Minestom/src/main/java/net/minestom/server/item/ItemStackImpl.java

package net.minestom.server.item;

import net.kyori.adventure.nbt.CompoundBinaryTag;
import net.minestom.server.ServerFlag;
import net.minestom.server.item.rule.VanillaStackingRule;
import net.minestom.server.tag.Tag;
import net.minestom.server.tag.TagHandler;
import org.jetbrains.annotations.Contract;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.util.function.Consumer;

record ItemStackImpl(Material material, int amount, ItemMetaImpl meta) implements ItemStack {
    static final @NotNull StackingRule DEFAULT_STACKING_RULE;

    static {
        if (ServerFlag.STACKING_RULE == null) {
            DEFAULT_STACKING_RULE = new VanillaStackingRule();
        } else {
            try {
                DEFAULT_STACKING_RULE = (StackingRule) ClassLoader.getSystemClassLoader()
                        .loadClass(ServerFlag.STACKING_RULE).getConstructor().newInstance();
            } catch (Exception e) {
                throw new RuntimeException("Could not instantiate default stacking rule", e);
            }
        }
    }

    static ItemStack create(Material material, int amount, ItemMetaImpl meta) {
        if (amount <= 0) return AIR;
        return new ItemStackImpl(material, amount, meta);
    }

    static ItemStack create(Material material, int amount) {
        return create(material, amount, ItemMetaImpl.EMPTY);
    }

    @Override
    public <T extends ItemMetaView<?>> @NotNull T meta(@NotNull Class<T> metaClass) {
        return ItemMetaViewImpl.construct(metaClass, meta);
    }

    @Override
    public @NotNull ItemStack with(@NotNull Consumer<ItemStack.@NotNull Builder> consumer) {
        ItemStack.Builder builder = builder();
        consumer.accept(builder);
        return builder.build();
    }

    @Override
    public @NotNull <V extends ItemMetaView.Builder, T extends ItemMetaView<V>> ItemStack withMeta(@NotNull Class<T> metaType,
                                                                                                   @NotNull Consumer<V> consumer) {
        return builder().meta(metaType, consumer).build();
    }

    @Override
    public @NotNull ItemStack withMeta(@NotNull Consumer<ItemMeta.@NotNull Builder> consumer) {
        return builder().meta(consumer).build();
    }

    @Override
    public @NotNull ItemStack withMaterial(@NotNull Material material) {
        return new ItemStackImpl(material, amount, meta);
    }

    @Override
    public @NotNull ItemStack withAmount(int amount) {
        return create(material, amount, meta);
    }

    @Override
    public @NotNull ItemStack consume(int amount) {
        return DEFAULT_STACKING_RULE.apply(this, currentAmount -> currentAmount - amount);
    }

    @Override
    public @NotNull ItemStack withMeta(@NotNull ItemMeta meta) {
        return new ItemStackImpl(material, amount, (ItemMetaImpl) meta);
    }

    @Override
    public boolean isSimilar(@NotNull ItemStack itemStack) {
        return material == itemStack.material() && meta.equals(itemStack.meta());
    }

    @Override
    public @NotNull CompoundBinaryTag toItemNBT() {
        CompoundBinaryTag.Builder builder = CompoundBinaryTag.builder()
                .putString("id", material.name())
                .putByte("Count", (byte) amount);
        CompoundBinaryTag nbt = meta.toNBT();
        if (nbt.size() > 0) builder.put("tag", nbt);
        return builder.build();
    }

    @Contract(value = "-> new", pure = true)
    private @NotNull ItemStack.Builder builder() {
        return new Builder(material, amount, new ItemMetaImpl.Builder(meta.tagHandler().copy()));
    }

    static final class Builder implements ItemStack.Builder {
        final Material material;
        int amount;
        ItemMetaImpl.Builder metaBuilder;

        Builder(Material material, int amount, ItemMetaImpl.Builder metaBuilder) {
            this.material = material;
            this.amount = amount;
            this.metaBuilder = metaBuilder;
        }

        Builder(Material material, int amount) {
            this(material, amount, new ItemMetaImpl.Builder(TagHandler.newHandler()));
        }

        @Override
        public ItemStack.@NotNull Builder amount(int amount) {
            this.amount = amount;
            return this;
        }

        @Override
        public ItemStack.@NotNull Builder meta(@NotNull TagHandler tagHandler) {
            return metaBuilder(new ItemMetaImpl.Builder(tagHandler.copy()));
        }

        @Override
        public ItemStack.@NotNull Builder meta(@NotNull CompoundBinaryTag compound) {
            return metaBuilder(new ItemMetaImpl.Builder(TagHandler.fromCompound(compound)));
        }

        @Override
        public ItemStack.@NotNull Builder meta(@NotNull ItemMeta itemMeta) {
            final TagHandler tagHandler = ((ItemMetaImpl) itemMeta).tagHandler();
            return metaBuilder(new ItemMetaImpl.Builder(tagHandler.copy()));
        }

        @Override
        public ItemStack.@NotNull Builder meta(@NotNull Consumer<ItemMeta.Builder> consumer) {
            consumer.accept(metaBuilder);
            return this;
        }

        @Override
        public <V extends ItemMetaView.Builder, T extends ItemMetaView<V>> ItemStack.@NotNull Builder meta(@NotNull Class<T> metaType,
                                                                                                           @NotNull Consumer<@NotNull V> itemMetaConsumer) {
            V view = ItemMetaViewImpl.constructBuilder(metaType, metaBuilder.tagHandler());
            itemMetaConsumer.accept(view);
            return this;
        }

        @Override
        public <T> void setTag(@NotNull Tag<T> tag, @Nullable T value) {
            this.metaBuilder.setTag(tag, value);
        }

        @Override
        public @NotNull ItemStack build() {
            return ItemStackImpl.create(material, amount, metaBuilder.build());
        }

        private ItemStack.@NotNull Builder metaBuilder(@NotNull ItemMetaImpl.Builder builder) {
            this.metaBuilder = builder;
            return this;
        }
    }
}