// SPDX-License-Identifier: MIT
pragma solidity ^0.6.12;

/**
 * @title Initializable
 *
 * @dev Contract module which provides access control mechanism, where
 * there is the initializer account that can be granted exclusive access to
 * specific functions.
 *
 * The initializer account will be tx.origin during contract deployment and will be removed on first use.
 * Use `onlyInitializer` modifier on contract initialize process.
 *
 * @author Stanisław Głogowski <stan@pillarproject.io>
 */
contract Initializable {
  address private initializer;

  // events

  /**
   * @dev Emitted after `onlyInitializer`
   * @param initializer initializer address
   */
  event Initialized(
    address initializer
  );

  // modifiers

  /**
   * @dev Throws if tx.origin is not the initializer
   */
  modifier onlyInitializer() {
    require(
      // solhint-disable-next-line avoid-tx-origin
      tx.origin == initializer,
      "Initializable: tx.origin is not the initializer"
    );

    /// @dev removes initializer
    initializer = address(0);

    _;

    emit Initialized(
      // solhint-disable-next-line avoid-tx-origin
      tx.origin
    );
  }

  /**
   * @dev Internal constructor
   */
  constructor()
    internal
  {
    // solhint-disable-next-line avoid-tx-origin
    initializer = tx.origin;
  }

   // external functions (views)

  /**
   * @notice Check if contract is initialized
   * @return true when contract is initialized
   */
  function isInitialized()
    external
    view
    returns (bool)
  {
    return initializer == address(0);
  }
}