// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;


/**
 * @title The Owned contract
 * @notice A contract with helpers for basic contract ownership.
 */
contract Owned {

  address public owner;
  address private pendingOwner;

  event OwnershipTransferRequested(
    address indexed from,
    address indexed to
  );
  event OwnershipTransferred(
    address indexed from,
    address indexed to
  );

  constructor() public {
    owner = msg.sender;
  }

  /**
   * @dev Allows an owner to begin transferring ownership to a new address,
   * pending.
   */
  function transferOwnership(address _to)
    external
    onlyOwner()
  {
    pendingOwner = _to;

    emit OwnershipTransferRequested(owner, _to);
  }

  /**
   * @dev Allows an ownership transfer to be completed by the recipient.
   */
  function acceptOwnership()
    external
  {
    require(msg.sender == pendingOwner, "Must be proposed owner");

    address oldOwner = owner;
    owner = msg.sender;
    pendingOwner = address(0);

    emit OwnershipTransferred(oldOwner, msg.sender);
  }

  /**
   * @dev Reverts if called by anyone other than the contract owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner, "Only callable by owner");
    _;
  }

}

interface AccessControllerInterface {
  function hasAccess(address user, bytes calldata data) external view returns (bool);
}

/**
 * @title SimpleWriteAccessController
 * @notice Gives access to accounts explicitly added to an access list by the
 * controller's owner.
 * @dev does not make any special permissions for externally, see
 * SimpleReadAccessController for that.
 */
contract SimpleWriteAccessController is AccessControllerInterface, Owned {

  bool public checkEnabled;
  mapping(address => bool) internal accessList;

  event AddedAccess(address user);
  event RemovedAccess(address user);
  event CheckAccessEnabled();
  event CheckAccessDisabled();

  constructor()
    public
  {
    checkEnabled = true;
  }

  /**
   * @notice Returns the access of an address
   * @param _user The address to query
   */
  function hasAccess(
    address _user,
    bytes memory
  )
    public
    view
    virtual
    override
    returns (bool)
  {
    return accessList[_user] || !checkEnabled;
  }

  /**
   * @notice Adds an address to the access list
   * @param _user The address to add
   */
  function addAccess(address _user)
    external
    onlyOwner()
  {
    if (!accessList[_user]) {
      accessList[_user] = true;

      emit AddedAccess(_user);
    }
  }

  /**
   * @notice Removes an address from the access list
   * @param _user The address to remove
   */
  function removeAccess(address _user)
    external
    onlyOwner()
  {
    if (accessList[_user]) {
      accessList[_user] = false;

      emit RemovedAccess(_user);
    }
  }

  /**
   * @notice makes the access check enforced
   */
  function enableAccessCheck()
    external
    onlyOwner()
  {
    if (!checkEnabled) {
      checkEnabled = true;

      emit CheckAccessEnabled();
    }
  }

  /**
   * @notice makes the access check unenforced
   */
  function disableAccessCheck()
    external
    onlyOwner()
  {
    if (checkEnabled) {
      checkEnabled = false;

      emit CheckAccessDisabled();
    }
  }

  /**
   * @dev reverts if the caller does not have access
   */
  modifier checkAccess() {
    require(hasAccess(msg.sender, msg.data), "No access");
    _;
  }
}