using System.Collections.Generic;
using System.Numerics;
using AcDream.App.Rendering.Wb;
using AcDream.Core.World;

namespace AcDream.App.Rendering;

/// <summary>Per-frame inputs for one <see cref="InteriorRenderer.DrawInside"/> flood.</summary>
public sealed class InteriorRenderContext
{
    /// <summary>Visible cells, closest-first (retail cell_draw_list). From PortalVisibilityFrame.</summary>
    public required IReadOnlyList<uint> OrderedVisibleCells { get; init; }

    /// <summary>The cells the assembler mapped a clip slot for (ClipFrameAssembly.CellIdToSlot.Keys =
    /// the GameWindow envCellShellFilter). A cell may appear in <see cref="OrderedVisibleCells"/> but
    /// reduce to IsNothingVisible in the assembler (no slot) — those are skipped. This is the
    /// membership filter; <see cref="OrderedVisibleCells"/> supplies the draw ORDER.</summary>
    public required IReadOnlySet<uint> DrawableCells { get; init; }

    /// <summary>Per-cell portal_view slots, in the same order retail setup_view(cell, i)
    /// selects them inside PView::DrawCells.</summary>
    public required IReadOnlyDictionary<uint, int[]> CellClipSlots { get; init; }

    public required int OutdoorSlot { get; init; }
    public required bool OutdoorVisible { get; init; }

    /// <summary>The 3-bucket entity split (<see cref="InteriorEntityPartition"/>). Only ByCell +
    /// LiveDynamic are used here; Outdoor scenery is drawn by the caller's landscape-through-door
    /// step (clipped to OutsideView).</summary>
    public required InteriorEntityPartition.Result Partition { get; init; }

    public required ICamera Camera { get; init; }
    public required FrustumPlanes? Frustum { get; init; }

    /// <summary>The full FFFF-suffixed landblock id of the player. Used as BOTH the synthetic
    /// per-cell entry id AND neverCullLandblockId so the degenerate (zero) synthetic AABB is never
    /// landblock-culled — per-entity frustum culling inside Draw still applies.</summary>
    public required uint? PlayerLandblockId { get; init; }

    public required HashSet<uint>? AnimatedEntityIds { get; init; }
}

/// <summary>
/// The interior render flood, matching retail PView::DrawCells @ 0x005a4840:
/// after the caller handles outside_view terrain + the depth-only clear, DrawCells
/// walks cell_draw_list from the end back to zero in separate stages: cell shells,
/// then each cell's object_list. The transparent shell pass is split out because
/// the modern renderer batches opaque/transparent surfaces separately.
/// </summary>
public sealed class InteriorRenderer
{
    private readonly EnvCellRenderer _envCells;
    private readonly WbDrawDispatcher _entities;

    // Reused single-cell filter set — cleared + repopulated per cell to avoid per-frame allocs.
    private readonly HashSet<uint> _oneCell = new(1);
    public InteriorRenderer(EnvCellRenderer envCells, WbDrawDispatcher entities)
    {
        _envCells = envCells;
        _entities = entities;
    }

    public void DrawInside(InteriorRenderContext ctx)
    {
        // Retail Loop 2: DrawEnvCell for each drawable cell, farthest-to-nearest
        // (cell_draw_list[cell_draw_num - 1] down to 0).
        for (int i = ctx.OrderedVisibleCells.Count - 1; i >= 0; i--)
        {
            uint cellId = ctx.OrderedVisibleCells[i];
            if (!TryBeginCell(ctx, cellId, out _)) continue;
            _oneCell.Clear();
            _oneCell.Add(cellId);
            ApplyMembershipOnlyRouting();
            _envCells.Render(WbRenderPass.Opaque, _oneCell);
        }

        // Retail Loop 3: Render::PortalList = cell->portal_view; DrawObjCellForDummies(cell).
        for (int i = ctx.OrderedVisibleCells.Count - 1; i >= 0; i--)
        {
            uint cellId = ctx.OrderedVisibleCells[i];
            if (!TryBeginCell(ctx, cellId, out _)) continue;
            _oneCell.Clear();
            _oneCell.Add(cellId);
            if (ctx.Partition.ByCell.TryGetValue(cellId, out var cellEntities) && cellEntities.Count > 0)
            {
                ApplyMembershipOnlyRouting();
                DrawEntityBucket(ctx, cellEntities, visibleCellIds: _oneCell);
            }
        }

        // Modern split of DrawEnvCell's transparent/additive batches, same reverse cell order.
        for (int i = ctx.OrderedVisibleCells.Count - 1; i >= 0; i--)
        {
            uint cellId = ctx.OrderedVisibleCells[i];
            if (!TryBeginCell(ctx, cellId, out _)) continue;
            _oneCell.Clear();
            _oneCell.Add(cellId);
            ApplyMembershipOnlyRouting();
            _envCells.Render(WbRenderPass.Transparent, _oneCell);
        }
    }

    private bool TryBeginCell(InteriorRenderContext ctx, uint cellId, out int[] slots)
    {
        if (ctx.DrawableCells.Contains(cellId))
        {
            ctx.CellClipSlots.TryGetValue(cellId, out slots!);
            slots ??= System.Array.Empty<int>();
            return true;
        }

        slots = System.Array.Empty<int>();
        return false;
    }

    private void ApplyMembershipOnlyRouting()
    {
        // PView membership controls which cell shell/object bucket is visited.
        // Do not turn the 2D portal view into gl_ClipDistance for indoor meshes:
        // that slices avatars and shell triangles at stairs/doorways instead of
        // matching retail's DrawMesh view-check-then-draw behavior.
        _envCells.SetClipRouting(null);
        _entities.ClearClipRouting();
    }

    // Draws one bucket of entities via the existing dispatcher, scoped to a synthetic single-entry
    // landblock list. visibleCellIds gates which entities pass the cell-membership walk (a single-cell
    // set for per-cell objects; null only for fallback/outdoor buckets where clip-slot routing owns cull).
    // The clip slot per entity comes from the SetClipRouting the caller installed (cellIdToSlot +
    // outdoorSlot + outdoorVisible) via ResolveEntitySlot.
    private void DrawEntityBucket(
        InteriorRenderContext ctx, IReadOnlyList<WorldEntity> bucket, HashSet<uint>? visibleCellIds)
        => DrawEntityBucket(
            ctx.Camera,
            ctx.Frustum,
            ctx.PlayerLandblockId,
            ctx.AnimatedEntityIds,
            bucket,
            visibleCellIds);

    public void DrawEntityBucket(
        ICamera camera,
        FrustumPlanes? frustum,
        uint? playerLandblockId,
        HashSet<uint>? animatedEntityIds,
        IReadOnlyList<WorldEntity> bucket,
        HashSet<uint>? visibleCellIds)
    {
        // LandblockId == neverCullLandblockId (PlayerLandblockId) ⇒ the degenerate (zero) AABB is
        // never landblock-frustum-culled; per-entity AABB culling inside Draw still applies.
        uint lbId = playerLandblockId ?? 0u;
        var entry = (lbId, Vector3.Zero, Vector3.Zero,
                     (IReadOnlyList<WorldEntity>)bucket,
                     (IReadOnlyDictionary<uint, WorldEntity>?)null);

        _entities.Draw(
            camera,
            new[] { entry },
            frustum,
            neverCullLandblockId: playerLandblockId,
            visibleCellIds: visibleCellIds,
            animatedEntityIds: animatedEntityIds);
    }
}