/**
 * Copyright 2017-2021, bZeroX, LLC. All Rights Reserved.
 * Licensed under the Apache License, Version 2.0.
 */

pragma solidity 0.5.17;

import "../openzeppelin/SafeERC20.sol";
import "../core/State.sol";
import "../mixins/VaultController.sol";
import "./FeesHelper.sol";

/**
 * @title The Interest User contract.
 * @notice This contract code comes from bZx. bZx is a protocol for tokenized margin
 * trading and lending https://bzx.network similar to the dYdX protocol.
 *
 * This contract pays loan interests.
 * */
contract InterestUser is VaultController, FeesHelper {
	using SafeERC20 for IERC20;

	/// Triggered whenever interest is paid to lender.
	event PayInterestTransfer(address indexed interestToken, address indexed lender, uint256 effectiveInterest);

	/**
	 * @notice Internal function to pay interest of a loan.
	 * @dev Calls _payInterestTransfer internal function to transfer tokens.
	 * @param lender The account address of the lender.
	 * @param interestToken The token address to pay interest with.
	 * */
	function _payInterest(address lender, address interestToken) internal {
		LenderInterest storage lenderInterestLocal = lenderInterest[lender][interestToken];

		uint256 interestOwedNow = 0;
		if (lenderInterestLocal.owedPerDay != 0 && lenderInterestLocal.updatedTimestamp != 0) {
			interestOwedNow = block.timestamp.sub(lenderInterestLocal.updatedTimestamp).mul(lenderInterestLocal.owedPerDay).div(1 days);

			lenderInterestLocal.updatedTimestamp = block.timestamp;

			if (interestOwedNow > lenderInterestLocal.owedTotal) interestOwedNow = lenderInterestLocal.owedTotal;

			if (interestOwedNow != 0) {
				lenderInterestLocal.paidTotal = lenderInterestLocal.paidTotal.add(interestOwedNow);
				lenderInterestLocal.owedTotal = lenderInterestLocal.owedTotal.sub(interestOwedNow);

				_payInterestTransfer(lender, interestToken, interestOwedNow);
			}
		} else {
			lenderInterestLocal.updatedTimestamp = block.timestamp;
		}
	}

	/**
	 * @notice Internal function to transfer tokens for the interest of a loan.
	 * @param lender The account address of the lender.
	 * @param interestToken The token address to pay interest with.
	 * @param interestOwedNow The amount of interest to pay.
	 * */
	function _payInterestTransfer(
		address lender,
		address interestToken,
		uint256 interestOwedNow
	) internal {
		uint256 lendingFee = interestOwedNow.mul(lendingFeePercent).div(10**20);
		/// TODO: refactor: data incapsulation violation and DRY design principles
		/// uint256 lendingFee = interestOwedNow.mul(lendingFeePercent).divCeil(10**20); is better but produces errors in tests because of this

		_payLendingFee(lender, interestToken, lendingFee);

		/// Transfers the interest to the lender, less the interest fee.
		vaultWithdraw(interestToken, lender, interestOwedNow.sub(lendingFee));

		/// Event Log
		emit PayInterestTransfer(interestToken, lender, interestOwedNow.sub(lendingFee));
	}
}