/*
 * SPDX-License-Identifier:    MIT
 */

pragma solidity ^0.4.24;

import "./TimeHelpers.sol";
import "./UnstructuredStorage.sol";


contract Initializable is TimeHelpers {
    using UnstructuredStorage for bytes32;

    // keccak256("aragonOS.initializable.initializationBlock")
    bytes32 internal constant INITIALIZATION_BLOCK_POSITION = 0xebb05b386a8d34882b8711d156f463690983dc47815980fb82aeeff1aa43579e;

    string private constant ERROR_ALREADY_INITIALIZED = "INIT_ALREADY_INITIALIZED";
    string private constant ERROR_NOT_INITIALIZED = "INIT_NOT_INITIALIZED";

    modifier onlyInit {
        require(getInitializationBlock() == 0, ERROR_ALREADY_INITIALIZED);
        _;
    }

    modifier isInitialized {
        require(hasInitialized(), ERROR_NOT_INITIALIZED);
        _;
    }

    /**
    * @return Block number in which the contract was initialized
    */
    function getInitializationBlock() public view returns (uint256) {
        return INITIALIZATION_BLOCK_POSITION.getStorageUint256();
    }

    /**
    * @return Whether the contract has been initialized by the time of the current block
    */
    function hasInitialized() public view returns (bool) {
        uint256 initializationBlock = getInitializationBlock();
        return initializationBlock != 0 && getBlockNumber() >= initializationBlock;
    }

    /**
    * @dev Function to be called by top level contract after initialization has finished.
    */
    function initialized() internal onlyInit {
        INITIALIZATION_BLOCK_POSITION.setStorageUint256(getBlockNumber());
    }

    /**
    * @dev Function to be called by top level contract after initialization to enable the contract
    *      at a future block number rather than immediately.
    */
    function initializedAt(uint256 _blockNumber) internal onlyInit {
        INITIALIZATION_BLOCK_POSITION.setStorageUint256(_blockNumber);
    }
}