// SPDX-License-Identifier: GPL-3.0

pragma solidity 0.8.6;

import "./RingBufferLib.sol";

/// @title Library for creating and managing a draw ring buffer.
library DrawRingBufferLib {
    /// @notice Draw buffer struct.
    struct Buffer {
        uint32 lastDrawId;
        uint32 nextIndex;
        uint32 cardinality;
    }

    /// @notice Helper function to know if the draw ring buffer has been initialized.
    /// @dev since draws start at 1 and are monotonically increased, we know we are uninitialized if nextIndex = 0 and lastDrawId = 0.
    /// @param _buffer The buffer to check.
    function isInitialized(Buffer memory _buffer) internal pure returns (bool) {
        return !(_buffer.nextIndex == 0 && _buffer.lastDrawId == 0);
    }

    /// @notice Push a draw to the buffer.
    /// @param _buffer The buffer to push to.
    /// @param _drawId The drawID to push.
    /// @return The new buffer.
    function push(Buffer memory _buffer, uint32 _drawId) internal pure returns (Buffer memory) {
        require(!isInitialized(_buffer) || _drawId == _buffer.lastDrawId + 1, "DRB/must-be-contig");

        return
            Buffer({
                lastDrawId: _drawId,
                nextIndex: uint32(RingBufferLib.nextIndex(_buffer.nextIndex, _buffer.cardinality)),
                cardinality: _buffer.cardinality
            });
    }

    /// @notice Get draw ring buffer index pointer.
    /// @param _buffer The buffer to get the `nextIndex` from.
    /// @param _drawId The draw id to get the index for.
    /// @return The draw ring buffer index pointer.
    function getIndex(Buffer memory _buffer, uint32 _drawId) internal pure returns (uint32) {
        require(isInitialized(_buffer) && _drawId <= _buffer.lastDrawId, "DRB/future-draw");

        uint32 indexOffset = _buffer.lastDrawId - _drawId;
        require(indexOffset < _buffer.cardinality, "DRB/expired-draw");

        uint256 mostRecent = RingBufferLib.newestIndex(_buffer.nextIndex, _buffer.cardinality);

        return uint32(RingBufferLib.offset(uint32(mostRecent), indexOffset, _buffer.cardinality));
    }
}