acdream/src/AcDream.App/Streaming/StreamingController.cs

using System;
using System.Collections.Generic;
using AcDream.Core.Terrain;
using AcDream.Core.World;

namespace AcDream.App.Streaming;

/// <summary>
/// Called once per frame from <c>GameWindow.OnUpdate</c>. Owns the
/// <see cref="StreamingRegion"/> and uses delegates into
/// <see cref="LandblockStreamer"/> so tests can inject fakes. All work
/// happens on the render thread; the streamer itself is background.
///
/// <remarks>
/// Threading: not thread-safe. All calls must happen on the render thread.
/// </remarks>
/// </summary>
public sealed class StreamingController
{
    private readonly Action<uint, LandblockStreamJobKind> _enqueueLoad;
    private readonly Action<uint> _enqueueUnload;
    private readonly Func<int, IReadOnlyList<LandblockStreamResult>> _drainCompletions;
    private readonly Action<LoadedLandblock, LandblockMeshData> _applyTerrain;
    private readonly Action<uint>? _removeTerrain;
    private readonly Action? _clearPendingLoads;
    private readonly GpuWorldState _state;
    private StreamingRegion? _region;

    // True while streaming is collapsed to the single dungeon landblock the
    // player stands in (the dungeon gate, #133 FPS). AC dungeons have NO
    // adjacent landblocks — neighbors are unrelated ocean-grid dungeons that
    // are never visible, so we stop loading the 25×25 window entirely.
    private bool _collapsed;

    // The dungeon landblock id we collapsed onto. Once collapsed we key the
    // gate on this STABLE landblock, not the per-frame insideDungeon signal:
    // CurrCell can momentarily resolve to null/outdoor mid-frame, and gating
    // expand on that flicker thrashes collapse↔expand (reload storms + a light
    // leak). We only expand when the observer actually moves to a different
    // landblock (teleport/portal out).
    private uint _collapsedCenter;

    /// <summary>
    /// Near-tier radius (LBs from observer that load full detail: terrain +
    /// scenery + entities). Set at construction; readable thereafter.
    /// </summary>
    /// <remarks>
    /// Mutating after the first <see cref="Tick"/> has no effect — the
    /// internal <see cref="StreamingRegion"/> snapshots both radii on its
    /// constructor. Treat as init-only post-Tick.
    /// </remarks>
    public int NearRadius { get; }

    /// <summary>
    /// Far-tier radius (LBs from observer that load terrain only). Set at
    /// construction; readable thereafter.
    /// </summary>
    /// <remarks>
    /// Mutating after the first <see cref="Tick"/> has no effect — see <see cref="NearRadius"/>.
    /// </remarks>
    public int FarRadius { get; }

    /// <summary>
    /// Cap on completions drained per <see cref="Tick"/> call. The cap is
    /// the GPU upload budget for one frame: terrain mesh + per-entity GfxObj
    /// sub-mesh uploads + texture uploads for one landblock take a few ms;
    /// applying 25 of them in a single frame produces a memory spike
    /// (observed: out-of-memory crash on the 5×5 first-frame load).
    ///
    /// <para>
    /// 4 is the original async-streamer value; it spreads a 5×5 first-frame
    /// load over ~7 frames (~116ms at 60fps), which is below the human
    /// perception threshold. Spawn races that previously dropped entities
    /// while landblocks were in flight are now handled by
    /// <see cref="GpuWorldState"/>'s pending-spawn list, so spreading
    /// completions doesn't lose any data.
    /// </para>
    /// </summary>
    public int MaxCompletionsPerFrame { get; set; } = 4;

    public StreamingController(
        Action<uint, LandblockStreamJobKind> enqueueLoad,
        Action<uint> enqueueUnload,
        Func<int, IReadOnlyList<LandblockStreamResult>> drainCompletions,
        Action<LoadedLandblock, LandblockMeshData> applyTerrain,
        GpuWorldState state,
        int nearRadius,
        int farRadius,
        Action<uint>? removeTerrain = null,
        Action? clearPendingLoads = null)
    {
        _enqueueLoad = enqueueLoad;
        _enqueueUnload = enqueueUnload;
        _drainCompletions = drainCompletions;
        _applyTerrain = applyTerrain;
        _removeTerrain = removeTerrain;
        _clearPendingLoads = clearPendingLoads;
        _state = state;
        NearRadius = nearRadius;
        FarRadius  = farRadius;
    }

    /// <summary>
    /// Advance one frame. <paramref name="observerCx"/>/<paramref name="observerCy"/>
    /// are landblock coordinates (0..255) of the current viewer — the camera
    /// in offline mode, the server-sent player position in live.
    ///
    /// <para>Two-tier model (Phase A.5 T13):</para>
    /// <list type="bullet">
    ///   <item><see cref="TwoTierDiff.ToLoadFar"/> → enqueue LoadFar (terrain only, no entities)</item>
    ///   <item><see cref="TwoTierDiff.ToLoadNear"/> → enqueue LoadNear (terrain + entities)</item>
    ///   <item><see cref="TwoTierDiff.ToPromote"/> → enqueue PromoteToNear (entity layer for already-loaded terrain)</item>
    ///   <item><see cref="TwoTierDiff.ToDemote"/> → drop entities on render thread immediately (terrain stays)</item>
    ///   <item><see cref="TwoTierDiff.ToUnload"/> → enqueue full unload</item>
    /// </list>
    /// </summary>
    public void Tick(int observerCx, int observerCy, bool insideDungeon = false)
    {
        uint centerId = StreamingRegion.EncodeLandblockId(observerCx, observerCy);

        if (_collapsed)
        {
            // Hysteresis. Cases:
            //  - Still in the SAME dungeon landblock → hold (sweep stragglers).
            //  - In a DIFFERENT dungeon cell (multi-landblock dungeon / new dungeon)
            //    → re-collapse onto it.
            //  - CurrCell flickered null but the player hasn't gone anywhere: the
            //    observer landblock reverts to the position-derived value, which for a
            //    dungeon is only ever the ADJACENT off-by-one landblock (negative cell-
            //    local Y). Hold — never expand on an adjacent flicker.
            //  - Genuinely left to a DISTANT landblock (portal/teleport out, always far
            //    from the ocean-grid dungeon block) → expand.
            if (insideDungeon && centerId != _collapsedCenter)
                EnterDungeonCollapse(observerCx, observerCy, centerId);
            else if (!insideDungeon && ChebyshevLandblocks(centerId, _collapsedCenter) > 1)
                ExitDungeonExpand(observerCx, observerCy);
            else
                SweepCollapsed();
        }
        else if (insideDungeon)
        {
            EnterDungeonCollapse(observerCx, observerCy, centerId);
        }
        else
        {
            NormalTick(observerCx, observerCy);
        }

        DrainAndApply();
    }

    /// <summary>
    /// Outdoor / building-interior streaming — the original two-tier model.
    /// </summary>
    private void NormalTick(int observerCx, int observerCy)
    {
        if (_region is null)
        {
            _region = new StreamingRegion(observerCx, observerCy, NearRadius, FarRadius);
            var bootstrap = _region.ComputeFirstTickDiff();
            foreach (var id in bootstrap.ToLoadNear) _enqueueLoad(id, LandblockStreamJobKind.LoadNear);
            foreach (var id in bootstrap.ToLoadFar)  _enqueueLoad(id, LandblockStreamJobKind.LoadFar);
            _region.MarkResidentFromBootstrap();
        }
        else if (_region.CenterX != observerCx || _region.CenterY != observerCy)
        {
            var diff = _region.RecenterTo(observerCx, observerCy);
            foreach (var id in diff.ToPromote)  _enqueueLoad(id, LandblockStreamJobKind.PromoteToNear);
            foreach (var id in diff.ToLoadNear) _enqueueLoad(id, LandblockStreamJobKind.LoadNear);
            foreach (var id in diff.ToLoadFar)  _enqueueLoad(id, LandblockStreamJobKind.LoadFar);
            foreach (var id in diff.ToDemote)   _state.RemoveEntitiesFromLandblock(id);
            foreach (var id in diff.ToUnload)   _enqueueUnload(id);
        }
    }

    /// <summary>
    /// Dungeon-entry edge: cancel the in-flight window load, unload every
    /// resident neighbor, and pin streaming to the player's single dungeon
    /// landblock. Retail-faithful — AC dungeons have no adjacent landblocks
    /// (ACE <c>LandblockManager.GetAdjacentIDs</c> returns empty for a dungeon);
    /// the 25×25 window was pulling in ~129 unrelated ocean-grid dungeons and
    /// their thousands of emitters (#133 FPS). Unloading them also tears down
    /// their lights, shrinking the static-light set toward retail's ≤40.
    /// </summary>
    private void EnterDungeonCollapse(int cx, int cy, uint centerId)
    {
        _collapsed = true;
        _collapsedCenter = centerId;
        _clearPendingLoads?.Invoke();

        foreach (var id in _state.LoadedLandblockIds)
            if (id != centerId) _enqueueUnload(id);

        // Pin a radius-0 region so RecenterTo never re-expands while inside,
        // and so the post-exit rebuild starts from a clean, consistent state.
        _region = new StreamingRegion(cx, cy, 0, 0);
        _region.MarkResidentFromBootstrap();

        // The dungeon landblock itself must be (or become) loaded. If a prior
        // ClearPendingLoads cancelled its queued load, re-enqueue it.
        if (!_state.IsLoaded(centerId))
            _enqueueLoad(centerId, LandblockStreamJobKind.LoadNear);
    }

    /// <summary>
    /// While collapsed, unload any landblock that finished loading after the
    /// collapse edge — a Load the worker had already dequeued before the
    /// <see cref="LandblockStreamer.ClearPendingLoads"/> control job took
    /// effect. At steady state only the dungeon landblock is resident, so this
    /// is a no-op.
    /// </summary>
    private void SweepCollapsed()
    {
        // Always preserve the true dungeon landblock (_collapsedCenter), never the
        // per-frame observer landblock — a CurrCell flicker must not unload the dungeon.
        foreach (var id in _state.LoadedLandblockIds)
            if (id != _collapsedCenter) _enqueueUnload(id);
    }

    /// <summary>Chebyshev distance in landblock cells between two landblock ids.</summary>
    private static int ChebyshevLandblocks(uint a, uint b)
    {
        int ax = (int)((a >> 24) & 0xFFu), ay = (int)((a >> 16) & 0xFFu);
        int bx = (int)((b >> 24) & 0xFFu), by = (int)((b >> 16) & 0xFFu);
        return Math.Max(Math.Abs(ax - bx), Math.Abs(ay - by));
    }

    /// <summary>
    /// Dungeon-exit edge (portal to outdoors / teleport): rebuild the full
    /// two-tier window at the new center and unload anything resident from the
    /// collapsed state that falls outside it.
    /// </summary>
    private void ExitDungeonExpand(int observerCx, int observerCy)
    {
        _collapsed = false;
        var rebuilt = new StreamingRegion(observerCx, observerCy, NearRadius, FarRadius);

        foreach (var id in _state.LoadedLandblockIds)
            if (!rebuilt.Resident.Contains(id)) _enqueueUnload(id);

        var boot = rebuilt.ComputeFirstTickDiff();
        foreach (var id in boot.ToLoadNear)
            if (!_state.IsLoaded(id)) _enqueueLoad(id, LandblockStreamJobKind.LoadNear);
        foreach (var id in boot.ToLoadFar)
            if (!_state.IsLoaded(id)) _enqueueLoad(id, LandblockStreamJobKind.LoadFar);
        rebuilt.MarkResidentFromBootstrap();
        _region = rebuilt;
    }

    /// <summary>
    /// Drain up to N completions per frame so a big diff doesn't spike GPU
    /// upload time. Remaining completions wait for the next frame.
    /// </summary>
    private void DrainAndApply()
    {
        var drained = _drainCompletions(MaxCompletionsPerFrame);
        foreach (var result in drained)
        {
            switch (result)
            {
                case LandblockStreamResult.Loaded loaded:
                    _applyTerrain(loaded.Landblock, loaded.MeshData);
                    _state.AddLandblock(loaded.Landblock);
                    break;
                case LandblockStreamResult.Promoted promoted:
                    _applyTerrain(promoted.Landblock, promoted.MeshData);
                    _state.AddEntitiesToExistingLandblock(promoted.LandblockId, promoted.Entities);
                    break;
                case LandblockStreamResult.Unloaded unloaded:
                    _state.RemoveLandblock(unloaded.LandblockId);
                    _removeTerrain?.Invoke(unloaded.LandblockId);
                    break;
                case LandblockStreamResult.Failed failed:
                    Console.WriteLine(
                        $"streaming: load failed for 0x{failed.LandblockId:X8}: {failed.Error}");
                    break;
                case LandblockStreamResult.WorkerCrashed crashed:
                    Console.WriteLine(
                        $"streaming: worker CRASHED: {crashed.Error}");
                    break;
            }
        }
    }
}