// SPDX-License-Identifier: GPL-3.0-or-later
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity ^0.7.0;

import "../openzeppelin/IERC20.sol";

import "../../contracts/interfaces/IAsset.sol";
import "../../contracts/interfaces/IWETH.sol";

abstract contract AssetHelpers {
    // solhint-disable-next-line var-name-mixedcase
    IWETH private immutable _weth;

    // Sentinel value used to indicate WETH with wrapping/unwrapping semantics. The zero address is a good choice for
    // multiple reasons: it is cheap to pass as a calldata argument, it is a known invalid token and non-contract, and
    // it is an address Pools cannot register as a token.
    address private constant _ETH = address(0);

    constructor(IWETH weth) {
        _weth = weth;
    }

    // solhint-disable-next-line func-name-mixedcase
    function _WETH() internal view returns (IWETH) {
        return _weth;
    }

    /**
     * @dev Returns true if `asset` is the sentinel value that represents ETH.
     */
    function _isETH(IAsset asset) internal pure returns (bool) {
        return address(asset) == _ETH;
    }

    /**
     * @dev Translates `asset` into an equivalent IERC20 token address. If `asset` represents ETH, it will be translated
     * to the WETH contract.
     */
    function _translateToIERC20(IAsset asset) internal view returns (IERC20) {
        return _isETH(asset) ? _WETH() : _asIERC20(asset);
    }

    /**
     * @dev Same as `_translateToIERC20(IAsset)`, but for an entire array.
     */
    function _translateToIERC20(IAsset[] memory assets) internal view returns (IERC20[] memory) {
        IERC20[] memory tokens = new IERC20[](assets.length);
        for (uint256 i = 0; i < assets.length; ++i) {
            tokens[i] = _translateToIERC20(assets[i]);
        }
        return tokens;
    }

    /**
     * @dev Interprets `asset` as an IERC20 token. This function should only be called on `asset` if `_isETH` previously
     * returned false for it, that is, if `asset` is guaranteed not to be the ETH sentinel value.
     */
    function _asIERC20(IAsset asset) internal pure returns (IERC20) {
        return IERC20(address(asset));
    }
}