/**
 * Copyright 2023 Circle Internet Financial, LTD. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * 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.
 */

pragma solidity 0.6.12;

import { AbstractFiatTokenV2 } from "./AbstractFiatTokenV2.sol";
import { EIP712Domain } from "./EIP712Domain.sol";
import { MessageHashUtils } from "../util/MessageHashUtils.sol";
import { SignatureChecker } from "../util/SignatureChecker.sol";

/**
 * @title EIP-2612
 * @notice Provide internal implementation for gas-abstracted approvals
 */
abstract contract EIP2612 is AbstractFiatTokenV2, EIP712Domain {
    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)")
    bytes32
        public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;

    mapping(address => uint256) private _permitNonces;

    /**
     * @notice Nonces for permit
     * @param owner Token owner's address (Authorizer)
     * @return Next nonce
     */
    function nonces(address owner) external view returns (uint256) {
        return _permitNonces[owner];
    }

    /**
     * @notice Verify a signed approval permit and execute if valid
     * @param owner     Token owner's address (Authorizer)
     * @param spender   Spender's address
     * @param value     Amount of allowance
     * @param deadline  The time at which the signature expires (unix time), or max uint256 value to signal no expiration
     * @param v         v of the signature
     * @param r         r of the signature
     * @param s         s of the signature
     */
    function _permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        _permit(owner, spender, value, deadline, abi.encodePacked(r, s, v));
    }

    /**
     * @notice Verify a signed approval permit and execute if valid
     * @dev EOA wallet signatures should be packed in the order of r, s, v.
     * @param owner      Token owner's address (Authorizer)
     * @param spender    Spender's address
     * @param value      Amount of allowance
     * @param deadline   The time at which the signature expires (unix time), or max uint256 value to signal no expiration
     * @param signature  Signature byte array signed by an EOA wallet or a contract wallet
     */
    function _permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        bytes memory signature
    ) internal {
        require(
            deadline == type(uint256).max || deadline >= now,
            "FiatTokenV2: permit is expired"
        );

        bytes32 typedDataHash = MessageHashUtils.toTypedDataHash(
            _domainSeparator(),
            keccak256(
                abi.encode(
                    PERMIT_TYPEHASH,
                    owner,
                    spender,
                    value,
                    _permitNonces[owner]++,
                    deadline
                )
            )
        );
        require(
            SignatureChecker.isValidSignatureNow(
                owner,
                typedDataHash,
                signature
            ),
            "EIP2612: invalid signature"
        );

        _approve(owner, spender, value);
    }
}