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This module defines the support library of the Takamaka language.
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/*
Copyright 2021 Fausto Spoto

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package io.takamaka.code.lang;

import java.math.BigInteger;

/**
 * A contract is a storage object with a balance of coin. It is controlled
 * by the methods of its code.
 */
@Exported
public abstract class Contract extends Storage {

	/**
	 * The balance of this contract.
	 */
	private BigInteger balance;

	/**
	 * The red balance of this contract.
	 */
	private BigInteger balanceRed;

	/**
	 * Builds a contract with zero balance.
	 */
	protected Contract() {
		this.balance = BigInteger.ZERO;
		this.balanceRed = BigInteger.ZERO;
	}

	/**
	 * Yields the balance of this contract.
	 * 
	 * @return the balance
	 */
	public final @View BigInteger balance() {
		return balance;
	}

	/**
	 * Yields the normal, green balance of this contract.
	 * This is synonym for {@link #balance()}.
	 * 
	 * @return the balance
	 */
	public final @View BigInteger balanceGreen() {
		return balance();
	}

	/**
	 * Yields the red balance of this contract.
	 * 
	 * @return the red balance
	 */
	public final @View BigInteger balanceRed() {
		return balanceRed;
	}

	@Override
	public @View String toString() {
		return "a contract";
	}

	/**
	 * Increases the balance of a contract by the given amount of coins,
	 * taken away from the balance of this contract.
	 * 
	 * @param beneficiary the beneficiary of the amount of coins
	 * @param amount the amount of coins
	 */
	private void pay(Contract beneficiary, BigInteger amount) {
		Takamaka.require(amount != null, "the paid amount cannot be null");
		Takamaka.require(amount.signum() >= 0, "the paid amount cannot be negative");
		if (balance.compareTo(amount) < 0)
			throw new InsufficientFundsError(amount.subtract(balance));

		balance = balance.subtract(amount);
		beneficiary.balance = beneficiary.balance.add(amount);
	}

	/**
	 * Called at the beginning of the instrumentation of a payable method or constructor.
	 * It sets the caller of the code and transfers the amount of coins to the contract.
	 * It is private, so that programmers cannot call
	 * it directly. Instead, instrumented code will call it by reflection.
	 * 
	 * @param payer the payer
	 * @param amount the amount of coins
	 */
	private void payableFromContract(Contract payer, BigInteger amount) {
		payer.pay(this, amount);
	}

	/**
	 * Called at the beginning of the instrumentation of a payable method or constructor.
	 * It sets the caller of the code and transfers the amount of coins to the contract.
	 * It is private, so that programmers cannot call
	 * it directly. Instead, instrumented code will call it by reflection.
	 *
	 * @param payer the payer
	 * @param amount the amount of coins
	 */
	@SuppressWarnings("unused")
	private void payableFromContract(Contract payer, int amount) {
		payableFromContract(payer, BigInteger.valueOf(amount));
	}

	/**
	 * Called at the beginning of the instrumentation of a payable method or constructor.
	 * It sets the caller of the code and transfers the amount of coins to the contract.
	 * It is private, so that programmers cannot call
	 * it directly. Instead, instrumented code will call it by reflection.
	 * 
	 * @param payer the payer
	 * @param amount the amount of coins
	 */
	@SuppressWarnings("unused")
	private void payableFromContract(Contract payer, long amount) {
		payableFromContract(payer, BigInteger.valueOf(amount));
	}

	/**
	 * Increases the red balance of a contract by the given amount of coins,
	 * taken away from the balance of this contract.
	 * 
	 * @param beneficiary the beneficiary of the amount of red coins
	 * @param amount the amount of red coins
	 */
	private void payRed(Contract beneficiary, BigInteger amount) {
		Takamaka.require(amount != null, "Payed amount cannot be null");
		Takamaka.require(amount.signum() >= 0, "Payed amount cannot be negative");
		if (balanceRed.compareTo(amount) < 0)
			throw new InsufficientFundsError(amount.subtract(balanceRed));
	
		balanceRed = balanceRed.subtract(amount);
		beneficiary.balanceRed = beneficiary.balanceRed.add(amount);
	}

	/**
	 * Called at the beginning of the instrumentation of a red payable entry method or constructor.
	 * It transfers the amount of coins to the entry.
	 * It is private, so that programmers cannot call
	 * it directly. Instead, instrumented code will call it by reflection.
	 * 
	 * @param caller the caller of the entry
	 * @param amount the amount of red coins
	 */
	private void redPayable(Contract caller, BigInteger amount) {
		caller.payRed(this, amount);
	}

	/**
	 * Called at the beginning of the instrumentation of a red payable entry method or constructor.
	 * It transfers the amount of red coins to the entry.
	 * It is private, so that programmers cannot call
	 * it directly. Instead, instrumented code will call it by reflection.
	 *
	 * @param caller the caller of the entry
	 * @param amount the amount of red coins
	 */
	@SuppressWarnings("unused")
	private void redPayable(Contract caller, int amount) {
		redPayable(caller, BigInteger.valueOf(amount));
	}

	/**
	 * Called at the beginning of the instrumentation of a red payable entry method or constructor.
	 * It transfers the amount of red coins to the entry.
	 * It is private, so that programmers cannot call
	 * it directly. Instead, instrumented code will call it by reflection.
	 * 
	 * @param caller the caller of the entry
	 * @param amount the amount of red coins
	 */
	@SuppressWarnings("unused")
	private void redPayable(Contract caller, long amount) {
		redPayable(caller, BigInteger.valueOf(amount));
	}
}