Mantle/src/main/java/slimeknights/mantle/network/packet/DropLecternBookPacket.java

package slimeknights.mantle.network.packet;

import lombok.AllArgsConstructor;
import net.minecraft.block.BlockState;
import net.minecraft.block.Blocks;
import net.minecraft.block.LecternBlock;
import net.minecraft.entity.player.ServerPlayerEntity;
import net.minecraft.item.ItemStack;
import net.minecraft.network.PacketBuffer;
import net.minecraft.tileentity.LecternTileEntity;
import net.minecraft.tileentity.TileEntity;
import net.minecraft.util.math.BlockPos;
import net.minecraft.world.server.ServerWorld;
import net.minecraftforge.fml.network.NetworkEvent.Context;
import slimeknights.mantle.item.ILecternBookItem;

/**
 * Packet to drop the book as item from lectern
 */
@AllArgsConstructor
public class DropLecternBookPacket implements IThreadsafePacket {
  private final BlockPos pos;

  public DropLecternBookPacket(PacketBuffer buffer) {
    this.pos = buffer.readBlockPos();
  }

  @Override
  public void encode(PacketBuffer buffer) {
    buffer.writeBlockPos(pos);
  }

  @Override
  public void handleThreadsafe(Context context) {
    ServerPlayerEntity player = context.getSender();
    if(player == null) {
      return;
    }

    ServerWorld world = player.getServerWorld();

    if(!world.isBlockLoaded(pos)) {
      return;
    }

    BlockState state = world.getBlockState(pos);

    if(state.getBlock() instanceof LecternBlock && state.get(LecternBlock.HAS_BOOK)) {
      TileEntity te = world.getTileEntity(pos);
      if(te instanceof LecternTileEntity) {
        LecternTileEntity lecternTe = (LecternTileEntity) te;

        ItemStack book = lecternTe.getBook().copy();
        if(!book.isEmpty()) {
          if(!player.addItemStackToInventory(book)) {
            player.dropItem(book, false, false);
          }

          lecternTe.clear();

          // fix lectern state
          world.setBlockState(pos, state.with(LecternBlock.POWERED, false).with(LecternBlock.HAS_BOOK, false), 3);
          world.notifyNeighborsOfStateChange(pos.down(), state.getBlock());
        }
      }
    }

  }
}