using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using AcDream.Core.Physics;
using AcDream.Core.Physics.Motion;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Types;
using Xunit;

using DRWMotionCommand = DatReaderWriter.Enums.MotionCommand;

namespace AcDream.Core.Tests.Physics.Motion;

// ─────────────────────────────────────────────────────────────────────────────
// MotionTableManagerTests — R2-Q3 conformance harness for the verbatim
// MotionTableManager pending-animation queue + tick-countdown completion
// machinery (r2-port-plan.md §3 Q3; oracle
// docs/research/2026-07-02-r2-motiontable/r2-motiontable-decomp.md §11).
//
// Fixture convention matches CMotionTableTests.cs's file-local Fixtures
// class. Most tests exercise MotionTableManager directly via its
// PendingAnimations/AnimationCounter inspection surface + a RecordingSink,
// bypassing GetObjectSequence entirely so the queue mechanics are pinned in
// isolation from the selection dispatcher (already covered by
// CMotionTableTests.cs).
// ─────────────────────────────────────────────────────────────────────────────

file static class Fixtures
{
    public static Animation MakeAnim(int numFrames, int numParts, Vector3 origin, Quaternion orientation)
    {
        var anim = new Animation();
        for (int f = 0; f < numFrames; f++)
        {
            var pf = new AnimationFrame((uint)numParts);
            for (int p = 0; p < numParts; p++)
                pf.Frames.Add(new Frame { Origin = origin, Orientation = orientation });
            anim.PartFrames.Add(pf);
        }
        return anim;
    }

    public static AnimData MakeAnimData(uint animId, float framerate)
        => new()
        {
            AnimId = (QualifiedDataId<Animation>)animId,
            LowFrame = 0,
            HighFrame = -1,
            Framerate = framerate,
        };

    public static MotionData MakeMotionData(uint animId, float framerate, byte bitfield = 0)
    {
        var md = new MotionData { Bitfield = bitfield };
        md.Anims.Add(MakeAnimData(animId, framerate));
        return md;
    }

    public static void AddLink(MotionTable mt, uint style, uint fromSubstate, uint toSubstate, MotionData data)
    {
        int outerKey = (int)((style << 16) | (fromSubstate & 0xFFFFFFu));
        if (!mt.Links.TryGetValue(outerKey, out var cmd))
        {
            cmd = new MotionCommandData();
            mt.Links[outerKey] = cmd;
        }
        cmd.MotionData[(int)toSubstate] = data;
    }

    public static void AddCycle(MotionTable mt, uint style, uint substate, MotionData data)
    {
        int key = (int)((style << 16) | (substate & 0xFFFFFFu));
        mt.Cycles[key] = data;
    }
}

/// <summary>Records every <see cref="IMotionDoneSink.MotionDone"/> call in order.</summary>
internal sealed class RecordingSink : IMotionDoneSink
{
    public readonly List<(uint Motion, bool Success)> Calls = new();
    public void MotionDone(uint motion, bool success) => Calls.Add((motion, success));
}

/// <summary>In-memory <see cref="IAnimationLoader"/> that never resolves.</summary>
file sealed class NullLoader : IAnimationLoader
{
    public Animation? LoadAnimation(uint id) => null;
}

/// <summary>In-memory <see cref="IAnimationLoader"/> test double.</summary>
file sealed class FakeLoader : IAnimationLoader
{
    private readonly Dictionary<uint, Animation> _anims = new();
    public void Register(uint id, Animation anim) => _anims[id] = anim;
    public Animation? LoadAnimation(uint id) => _anims.TryGetValue(id, out var a) ? a : null;
}

public sealed class MotionTableManagerTests
{
    // Real retail command words (DatReaderWriter.Enums.MotionCommand),
    // matching CMotionTableTests.cs's fixture conventions.
    private const uint Ready = 0x41000003u;         // cycle, == ReadySentinel
    private const uint WalkForward = 0x45000005u;   // cycle
    private const uint RunForward = 0x44000007u;    // cycle
    private const uint ThrustMed = 0x10000058u;     // action only
    private const uint NonCombatStyle = 0x8000003Du; // style, top bit set
    private const uint HandCombatStyle = 0x8000003Cu; // style, top bit set

    private static (MotionTableManager mgr, RecordingSink sink, MotionState state, CSequence seq) MakeManager(CMotionTable? table = null)
    {
        var sink = new RecordingSink();
        var state = new MotionState();
        var seq = new CSequence(new NullLoader());
        var mgr = new MotionTableManager(table, state, seq, sink);
        return (mgr, sink, state, seq);
    }

    // ── add_to_queue / basic queueing ───────────────────────────────────

    [Fact]
    public void AddToQueue_AppendsNode_InOrder()
    {
        var (mgr, _, _, _) = MakeManager();

        mgr.AddToQueue(WalkForward, 3);
        mgr.AddToQueue(RunForward, 5);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(2, list.Count);
        Assert.Equal(WalkForward, list[0].Motion);
        Assert.Equal(3u, list[0].NumAnims);
        Assert.Equal(RunForward, list[1].Motion);
        Assert.Equal(5u, list[1].NumAnims);
    }

    // ── countdown-chain: ONE AnimationDone completing MULTIPLE entries ──

    [Fact]
    public void AnimationDone_CounterRollover_CompletesMultipleQueuedEntries_InOneCall()
    {
        // Two zero-duration-relative-to-each-other entries stacked so a
        // single tick (counter=1) pops BOTH: first has NumAnims=1 (<=1 on
        // the first increment), and after popping it counter -= 1 => back to
        // 0... but decomp's while-loop re-tests the NEW head against the
        // SAME counter value within the same AnimationDone call (no re-
        // increment between pops) — so a second entry with NumAnims<=0
        // (i.e. 0) also pops in the same call.
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 1); // pops when counter reaches 1
        mgr.AddToQueue(RunForward, 0);  // zero-duration -> pops same call once counter>=0

        mgr.AnimationDone(true);

        Assert.Equal(2, sink.Calls.Count);
        Assert.Equal((WalkForward, true), sink.Calls[0]);
        Assert.Equal((RunForward, true), sink.Calls[1]);
        Assert.Empty(mgr.PendingAnimations);
        // Drained-list counter reset.
        Assert.Equal(0, mgr.AnimationCounter);
    }

    [Fact]
    public void AnimationDone_MultiTickCountdown_PopsOnlyWhenCounterReachesDuration()
    {
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 3); // needs counter >= 3 to pop

        mgr.AnimationDone(true); // counter=1
        Assert.Empty(sink.Calls);
        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(1, mgr.AnimationCounter);

        mgr.AnimationDone(true); // counter=2
        Assert.Empty(sink.Calls);
        Assert.Equal(2, mgr.AnimationCounter);

        mgr.AnimationDone(true); // counter=3 -> pops, counter -= 3 -> 0, list drains -> reset stays 0
        Assert.Single(sink.Calls);
        Assert.Equal((WalkForward, true), sink.Calls[0]);
        Assert.Empty(mgr.PendingAnimations);
        Assert.Equal(0, mgr.AnimationCounter);
    }

    [Fact]
    public void AnimationDone_LeftoverCounter_ResetOnlyWhenListFullyDrains()
    {
        // Two entries: first pops on tick 1 (duration 1), second needs
        // duration 5. After the first pop, counter = 1 - 1 = 0, but the
        // list is NOT empty (second entry remains) -> counter must NOT be
        // force-reset to something else; it stays at the algebraic value (0).
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 1);
        mgr.AddToQueue(RunForward, 5);

        mgr.AnimationDone(true); // counter=1 -> pops Walk (1<=1), counter -= 1 = 0; Run(5) remains, 0<=5? no.

        Assert.Single(sink.Calls);
        Assert.Equal((WalkForward, true), sink.Calls[0]);
        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(RunForward, mgr.PendingAnimations.First().Motion);
        Assert.Equal(0, mgr.AnimationCounter);
    }

    [Fact]
    public void AnimationDone_EmptyQueue_IsNoOp()
    {
        var (mgr, sink, _, _) = MakeManager();

        mgr.AnimationDone(true);

        Assert.Empty(sink.Calls);
        Assert.Equal(0, mgr.AnimationCounter);
    }

    // ── zero-tick sweep (CheckForCompletedMotions) vs counter sweep (AnimationDone) ──

    [Fact]
    public void CheckForCompletedMotions_PopsOnlyZeroTickHeads_NeverIncrementsCounter()
    {
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 0); // zero-tick: pops immediately
        mgr.AddToQueue(RunForward, 2);  // non-zero: stays

        mgr.CheckForCompletedMotions();

        Assert.Single(sink.Calls);
        Assert.Equal((WalkForward, true), sink.Calls[0]); // success hardcoded true
        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(RunForward, mgr.PendingAnimations.First().Motion);
        Assert.Equal(0, mgr.AnimationCounter); // untouched
    }

    [Fact]
    public void CheckForCompletedMotions_NonZeroHead_DoesNotPop()
    {
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 4);

        mgr.CheckForCompletedMotions();

        Assert.Empty(sink.Calls);
        Assert.Single(mgr.PendingAnimations);
    }

    [Fact]
    public void UseTime_IsAliasFor_CheckForCompletedMotions()
    {
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 0);

        mgr.UseTime();

        Assert.Single(sink.Calls);
        Assert.Equal((WalkForward, true), sink.Calls[0]);
    }

    [Fact]
    public void AnimationDone_Distinguished_FromCheckForCompletedMotions_ByCounterUse()
    {
        // A node with NumAnims=1 does NOT pop via CheckForCompletedMotions
        // (which only pops EXACTLY zero), but DOES pop via one AnimationDone
        // tick (counter reaches 1).
        var (mgrA, sinkA, _, _) = MakeManager();
        mgrA.AddToQueue(WalkForward, 1);
        mgrA.CheckForCompletedMotions();
        Assert.Empty(sinkA.Calls);
        Assert.Single(mgrA.PendingAnimations);

        var (mgrB, sinkB, _, _) = MakeManager();
        mgrB.AddToQueue(WalkForward, 1);
        mgrB.AnimationDone(true);
        Assert.Single(sinkB.Calls);
        Assert.Empty(mgrB.PendingAnimations);
    }

    // ── action-class completion pops MotionState's action FIFO ──────────

    [Fact]
    public void AnimationDone_ActionClassMotion_PopsActionHead()
    {
        var (mgr, sink, state, _) = MakeManager();
        state.AddAction(ThrustMed, 1f);
        Assert.Single(state.Actions);

        mgr.AddToQueue(ThrustMed, 0); // zero-duration -> pops on first tick

        mgr.AnimationDone(true);

        Assert.Empty(state.Actions); // popped
        Assert.Single(sink.Calls);
        Assert.Equal((ThrustMed, true), sink.Calls[0]);
    }

    [Fact]
    public void CheckForCompletedMotions_ActionClassMotion_PopsActionHead()
    {
        var (mgr, sink, state, _) = MakeManager();
        state.AddAction(ThrustMed, 1f);

        mgr.AddToQueue(ThrustMed, 0);
        mgr.CheckForCompletedMotions();

        Assert.Empty(state.Actions);
        Assert.Single(sink.Calls);
    }

    [Fact]
    public void AnimationDone_NonActionClassMotion_DoesNotTouchActionFifo()
    {
        var (mgr, _, state, _) = MakeManager();
        state.AddAction(ThrustMed, 1f);

        mgr.AddToQueue(WalkForward, 0); // cycle-class, not action-class
        mgr.AnimationDone(true);

        Assert.Single(state.Actions); // untouched
    }

    // ── enter/exit-world drains fire MotionDone(success=false) ──────────

    [Fact]
    public void HandleExitWorld_DrainsEntireQueue_FiringMotionDoneFalse_ForEveryEntry()
    {
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 0);
        mgr.AddToQueue(RunForward, 0);
        mgr.AddToQueue(ThrustMed, 0);

        mgr.HandleExitWorld();

        Assert.Equal(3, sink.Calls.Count);
        Assert.All(sink.Calls, c => Assert.False(c.Success));
        Assert.Empty(mgr.PendingAnimations);
    }

    [Fact]
    public void HandleExitWorld_NonZeroDurationEntries_StillFullyDrained()
    {
        // Drain loops AnimationDone(false) until head_==0, incrementing the
        // counter each call — even non-zero-duration entries eventually pop.
        var (mgr, sink, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 3);

        mgr.HandleExitWorld();

        Assert.Single(sink.Calls);
        Assert.Equal((WalkForward, false), sink.Calls[0]);
        Assert.Empty(mgr.PendingAnimations);
    }

    [Fact]
    public void HandleEnterWorld_DrainsQueue_AndStripsLinkAnimations()
    {
        var loader = new FakeLoader();
        uint linkAnim = 0x03000200u, cycleAnim = 0x03000201u;
        loader.Register(linkAnim, Fixtures.MakeAnim(2, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(cycleAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));

        var sink = new RecordingSink();
        var state = new MotionState { Style = NonCombatStyle, Substate = Ready, SubstateMod = 1f };
        var seq = new CSequence(loader);
        // Build a link + cyclic tail directly (bypassing GetObjectSequence).
        CMotionTable.AddMotion(seq, Fixtures.MakeMotionData(linkAnim, 30f), 1f);
        CMotionTable.AddMotion(seq, Fixtures.MakeMotionData(cycleAnim, 30f), 1f);
        Assert.Equal(2, seq.Count);

        var mgr = new MotionTableManager(null, state, seq, sink);
        mgr.AddToQueue(WalkForward, 0);

        mgr.HandleEnterWorld();

        // Queue drained, MotionDone(false) fired.
        Assert.Single(sink.Calls);
        Assert.False(sink.Calls[0].Success);
        Assert.Empty(mgr.PendingAnimations);
        // Link animation stripped — only the cyclic tail remains.
        Assert.Equal(1, seq.Count);
    }

    [Fact]
    public void HandleEnterWorld_EmptyQueue_StillStripsLinkAnimations_NoOpOnDrain()
    {
        var loader = new FakeLoader();
        uint linkAnim = 0x03000210u, cycleAnim = 0x03000211u;
        loader.Register(linkAnim, Fixtures.MakeAnim(2, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(cycleAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));

        var sink = new RecordingSink();
        var state = new MotionState();
        var seq = new CSequence(loader);
        CMotionTable.AddMotion(seq, Fixtures.MakeMotionData(linkAnim, 30f), 1f);
        CMotionTable.AddMotion(seq, Fixtures.MakeMotionData(cycleAnim, 30f), 1f);

        var mgr = new MotionTableManager(null, state, seq, sink);

        mgr.HandleEnterWorld();

        Assert.Empty(sink.Calls);
        Assert.Equal(1, seq.Count); // link stripped, cyclic tail remains
    }

    // ── truncate blocked/allowed matrices for BOTH class masks ──────────

    [Fact]
    public void RemoveRedundantLinks_CycleClassTail_EarlierSameMotion_NoBlocker_Truncates()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5); // earlier same-motion, non-zero
        mgr.AddToQueue(WalkForward, 3); // new tail, same motion -> matches the
                                          // earlier node immediately (no
                                          // intervening node to block) ->
                                          // truncate walks tail_..matched
                                          // EXCLUSIVE, so the TAIL node itself
                                          // (this new entry) is in the walked
                                          // range and gets zeroed; the earlier
                                          // matched node (the stop boundary)
                                          // is untouched.

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(2, list.Count);
        Assert.Equal(5u, list[0].NumAnims); // matched node (stop boundary) untouched
        Assert.Equal(0u, list[1].NumAnims); // the redundant re-issue itself, zeroed
    }

    [Fact]
    public void RemoveRedundantLinks_CycleClassTail_WithInterveningZeroTickNode_Truncates()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);       // earlier match
        mgr.AddToQueue(ThrustMed, 0);          // intervening, ZERO ticks -> does not block (only non-zero blocks)
        mgr.AddToQueue(WalkForward, 3);        // new tail, same motion

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims);   // matched node (stop boundary) untouched
        Assert.Equal(0u, list[1].NumAnims);   // already zero (unaffected either way)
        Assert.Equal(0u, list[2].NumAnims);   // the new tail — ALSO in the truncation range
                                                // (truncate walks tail..matched EXCLUSIVE, so
                                                // the tail itself IS zeroed too)
    }

    [Fact]
    public void RemoveRedundantLinks_CycleClassTail_InterveningDifferentCycle_NotBlocked_Truncates()
    {
        // Bit decomposition (verified): 0xb0000000 == STYLE(0x80000000) |
        // MODIFIER(0x20000000) | ACTION(0x10000000) — it deliberately
        // EXCLUDES the cycle-class bit (0x40000000) itself. So a DIFFERENT
        // intervening CYCLE (RunForward) does NOT block a WalkForward
        // cycle-tail scan; two cycles naturally supersede each other via the
        // base-cycle rebuild mechanism.
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);   // earlier match candidate
        mgr.AddToQueue(RunForward, 4);    // intervening, non-zero, CYCLE-class but not in 0xb0000000 -> does not block
        mgr.AddToQueue(WalkForward, 3);   // new tail, same motion as the earlier node

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims);   // matched (stop boundary), untouched
        Assert.Equal(0u, list[1].NumAnims);   // truncated — RunForward zeroed
        Assert.Equal(0u, list[2].NumAnims);   // truncated — the new tail itself zeroed
    }

    [Fact]
    public void RemoveRedundantLinks_CycleClassTail_BlockedByInterveningNonZeroModifierClassNode()
    {
        // 0xb0000000 DOES include the modifier-class bit (0x20000000) — a
        // pure modifier-class node with non-zero ticks blocks a cycle-tail
        // collapse (can't safely erase an active modifier's queue entry).
        var (mgr, _, _, _) = MakeManager();
        const uint pureModifier = 0x20000099u; // modifier-class only, no cycle/action/style bits
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(pureModifier, 2); // non-zero, matches 0xb0000000 -> BLOCKS
        mgr.AddToQueue(WalkForward, 3);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        // Blocked -> nothing truncated, all NumAnims preserved as queued.
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(2u, list[1].NumAnims);
        Assert.Equal(3u, list[2].NumAnims);
    }

    [Fact]
    public void RemoveRedundantLinks_CycleClassTail_BlockedByInterveningNonZeroActionClassNode()
    {
        // 0xb0000000 also includes the action-class bit (0x10000000).
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(ThrustMed, 2); // non-zero, action-class -> matches 0xb0000000 -> BLOCKS
        mgr.AddToQueue(WalkForward, 3);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(2u, list[1].NumAnims); // untouched — blocked
        Assert.Equal(3u, list[2].NumAnims); // untouched — blocked
    }

    [Fact]
    public void RemoveRedundantLinks_CycleClassTail_BlockedByInterveningNonZeroStyleClassNode()
    {
        // 0xb0000000 also includes the style-class top bit (0x80000000).
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(HandCombatStyle, 2); // non-zero, style-class -> matches 0xb0000000 -> BLOCKS
        mgr.AddToQueue(WalkForward, 3);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(2u, list[1].NumAnims);
        Assert.Equal(3u, list[2].NumAnims);
    }

    [Fact]
    public void RemoveRedundantLinks_StyleClassTail_EarlierSameMotion_Truncates()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(HandCombatStyle, 5);   // style-class (top bit set), earlier match
        mgr.AddToQueue(ThrustMed, 0);          // zero-tick intervening, no block
        mgr.AddToQueue(HandCombatStyle, 3);    // new tail, same style motion

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(0u, list[1].NumAnims);
        Assert.Equal(0u, list[2].NumAnims);
    }

    [Fact]
    public void RemoveRedundantLinks_StyleClassTail_BlockedByInterveningNonZeroModifierClassNode()
    {
        // Style-class tail scan blocks on the WIDER 0x70000000 mask
        // (cycle|action|modifier) -- a pure modifier-class node DOES block
        // here, unlike the cycle-class tail scan above.
        var (mgr, _, _, _) = MakeManager();
        const uint pureModifier = 0x20000099u;
        mgr.AddToQueue(HandCombatStyle, 5);
        mgr.AddToQueue(pureModifier, 2); // non-zero, matches 0x70000000 -> BLOCKS
        mgr.AddToQueue(HandCombatStyle, 3);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(2u, list[1].NumAnims); // untouched — blocked
        Assert.Equal(3u, list[2].NumAnims); // untouched — blocked
    }

    [Fact]
    public void RemoveRedundantLinks_StyleClassTail_BlockedByInterveningNonZeroCycleClassNode()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(HandCombatStyle, 5);
        mgr.AddToQueue(WalkForward, 4); // non-zero, cycle-class -> matches 0x70000000 too -> BLOCKS
        mgr.AddToQueue(HandCombatStyle, 3);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(4u, list[1].NumAnims);
        Assert.Equal(3u, list[2].NumAnims);
    }

    [Fact]
    public void RemoveRedundantLinks_NoEarlierMatch_ScanExhausts_NoTruncation()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(RunForward, 4);
        mgr.AddToQueue(WalkForward, 3); // no earlier WalkForward anywhere

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(2, list.Count);
        Assert.Equal(4u, list[0].NumAnims);
        Assert.Equal(3u, list[1].NumAnims);
    }

    [Fact]
    public void RemoveRedundantLinks_TrailingZeroTickNodesSkipped_BeforeScanning()
    {
        // Tail itself is zero-tick -> skip backward past it to find the
        // "effective tail" for the class dispatch.
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(WalkForward, 0); // trailing zero-tick — skipped as "effective tail" search

        var list = mgr.PendingAnimations.ToList();
        // Effective tail (after skip) = list[0] (WalkForward, 5) itself —
        // scanning backward from it finds nothing earlier -> no truncation.
        Assert.Equal(2, list.Count);
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(0u, list[1].NumAnims);
    }

    [Fact]
    public void RemoveRedundantLinks_AllZeroTickNodes_ScanBottomsOut_ReturnsQuietly()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 0);
        mgr.AddToQueue(RunForward, 0);

        // Must not throw; nothing to truncate.
        mgr.RemoveRedundantLinks();

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(2, list.Count);
        Assert.Equal(0u, list[0].NumAnims);
        Assert.Equal(0u, list[1].NumAnims);
    }

    [Fact]
    public void RemoveRedundantLinks_EmptyQueue_IsNoOp()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.RemoveRedundantLinks(); // must not throw
        Assert.Empty(mgr.PendingAnimations);
    }

    [Fact]
    public void RemoveRedundantLinks_ModifierOrActionClassTail_NoScanPerformed()
    {
        // A pure modifier-class or action-class tail motion takes NEITHER
        // the cycle-tail nor the style-tail branch in retail -> no scan, no
        // truncation, regardless of what precedes it.
        var (mgr, _, _, _) = MakeManager();
        const uint pureModifier = 0x20000099u;
        mgr.AddToQueue(pureModifier, 5);
        mgr.AddToQueue(pureModifier, 3); // same motion id repeated, but tail is modifier-class -> no truncation path

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(2, list.Count);
        Assert.Equal(5u, list[0].NumAnims);
        Assert.Equal(3u, list[1].NumAnims);
    }

    // ── truncate_animation_list: zeroes in place, nodes stay queued ─────

    [Fact]
    public void Truncate_ViaRedundantCollapse_NodesStayQueued_OnlyNumAnimsZeroed()
    {
        // RunForward is a DIFFERENT cycle-class motion — not in the
        // 0xb0000000 cycle-tail block mask (which excludes the cycle bit) —
        // so it does not block WalkForward's re-match scan and gets
        // truncated (zeroed in place, still queued) along with the tail.
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(RunForward, 2); // will get zeroed but not removed
        mgr.AddToQueue(WalkForward, 3);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count); // node count UNCHANGED — truncate never unlinks
        Assert.Equal(RunForward, list[1].Motion); // motion id preserved, only NumAnims zeroed
        Assert.Equal(0u, list[1].NumAnims);
    }

    [Fact]
    public void Truncate_StripsLinkAnimationsFromSequence_ByTotalRemovedTicks()
    {
        var loader = new FakeLoader();
        uint link1 = 0x03000300u, link2 = 0x03000301u, cyc = 0x03000302u;
        loader.Register(link1, Fixtures.MakeAnim(1, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(link2, Fixtures.MakeAnim(1, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(cyc, Fixtures.MakeAnim(1, 1, Vector3.Zero, Quaternion.Identity));

        var sink = new RecordingSink();
        var state = new MotionState();
        var seq = new CSequence(loader);
        // Build a 3-node sequence: link1, link2 (both before first_cyclic-ish),
        // cyc (the cyclic tail — append_animation slides first_cyclic to it).
        CMotionTable.AddMotion(seq, Fixtures.MakeMotionData(link1, 30f), 1f);
        CMotionTable.AddMotion(seq, Fixtures.MakeMotionData(link2, 30f), 1f);
        CMotionTable.AddMotion(seq, Fixtures.MakeMotionData(cyc, 30f), 1f);
        Assert.Equal(3, seq.Count);

        var mgr = new MotionTableManager(null, state, seq, sink);
        mgr.AddToQueue(WalkForward, 2); // earlier match, non-zero
        mgr.AddToQueue(WalkForward, 2); // new tail, same motion -> truncates the earlier
                                          // one's successor range (which is just this
                                          // node itself, ticks=2) -> RemoveLinkAnimations(2)

        // RemoveLinkAnimations(2) removes up to 2 predecessors of first_cyclic
        // (link2, then link1) from the live sequence.
        Assert.Equal(1, seq.Count); // only the cyclic tail (cyc) remains
    }

    // ── rapid same-motion re-issue -> collapse (Fix B replacement proof) ──

    [Fact]
    public void RapidSameMotionReissue_ThroughAddToQueue_CollapsesRedundantMiddleNodes()
    {
        // Enqueue walk, run, walk, run quickly. Bit decomposition of the
        // cycle-tail block mask (0xb0000000 = STYLE|MODIFIER|ACTION,
        // deliberately EXCLUDING the cycle bit 0x40000000): a DIFFERENT
        // real cycle in between does NOT block a cycle-tail scan, so:
        //   1. add W(5)                          -> [W5]
        //   2. add R(4): tail=R, scan W5 -> no match (diff motion), no
        //      block (W not in 0xb0000000) -> scan exhausts -> [W5,R4]
        //   3. add W(3): tail=W, scan R4 -> no match, no block -> scan W5
        //      -> MATCH (same motion, non-zero) -> truncate(W5..tail
        //      exclusive) zeroes R4 and this new W3 -> [W5, R0, W0]
        //   4. add R(2): tail=R, scan W0(NumAnims=0, fails the non-zero
        //      match requirement) -> no block (0 ticks) -> scan R0
        //      (NumAnims=0, fails non-zero match requirement too) -> no
        //      block -> scan W5 -> no match (diff motion), no block ->
        //      scan exhausts -> nothing new truncated -> [W5, R0, W0, R2]
        // This is the Fix-B-replacement proof: the FIRST redundant
        // walk->run->walk sequence collapses down to just the original
        // WalkForward(5) plus the freshly-added RunForward(2) — matching
        // "rapid re-issue of the same locomotion collapses" without
        // inventing a bespoke locomotion-low-byte special case (H6).
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(RunForward, 4);
        mgr.AddToQueue(WalkForward, 3);
        mgr.AddToQueue(RunForward, 2);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(4, list.Count);
        Assert.Equal(5u, list[0].NumAnims); // original WalkForward — the surviving anchor
        Assert.Equal(0u, list[1].NumAnims); // RunForward — truncated by step 3's collapse
        Assert.Equal(0u, list[2].NumAnims); // WalkForward (re-issue) — truncated by step 3's collapse
        Assert.Equal(2u, list[3].NumAnims); // newest RunForward — survives (its own scan found no match)
    }

    [Fact]
    public void RapidSameMotionReissue_ZeroTickIntervening_DoesCollapse()
    {
        // When the intervening entries are ZERO-tick (already-instant / a
        // fast-path re-speed that queued 0 outTicks), the scan is NOT
        // blocked (only non-zero nodes block) and the collapse proceeds —
        // this IS the realistic Fix-B-replacement shape: rapid re-speeds of
        // the SAME cycle produce zero-outTicks entries between the real
        // queue events.
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(WalkForward, 0); // e.g. a fast-path re-speed, zero outTicks
        mgr.AddToQueue(WalkForward, 3); // new tail, same motion

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(3, list.Count);
        Assert.Equal(5u, list[0].NumAnims); // matched node preserved
        Assert.Equal(0u, list[1].NumAnims); // already zero
        Assert.Equal(0u, list[2].NumAnims); // truncated
    }

    // ── the 2026-05-03 golden: cyclic->cyclic walk->run, truncate NOT firing ──

    [Fact]
    public void Golden_CyclicToCyclicWalkThenRun_BothNodesQueued_TruncateNotFiring()
    {
        // Quoted golden (Fix B comment block, r2-port-plan.md H6): cyclic->
        // cyclic transitions produce add_to_queue(0x45000005) [WalkForward]
        // followed by add_to_queue(0x44000007) [RunForward], with truncate
        // NOT firing (different motion ids -> remove_redundant_links' match
        // test never succeeds).
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 3);
        mgr.AddToQueue(RunForward, 4);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(2, list.Count);
        Assert.Equal(WalkForward, list[0].Motion);
        Assert.Equal(3u, list[0].NumAnims); // untouched — no truncation
        Assert.Equal(RunForward, list[1].Motion);
        Assert.Equal(4u, list[1].NumAnims); // untouched
    }

    // ── initialize_state ──────────────────────────────────────────────

    [Fact]
    public void InitializeState_QueuesReadySentinel_WithSetDefaultStateOutTicks()
    {
        var loader = new FakeLoader();
        uint readyAnim = 0x03000400u;
        loader.Register(readyAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));

        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        mt.StyleDefaults[(DRWMotionCommand)NonCombatStyle] = (DRWMotionCommand)Ready;
        Fixtures.AddCycle(mt, NonCombatStyle, Ready, Fixtures.MakeMotionData(readyAnim, 30f));

        var cmt = new CMotionTable(mt);
        var sink = new RecordingSink();
        var state = new MotionState();
        var seq = new CSequence(loader);
        var mgr = new MotionTableManager(cmt, state, seq, sink);

        mgr.InitializeState();

        Assert.Equal(NonCombatStyle, state.Style);
        Assert.Equal(Ready, state.Substate);
        Assert.Single(mgr.PendingAnimations);
        var node = mgr.PendingAnimations.First();
        Assert.Equal(MotionTableManager.ReadySentinel, node.Motion);
        // SetDefaultState outTicks = cyclic.num_anims - 1 = 1 - 1 = 0.
        Assert.Equal(0u, node.NumAnims);
    }

    [Fact]
    public void InitializeState_NoTableLoaded_QueuesSentinelWithZeroTicks_NoThrow()
    {
        var sink = new RecordingSink();
        var state = new MotionState();
        var seq = new CSequence(new NullLoader());
        var mgr = new MotionTableManager(null, state, seq, sink);

        mgr.InitializeState();

        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(MotionTableManager.ReadySentinel, mgr.PendingAnimations.First().Motion);
        Assert.Equal(0u, mgr.PendingAnimations.First().NumAnims);
    }

    // ── PerformMovement error-code matrix ────────────────────────────────

    [Fact]
    public void PerformMovement_NoTableLoaded_ReturnsError7()
    {
        var (mgr, _, _, _) = MakeManager(table: null);

        uint result = mgr.PerformMovement(MotionTableMovement.Interpreted(WalkForward, 1f));

        Assert.Equal(MotionTableManagerError.NoTable, result);
        Assert.Equal(7u, result);
    }

    [Fact]
    public void PerformMovement_InterpretedCommand_Success_QueuesMotionWithOutTicks_ReturnsZero()
    {
        var loader = new FakeLoader();
        uint readyAnim = 0x03000500u, walkAnim = 0x03000501u, linkAnim = 0x03000502u;
        loader.Register(readyAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(walkAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(linkAnim, Fixtures.MakeAnim(2, 1, Vector3.Zero, Quaternion.Identity));

        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        mt.StyleDefaults[(DRWMotionCommand)NonCombatStyle] = (DRWMotionCommand)Ready;
        Fixtures.AddCycle(mt, NonCombatStyle, Ready, Fixtures.MakeMotionData(readyAnim, 30f));
        Fixtures.AddCycle(mt, NonCombatStyle, WalkForward, Fixtures.MakeMotionData(walkAnim, 30f));
        Fixtures.AddLink(mt, NonCombatStyle, Ready, WalkForward, Fixtures.MakeMotionData(linkAnim, 30f));

        var cmt = new CMotionTable(mt);
        var sink = new RecordingSink();
        var state = new MotionState { Style = NonCombatStyle, Substate = Ready, SubstateMod = 1f };
        var seq = new CSequence(loader);
        var mgr = new MotionTableManager(cmt, state, seq, sink);

        uint result = mgr.PerformMovement(MotionTableMovement.Interpreted(WalkForward, 1f));

        Assert.Equal(MotionTableManagerError.Success, result);
        Assert.Equal(WalkForward, state.Substate);
        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(WalkForward, mgr.PendingAnimations.First().Motion);
        // outTicks = link(1) + cycle(1) - 1 = 1
        Assert.Equal(1u, mgr.PendingAnimations.First().NumAnims);
    }

    [Fact]
    public void PerformMovement_InterpretedCommand_Failure_ReturnsError0x43_NoQueue()
    {
        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        // No cycles registered at all -> DoObjectMotion fails.
        var cmt = new CMotionTable(mt);
        var (mgr, _, state, _) = MakeManager(cmt);
        state.Style = NonCombatStyle;
        state.Substate = Ready;
        state.SubstateMod = 1f;

        uint result = mgr.PerformMovement(MotionTableMovement.Interpreted(WalkForward, 1f));

        Assert.Equal(MotionTableManagerError.MotionFailed, result);
        Assert.Equal(0x43u, result);
        Assert.Empty(mgr.PendingAnimations);
    }

    [Fact]
    public void PerformMovement_StopInterpretedCommand_Success_QueuesReadySentinel()
    {
        var loader = new FakeLoader();
        uint runAnim = 0x03000510u, readyAnim = 0x03000511u, exitLinkAnim = 0x03000512u;
        loader.Register(runAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(readyAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(exitLinkAnim, Fixtures.MakeAnim(2, 1, Vector3.Zero, Quaternion.Identity));

        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        mt.StyleDefaults[(DRWMotionCommand)NonCombatStyle] = (DRWMotionCommand)Ready;
        Fixtures.AddCycle(mt, NonCombatStyle, RunForward, Fixtures.MakeMotionData(runAnim, 30f));
        Fixtures.AddCycle(mt, NonCombatStyle, Ready, Fixtures.MakeMotionData(readyAnim, 30f));
        Fixtures.AddLink(mt, NonCombatStyle, RunForward, Ready, Fixtures.MakeMotionData(exitLinkAnim, 30f));

        var cmt = new CMotionTable(mt);
        var sink = new RecordingSink();
        var state = new MotionState { Style = NonCombatStyle, Substate = RunForward, SubstateMod = 1f };
        var seq = new CSequence(loader);
        var mgr = new MotionTableManager(cmt, state, seq, sink);
        Assert.True(cmt.DoObjectMotion(RunForward, state, seq, 1f, out _));

        uint result = mgr.PerformMovement(MotionTableMovement.StopInterpreted(RunForward, 1f));

        Assert.Equal(MotionTableManagerError.Success, result);
        Assert.Equal(Ready, state.Substate); // re-driven to style default
        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(MotionTableManager.ReadySentinel, mgr.PendingAnimations.First().Motion);
    }

    [Fact]
    public void PerformMovement_StopInterpretedCommand_Failure_ReturnsError0x43_NoQueue()
    {
        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        var cmt = new CMotionTable(mt);
        var (mgr, _, state, _) = MakeManager(cmt);
        // No modifier and no matching current substate -> StopObjectMotion fails.
        state.Style = NonCombatStyle;
        state.Substate = Ready;
        state.SubstateMod = 1f;
        const uint unrelatedModifier = 0x20000099u;

        uint result = mgr.PerformMovement(MotionTableMovement.StopInterpreted(unrelatedModifier, 1f));

        Assert.Equal(MotionTableManagerError.MotionFailed, result);
        Assert.Empty(mgr.PendingAnimations);
    }

    [Fact]
    public void PerformMovement_StopCompletely_UnconditionallyQueuesReadySentinel_EvenOnNoOpStop()
    {
        // Even when StopObjectCompletely finds nothing to stop (returns
        // false), PerformMovement STILL queues the Ready sentinel
        // unconditionally (decomp §11 note) and returns success.
        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        // No StyleDefaults entry -> the final StopSequenceMotion(substate=0,...)
        // call inside StopObjectCompletely can't resolve a style default either,
        // but that's fine: Case A requires substate==0x40000000-class AND ==
        // state.Substate; with Substate=0 (default MotionState ctor) neither
        // stop mechanism matches anything -> both return false -> overall false.
        var cmt = new CMotionTable(mt);
        var (mgr, _, state, _) = MakeManager(cmt);
        // state.Substate stays 0 (default) -> StopObjectCompletely no-ops.

        uint result = mgr.PerformMovement(MotionTableMovement.StopCompletely());

        Assert.Equal(MotionTableManagerError.Success, result);
        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(MotionTableManager.ReadySentinel, mgr.PendingAnimations.First().Motion);
    }

    [Fact]
    public void PerformMovement_StopCompletely_DrainsModifiers_QueuesReadySentinel()
    {
        var loader = new FakeLoader();
        uint runAnim = 0x03000520u, readyAnim = 0x03000521u, exitLinkAnim = 0x03000522u;
        loader.Register(runAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(readyAnim, Fixtures.MakeAnim(4, 1, Vector3.Zero, Quaternion.Identity));
        loader.Register(exitLinkAnim, Fixtures.MakeAnim(2, 1, Vector3.Zero, Quaternion.Identity));

        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        mt.StyleDefaults[(DRWMotionCommand)NonCombatStyle] = (DRWMotionCommand)Ready;
        Fixtures.AddCycle(mt, NonCombatStyle, RunForward, Fixtures.MakeMotionData(runAnim, 30f));
        Fixtures.AddCycle(mt, NonCombatStyle, Ready, Fixtures.MakeMotionData(readyAnim, 30f));
        Fixtures.AddLink(mt, NonCombatStyle, RunForward, Ready, Fixtures.MakeMotionData(exitLinkAnim, 30f));

        var cmt = new CMotionTable(mt);
        var sink = new RecordingSink();
        var state = new MotionState { Style = NonCombatStyle, Substate = RunForward, SubstateMod = 1f };
        var seq = new CSequence(loader);
        var mgr = new MotionTableManager(cmt, state, seq, sink);
        Assert.True(cmt.DoObjectMotion(RunForward, state, seq, 1f, out _));

        uint result = mgr.PerformMovement(MotionTableMovement.StopCompletely());

        Assert.Equal(MotionTableManagerError.Success, result);
        Assert.Equal(Ready, state.Substate);
        Assert.Single(mgr.PendingAnimations);
        Assert.Equal(MotionTableManager.ReadySentinel, mgr.PendingAnimations.First().Motion);
    }

    [Fact]
    public void PerformMovement_UnhandledType_ReturnsNotHandled_NoQueue()
    {
        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        var cmt = new CMotionTable(mt);
        var (mgr, _, _, _) = MakeManager(cmt);

        uint result = mgr.PerformMovement(new MotionTableMovement(MovementType.RawCommand, WalkForward, 1f));

        Assert.Equal(MotionTableManagerError.NotHandled, result);
        Assert.Empty(mgr.PendingAnimations);
    }

    [Fact]
    public void PerformMovement_StopRawCommand_ReturnsNotHandled()
    {
        var mt = new MotionTable { DefaultStyle = (DRWMotionCommand)NonCombatStyle };
        var cmt = new CMotionTable(mt);
        var (mgr, _, _, _) = MakeManager(cmt);

        uint result = mgr.PerformMovement(new MotionTableMovement(MovementType.StopRawCommand, WalkForward, 1f));

        Assert.Equal(MotionTableManagerError.NotHandled, result);
    }

    // ── AddToQueue calls RemoveRedundantLinks immediately (opportunistic) ──

    [Fact]
    public void AddToQueue_CallsRemoveRedundantLinks_Immediately_NotDeferred()
    {
        var (mgr, _, _, _) = MakeManager();
        mgr.AddToQueue(WalkForward, 5);
        mgr.AddToQueue(ThrustMed, 0);

        // Adding a third same-motion WalkForward should IMMEDIATELY trigger
        // the collapse as part of THIS AddToQueue call (not deferred to a
        // later explicit RemoveRedundantLinks() call).
        mgr.AddToQueue(WalkForward, 3);

        var list = mgr.PendingAnimations.ToList();
        Assert.Equal(0u, list[1].NumAnims); // already truncated by the time AddToQueue returns
        Assert.Equal(0u, list[2].NumAnims);
    }
}