using System.Numerics;
using AcDream.App.Rendering.Scene;
using AcDream.App.Rendering.Wb;

namespace AcDream.App.Rendering.Walk;

/// <summary>
/// Campaign FW stage FW3.2a: the walk→draw population layer. Turns one
/// cell's already-classified static content into <see cref="OrderedDrawCommand"/>
/// appends (opaque, walk order), per-instance deferred-alpha submissions
/// (translucent), and selection-scene publications (picking) — WITHOUT any
/// production frame wiring. <c>WorldSceneRenderer</c> does not call this
/// class yet; FW3.2b roots it into the real frame.
///
/// <para><b>Why per-entity append instead of the classic material grouping</b>:
/// under <see cref="WorldDepthContract"/>'s depth-compare Less, opaque draw
/// order is pixel-relevant ONLY for coplanar surfaces (a rug on a floor, a
/// shell over terrain) — and retail resolves those by first-drawn-wins in
/// ITS walk/cell-content order, not by any texture/material grouping. So
/// this populator appends one <see cref="OrderedDrawCommand"/> per (entity,
/// opaque batch) in the SAME order the caller's <c>records</c> span presents
/// them — never material-grouped, never re-sorted. Translucent batches go to
/// the SAME <see cref="RetailAlphaQueue"/> the classic/packed paths already
/// use (global far→near re-sort still applies; walk-order submission only
/// improves retail's submission-order tie-break fidelity for coincident
/// distances — <c>WbDrawDispatcher.DeferTransparentGroups</c>'s own doc
/// comment cites the same <c>CShadowPart::insertion_sort</c> stability this
/// preserves).</para>
///
/// <para>Reads no retained scene state itself: every method takes the target
/// <see cref="OrderedDrawStream"/> and a caller-supplied span of already
/// -queried <see cref="RenderProjectionRecord"/>s (from
/// <c>RenderSceneQuery.CopyCellStaticsTo</c> / <c>CopyIndexTo</c>). Owns only
/// two small per-call scratch lists — the classify seam's per-entity output
/// — reused across records to keep this hot path allocation-free after
/// warmup.</para>
/// </summary>
internal sealed class WalkStaticStreamPopulator
{
    private readonly WbDrawDispatcher _dispatcher;
    private readonly List<WbDrawDispatcher.WalkClassifiedBatch> _batchScratch = new();
    private readonly List<WbDrawDispatcher.WalkClassifiedSelectionPart> _selectionScratch = new();

    internal WalkStaticStreamPopulator(WbDrawDispatcher dispatcher)
    {
        _dispatcher = dispatcher ?? throw new ArgumentNullException(nameof(dispatcher));
    }

    /// <summary>
    /// Populates <paramref name="stream"/> from one indoor cell's static
    /// content (<c>RenderProjectionClass.IndoorCellStatic</c> —
    /// <c>RenderSceneQuery.CopyCellStaticsTo</c>). <paramref name="stage"/>
    /// is caller-selected per the walk turn this cell's content belongs to
    /// — <see cref="WalkDrawStage.CellStatic"/> for an ordinary
    /// <c>PView::DrawCells</c> flood, <see cref="WalkDrawStage.LookInStatic"/>
    /// for a <c>ConstructView(CBldPortal)</c> look-in, or
    /// <see cref="WalkDrawStage.BuildingShell"/> for a building's own
    /// exterior shell content.
    /// </summary>
    internal void PopulateCell(
        OrderedDrawStream stream,
        WalkDrawStage stage,
        uint cellId,
        ReadOnlySpan<RenderProjectionRecord> records,
        uint tupleLandblockId,
        Vector3 cameraWorldPosition,
        Matrix4x4 viewProjection,
        IWalkLookInViewSource? views = null,
        int viewRouteIndex = -1,
        List<WbDrawDispatcher.WalkClassifiedBatch>? alphaSubmissions = null)
    {
        ArgumentNullException.ThrowIfNull(stream);
        for (int i = 0; i < records.Length; i++)
        {
            ClassifyAndAppend(
                stream, stage, cellId, in records[i], tupleLandblockId,
                cameraWorldPosition, viewProjection,
                liveDynamic: false, views, viewRouteIndex, alphaSubmissions);
        }
    }

    /// <summary>
    /// The landscape entry point: outdoor static content
    /// (<c>RenderProjectionClass.OutdoorStatic</c> —
    /// <c>RenderSceneQuery.CopyIndexTo(RenderSceneIndex.OutdoorStatic, ...)</c>)
    /// at <see cref="WalkDrawStage.OutdoorStatic"/>, the terrain-adjacent
    /// stage <c>LScape::draw</c> visits a landblock's static objects at
    /// alongside its ground mesh (see that stage value's own doc comment).
    /// <paramref name="cellId"/> is the OUTDOOR landblock id — outdoor
    /// statics have no EnvCell of their own, so this is walk-order
    /// provenance only, not a clip-slot key.
    /// </summary>
    internal void PopulateOutdoorStatics(
        OrderedDrawStream stream,
        uint cellId,
        ReadOnlySpan<RenderProjectionRecord> records,
        uint tupleLandblockId,
        Vector3 cameraWorldPosition,
        Matrix4x4 viewProjection,
        IWalkLookInViewSource? views = null,
        int viewRouteIndex = -1,
        ISet<RenderProjectionId>? drawnOnce = null,
        List<WbDrawDispatcher.WalkClassifiedBatch>? alphaSubmissions = null)
    {
        ArgumentNullException.ThrowIfNull(stream);
        for (int i = 0; i < records.Length; i++)
        {
            if (drawnOnce is not null && !drawnOnce.Add(records[i].Id))
                continue;
            ClassifyAndAppend(
                stream, WalkDrawStage.OutdoorStatic, cellId, in records[i],
                tupleLandblockId, cameraWorldPosition, viewProjection,
                liveDynamic: false, views, viewRouteIndex, alphaSubmissions);
        }
    }

    internal void PopulateCellDynamics(
        OrderedDrawStream stream,
        uint cellId,
        ReadOnlySpan<RenderProjectionRecord> records,
        uint tupleLandblockId,
        Vector3 cameraWorldPosition,
        Matrix4x4 viewProjection,
        IWalkLookInViewSource? lookInViews = null,
        int lookInRouteIndex = -1,
        ISet<RenderProjectionId>? drawnOnce = null,
        List<WbDrawDispatcher.WalkClassifiedBatch>? alphaSubmissions = null)
    {
        ArgumentNullException.ThrowIfNull(stream);
        for (int i = 0; i < records.Length; i++)
        {
            if (drawnOnce is not null && !drawnOnce.Add(records[i].Id))
                continue;
            ClassifyAndAppend(
                stream,
                WalkDrawStage.Dynamic,
                cellId,
                in records[i],
                tupleLandblockId,
                cameraWorldPosition,
                viewProjection,
                liveDynamic: true,
                lookInViews,
                lookInRouteIndex,
                alphaSubmissions);
        }
    }

    private void ClassifyAndAppend(
        OrderedDrawStream stream,
        WalkDrawStage stage,
        uint cellId,
        in RenderProjectionRecord record,
        uint tupleLandblockId,
        Vector3 cameraWorldPosition,
        Matrix4x4 viewProjection,
        bool liveDynamic = false,
        IWalkLookInViewSource? lookInViews = null,
        int lookInRouteIndex = -1,
        List<WbDrawDispatcher.WalkClassifiedBatch>? alphaSubmissions = null)
    {
        _batchScratch.Clear();
        _selectionScratch.Clear();
        _dispatcher.ClassifyEntityForWalk(
            in record,
            tupleLandblockId,
            _batchScratch,
            _selectionScratch,
            liveDynamic,
            lookInViews,
            lookInRouteIndex,
            cellId);

        for (int i = 0; i < _batchScratch.Count; i++)
        {
            WbDrawDispatcher.WalkClassifiedBatch batch = _batchScratch[i];
            if (batch.IsOpaque)
            {
                stream.Append(new OrderedDrawCommand(
                    batch.Key, batch.Transform, stage, cellId, batch.ClipSlot,
                    batch.Lights, batch.IndoorFlag, batch.Alpha,
                    batch.SelectionLighting, batch.DetailCategory));
            }
            else
            {
                if (alphaSubmissions is null)
                {
                    _dispatcher.SubmitWalkAlphaInstance(
                        in batch, cameraWorldPosition, viewProjection);
                }
                else
                {
                    alphaSubmissions.Add(batch);
                }
            }
        }

        for (int i = 0; i < _selectionScratch.Count; i++)
        {
            WbDrawDispatcher.WalkClassifiedSelectionPart part = _selectionScratch[i];
            _dispatcher.PublishWalkSelectionPart(in part);
        }
    }
}