation = RedstoneImplementation.VANILLA;
                 log("Using the Vanilla redstone implementation.");
@@ -118,6 +118,10 @@ public class PaperWorldConfig {
                 redstoneImplementation = RedstoneImplementation.EIGENCRAFT;
                 log("Using Eigencraft's redstone implementation by theosib.");
                 break;
+            case "alternate-current":
+                redstoneImplementation = RedstoneImplementation.ALTERNATE_CURRENT;
+                log("Using Alternate Current's redstone implementation by Space Walker.");
+                break;
         }
     }
 
diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
index 443ef9d81e769c26ebd5a7d72078ed0f43306a7e..960b7248228d97547bfc2410d234adab4a548a7b 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -216,6 +216,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
     public final UUID uuid;
     public boolean hasPhysicsEvent = true; // Paper
     public boolean hasEntityMoveEvent = false; // Paper
+    private final alternate.current.wire.WireHandler wireHandler = new alternate.current.wire.WireHandler(this); // Paper - optimize redstone (Alternate Current)
     public static Throwable getAddToWorldStackTrace(Entity entity) {
         return new Throwable(entity + " Added to world at " + new java.util.Date());
     }
@@ -2481,6 +2482,13 @@ public class ServerLevel extends Level implements WorldGenLevel {
         return this.entityManager.canPositionTick(pos.toLong()); // Paper
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public alternate.current.wire.WireHandler getWireHandler() {
+        return wireHandler;
+    }
+    // Paper end
+
     private final class EntityCallbacks implements LevelCallback<Entity> {
 
         EntityCallbacks() {}
diff --git a/src/main/java/net/minecraft/world/level/Level.java b/src/main/java/net/minecraft/world/level/Level.java
index e3052c32624538d5394bf098c3b5db84e4cdb9b4..50614c99303da341dcb6c89295f65f7e46c6f139 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -1443,4 +1443,15 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
         return ret;
     }
     // Paper end
+
+    // Paper start - optimize redstone (Alternate Current)
+    public alternate.current.wire.WireHandler getWireHandler() {
+        // This method is overridden in ServerLevel.
+        // Since Paper is a server platform there is no risk
+        // of this implementation being called. It is here
+        // only so this method can be called without casting
+        // an instance of Level to ServerLevel.
+        return null;
+    }
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/world/level/block/BasePressurePlateBlock.java b/src/main/java/net/minecraft/world/level/block/BasePressurePlateBlock.java
index f9aaec28be3e7a191981d30b361e369d7fea2c9e..da7044e6affbbd364e997abe5a3c76459f4c35cf 100644
--- a/src/main/java/net/minecraft/world/level/block/BasePressurePlateBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/BasePressurePlateBlock.java
@@ -153,6 +153,18 @@ public abstract class BasePressurePlateBlock extends Block {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return dir == Direction.UP;
+    }
+    // Paper end
+
     @Override
     public PushReaction getPistonPushReaction(BlockState state) {
         return PushReaction.DESTROY;
diff --git a/src/main/java/net/minecraft/world/level/block/ButtonBlock.java b/src/main/java/net/minecraft/world/level/block/ButtonBlock.java
index a0194e78913017693df7d92516dfbacb1153a1c2..f935719c569e2286d1089a7e3e5dadff22323c36 100644
--- a/src/main/java/net/minecraft/world/level/block/ButtonBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/ButtonBlock.java
@@ -159,6 +159,18 @@ public abstract class ButtonBlock extends FaceAttachedHorizontalDirectionalBlock
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return getConnectedDirection(state) == dir;
+    }
+    // Paper end
+
     @Override
     public void tick(BlockState state, ServerLevel world, BlockPos pos, RandomSource random) {
         if ((Boolean) state.getValue(ButtonBlock.POWERED)) {
diff --git a/src/main/java/net/minecraft/world/level/block/DaylightDetectorBlock.java b/src/main/java/net/minecraft/world/level/block/DaylightDetectorBlock.java
index 16504b8be08064e61b013fa943f692816612cbd0..a2016e8b3860171e0f6101f4a2a724e44dee48d7 100644
--- a/src/main/java/net/minecraft/world/level/block/DaylightDetectorBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/DaylightDetectorBlock.java
@@ -101,6 +101,13 @@ public class DaylightDetectorBlock extends BaseEntityBlock {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+    // Paper end
+
     @Override
     public BlockEntity newBlockEntity(BlockPos pos, BlockState state) {
         return new DaylightDetectorBlockEntity(pos, state);
diff --git a/src/main/java/net/minecraft/world/level/block/DiodeBlock.java b/src/main/java/net/minecraft/world/level/block/DiodeBlock.java
index aa4ed127fe463fad1bf7ddadb54e93958ee970c7..02bf8a15f9bc233361c0c2b2e0e3ec481700f706 100644
--- a/src/main/java/net/minecraft/world/level/block/DiodeBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/DiodeBlock.java
@@ -159,6 +159,18 @@ public abstract class DiodeBlock extends HorizontalDirectionalBlock {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return state.getValue(FACING) == dir;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return state.getValue(FACING) == dir;
+    }
+    // Paper end
+
     @Override
     public BlockState getStateForPlacement(BlockPlaceContext ctx) {
         return (BlockState) this.defaultBlockState().setValue(DiodeBlock.FACING, ctx.getHorizontalDirection().getOpposite());
diff --git a/src/main/java/net/minecraft/world/level/block/LecternBlock.java b/src/main/java/net/minecraft/world/level/block/LecternBlock.java
index 5ef0705bae9b4ca2cda4f17aeefc0fe657040160..8398fd1b346c87cc1e1fe4ee93774a156a4e1945 100644
--- a/src/main/java/net/minecraft/world/level/block/LecternBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/LecternBlock.java
@@ -221,6 +221,18 @@ public class LecternBlock extends BaseEntityBlock {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return dir == Direction.UP;
+    }
+    // Paper end;
+
     @Override
     public int getSignal(BlockState state, BlockGetter world, BlockPos pos, Direction direction) {
         return (Boolean) state.getValue(LecternBlock.POWERED) ? 15 : 0;
diff --git a/src/main/java/net/minecraft/world/level/block/LeverBlock.java b/src/main/java/net/minecraft/world/level/block/LeverBlock.java
index 057ff8ba1c924c032a03389dcf4f99b4b386fb0a..997ac10a5236efcb6627a90dc65259d2b93ae6d1 100644
--- a/src/main/java/net/minecraft/world/level/block/LeverBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/LeverBlock.java
@@ -166,6 +166,18 @@ public class LeverBlock extends FaceAttachedHorizontalDirectionalBlock {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return getConnectedDirection(state) == dir;
+    }
+    // Paper end
+
     private void updateNeighbours(BlockState state, Level world, BlockPos pos) {
         world.updateNeighborsAt(pos, this);
         world.updateNeighborsAt(pos.relative(getConnectedDirection(state).getOpposite()), this);
diff --git a/src/main/java/net/minecraft/world/level/block/LightningRodBlock.java b/src/main/java/net/minecraft/world/level/block/LightningRodBlock.java
index 47625532a39e6b80c9452c75604369c0ddb78fbd..1df5679ba50c4ef6237e0e28ea80cce776b324c5 100644
--- a/src/main/java/net/minecraft/world/level/block/LightningRodBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/LightningRodBlock.java
@@ -166,4 +166,16 @@ public class LightningRodBlock extends RodBlock implements SimpleWaterloggedBloc
     public boolean isSignalSource(BlockState state) {
         return true;
     }
+
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return state.getValue(FACING) == dir;
+    }
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/world/level/block/ObserverBlock.java b/src/main/java/net/minecraft/world/level/block/ObserverBlock.java
index 7b45d6b9a005036ca5051d089a7be792eb87012f..25c2c44bde443ab08734253ed7c98c81a345e573 100644
--- a/src/main/java/net/minecraft/world/level/block/ObserverBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/ObserverBlock.java
@@ -90,6 +90,18 @@ public class ObserverBlock extends DirectionalBlock {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return state.getValue(FACING) == dir;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return state.getValue(FACING) == dir;
+    }
+    // Paper end
+
     @Override
     public int getDirectSignal(BlockState state, BlockGetter world, BlockPos pos, Direction direction) {
         return state.getSignal(world, pos, direction);
diff --git a/src/main/java/net/minecraft/world/level/block/PoweredBlock.java b/src/main/java/net/minecraft/world/level/block/PoweredBlock.java
index 0afffc33f3be221a28c62115f493808aeffb1bd8..0bd23df47085d578102a28157e309b585f4231f8 100644
--- a/src/main/java/net/minecraft/world/level/block/PoweredBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/PoweredBlock.java
@@ -16,6 +16,13 @@ public class PoweredBlock extends Block {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(net.minecraft.world.level.Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+    // Paper end
+
     @Override
     public int getSignal(BlockState state, BlockGetter world, BlockPos pos, Direction direction) {
         return 15;
diff --git a/src/main/java/net/minecraft/world/level/block/RedStoneWireBlock.java b/src/main/java/net/minecraft/world/level/block/RedStoneWireBlock.java
index f7cda51086043bf4b1b613450639d8b44b418013..645cf8b1c81334cce91ec668dda00e3c546916f6 100644
--- a/src/main/java/net/minecraft/world/level/block/RedStoneWireBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/RedStoneWireBlock.java
@@ -253,7 +253,7 @@ public class RedStoneWireBlock extends Block {
         return floor.isFaceSturdy(world, pos, Direction.UP) || floor.is(Blocks.HOPPER);
     }
 
-    // Paper start - Optimize redstone
+    // Paper start - Optimize redstone (Eigencraft)
     // The bulk of the new functionality is found in RedstoneWireTurbo.java
     com.destroystokyo.paper.util.RedstoneWireTurbo turbo = new com.destroystokyo.paper.util.RedstoneWireTurbo(this);
 
@@ -460,7 +460,13 @@ public class RedStoneWireBlock extends Block {
     @Override
     public void onPlace(BlockState state, Level world, BlockPos pos, BlockState oldState, boolean notify) {
         if (!oldState.is(state.getBlock()) && !world.isClientSide) {
-            this.updateSurroundingRedstone(world, pos, state, null); // Paper - Optimize redstone
+            // Paper start - optimize redstone - replace call to updatePowerStrength
+            if (world.paperConfig.redstoneImplementation == com.destroystokyo.paper.PaperWorldConfig.RedstoneImplementation.ALTERNATE_CURRENT) {
+                world.getWireHandler().onWireAdded(pos); // Alternate Current
+            } else {
+                this.updateSurroundingRedstone(world, pos, state, null); // vanilla/Eigencraft
+            }
+            // Paper end
             Iterator iterator = Direction.Plane.VERTICAL.iterator();
 
             while (iterator.hasNext()) {
@@ -487,7 +493,13 @@ public class RedStoneWireBlock extends Block {
                     world.updateNeighborsAt(pos.relative(enumdirection), this);
                 }
 
-                this.updateSurroundingRedstone(world, pos, state, null); // Paper - Optimize redstone
+                // Paper start - optimize redstone - replace call to updatePowerStrength
+                if (world.paperConfig.redstoneImplementation == com.destroystokyo.paper.PaperWorldConfig.RedstoneImplementation.ALTERNATE_CURRENT) {
+                    world.getWireHandler().onWireRemoved(pos, state); // Alternate Current
+                } else {
+                    this.updateSurroundingRedstone(world, pos, state, null); // vanilla/Eigencraft
+                }
+                // Paper end
                 this.updateNeighborsOfNeighboringWires(world, pos);
             }
         }
@@ -521,8 +533,14 @@ public class RedStoneWireBlock extends Block {
     @Override
     public void neighborChanged(BlockState state, Level world, BlockPos pos, Block sourceBlock, BlockPos sourcePos, boolean notify) {
         if (!world.isClientSide) {
+            // Paper start - optimize redstone (Alternate Current)
+            // Alternate Current handles breaking of redstone wires in the WireHandler.
+            if (world.paperConfig.redstoneImplementation == com.destroystokyo.paper.PaperWorldConfig.RedstoneImplementation.ALTERNATE_CURRENT) {
+                world.getWireHandler().onWireUpdated(pos);
+            } else
+            // Paper end
             if (state.canSurvive(world, pos)) {
-                this.updateSurroundingRedstone(world, pos, state, sourcePos); // Paper - Optimize redstone
+                this.updateSurroundingRedstone(world, pos, state, sourcePos); // Paper - Optimize redstone (Eigencraft)
             } else {
                 dropResources(state, world, pos);
                 world.removeBlock(pos, false);
diff --git a/src/main/java/net/minecraft/world/level/block/RedstoneTorchBlock.java b/src/main/java/net/minecraft/world/level/block/RedstoneTorchBlock.java
index da07fce0cf7c9fbdb57d2c59e431b59bf583bf50..ac178507010a8c879ccf28764166b100c4a32788 100644
--- a/src/main/java/net/minecraft/world/level/block/RedstoneTorchBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/RedstoneTorchBlock.java
@@ -139,6 +139,18 @@ public class RedstoneTorchBlock extends TorchBlock {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return dir != Direction.UP;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return dir == Direction.DOWN;
+    }
+    // Paper end
+
     @Override
     public void animateTick(BlockState state, Level world, BlockPos pos, RandomSource random) {
         if ((Boolean) state.getValue(RedstoneTorchBlock.LIT)) {
diff --git a/src/main/java/net/minecraft/world/level/block/RedstoneWallTorchBlock.java b/src/main/java/net/minecraft/world/level/block/RedstoneWallTorchBlock.java
index e5a4525ae64454ec1400de1e4e7945b2caa675f8..cbc2dc375053e304bdcd40b517028dd931056b54 100644
--- a/src/main/java/net/minecraft/world/level/block/RedstoneWallTorchBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/RedstoneWallTorchBlock.java
@@ -76,6 +76,13 @@ public class RedstoneWallTorchBlock extends RedstoneTorchBlock {
         return state.getValue(LIT) && state.getValue(FACING) != direction ? 15 : 0;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return state.getValue(FACING) != dir;
+    }
+    // Paper end
+
     @Override
     public BlockState rotate(BlockState state, Rotation rotation) {
         return Blocks.WALL_TORCH.rotate(state, rotation);
diff --git a/src/main/java/net/minecraft/world/level/block/SculkSensorBlock.java b/src/main/java/net/minecraft/world/level/block/SculkSensorBlock.java
index bdb6875dff56b7b909bfa9ddc58570d8dfafca8e..ec00dc5bcd2a5ab0dd3e70ddc6bc29673da9da10 100644
--- a/src/main/java/net/minecraft/world/level/block/SculkSensorBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/SculkSensorBlock.java
@@ -224,6 +224,13 @@ public class SculkSensorBlock extends BaseEntityBlock implements SimpleWaterlogg
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+    // Paper end
+
     @Override
     public int getSignal(BlockState state, BlockGetter world, BlockPos pos, Direction direction) {
         return (Integer) state.getValue(SculkSensorBlock.POWER);
diff --git a/src/main/java/net/minecraft/world/level/block/TargetBlock.java b/src/main/java/net/minecraft/world/level/block/TargetBlock.java
index 69eaf1341d282c4783dab84533ea2c053deed529..f2839769d49f9158c163908ec597c5ed7e0f49f8 100644
--- a/src/main/java/net/minecraft/world/level/block/TargetBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/TargetBlock.java
@@ -112,6 +112,13 @@ public class TargetBlock extends Block {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+    // Paper end
+
     @Override
     protected void createBlockStateDefinition(StateDefinition.Builder<Block, BlockState> builder) {
         builder.add(OUTPUT_POWER);
diff --git a/src/main/java/net/minecraft/world/level/block/TrappedChestBlock.java b/src/main/java/net/minecraft/world/level/block/TrappedChestBlock.java
index 184c70cd2954f4904518c3fee2a377d9c4e81cc3..316fd2758a3a981fd1a5e3603a4b7a064270f7fb 100644
--- a/src/main/java/net/minecraft/world/level/block/TrappedChestBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/TrappedChestBlock.java
@@ -36,6 +36,18 @@ public class TrappedChestBlock extends ChestBlock {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(net.minecraft.world.level.Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(net.minecraft.world.level.Level level, BlockPos pos, BlockState state, Direction dir) {
+        return dir == Direction.UP;
+    }
+    // Paper end
+
     @Override
     public int getSignal(BlockState state, BlockGetter world, BlockPos pos, Direction direction) {
         return Mth.clamp(ChestBlockEntity.getOpenCount(world, pos), 0, 15);
diff --git a/src/main/java/net/minecraft/world/level/block/TripWireHookBlock.java b/src/main/java/net/minecraft/world/level/block/TripWireHookBlock.java
index 004dce26ff073f1de52a84cd425c4f60fdab5e50..90555e0cef5936aa5e63821e65abb84fec001fd7 100644
--- a/src/main/java/net/minecraft/world/level/block/TripWireHookBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/TripWireHookBlock.java
@@ -266,6 +266,18 @@ public class TripWireHookBlock extends Block {
         return true;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    @Override
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return true;
+    }
+
+    @Override
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return state.getValue(FACING) == dir;
+    }
+    // Paper end
+
     @Override
     public BlockState rotate(BlockState state, Rotation rotation) {
         return (BlockState) state.setValue(TripWireHookBlock.FACING, rotation.rotate((Direction) state.getValue(TripWireHookBlock.FACING)));
diff --git a/src/main/java/net/minecraft/world/level/block/state/BlockBehaviour.java b/src/main/java/net/minecraft/world/level/block/state/BlockBehaviour.java
index 771c6cf992664b65ffbf4ae0192bc7b09f77c2e6..939aca929038b90738c9b78c2fc3611088b18e72 100644
--- a/src/main/java/net/minecraft/world/level/block/state/BlockBehaviour.java
+++ b/src/main/java/net/minecraft/world/level/block/state/BlockBehaviour.java
@@ -188,6 +188,16 @@ public abstract class BlockBehaviour {
         return false;
     }
 
+    // Paper start - optimize redstone (Alternate Current)
+    public boolean isSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return false;
+    }
+
+    public boolean isDirectSignalSourceTo(Level level, BlockPos pos, BlockState state, Direction dir) {
+        return false;
+    }
+    // Paper end
+
     /** @deprecated */
     @Deprecated
     public PushReaction getPistonPushReaction(BlockState state) {
@@ -866,6 +876,16 @@ public abstract class BlockBehaviour {
             return this.getBlock().isSignalSource(this.asState());
         }
 
+        // Paper start - optimize redstone (Alternate Current)
+        public boolean isSignalSourceTo(Level level, BlockPos pos, Direction dir) {
+            return this.getBlock().isSignalSourceTo(level, pos, this.asState(), dir);
+        }
+
+        public boolean isDirectSignalSourceTo(Level level, BlockPos pos, Direction dir) {
+            return this.getBlock().isDirectSignalSourceTo(level, pos, this.asState(), dir);
+        }
+        // Paper end
+
         public int getSignal(BlockGetter world, BlockPos pos, Direction direction) {
             return this.getBlock().getSignal(this.asState(), world, pos, direction);
         }