// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.12;

import {ERC20} from '../../dependencies/openzeppelin/contracts/ERC20.sol';

/**
 * @title ERC20Mintable
 * @dev ERC20 minting logic
 */
contract MintableERC20 is ERC20 {

  bytes public constant EIP712_REVISION = bytes('1');
  bytes32 internal constant EIP712_DOMAIN =
    keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)');
  bytes32 public constant PERMIT_TYPEHASH =
    keccak256('Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)');

  mapping(address => uint256) public _nonces;

  bytes32 public DOMAIN_SEPARATOR;

  constructor(
    string memory name,
    string memory symbol,
    uint8 decimals
  ) public ERC20(name, symbol) {

    uint256 chainId;

    assembly {
      chainId := chainid()
    }

    DOMAIN_SEPARATOR = keccak256(
      abi.encode(
        EIP712_DOMAIN,
        keccak256(bytes(name)),
        keccak256(EIP712_REVISION),
        chainId,
        address(this)
      )
    );
    _setupDecimals(decimals);
  }

  function permit(
    address owner,
    address spender,
    uint256 value,
    uint256 deadline,
    uint8 v,
    bytes32 r,
    bytes32 s
  ) external {
    require(owner != address(0), 'INVALID_OWNER');
    //solium-disable-next-line
    require(block.timestamp <= deadline, 'INVALID_EXPIRATION');
    uint256 currentValidNonce = _nonces[owner];
    bytes32 digest =
      keccak256(
        abi.encodePacked(
          '\x19\x01',
          DOMAIN_SEPARATOR,
          keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, currentValidNonce, deadline))
        )
      );
    require(owner == ecrecover(digest, v, r, s), 'INVALID_SIGNATURE');
    _nonces[owner] = currentValidNonce.add(1);
    _approve(owner, spender, value);
  }

  /**
   * @dev Function to mint tokens
   * @param value The amount of tokens to mint.
   * @return A boolean that indicates if the operation was successful.
   */
  function mint(uint256 value) public returns (bool) {
    _mint(_msgSender(), value);
    return true;
  }
}