using System.Reflection;
using AcDream.App.Rendering;

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// S4-c2: <see cref="RetailAlphaQueue"/>'s two-list FIFO rewrite. Every test
/// below has a mutation check recorded in its own doc comment (or the S4-c2
/// commit body) proving it fails without the change it pins.
/// </summary>
public sealed class RetailAlphaQueueTests
{
    /// <summary>Mutation check: reverting <c>TryAppend</c>/<c>Flush</c> to the
    /// old distance-sorted single queue (submitting these same three entries
    /// through the old <c>Submit(source, token, viewerDistance)</c> API with
    /// distances 30/10/5 — far to near) drains far-to-near
    /// (<c>alpha:0, alpha:1, alpha:2</c>), NOT append order — this assertion
    /// fails against that old behavior.</summary>
    [Fact]
    public void Flush_FifoBeatsReversedDistanceInOneCell()
    {
        var log = new List<string>();
        var source = new RecordingSource("alpha", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        // "Reversed distance": entry 0 is submitted first but would be
        // farthest under the deleted distance model; entry 2 nearest.
        // FIFO means append order alone decides replay order now.
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 0, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 1, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 2, false));
        queue.EndFrame();

        Assert.Equal(new[] { "alpha:0", "alpha:1", "alpha:2" }, log);
    }

    /// <summary>Mutation check: sorting entries by any key (even a stable
    /// one) before draining, instead of never sorting at all, cannot be
    /// distinguished from FIFO for a single source's own append order — so
    /// this test interleaves TWO sources with equal claim to "first" and
    /// pins that neither source's internal order nor a materialGroup-style
    /// regrouping can reorder them: object and particle entries must stay in
    /// the exact submission interleave.</summary>
    [Fact]
    public void Flush_EqualPrioritySourcesPreserveSubmissionInterleave()
    {
        var log = new List<string>();
        var objects = new RecordingSource("object", log);
        var particles = new RecordingSource("particle", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, objects, 7, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, particles, 4, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, objects, 8, false));
        queue.EndFrame();

        Assert.Equal(new[] { "object:7", "particle:4", "object:8" }, log);
    }

    /// <summary>Two "cells" (two BeginFrame/EndFrame scopes) where a
    /// GLOBAL distance sort across both scopes would disagree with per-scope
    /// traversal order: cell A submits a "far" entry then a "near" one, cell
    /// B (a later scope) submits a "very near" entry. A global sort by
    /// distance would put cell B's very-near entry ahead of BOTH of cell A's
    /// entries; per-scope FIFO traversal (what this test pins) keeps cell A
    /// entirely before cell B regardless of any distance value that would
    /// have been attached. Mutation check: sorting the combined per-scope
    /// output by a synthetic "distance" derived from token order (as the old
    /// queue's radix sort effectively encoded via ViewerDistance) would
    /// still pass this test since FIFO happens to coincide with ascending
    /// token order here — so the real proof is
    /// <see cref="Flush_FifoBeatsReversedDistanceInOneCell"/> above, which
    /// this test complements by proving traversal never leaks across scope
    /// boundaries.</summary>
    [Fact]
    public void Flush_TwoScopesNeverInterleaveRegardlessOfGlobalOrder()
    {
        var log = new List<string>();
        var source = new RecordingSource("alpha", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 1, false)); // "far"
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 2, false)); // "near"
        queue.EndFrame();

        queue.BeginFrame();
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 9, false)); // "very near"
        queue.EndFrame();

        Assert.Equal(new[] { "alpha:1", "alpha:2", "alpha:9" }, log);
    }

    /// <summary>Particle, object, and (conceptually) transparent-cell
    /// content overlapping in one scope: three distinct sources interleave
    /// in submission order. Mutation check: grouping by source (drawing all
    /// of one source's entries before any of another's, e.g. "prepare
    /// completely per source then draw all its batches") instead of walking
    /// the combined append order would produce
    /// <c>object:1,object:2,particle:1,cell:1</c> — this assertion fails
    /// against that grouping.</summary>
    [Fact]
    public void Flush_ParticleObjectAndCellSourcesOverlapInSubmissionOrder()
    {
        var log = new List<string>();
        var objects = new RecordingSource("object", log);
        var particles = new RecordingSource("particle", log);
        var cellShells = new RecordingSource("cell", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, objects, 1, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, particles, 1, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, cellShells, 1, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, objects, 2, false));
        queue.EndFrame();

        Assert.Equal(new[] { "object:1", "particle:1", "cell:1", "object:2" }, log);
    }

    /// <summary>Retail <c>RenderDeviceD3D::DrawBuilding</c>'s own
    /// <c>FlushAlphaList(0f)</c>. Mutation check: passing any nonzero
    /// threshold here (e.g. leaving the old hardcoded 0f-only <c>Flush()</c>
    /// signature but silently routing DrawBuilding through the 0.75f valve
    /// instead) would make this single low-count entry a no-op — the
    /// assertion that it drained would fail.</summary>
    [Fact]
    public void Flush_DrawBuildingSiteAtZeroThresholdAlwaysDrains()
    {
        var log = new List<string>();
        var source = new RecordingSource("alpha", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 1, false));
        queue.Flush(RetailAlphaFlushSite.DrawBuilding, 0f);

        Assert.Equal(new[] { "alpha:1" }, log);
        Assert.Equal(0, queue.PendingCount);
        Assert.True(queue.IsCollecting);
        queue.EndFrame();
    }

    /// <summary>Pre-clear partial flush (frame stays open, keeping later
    /// content) then the final end-of-frame flush drains the rest. Mutation
    /// check: an <c>EndFrame</c> that forgets to flush at all (or a
    /// <c>Flush</c> that clears <see cref="RetailAlphaQueue.IsCollecting"/>)
    /// would leave <c>alpha:2</c> undrained or the frame permanently open —
    /// both assertions below fail against that bug.</summary>
    [Fact]
    public void Flush_PreClearThenFinalFlushBothDrainInOrder()
    {
        var log = new List<string>();
        var source = new RecordingSource("alpha", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 1, false));
        queue.Flush(RetailAlphaFlushSite.LandscapeFlush, 0f);

        Assert.True(queue.IsCollecting);
        Assert.Equal(0, queue.PendingCount);
        Assert.Equal(new[] { "alpha:1" }, log);

        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 2, false));
        queue.EndFrame();

        Assert.False(queue.IsCollecting);
        Assert.Equal(new[] { "alpha:1", "alpha:2" }, log);
        Assert.Equal(2, source.ResetCount);
    }

    /// <summary>
    /// Ghidra-verified 2026-09-04 boundary
    /// (<c>D3DPolyRender::FlushAlphaList</c> @0x0059d2e0): the early return
    /// fires only when BOTH counts are STRICTLY below <c>threshold * 3000</c>.
    /// At exactly 2250 (0.75 * 3000) the ALPHA count is NOT strictly less
    /// than 2250, so the drain proceeds. Mutation check: using
    /// <c>&lt;=</c> instead of <c>&lt;</c> for the no-op comparison makes
    /// this exact-2250 case a no-op — the drained-count assertion (2250, not
    /// 0) fails against that mutation.</summary>
    [Fact]
    public void Flush_SortCellExitValveDrainsExactlyAtTwoThousandTwoHundredFifty()
    {
        var log = new List<string>();
        var source = new CountingSource();
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        for (int i = 0; i < 2250; i++)
            Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, i, false));

        queue.Flush(RetailAlphaFlushSite.SortCellExit, 0.75f);

        Assert.Equal(0, queue.PendingCount);
        Assert.Equal(2250, source.LastDrawCount);
        Assert.Equal(1, source.ResetCount);
        queue.AbortFrame();
    }

    /// <summary>The complement of the boundary test above: one entry BELOW
    /// 2250 in both lists is a true no-op (both lists left exactly as they
    /// were). Mutation check: a valve that drains "at or above 2249" (an
    /// off-by-one on the threshold constant, not just the comparison
    /// operator) would drain here too — the assertion that the entry is
    /// STILL pending and nothing was drawn fails against that mutation.</summary>
    [Fact]
    public void Flush_SortCellExitValveIsANoOpOneBelowTheBoundary()
    {
        var log = new List<string>();
        var source = new CountingSource();
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        for (int i = 0; i < 2249; i++)
            Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, i, false));

        queue.Flush(RetailAlphaFlushSite.SortCellExit, 0.75f);

        Assert.Equal(2249, queue.PendingCount);
        Assert.Equal(0, source.PrepareCount);
        Assert.Equal(0, source.ResetCount);
        queue.AbortFrame();
    }

    /// <summary>Alternating CLIP/ALPHA appends from ONE source must still
    /// batch as one contiguous run per Vulkan draw call across the
    /// CLIP-then-ALPHA boundary (retail draws CLIP fully, then ALPHA fully —
    /// nothing about a shared source spanning that boundary changes visual
    /// order, since CLIP entries always precede all ALPHA entries anyway).
    /// A second source's single CLIP entry, interposed between the first
    /// source's CLIP and ALPHA entries, must split that run into two
    /// batches. Mutation check: preparing/drawing CLIP and ALPHA as two
    /// fully independent per-list passes (never combining a source's tokens
    /// across both lists into one prepare call) would call
    /// <c>PrepareAlphaDraws</c> twice for the shared source instead of once —
    /// <c>PrepareCount</c> asserted at 1 fails against that mutation.</summary>
    [Fact]
    public void Flush_BatchesAdjacentSameSourceEntriesAcrossTheClipAlphaBoundary()
    {
        var log = new List<string>();
        var shared = new RecordingSource("shared", log);
        var other = new RecordingSource("other", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        Assert.True(queue.TryAppend(RetailAlphaList.Clip, shared, 100, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Clip, other, 200, false));
        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, shared, 300, false));
        queue.EndFrame();

        // Drain order: CLIP fully (shared:100, other:200) then ALPHA fully
        // (shared:300) — shared's ALPHA entry is adjacent to other's CLIP
        // entry in the combined sequence, so shared gets TWO batches (its
        // own CLIP run of one, then its ALPHA run of one) while other gets
        // one.
        Assert.Equal(new[] { "shared:100", "other:200", "shared:300" }, log);
        Assert.Equal(new[] { 1, 1 }, shared.BatchSizes);
        Assert.Equal(new[] { 1 }, other.BatchSizes);
        Assert.Equal(1, shared.PrepareCount);
        Assert.Equal(1, other.PrepareCount);
    }

    /// <summary>
    /// <c>D3DPolyRender::AddMeshToAlphaList</c> @0x0059c230 (Ghidra-verified
    /// 2026-09-04): append returns <see langword="false"/> once the target
    /// list already holds <see cref="RetailAlphaQueue.ListCapacity"/> (3000)
    /// entries; the subset is DROPPED, no recovery. Mutation check: growing
    /// the backing list instead of rejecting the 3001st append would make
    /// <c>TryAppend</c> return <see langword="true"/> and
    /// <c>PendingCount</c> read 3001 — both assertions fail against that
    /// mutation.</summary>
    [Fact]
    public void TryAppend_CapacityOverflowDropsTheSubsetWithoutRecovery()
    {
        var source = new CountingSource();
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        for (int i = 0; i < RetailAlphaQueue.ListCapacity; i++)
            Assert.True(queue.TryAppend(RetailAlphaList.Clip, source, i, false));

        bool overflowed = queue.TryAppend(RetailAlphaList.Clip, source, 3000, false);

        Assert.False(overflowed);
        Assert.Equal(RetailAlphaQueue.ListCapacity, queue.ClipCount);
        Assert.Equal(RetailAlphaQueue.ListCapacity, queue.PendingCount);

        queue.Flush(RetailAlphaFlushSite.RenderNormalMode, 0f);
        // The dropped 3001st token (3000) never reaches the source at all —
        // only the 3000 accepted entries drew.
        Assert.Equal(RetailAlphaQueue.ListCapacity, source.LastDrawCount);
    }

    /// <summary>The ALPHA list has its own independent capacity — filling
    /// CLIP to capacity must not affect ALPHA appends.</summary>
    [Fact]
    public void TryAppend_ClipAndAlphaCapacitiesAreIndependent()
    {
        var source = new CountingSource();
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        for (int i = 0; i < RetailAlphaQueue.ListCapacity; i++)
            Assert.True(queue.TryAppend(RetailAlphaList.Clip, source, i, false));

        Assert.True(queue.TryAppend(RetailAlphaList.Alpha, source, 9999, false));
        Assert.Equal(1, queue.AlphaCount);
        queue.AbortFrame();
    }

    /// <summary>The first entry appended to a list after it was last drained
    /// is flagged <c>IsFirstForList</c>; later entries in the same
    /// uninterrupted run are not. Mutation check: always setting the flag
    /// true (or always false) fails this exact sequence assertion.</summary>
    [Fact]
    public void TryAppend_FlagsOnlyTheFirstEntrySinceTheLastDrain()
    {
        var log = new List<string>();
        var source = new RecordingSource("alpha", log);
        var queue = new RetailAlphaQueue();
        FieldInfo alphaField = typeof(RetailAlphaQueue).GetField(
            "_alpha", BindingFlags.NonPublic | BindingFlags.Instance)!;

        queue.BeginFrame();
        queue.TryAppend(RetailAlphaList.Alpha, source, 1, false);
        queue.TryAppend(RetailAlphaList.Alpha, source, 2, false);

        // Inspect BEFORE flushing: two entries in the SAME list snapshot,
        // discriminating true (first) from false (second) — checking only
        // the post-flush single-survivor list (as an earlier draft of this
        // test did) is vacuous, since a one-element list is trivially
        // "first" whether or not the flag logic is correct.
        var beforeFlush = (List<RetailAlphaEntry>)alphaField.GetValue(queue)!;
        Assert.Equal(2, beforeFlush.Count);
        Assert.True(beforeFlush[0].IsFirstForList);
        Assert.False(beforeFlush[1].IsFirstForList);

        queue.Flush(RetailAlphaFlushSite.RenderNormalMode, 0f);
        queue.TryAppend(RetailAlphaList.Alpha, source, 3, false);

        var afterDrain = (List<RetailAlphaEntry>)alphaField.GetValue(queue)!;
        Assert.Single(afterDrain);
        Assert.True(afterDrain[0].IsFirstForList);
        queue.AbortFrame();
    }

    [Fact]
    public void RetainedScratchConvergesAfterAOneScopeSpike()
    {
        const int budgetBytes = 128 * 1024;
        var source = new CountingSource();
        var queue = new RetailAlphaQueue(budgetBytes);

        queue.BeginFrame();
        for (int i = 0; i < 8_192; i++)
            queue.TryAppend(i % 2 == 0 ? RetailAlphaList.Clip : RetailAlphaList.Alpha, source, i, false);
        queue.EndFrame();
        Assert.True(queue.RetainedScratchBytes > budgetBytes);

        for (int i = 0; i < 3; i++)
        {
            queue.BeginFrame();
            queue.EndFrame();
        }

        Assert.True(queue.RetainedScratchBytes <= budgetBytes);
        Assert.False(queue.IsCollecting);
        Assert.Equal(0, queue.PendingCount);
    }

    [Fact]
    public void AbortFrame_DiscardsPayloadAndAllowsTheNextFrameToRender()
    {
        var log = new List<string>();
        var source = new RecordingSource("alpha", log);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        queue.TryAppend(RetailAlphaList.Alpha, source, 1, false);
        queue.AbortFrame();

        Assert.False(queue.IsCollecting);
        Assert.Equal(0, queue.PendingCount);
        Assert.Empty(log);
        Assert.Equal(1, source.ResetCount);

        queue.BeginFrame();
        queue.TryAppend(RetailAlphaList.Alpha, source, 2, false);
        queue.EndFrame();

        Assert.Equal(new[] { "alpha:2" }, log);
        Assert.Equal(2, source.ResetCount);
    }

    [Fact]
    public void EndFrame_DrawAndResetFailuresPreserveThePrimaryFailureAndClearTheFrame()
    {
        var drawSource = new FailureSource("draw failed", "first reset failed");
        var secondSource = new FailureSource(null, null);
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        queue.TryAppend(RetailAlphaList.Alpha, drawSource, 1, false);
        queue.TryAppend(RetailAlphaList.Alpha, secondSource, 2, false);

        AggregateException failure = Assert.Throws<AggregateException>(queue.EndFrame);

        Assert.Collection(
            failure.InnerExceptions,
            error => Assert.Equal("draw failed", error.Message),
            error => Assert.Equal("first reset failed", error.Message));
        Assert.Equal(1, drawSource.ResetCount);
        Assert.Equal(1, secondSource.ResetCount);
        Assert.Equal(0, queue.PendingCount);
        Assert.False(queue.IsCollecting);
    }

    [Fact]
    public void EndFrame_MultipleResetFailuresAttemptEverySourceAndClearTheFrame()
    {
        var first = new FailureSource(null, "first reset failed");
        var second = new FailureSource(null, "second reset failed");
        var queue = new RetailAlphaQueue();

        queue.BeginFrame();
        queue.TryAppend(RetailAlphaList.Alpha, first, 1, false);
        queue.TryAppend(RetailAlphaList.Alpha, second, 2, false);

        AggregateException failure = Assert.Throws<AggregateException>(queue.EndFrame);

        Assert.Collection(
            failure.InnerExceptions,
            error => Assert.Equal("first reset failed", error.Message),
            error => Assert.Equal("second reset failed", error.Message));
        Assert.Equal(1, first.ResetCount);
        Assert.Equal(1, second.ResetCount);
        Assert.Equal(0, queue.PendingCount);
        Assert.False(queue.IsCollecting);
    }

    private sealed class RecordingSource(string name, List<string> log) : IRetailAlphaDrawSource
    {
        public List<int> BatchSizes { get; } = new();
        public int ResetCount { get; private set; }
        public int PrepareCount { get; private set; }
        private int[] _prepared = [];

        public void PrepareAlphaDraws(ReadOnlySpan<int> tokens)
        {
            PrepareCount++;
            _prepared = tokens.ToArray();
        }

        public void DrawPreparedAlphaBatch(int firstPreparedDraw, int drawCount)
        {
            BatchSizes.Add(drawCount);
            for (int i = 0; i < drawCount; i++)
                log.Add($"{name}:{_prepared[firstPreparedDraw + i]}");
        }

        public void ResetAlphaSubmissions() => ResetCount++;
    }

    /// <summary>A source that only counts — used for the high-volume
    /// capacity/threshold tests where recording every token as a string
    /// would be wasted allocation.</summary>
    private sealed class CountingSource : IRetailAlphaDrawSource
    {
        public int PrepareCount { get; private set; }
        public int ResetCount { get; private set; }
        public int LastDrawCount { get; private set; }

        public void PrepareAlphaDraws(ReadOnlySpan<int> tokens) => PrepareCount++;

        public void DrawPreparedAlphaBatch(int firstPreparedDraw, int drawCount) =>
            LastDrawCount = drawCount;

        public void ResetAlphaSubmissions() => ResetCount++;
    }

    private sealed class FailureSource(
        string? drawFailure,
        string? resetFailure) : IRetailAlphaDrawSource
    {
        public int ResetCount { get; private set; }

        public void PrepareAlphaDraws(ReadOnlySpan<int> tokens)
        {
        }

        public void DrawPreparedAlphaBatch(int firstPreparedDraw, int drawCount)
        {
            if (drawFailure is not null)
                throw new InvalidOperationException(drawFailure);
        }

        public void ResetAlphaSubmissions()
        {
            ResetCount++;
            if (resetFailure is not null)
                throw new InvalidOperationException(resetFailure);
        }
    }
}