Code/net/minecraft/world/level/block/entity/LecternBlockEntity.java

package net.minecraft.world.level.block.entity;

import javax.annotation.Nullable;
import net.minecraft.commands.CommandSource;
import net.minecraft.commands.CommandSourceStack;
import net.minecraft.core.BlockPos;
import net.minecraft.core.Direction;
import net.minecraft.core.HolderLookup;
import net.minecraft.core.component.DataComponents;
import net.minecraft.nbt.CompoundTag;
import net.minecraft.nbt.NbtOps;
import net.minecraft.nbt.Tag;
import net.minecraft.network.chat.Component;
import net.minecraft.resources.RegistryOps;
import net.minecraft.server.level.ServerLevel;
import net.minecraft.util.Mth;
import net.minecraft.world.Clearable;
import net.minecraft.world.Container;
import net.minecraft.world.MenuProvider;
import net.minecraft.world.entity.item.ItemEntity;
import net.minecraft.world.entity.player.Inventory;
import net.minecraft.world.entity.player.Player;
import net.minecraft.world.inventory.AbstractContainerMenu;
import net.minecraft.world.inventory.ContainerData;
import net.minecraft.world.inventory.LecternMenu;
import net.minecraft.world.item.ItemStack;
import net.minecraft.world.item.component.WritableBookContent;
import net.minecraft.world.item.component.WrittenBookContent;
import net.minecraft.world.level.block.LecternBlock;
import net.minecraft.world.level.block.state.BlockState;
import net.minecraft.world.phys.Vec2;
import net.minecraft.world.phys.Vec3;

public class LecternBlockEntity extends BlockEntity implements Clearable, MenuProvider {
    public static final int DATA_PAGE = 0;
    public static final int NUM_DATA = 1;
    public static final int SLOT_BOOK = 0;
    public static final int NUM_SLOTS = 1;
    private final Container bookAccess = new Container() {
        @Override
        public int getContainerSize() {
            return 1;
        }

        @Override
        public boolean isEmpty() {
            return LecternBlockEntity.this.book.isEmpty();
        }

        @Override
        public ItemStack getItem(int p_59580_) {
            return p_59580_ == 0 ? LecternBlockEntity.this.book : ItemStack.EMPTY;
        }

        @Override
        public ItemStack removeItem(int p_59582_, int p_59583_) {
            if (p_59582_ == 0) {
                ItemStack itemstack = LecternBlockEntity.this.book.split(p_59583_);
                if (LecternBlockEntity.this.book.isEmpty()) {
                    LecternBlockEntity.this.onBookItemRemove();
                }

                return itemstack;
            } else {
                return ItemStack.EMPTY;
            }
        }

        @Override
        public ItemStack removeItemNoUpdate(int p_59590_) {
            if (p_59590_ == 0) {
                ItemStack itemstack = LecternBlockEntity.this.book;
                LecternBlockEntity.this.book = ItemStack.EMPTY;
                LecternBlockEntity.this.onBookItemRemove();
                return itemstack;
            } else {
                return ItemStack.EMPTY;
            }
        }

        @Override
        public void setItem(int p_59585_, ItemStack p_59586_) {
        }

        @Override
        public int getMaxStackSize() {
            return 1;
        }

        @Override
        public void setChanged() {
            LecternBlockEntity.this.setChanged();
        }

        @Override
        public boolean stillValid(Player p_59588_) {
            return Container.stillValidBlockEntity(LecternBlockEntity.this, p_59588_) && LecternBlockEntity.this.hasBook();
        }

        @Override
        public boolean canPlaceItem(int p_59592_, ItemStack p_59593_) {
            return false;
        }

        @Override
        public void clearContent() {
        }
    };
    private final ContainerData dataAccess = new ContainerData() {
        @Override
        public int get(int p_59600_) {
            return p_59600_ == 0 ? LecternBlockEntity.this.page : 0;
        }

        @Override
        public void set(int p_59602_, int p_59603_) {
            if (p_59602_ == 0) {
                LecternBlockEntity.this.setPage(p_59603_);
            }
        }

        @Override
        public int getCount() {
            return 1;
        }
    };
    ItemStack book = ItemStack.EMPTY;
    int page;
    private int pageCount;

    public LecternBlockEntity(BlockPos p_155622_, BlockState p_155623_) {
        super(BlockEntityType.LECTERN, p_155622_, p_155623_);
    }

    public ItemStack getBook() {
        return this.book;
    }

    public boolean hasBook() {
        return this.book.has(DataComponents.WRITABLE_BOOK_CONTENT) || this.book.has(DataComponents.WRITTEN_BOOK_CONTENT);
    }

    public void setBook(ItemStack p_59537_) {
        this.setBook(p_59537_, null);
    }

    void onBookItemRemove() {
        this.page = 0;
        this.pageCount = 0;
        LecternBlock.resetBookState(null, this.getLevel(), this.getBlockPos(), this.getBlockState(), false);
    }

    public void setBook(ItemStack p_59539_, @Nullable Player p_59540_) {
        this.book = this.resolveBook(p_59539_, p_59540_);
        this.page = 0;
        this.pageCount = getPageCount(this.book);
        this.setChanged();
    }

    void setPage(int p_59533_) {
        int i = Mth.clamp(p_59533_, 0, this.pageCount - 1);
        if (i != this.page) {
            this.page = i;
            this.setChanged();
            LecternBlock.signalPageChange(this.getLevel(), this.getBlockPos(), this.getBlockState());
        }
    }

    public int getPage() {
        return this.page;
    }

    public int getRedstoneSignal() {
        float f = this.pageCount > 1 ? this.getPage() / (this.pageCount - 1.0F) : 1.0F;
        return Mth.floor(f * 14.0F) + (this.hasBook() ? 1 : 0);
    }

    private ItemStack resolveBook(ItemStack p_59555_, @Nullable Player p_59556_) {
        if (this.level instanceof ServerLevel serverlevel) {
            WrittenBookContent.resolveForItem(p_59555_, this.createCommandSourceStack(p_59556_, serverlevel), p_59556_);
        }

        return p_59555_;
    }

    private CommandSourceStack createCommandSourceStack(@Nullable Player p_59535_, ServerLevel p_370159_) {
        String s;
        Component component;
        if (p_59535_ == null) {
            s = "Lectern";
            component = Component.literal("Lectern");
        } else {
            s = p_59535_.getName().getString();
            component = p_59535_.getDisplayName();
        }

        Vec3 vec3 = Vec3.atCenterOf(this.worldPosition);
        return new CommandSourceStack(CommandSource.NULL, vec3, Vec2.ZERO, p_370159_, 2, s, component, p_370159_.getServer(), p_59535_);
    }

    @Override
    protected void loadAdditional(CompoundTag p_331238_, HolderLookup.Provider p_333677_) {
        super.loadAdditional(p_331238_, p_333677_);
        RegistryOps<Tag> registryops = p_333677_.createSerializationContext(NbtOps.INSTANCE);
        this.book = p_331238_.read("Book", ItemStack.CODEC, registryops)
            .map(p_395437_ -> this.resolveBook(p_395437_, null))
            .orElse(ItemStack.EMPTY);
        this.pageCount = getPageCount(this.book);
        this.page = Mth.clamp(p_331238_.getIntOr("Page", 0), 0, this.pageCount - 1);
    }

    @Override
    protected void saveAdditional(CompoundTag p_187509_, HolderLookup.Provider p_331979_) {
        super.saveAdditional(p_187509_, p_331979_);
        if (!this.getBook().isEmpty()) {
            RegistryOps<Tag> registryops = p_331979_.createSerializationContext(NbtOps.INSTANCE);
            p_187509_.store("Book", ItemStack.CODEC, registryops, this.getBook());
            p_187509_.putInt("Page", this.page);
        }
    }

    @Override
    public void clearContent() {
        this.setBook(ItemStack.EMPTY);
    }

    @Override
    public void preRemoveSideEffects(BlockPos p_394910_, BlockState p_391731_) {
        if (p_391731_.getValue(LecternBlock.HAS_BOOK) && this.level != null) {
            Direction direction = p_391731_.getValue(LecternBlock.FACING);
            ItemStack itemstack = this.getBook().copy();
            float f = 0.25F * direction.getStepX();
            float f1 = 0.25F * direction.getStepZ();
            ItemEntity itementity = new ItemEntity(
                this.level, p_394910_.getX() + 0.5 + f, p_394910_.getY() + 1, p_394910_.getZ() + 0.5 + f1, itemstack
            );
            itementity.setDefaultPickUpDelay();
            this.level.addFreshEntity(itementity);
        }
    }

    @Override
    public AbstractContainerMenu createMenu(int p_59562_, Inventory p_59563_, Player p_59564_) {
        return new LecternMenu(p_59562_, this.bookAccess, this.dataAccess);
    }

    @Override
    public Component getDisplayName() {
        return Component.translatable("container.lectern");
    }

    private static int getPageCount(ItemStack p_330049_) {
        WrittenBookContent writtenbookcontent = p_330049_.get(DataComponents.WRITTEN_BOOK_CONTENT);
        if (writtenbookcontent != null) {
            return writtenbookcontent.pages().size();
        } else {
            WritableBookContent writablebookcontent = p_330049_.get(DataComponents.WRITABLE_BOOK_CONTENT);
            return writablebookcontent != null ? writablebookcontent.pages().size() : 0;
        }
    }
}