pragma solidity ^0.4.24;

import "zos-lib/contracts/Initializable.sol";
import "../Roles.sol";


contract SignerRole is Initializable {
    using Roles for Roles.Role;

    event SignerAdded(address indexed account);
    event SignerRemoved(address indexed account);

    Roles.Role private signers;

    function initialize(address sender) public initializer {
        if (!isSigner(sender)) {
            _addSigner(sender);
        }
    }

    modifier onlySigner() {
        require(isSigner(msg.sender));
        _;
    }

    function isSigner(address account) public view returns (bool) {
        return signers.has(account);
    }

    function addSigner(address account) public onlySigner {
        _addSigner(account);
    }

    function renounceSigner() public {
        _removeSigner(msg.sender);
    }

    function _addSigner(address account) internal {
        signers.add(account);
        emit SignerAdded(account);
    }

    function _removeSigner(address account) internal {
        signers.remove(account);
        emit SignerRemoved(account);
    }

    uint256[50] private ______gap;
}