// simplemoney.capability.Money
package xaser.simplemoney.capability;

import xaser.simplemoney.network.NetworkHandler;
import xaser.simplemoney.network.UpdateMoneyMessage;
import net.minecraftforge.common.capabilities.CapabilityManager;

/**
 * Default implementation of Money capability.
 */
public class Money implements IMoney {

    private int money = 0;

    public static void register() {
        CapabilityManager.INSTANCE.register(IMoney.class, new MoneyStorage(), Money.class);
    }

    private void onMoneyUpdate() {
        NetworkHandler.NETWORK.sendTo(new UpdateMoneyMessage(money), this.)
    }

    /**
     * Getter for the money field.
     * @return  The amount of money.
     */
    @Override
    public int getMoney() {
        return money;
    }

    /**
     * Adds the specified amount to the money balance.
     * @param amount    Positive or negative value to addMoney to the current amount of money.
     * @throws IllegalArgumentException
     */
    @Override
    public void addMoney(int amount) throws IllegalArgumentException {
        // TODO: make sure that Java 8 feature addExact causes no trouble.
        int new_value = Math.addExact(money, amount);   // Use addExact to automatically throw exception on overflow.

        if (new_value < 0) {
            throw new IllegalArgumentException("Addition resulted in negative value. Cannot have negative balance.");
        }
        else {
            money = new_value;
            onMoneyUpdate();
        }
    }

    /**
     * Sets the money balance to the specified amount.
     * @param amount Positive value to be assigned to the money field.
     * @throws IllegalArgumentException
     */
    @Override
    public void setMoney(int amount) throws IllegalArgumentException {
        if(amount < 0) {
            throw new IllegalArgumentException("Amount is negative. Cannot have negative balance.");
        }
        else {
            money = amount;
            onMoneyUpdate();
        }
    }
}


// simplemoney.network.UpdateMoneyMessage
package xaser.simplemoney.network;

import io.netty.buffer.ByteBuf;
import xaser.simplemoney.capability.IMoney;
import xaser.simplemoney.capability.MoneyProvider;
import net.minecraft.client.Minecraft;
import net.minecraft.util.IThreadListener;
import net.minecraftforge.fml.common.network.simpleimpl.IMessage;
import net.minecraftforge.fml.common.network.simpleimpl.IMessageHandler;
import net.minecraftforge.fml.common.network.simpleimpl.MessageContext;

/** Notification message that informs the player about an update of his money value.
 */
public class UpdateMoneyMessage implements IMessage {
    private int updated_value = 0;

    // Default constructor REQUIRED!
    public UpdateMoneyMessage() {
    }

    public UpdateMoneyMessage(int updated_value) {
        this.updated_value = updated_value;
    }

    @Override
    public void toBytes(ByteBuf buf) {
        buf.writeInt(updated_value);
    }

    @Override
    public void fromBytes(ByteBuf buf) {
        this.updated_value = buf.readInt();
    }

    public static class Handler implements IMessageHandler<UpdateMoneyMessage, IMessage> {

        @Override
        public IMessage onMessage(final UpdateMoneyMessage message, MessageContext ctx) {

            // Schedule the update of the money value in the main thread.
            // Packet is Client bound, so we do not need to check sides!
            IThreadListener mainThread = Minecraft.getMinecraft();
            mainThread.addScheduledTask(new Runnable() {
                @Override
                public void run() {
                    IMoney playerMoney = Minecraft.getMinecraft().thePlayer.getCapability(MoneyProvider.MONEY_CAPABILITY, null);
                    playerMoney.setMoney(message.updated_value);
                }
            });

            return null;    // Do not send a response, we have TCP guaranteed delivery anyway.
        }
    }
}