namespace AcDream.App.Streaming;

/// <summary>
/// Classifies both whether the player crosses an AC landblock boundary and
/// whether acdream's asynchronous streaming origin must recenter. These are
/// distinct while a teleport destination is aimed but not yet placed. Cell
/// identity comes from the complete retail <c>Position</c>, never from its frame
/// coordinates: dungeon EnvCells may have valid negative local origins.
/// </summary>
/// <remarks>
/// Retail carries <c>Position::objcell_id</c> through
/// <c>SmartBox::TeleportPlayer</c> (0x00453910) into
/// <c>CPhysicsObj::SetPositionSimple</c> (0x005162B0). acdream's asynchronous
/// streaming layer needs this extra comparison, but preserves that identity rule.
/// See <c>docs/research/2026-07-13-same-dungeon-respawn-landblock-identity-pseudocode.md</c>.
/// </remarks>
internal readonly record struct TeleportLandblockTransition(
    uint SourceLandblockId,
    uint DestinationLandblockId,
    uint StreamingCenterLandblockId)
{
    public bool CrossesLandblock => SourceLandblockId != DestinationLandblockId;
    public bool ChangesStreamingCenter =>
        StreamingCenterLandblockId != DestinationLandblockId;

    /// <summary>
    /// Build the transition from the player's current cell and the received
    /// destination cell. A zero source can occur before initial placement; in
    /// that case the current streaming center is the only valid identity fallback.
    /// </summary>
    public static TeleportLandblockTransition Classify(
        uint sourceCellId,
        uint destinationCellId,
        uint currentStreamingCenterLandblockId)
    {
        uint sourceLandblockId = sourceCellId != 0
            ? NormalizeLandblockId(sourceCellId)
            : NormalizeLandblockId(currentStreamingCenterLandblockId);

        return new TeleportLandblockTransition(
            sourceLandblockId,
            NormalizeLandblockId(destinationCellId),
            NormalizeLandblockId(currentStreamingCenterLandblockId));
    }

    private static uint NormalizeLandblockId(uint cellOrLandblockId)
        => (cellOrLandblockId & 0xFFFF0000u) | 0xFFFFu;
}