namespace AcDream.App.Streaming;

/// <summary>
/// The live landblock window the reveal gate measures. Retail has exactly one
/// landscape square — <c>LScape::mid_radius</c>, assigned directly from the
/// user's <c>Render.LandscapeDrawDistance</c> preference
/// (<c>SmartBox::SetRegion</c> @0x004531F0;
/// <c>Render_LandscapeDrawDistance_Values</c> @0x007CA988 = {3,5,8,11,15,25},
/// default 8) — and that same square is simultaneously the loaded set, the
/// drawn set, and the set <c>LScape::PreFetchCells</c> @0x00505660 blocks on.
/// acdream splits the loaded landscape into a Near tier (full publication) and
/// a Far tier (terrain render + terrain collision), so the reveal window is a
/// pair rather than a single number; <see cref="FarRadius"/> is the structural
/// analogue of retail's <c>mid_radius</c> because it bounds everything the
/// user can see (fog end is <c>FarRadius * 192 m * 0.95</c>).
/// </summary>
internal readonly record struct StreamingRevealWindow(
    int NearRadius,
    int FarRadius);

/// <summary>
/// One evaluation of the destination domains guarded by
/// <see cref="WorldRevealReadinessBarrier"/>. Keeping the individual facts in
/// the canonical owner lets diagnostics and automation observe readiness
/// without duplicating (and eventually drifting from) the reveal predicate.
/// </summary>
internal readonly record struct WorldRevealReadinessSnapshot(
    uint DestinationCell,
    bool IsIndoor,
    bool IsUnhydratable,
    int RequiredRenderRadius,
    int RequiredNearRadius,
    bool IsRenderNeighborhoodReady,
    bool AreCompositeTexturesReady,
    bool IsCollisionReady)
{
    public bool HasDestination => DestinationCell != 0u;

    public bool IsReady => HasDestination
        && (IsUnhydratable
            || (IsRenderNeighborhoodReady
                && AreCompositeTexturesReady
                && IsCollisionReady));
}

/// <summary>
/// Joins the render-publication, texture, and collision domains that must be
/// complete before the normal world viewport is revealed. Retail keeps
/// <c>SmartBox::position_update_complete</c> false while
/// <c>CellManager::blocking_for_cells</c> is set
/// (<c>SmartBox::UseTime</c>, 0x00455410). acdream loads those domains
/// asynchronously, so login and portal arrival must share this explicit
/// equivalent of retail's single blocking-cell edge.
///
/// <para>
/// #280: the outdoor gate is DERIVED from the live streaming window, never
/// hardcoded. Retail cannot stream farther than it gates because it has only
/// one number (<c>LScape::SetMidRadius</c> @0x00504C00 sets
/// <c>mid_width = radius * 2 + 1</c> and <c>LScape::update_block</c>
/// @0x005063A0 allocates exactly that array). A fixed reveal radius under a
/// configurable streaming window reintroduces the decoupling the moment the
/// preset changes, which is the whole defect.
/// </para>
/// </summary>
internal sealed class WorldRevealReadinessBarrier
{
    private readonly Func<StreamingRevealWindow> _revealWindow;
    private readonly Func<uint, int, int, bool> _isRenderNeighborhoodReady;
    private readonly Func<uint, bool> _isSpawnCellReady;
    private readonly Func<uint, int, bool> _isTerrainNeighborhoodReady;
    private readonly Func<bool> _areCompositeTexturesReady;
    private readonly Action<uint, int> _prepareCompositeTextures;
    private readonly Action _invalidateCompositeTextures;
    private readonly Func<uint, bool> _isSpawnClaimUnhydratable;

    public WorldRevealReadinessBarrier(
        Func<StreamingRevealWindow> revealWindow,
        Func<uint, int, int, bool> isRenderNeighborhoodReady,
        Func<uint, bool> isSpawnCellReady,
        Func<uint, int, bool> isTerrainNeighborhoodReady,
        Func<bool> areCompositeTexturesReady,
        Action<uint, int> prepareCompositeTextures,
        Action invalidateCompositeTextures,
        Func<uint, bool> isSpawnClaimUnhydratable)
    {
        _revealWindow = revealWindow
            ?? throw new ArgumentNullException(nameof(revealWindow));
        _isRenderNeighborhoodReady = isRenderNeighborhoodReady
            ?? throw new ArgumentNullException(nameof(isRenderNeighborhoodReady));
        _isSpawnCellReady = isSpawnCellReady
            ?? throw new ArgumentNullException(nameof(isSpawnCellReady));
        _isTerrainNeighborhoodReady = isTerrainNeighborhoodReady
            ?? throw new ArgumentNullException(nameof(isTerrainNeighborhoodReady));
        _areCompositeTexturesReady = areCompositeTexturesReady
            ?? throw new ArgumentNullException(nameof(areCompositeTexturesReady));
        _prepareCompositeTextures = prepareCompositeTextures
            ?? throw new ArgumentNullException(nameof(prepareCompositeTextures));
        _invalidateCompositeTextures = invalidateCompositeTextures
            ?? throw new ArgumentNullException(nameof(invalidateCompositeTextures));
        _isSpawnClaimUnhydratable = isSpawnClaimUnhydratable
            ?? throw new ArgumentNullException(nameof(isSpawnClaimUnhydratable));
    }

    /// <summary>
    /// Starts a new reveal lifetime. Texture readiness is destination-scoped;
    /// carrying the prior login/portal result across a new destination would
    /// open the barrier before that destination's composites were uploaded.
    /// </summary>
    public void Begin() => _invalidateCompositeTextures();

    /// <summary>
    /// Advances render-thread texture preparation once the static meshes the
    /// composite domain covers have been published.
    ///
    /// <para>
    /// D3: the composite domain is entity-scoped
    /// (<c>WbDrawDispatcher.IsCompositeWarmupCandidate</c> filters entities by
    /// Chebyshev landblock radius) and Far-tier builds carry no entities at all
    /// (<c>LandblockBuildFactory</c>), so the honest composite domain is the
    /// NEAR radius. Widening it over Far rings would walk the whole outer
    /// window to warm nothing.
    /// </para>
    ///
    /// <para>
    /// The TRIGGER is therefore scoped the same way. Pre-#280 the gate and the
    /// composite domain were the same radius-1 square, so gating warmup on the
    /// whole gate cost nothing. #280 widened the gate to the entire Far window
    /// without widening the domain; keeping the old trigger would have pushed
    /// every composite upload behind the last outer-ring landblock and made
    /// the hold longer than the streaming work alone requires. Warming as soon
    /// as the Near sub-window is published restores the overlap. The reveal
    /// gate itself is untouched: <see cref="Evaluate"/> still requires the
    /// full window AND composite readiness.
    /// </para>
    /// </summary>
    public void Prepare(uint destinationCell)
    {
        if (destinationCell == 0 || _isSpawnClaimUnhydratable(destinationCell))
            return;

        StreamingRevealWindow required = RequiredWindow(destinationCell);
        if (_isRenderNeighborhoodReady(
                destinationCell,
                required.NearRadius,
                required.NearRadius))
        {
            _prepareCompositeTextures(destinationCell, required.NearRadius);
        }
    }

    /// <summary>
    /// True only when the same destination is drawable and collidable. An
    /// impossible indoor claim intentionally crosses the barrier so the
    /// existing loud unhydratable-placement path can expose invalid server
    /// data. A merely slow hydratable claim never crosses early.
    /// </summary>
    public bool IsReady(uint destinationCell)
        => Evaluate(destinationCell).IsReady;

    /// <summary>
    /// Evaluates each readiness domain once and returns the complete decision.
    /// Consumers must use this snapshot rather than reimplementing the join.
    /// </summary>
    public WorldRevealReadinessSnapshot Evaluate(uint destinationCell)
    {
        if (destinationCell == 0)
            return default;

        bool isIndoor = IsIndoor(destinationCell);
        StreamingRevealWindow required = RequiredWindow(destinationCell);
        if (_isSpawnClaimUnhydratable(destinationCell))
        {
            return new WorldRevealReadinessSnapshot(
                destinationCell,
                isIndoor,
                IsUnhydratable: true,
                required.FarRadius,
                required.NearRadius,
                IsRenderNeighborhoodReady: false,
                AreCompositeTexturesReady: false,
                IsCollisionReady: false);
        }

        bool renderReady = _isRenderNeighborhoodReady(
            destinationCell,
            required.NearRadius,
            required.FarRadius);
        bool compositesReady = renderReady && _areCompositeTexturesReady();
        bool collisionReady = renderReady && compositesReady
            && (isIndoor
                ? _isSpawnCellReady(destinationCell)
                : _isTerrainNeighborhoodReady(
                    destinationCell,
                    required.FarRadius));

        return new WorldRevealReadinessSnapshot(
            destinationCell,
            isIndoor,
            IsUnhydratable: false,
            required.FarRadius,
            required.NearRadius,
            renderReady,
            compositesReady,
            collisionReady);
    }

    /// <summary>
    /// The window this destination must satisfy, read LIVE from the streaming
    /// configuration on every call. Retail's answer to a mid-hold radius
    /// change is <c>SmartBox::set_mid_radius</c> @0x00453180: reset the cell
    /// manager, re-radius the landscape, and re-arm the blocking prefetch at
    /// the NEW value — never finish the old hold at the old radius.
    ///
    /// <para>
    /// Indoor destinations take retail's EnvCell arm
    /// (<c>CEnvCell::PreFetchCells</c> @0x0052D1E0), which walks the cell's own
    /// visible-cell graph rather than the landscape square, so the outdoor
    /// ring is not required and the radius is zero.
    /// </para>
    /// </summary>
    internal StreamingRevealWindow RequiredWindow(uint destinationCell)
    {
        if (IsIndoor(destinationCell))
            return new StreamingRevealWindow(0, 0);

        StreamingRevealWindow window = _revealWindow();
        int far = Math.Max(0, window.FarRadius);
        int near = Math.Clamp(window.NearRadius, 0, far);
        return new StreamingRevealWindow(near, far);
    }

    /// <summary>
    /// The outdoor gate's outer radius — retail's <c>mid_radius</c>. Callers
    /// that reserve destination streaming capacity must use exactly this value
    /// so the prefetch square and the blocked square stay identical, as they
    /// are in retail by construction.
    /// </summary>
    internal int RequiredRenderRadius(uint destinationCell) =>
        RequiredWindow(destinationCell).FarRadius;

    private static bool IsIndoor(uint cellId) => (cellId & 0xFFFFu) >= 0x0100u;
}