/*
 *  ProtocolLib - Bukkit server library that allows access to the Minecraft protocol.
 *  Copyright (C) 2012 Kristian S. Stangeland
 *
 *  This program is free software; you can redistribute it and/or modify it under the terms of the
 *  GNU General Public License as published by the Free Software Foundation; either version 2 of
 *  the License, or (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 *  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *  See the GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along with this program;
 *  if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
 *  02111-1307 USA
 */

package com.comphenix.protocol.concurrency;

import com.google.common.base.Objects;
import com.google.common.collect.Range;

import java.util.HashSet;
import java.util.Map;
import java.util.NavigableMap;
import java.util.Set;
import java.util.TreeMap;

/**
 * Represents a generic store of intervals and associated values. No two intervals
 * can overlap in this representation.
 * <p>
 * Note that this implementation is not thread safe.
 * 
 * @author Kristian
 *
 * @param <TKey> - type of the key. Must implement Comparable.
 * @param <TValue> - type of the value to associate.
 */
public abstract class AbstractIntervalTree<TKey extends Comparable<TKey>, TValue> {
    
    protected enum State {
        OPEN,
        CLOSE,
        BOTH
    }
    
    /**
     * Represents a range and a value in this interval tree.
     */
    public class Entry implements Map.Entry<Range<TKey>, TValue> {
        private final EndPoint left;
        private final EndPoint right;

        Entry(EndPoint left, EndPoint right) {
            if (left == null)
                throw new IllegalAccessError("left cannot be NUll");
            if (right == null)
                throw new IllegalAccessError("right cannot be NUll");
            if (left.key.compareTo(right.key) > 0)
                throw new IllegalArgumentException(
                        "Left key (" + left.key + ") cannot be greater than the right key (" + right.key + ")");
            
            this.left = left;
            this.right = right;
        }

        @Override
        public Range<TKey> getKey() {
            return Range.closed(left.key, right.key);
        }

        @Override
        public TValue getValue() {
            return left.value;
        }

        @Override
        public TValue setValue(TValue value) {
            TValue old = left.value;
            
            // Set both end points
            left.value = value;
            right.value = value;
            return old;
        }
        
        @SuppressWarnings("rawtypes")
        @Override
        public boolean equals(Object obj) {
            // Quick equality check
            if (obj == this) {
                return true;
            } else if (obj instanceof AbstractIntervalTree.Entry) {
                return Objects.equal(left.key, ((AbstractIntervalTree.Entry) obj).left.key) &&
                       Objects.equal(right.key, ((AbstractIntervalTree.Entry) obj).right.key) &&
                       Objects.equal(left.value, ((AbstractIntervalTree.Entry) obj).left.value);
            } else {
                return false;
            }
        }
        
        @Override
        public int hashCode() {
            return Objects.hashCode(left.key, right.key, left.value);
        }
        
        @Override
        public String toString() {
            return String.format("Value %s at [%s, %s]", left.value, left.key, right.key);
        }
    }
    
    /**
     * Represents a single end point (open, close or both) of a range.
     */
    protected class EndPoint {
        
        // Whether or not the end-point is opening a range, closing a range or both.
        public State state;
        
        // The value this range contains
        public TValue value;
        
        // The key of this end point
        public TKey key;

        public EndPoint(State state, TKey key, TValue value) {
            this.state = state;
            this.key = key;
            this.value = value;
        }
    }
    
    // To quickly look up ranges we'll index them by endpoints
    protected NavigableMap<TKey, EndPoint> bounds = new TreeMap<>();
    
    /**
     * Removes every interval that intersects with the given range.
     * @param lowerBound - lowest value to remove.
     * @param upperBound - highest value to remove.
     * @return Intervals that were removed
     */
    public Set<Entry> remove(TKey lowerBound, TKey upperBound) {
        return remove(lowerBound, upperBound, false);
    }
    
    /**
     * Removes every interval that intersects with the given range.
     * @param lowerBound - lowest value to remove.
     * @param upperBound - highest value to remove.
     * @param preserveDifference - whether or not to preserve the intervals that are partially outside.
     * @return Intervals that were removed
     */
    public Set<Entry> remove(TKey lowerBound, TKey upperBound, boolean preserveDifference) {
        checkBounds(lowerBound, upperBound);
        NavigableMap<TKey, EndPoint> range = bounds.subMap(lowerBound, true, upperBound, true);
        
        EndPoint first = getNextEndPoint(lowerBound, true);
        EndPoint last = getPreviousEndPoint(upperBound, true);
        
        // Used while resizing intervals
        EndPoint previous = null;
        EndPoint next = null;
        
        Set<Entry> resized = new HashSet<>();
        Set<Entry> removed = new HashSet<>();
        
        // Remove the previous element too. A close end-point must be preceded by an OPEN end-point.
        if (first != null && first.state == State.CLOSE) {
            previous = getPreviousEndPoint(first.key, false);
            
            // Add the interval back
            if (previous != null) {
                removed.add(getEntry(previous, first));
            }
        }
        
        // Get the closing element too.
        if (last != null && last.state == State.OPEN) {
            next = getNextEndPoint(last.key, false);
        
            if (next != null) {
                removed.add(getEntry(last, next));
            }
        }
        
        // Now remove both ranges
        removeEntrySafely(previous, first);
        removeEntrySafely(last, next);
        
        // Add new resized intervals
        if (preserveDifference) {
            if (previous != null) {
                resized.add(putUnsafe(previous.key, decrementKey(lowerBound), previous.value));
            }
            if (next != null) {
                resized.add(putUnsafe(incrementKey(upperBound), next.key, next.value));
            }
        }
        
        // Get the removed entries too
        getEntries(removed, range);
        invokeEntryRemoved(removed);
        
        if (preserveDifference) {
            invokeEntryAdded(resized);
        }
        
        // Remove the range as well
        range.clear();
        return removed;
    }
    
    /**
     * Retrieve the entry from a given set of end points.
     * @param left - leftmost end point.
     * @param right - rightmost end point.
     * @return The associated entry.
     */
    protected Entry getEntry(EndPoint left, EndPoint right) {
        if (left == null)
            throw new IllegalArgumentException("left endpoint cannot be NULL.");
        if (right == null)
            throw new IllegalArgumentException("right endpoint cannot be NULL.");
        
        // Make sure the order is correct
        if (right.key.compareTo(left.key) < 0) {
            return getEntry(right, left);
        } else {
            return new Entry(left, right);
        }
    }
    
    private void removeEntrySafely(EndPoint left, EndPoint right) {
        if (left != null && right != null) {
            bounds.remove(left.key);
            bounds.remove(right.key);
        }
    }
    
    // Adds a given end point
    protected EndPoint addEndPoint(TKey key, TValue value, State state) {
        EndPoint endPoint = bounds.get(key);
        
        if (endPoint != null) {
            endPoint.state = State.BOTH;
        } else {
            endPoint = new EndPoint(state, key, value);
            bounds.put(key, endPoint);
        }
        return endPoint;
    }
    
    /**
     * Associates a given interval of keys with a certain value. Any previous
     * association will be overwritten in the given interval.
     * <p>
     * Overlapping intervals are not permitted. A key can only be associated with a single value.
     * 
     * @param lowerBound - the minimum key (inclusive).
     * @param upperBound - the maximum key (inclusive).
     * @param value - the value, or NULL to reset this range.
     */
    public void put(TKey lowerBound, TKey upperBound, TValue value) {
        // While we don't permit overlapping intervals, we'll still allow overwriting existing intervals.
        remove(lowerBound, upperBound, true);
        invokeEntryAdded(putUnsafe(lowerBound, upperBound, value));
    }
    
    /**
     * Associates a given interval without performing any interval checks.
     * @param lowerBound - the minimum key (inclusive).
     * @param upperBound - the maximum key (inclusive).
     * @param value - the value, or NULL to reset the range.
     */
    private Entry putUnsafe(TKey lowerBound, TKey upperBound, TValue value) {
        // OK. Add the end points now
        if (value != null) {
            EndPoint left = addEndPoint(lowerBound, value, State.OPEN);
            EndPoint right = addEndPoint(upperBound, value, State.CLOSE);

            return new Entry(left, right);
        } else {
            return null;
        }
    }
    
    /**
     * Used to verify the validity of the given interval.
     * @param lowerBound - lower bound (inclusive).
     * @param upperBound - upper bound (inclusive).
     */
    private void checkBounds(TKey lowerBound, TKey upperBound) {
        if (lowerBound == null)
            throw new IllegalAccessError("lowerbound cannot be NULL.");
        if (upperBound == null)
            throw new IllegalAccessError("upperBound cannot be NULL.");
        if (upperBound.compareTo(lowerBound) < 0)
            throw new IllegalArgumentException("upperBound cannot be less than lowerBound.");
    }
    
    /**
     * Determines if the given key is within an interval.
     * @param key - key to check.
     * @return TRUE if the given key is within an interval in this tree, FALSE otherwise.
     */
    public boolean containsKey(TKey key) {
        return getEndPoint(key) != null;
    }
    
    /**
     * Enumerates over every range in this interval tree.
     * @return Number of ranges.
     */
    public Set<Entry> entrySet() {
        // Don't mind the Java noise
        Set<Entry> result = new HashSet<>();
        getEntries(result, bounds);
        return result;
    }
    
    /**
     * Remove every interval.
     */
    public void clear() {
        if (!bounds.isEmpty()) {
            remove(bounds.firstKey(), bounds.lastKey());
        }
    }
    
    /**
     * Converts a map of end points into a set of entries.
     * @param destination - set of entries.
     * @param map - a map of end points.
     */
    private void getEntries(Set<Entry> destination, NavigableMap<TKey, EndPoint> map) {
        Map.Entry<TKey, EndPoint> last = null;
        
        for (Map.Entry<TKey, EndPoint> entry : map.entrySet()) {
            switch (entry.getValue().state) {
            case BOTH:
                EndPoint point = entry.getValue();
                destination.add(new Entry(point, point));
                break;
            case CLOSE:
                if (last != null) {
                    destination.add(new Entry(last.getValue(), entry.getValue()));
                }
                break;
            case OPEN:
                // We don't know the full range yet
                last = entry;
                break;
            default:
                throw new IllegalStateException("Illegal open/close state detected.");
            }
        }
    }
    
    /**
     * Inserts every range from the given tree into the current tree.
     * @param other - the other tree to read from.
     */
    public void putAll(AbstractIntervalTree<TKey, TValue> other) {
        // Naively copy every range.
        for (Entry entry : other.entrySet()) {
            put(entry.left.key, entry.right.key, entry.getValue());
        }
    }
    
    /**
     * Retrieves the value of the range that matches the given key, or NULL if nothing was found.
     * @param key - the level to read for.
     * @return The correct amount of experience, or NULL if nothing was recorded.
     */
    public TValue get(TKey key) {
        EndPoint point = getEndPoint(key);

        if (point != null)
            return point.value;
        else
            return null;
    }
    
    /**
     * Get the left-most end-point associated with this key.
     * @param key - key to search for.
     * @return The end point found, or NULL.
     */
    protected EndPoint getEndPoint(TKey key) {
        EndPoint ends = bounds.get(key);
        
        if (ends != null) {
            // Always return the end point to the left
            if (ends.state == State.CLOSE) {
                Map.Entry<TKey, EndPoint> left = bounds.floorEntry(decrementKey(key));
                return left != null ? left.getValue() : null;
                
            } else {
                return ends;
            }
            
        } else {
            // We need to determine if the point intersects with a range
            Map.Entry<TKey, EndPoint> left = bounds.floorEntry(key);
            
            // We only need to check to the left
            if (left != null && left.getValue().state == State.OPEN) {
                return left.getValue();
            } else {
                return null;
            }
        }
    }
    
    /**
     * Get the previous end point of a given key.
     * @param point - the point to search with.
     * @param inclusive - whether or not to include the current point in the search.
     * @return The previous end point of a given given key, or NULL if not found.
     */
    protected EndPoint getPreviousEndPoint(TKey point, boolean inclusive) {
        if (point != null) {
            Map.Entry<TKey, EndPoint> previous = bounds.floorEntry(inclusive ? point : decrementKey(point));
        
            if (previous != null)
                return previous.getValue();
        }
        return null;
    }
    
    /**
     * Get the next end point of a given key.
     * @param point - the point to search with.
     * @param inclusive - whether or not to include the current point in the search.
     * @return The next end point of a given given key, or NULL if not found.
     */
    protected EndPoint getNextEndPoint(TKey point, boolean inclusive) {
        if (point != null) {
            Map.Entry<TKey, EndPoint> next = bounds.ceilingEntry(inclusive ? point : incrementKey(point));
        
            if (next != null)
                return next.getValue();
        }
        return null;
    }

    private void invokeEntryAdded(Entry added) {
        if (added != null) {
            onEntryAdded(added);
        }
    }
    
    private void invokeEntryAdded(Set<Entry> added) {
        for (Entry entry : added) {
            onEntryAdded(entry);
        }
    }

    private void invokeEntryRemoved(Set<Entry> removed) {
        for (Entry entry : removed) {
            onEntryRemoved(entry);
        }
    }
    
    // Listeners for added or removed entries
    /**
     * Invoked when an entry is added.
     * @param added - the entry that was added.
     */
    protected void onEntryAdded(Entry added) { }
    
    /**
     * Invoked when an entry is removed.
     * @param removed - the removed entry.
     */
    protected void onEntryRemoved(Entry removed) { }
    
    // Helpers for decrementing or incrementing key values
    /**
     * Decrement the given key by one unit.
     * @param key - the key that should be decremented.
     * @return The new decremented key.
     */
    protected abstract TKey decrementKey(TKey key);
    
    /**
     * Increment the given key by one unit.
     * @param key - the key that should be incremented.
     * @return The new incremented key.
     */
    protected abstract TKey incrementKey(TKey key);
}