pragma solidity 0.5.17;

library LockUtils {
    struct Lock {
        address creator;
        uint96 expiresAt;
    }

    /// @notice The LockSet is like an array of unique `uint256`s,
    /// but additionally supports O(1) membership tests and removals.
    /// @dev Because the LockSet relies on a mapping,
    /// it can only be used in storage, not in memory.
    struct LockSet {
        // locks[positions[lock.creator] - 1] = lock
        Lock[] locks;
        mapping(address => uint256) positions;
    }

    /// @notice Check whether the LockSet `self` contains a lock by `creator`
    function contains(LockSet storage self, address creator)
        internal
        view
        returns (bool)
    {
        return (self.positions[creator] != 0);
    }

    function getLockTime(LockSet storage self, address creator)
        internal
        view
        returns (uint96)
    {
        uint256 positionPlusOne = self.positions[creator];
        if (positionPlusOne == 0) {
            return 0;
        }
        return self.locks[positionPlusOne - 1].expiresAt;
    }

    /// @notice Set the lock of `creator` to `expiresAt`,
    /// overriding the current value if any.
    function setLock(
        LockSet storage self,
        address _creator,
        uint96 _expiresAt
    ) internal {
        uint256 positionPlusOne = self.positions[_creator];
        Lock memory lock = Lock(_creator, _expiresAt);
        // No existing lock
        if (positionPlusOne == 0) {
            self.locks.push(lock);
            self.positions[_creator] = self.locks.length;
            // Existing lock present
        } else {
            self.locks[positionPlusOne - 1].expiresAt = _expiresAt;
        }
    }

    /// @notice Remove the lock of `creator`.
    /// If no lock present, do nothing.
    function releaseLock(LockSet storage self, address _creator) internal {
        uint256 positionPlusOne = self.positions[_creator];
        if (positionPlusOne != 0) {
            uint256 lockCount = self.locks.length;
            if (positionPlusOne != lockCount) {
                // Not the last lock,
                // so we need to move the last lock into the emptied position.
                Lock memory lastLock = self.locks[lockCount - 1];
                self.locks[positionPlusOne - 1] = lastLock;
                self.positions[lastLock.creator] = positionPlusOne;
            }
            self.locks.length--;
            self.positions[_creator] = 0;
        }
    }

    /// @notice Return the locks of the LockSet `self`.
    function enumerate(LockSet storage self)
        internal
        view
        returns (Lock[] memory)
    {
        return self.locks;
    }
}