// SPDX-License-Identifier: Apache-2.0

pragma solidity ^0.6.0;

import {SafeMath} from '@openzeppelin/contracts/math/SafeMath.sol';
import {IEuropean} from './interface/IEuropean.sol';

/**
 * @dev Contract module which provides a timed access control mechanism,
 * specifically to model a European Option with an expiry and settlement phase.
 * It must be used through inheritance which provides several modifiers.
 */
contract European is IEuropean {
    using SafeMath for uint256;

    string internal constant ERR_INIT_EXPIRED = 'Cannot init expired';
    string internal constant ERR_EXPIRED = 'Contract has expired';
    string internal constant ERR_NOT_EXPIRED = 'Contract not expired';
    string internal constant ERR_WINDOW_ZERO = 'Window cannot be zero';

    // expiry timestamp
    uint256 public override expiryTime;

    // window post expiry
    uint256 public override windowSize;

    modifier setExpiry(uint256 _expiryTime, uint256 _windowSize) {
        require(_expiryTime > block.timestamp, ERR_INIT_EXPIRED);
        require(_windowSize > 0, ERR_WINDOW_ZERO);

        expiryTime = _expiryTime;
        windowSize = _windowSize;

        _;
    }

    /**
     * @dev Throws if called before the configured timestamp
     */
    modifier hasExpired() {
        // solium-disable-next-line security/no-block-members
        require(block.timestamp > expiryTime, ERR_NOT_EXPIRED);
        _;
    }

    /**
     * @dev Throws if called after the configured timestamp
     */
    modifier notExpired() {
        // solium-disable-next-line security/no-block-members
        require(block.timestamp <= expiryTime, ERR_EXPIRED);
        _;
    }

    /**
     * @dev Throws if called after the exercise window has expired
     */
    modifier canExercise() {
        // solium-disable-next-line security/no-block-members
        require(block.timestamp > expiryTime, ERR_NOT_EXPIRED);
        // solium-disable-next-line security/no-block-members
        require(block.timestamp <= expiryTime.add(windowSize), ERR_EXPIRED);
        _;
    }

    /**
     * @dev Returns true if the `expiryTime + windowSize` has elapsed.
     */
    function canExit() external override returns (bool) {
        // solium-disable-next-line security/no-block-members
        return block.timestamp > expiryTime.add(windowSize);
    }
}