Minestom/src/main/java/net/minestom/server/tag/Tag.java

package net.minestom.server.tag;

import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;
import net.minestom.server.item.ItemStack;
import org.jetbrains.annotations.ApiStatus;
import org.jetbrains.annotations.Contract;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import org.jglrxavpok.hephaistos.nbt.*;
import org.jglrxavpok.hephaistos.nbt.mutable.MutableNBTCompound;

import java.util.function.Function;
import java.util.function.Supplier;

/**
 * Represents a key to retrieve or change a value.
 * <p>
 * All tags are serializable.
 *
 * @param <T> the tag type
 */
@ApiStatus.NonExtendable
public class Tag<T> {
    private static final Object2IntOpenHashMap<String> INDEX_MAP = new Object2IntOpenHashMap<>();
    private static int lastIndex = 0; // Synchronized on INDEX_MAP

    static {
        INDEX_MAP.defaultReturnValue(-1);
    }

    private final String key;
    private final Function<NBT, T> readFunction;
    private final Function<T, NBT> writeFunction;
    private final Supplier<T> defaultValue;

    final int index;

    protected Tag(@NotNull String key,
                  @NotNull Function<NBT, T> readFunction,
                  @NotNull Function<T, NBT> writeFunction,
                  @Nullable Supplier<T> defaultValue) {
        this.key = key;
        this.readFunction = readFunction;
        this.writeFunction = writeFunction;
        this.defaultValue = defaultValue;

        // Potentially very hot code!
        // First try to get the index from the cpu cache
        // If it's not there, synchronization is required
        int index = INDEX_MAP.getInt(key);
        if (index == -1) {
            synchronized (INDEX_MAP) {
                index = INDEX_MAP.getInt(key);
                if (index == -1) {
                    index = lastIndex++;
                    INDEX_MAP.put(key, index);
                }
            }
        }
        this.index = index;
    }

    static <T, N extends NBT> Tag<T> tag(@NotNull String key,
                                         @NotNull Class<N> nbtClass,
                                         @NotNull Function<N, T> readFunction,
                                         @NotNull Function<T, N> writeFunction) {
        return new Tag<T>(key, (Function<NBT, T>) readFunction, (Function<T, NBT>) writeFunction, null);
    }

    /**
     * Returns the key used to navigate inside the holder nbt.
     *
     * @return the tag key
     */
    public @NotNull String getKey() {
        return key;
    }

    @Contract(value = "_ -> new", pure = true)
    public Tag<T> defaultValue(@NotNull Supplier<T> defaultValue) {
        return new Tag<>(key, readFunction, writeFunction, defaultValue);
    }

    @Contract(value = "_ -> new", pure = true)
    public Tag<T> defaultValue(@NotNull T defaultValue) {
        return defaultValue(() -> defaultValue);
    }

    @Contract(value = "_, _ -> new", pure = true)
    public <R> Tag<R> map(@NotNull Function<T, R> readMap,
                          @NotNull Function<R, T> writeMap) {
        return new Tag<>(key,
                // Read
                readFunction.andThen(t -> {
                    if (t == null) return null;
                    return readMap.apply(t);
                }),
                // Write
                writeMap.andThen(writeFunction),
                // Default value
                () -> readMap.apply(createDefault()));
    }

    public @Nullable T read(@NotNull NBTCompoundLike nbt) {
        final String key = this.key;
        if (key.isEmpty()) {
            // Special handling for view tag
            return convertToValue(nbt.toCompound());
        }
        final NBT subTag = nbt.get(key);
        return convertToValue(subTag);
    }

    T createDefault() {
        final var supplier = defaultValue;
        return supplier != null ? supplier.get() : null;
    }

    public void write(@NotNull MutableNBTCompound nbtCompound, @Nullable T value) {
        final String key = this.key;
        if (value != null) {
            final NBT nbt = writeFunction.apply(value);
            if (key.isEmpty()) nbtCompound.copyFrom((NBTCompoundLike) nbt);
            else nbtCompound.set(key, nbt);
        } else {
            if (key.isEmpty()) nbtCompound.clear();
            else nbtCompound.remove(key);
        }
    }

    public void writeUnsafe(@NotNull MutableNBTCompound nbtCompound, @Nullable Object value) {
        //noinspection unchecked
        write(nbtCompound, (T) value);
    }

    T convertToValue(NBT nbt) {
        final T result;
        try {
            if (nbt == null || (result = readFunction.apply(nbt)) == null)
                return createDefault();
            return result;
        } catch (ClassCastException e) {
            return createDefault();
        }
    }

    NBT convertToNbt(T value) {
        return writeFunction.apply(value);
    }

    public static @NotNull Tag<Byte> Byte(@NotNull String key) {
        return tag(key, NBTByte.class, NBTByte::getValue, NBT::Byte);
    }

    public static @NotNull Tag<Short> Short(@NotNull String key) {
        return tag(key, NBTShort.class, NBTShort::getValue, NBT::Short);
    }

    public static @NotNull Tag<Integer> Integer(@NotNull String key) {
        return tag(key, NBTInt.class, NBTInt::getValue, NBT::Int);
    }

    public static @NotNull Tag<Long> Long(@NotNull String key) {
        return tag(key, NBTLong.class, NBTLong::getValue, NBT::Long);
    }

    public static @NotNull Tag<Float> Float(@NotNull String key) {
        return tag(key, NBTFloat.class, NBTFloat::getValue, NBT::Float);
    }

    public static @NotNull Tag<Double> Double(@NotNull String key) {
        return tag(key, NBTDouble.class, NBTDouble::getValue, NBT::Double);
    }

    public static @NotNull Tag<String> String(@NotNull String key) {
        return tag(key, NBTString.class, NBTString::getValue, NBT::String);
    }

    public static <T extends NBT> @NotNull Tag<T> NBT(@NotNull String key) {
        //noinspection unchecked
        return tag(key, NBT.class, nbt -> (T) nbt, t -> t);
    }

    /**
     * Create a wrapper around a compound.
     *
     * @param key        the tag key
     * @param serializer the tag serializer
     * @param <T>        the tag type
     * @return the created tag
     */
    public static <T> @NotNull Tag<T> Structure(@NotNull String key, @NotNull TagSerializer<T> serializer) {
        return tag(key, NBTCompound.class,
                nbt -> serializer.read(TagHandler.fromCompound(nbt)),
                (value) -> {
                    TagHandler handler = TagHandler.newHandler();
                    serializer.write(handler, value);
                    return handler.asCompound();
                });
    }

    public static <T> @NotNull Tag<T> View(@NotNull TagSerializer<T> serializer) {
        return tag("", NBTCompound.class,
                nbt -> serializer.read(TagHandler.fromCompound(nbt)),
                (value) -> {
                    TagHandler handler = TagHandler.newHandler();
                    serializer.write(handler, value);
                    return handler.asCompound();
                });
    }

    public static @NotNull Tag<ItemStack> ItemStack(@NotNull String key) {
        return tag(key, NBTCompound.class, ItemStack::fromItemNBT, ItemStack::toItemNBT);
    }
}