using System;
using System.Numerics;
using AcDream.Core.Physics;

namespace AcDream.App.Input;

/// <summary>
/// Input state for a single frame of player movement.
/// </summary>
public readonly record struct MovementInput(
    bool Forward = false,
    bool Backward = false,
    bool StrafeLeft = false,
    bool StrafeRight = false,
    bool TurnLeft = false,
    bool TurnRight = false,
    bool Run = false,
    float MouseDeltaX = 0f,
    bool Jump = false);

/// <summary>
/// Result of a single frame's movement update.
///
/// <para>
/// <b>Wire vs. local animation command.</b> ACE's <c>MovementData</c>
/// (<c>ACE.Server/Network/Motion/MovementData.cs</c>) only computes
/// <c>interpState.ForwardSpeed</c> for raw <c>WalkForward</c>/
/// <c>WalkBackwards</c> — on every other command the <c>else</c> branch
/// passes through command without setting speed, leaving observers with
/// <c>speed=0</c>. The client therefore has to send <c>WalkForward</c>
/// (with <c>HoldKey.Run</c> for running) and let ACE auto-upgrade to
/// <c>RunForward</c> for broadcast. But the LOCAL view wants the run
/// cycle immediately, so we carry a separate
/// <see cref="LocalAnimationCommand"/> for the player's own renderer.
/// </para>
/// <para>
/// <see cref="IsRunning"/> — true when the player is holding Shift to run.
/// Used by the GameWindow when building the outbound MoveToState's
/// CURRENT_HOLD_KEY (2=Run) vs (1=None).
/// </para>
/// </summary>
public readonly record struct MovementResult(
    Vector3 Position,
    uint CellId,
    bool IsOnGround,
    bool MotionStateChanged,
    uint? ForwardCommand,            // wire-side command (WalkForward / WalkBackward / …)
    uint? SidestepCommand,
    uint? TurnCommand,
    float? ForwardSpeed,
    float? SidestepSpeed,
    float? TurnSpeed,
    bool IsRunning = false,
    uint? LocalAnimationCommand = null,   // which cycle to play on the local player (RunForward when running)
    // K-fix5 (2026-04-26): cycle-pace multiplier for the LOCAL animation
    // sequencer. Decoupled from ForwardSpeed so the wire can keep sending
    // 1.0 for WalkBackward (ACE-compatible) while the animation plays at
    // runRate × so the cycle visually matches the run-speed velocity.
    // Forward+Run = runRate (same as ForwardSpeed); Backward+Run, Strafe+Run
    // = runRate (where ForwardSpeed is 1.0 / null); everything else = 1.0.
    float LocalAnimationSpeed = 1f,
    bool JustLanded = false,              // true on the single frame we transitioned airborne → grounded
    float? JumpExtent = null,       // non-null when a jump was triggered this frame
    Vector3? JumpVelocity = null);  // world-space launch velocity (sent in jump packet)

/// <summary>
/// Portal-space state for the player movement controller.
/// PortalSpace freezes all movement input while the server is moving the
/// player through a portal — resumed once the destination UpdatePosition
/// arrives and the player is snapped to the new location.
/// While in PortalSpace, Update returns immediately with a zero-movement
/// result so no WASD input or physics is processed.
/// </summary>
public enum PlayerState { InWorld, PortalSpace }

/// <summary>
/// Per-frame player movement controller. Reads input, drives the
/// ported PhysicsBody + MotionInterpreter, tracks motion state for
/// animation + server messages.
///
/// Architecture:
///   - PhysicsBody owns integration: gravity, friction, sub-stepping,
///     velocity clamping — all from the decompiled retail client.
///   - MotionInterpreter owns the motion state machine: walk/run/jump
///     validation, state tracking, speed constants from the retail dat.
///   - PhysicsEngine.Resolve is still used each frame to snap the player
///     to terrain/cell floor Z and detect ground contact.
/// </summary>
public sealed class PlayerMovementController
{
    private readonly PhysicsEngine _physics;
    private readonly PhysicsBody _body;
    private readonly MotionInterpreter _motion;
    private readonly PlayerWeenie _weenie;

    public float MouseTurnSensitivity { get; set; } = 0.003f;

    /// <summary>
    /// Maximum Z increase per movement step before the move is rejected.
    /// Retail's <c>step_up_height</c> for human characters is ~0.4 m (hip-
    /// level). Setting this too high lets the player teleport up small
    /// buildings via the step-up scan finding any walkable polygon within
    /// reach (Bug 3 in L.2.3 testing — walking into a steep slope mounted
    /// the building's flat top instead of sliding off the slope).
    /// Authoritative source is the player's <c>Setup.StepUpHeight</c> set
    /// in GameWindow.cs at world-entry time.
    /// </summary>
    public float StepUpHeight { get; set; } = 0.4f;

    /// <summary>
    /// L.2.3a (2026-04-29): how far below the foot the step-down probe
    /// reaches when transitioning between surfaces. Retail's
    /// <c>step_down_height</c> for human characters is ~0.4 m. With the
    /// previous 4 cm hardcoded value, walking off the top of a stair onto
    /// the ground 25 cm below produced a one-frame contact-plane gap — the
    /// animation system briefly flickered to falling.
    /// </summary>
    public float StepDownHeight { get; set; } = 0.4f;

    /// <summary>
    /// Current portal-space state. Set to PortalSpace when the server sends
    /// PlayerTeleport (0xF751); set back to InWorld once the destination
    /// UpdatePosition arrives and the player is snapped to the new cell.
    /// While in PortalSpace, Update returns immediately with a zero-movement
    /// result so no WASD input or physics is processed.
    /// </summary>
    public PlayerState State { get; set; } = PlayerState.InWorld;

    public float Yaw { get; set; }
    public Vector3 Position => _body.Position;
    public uint CellId { get; private set; }

    public bool IsAirborne => !_body.OnWalkable;

    /// <summary>
    /// Current vertical (Z-axis) velocity of the physics body.
    /// Positive = rising, negative = falling.  Exposed for tests and HUD.
    /// </summary>
    public float VerticalVelocity => _body.Velocity.Z;

    /// <summary>Full 3D world-space velocity of the physics body. Exposed for diagnostic logging.</summary>
    public Vector3 BodyVelocity => _body.Velocity;

    // Jump charge state.
    private bool _jumpCharging;
    private float _jumpExtent;
    // K-fix6 (2026-04-26): retail's PowerBar charge constant for jump is
    // not legible in the named decomp (the divisor was clobbered in
    // GetPowerBarLevel's FPU stack reordering at FUN_0056ade0). 2.0/s
    // (full charge in 0.5s) feels matches retail muscle memory better
    // than the previous 1.0/s — a tap gives a noticeable hop, half-hold
    // a meaningful jump, full-hold the maximum extent. The vertical
    // velocity formula itself (height × 19.6 → vz) is unchanged and
    // matches retail byte-for-byte; only the time-to-fill is faster.
    private const float JumpChargeRate = 2.0f;

    // Airborne → grounded transition detection. Flipped on every frame where
    // the body transitions from airborne to on-walkable; used by the GameWindow
    // to drive the landing animation cycle.
    private bool _wasAirborneLastFrame;

    // Previous frame's motion commands for change detection.
    private uint? _prevForwardCmd;
    private uint? _prevSidestepCmd;
    private uint? _prevTurnCmd;
    private float? _prevForwardSpeed;
    private bool _prevRunHold;
    private uint? _prevLocalAnimCmd;

    // Heartbeat timer.
    private float _heartbeatAccum;
    public const float HeartbeatInterval = 0.2f;  // 200ms
    public bool HeartbeatDue { get; private set; }

    public PlayerMovementController(PhysicsEngine physics)
    {
        _physics = physics;

        _body = new PhysicsBody
        {
            State = PhysicsStateFlags.Gravity | PhysicsStateFlags.ReportCollisions,
        };

        // Default skills — tuned toward mid-retail feel. Real characters'
        // skills come from PlayerDescription (0xF7B0/0x0013) which we don't
        // parse yet; override via env vars:
        //   ACDREAM_RUN_SKILL, ACDREAM_JUMP_SKILL
        // K-fix6 (2026-04-26): bumped default jump skill from 200 → 300.
        // Retail formula: height = (skill/(skill+1300))*22.2 + 0.05 (extent=1):
        //   skill=200 → 3.01m max (felt too low — user complaint)
        //   skill=300 → 4.21m max (closer to a typical retail mid-tier
        //                          character's "I can clear that fence" hop)
        // Until #7 ships and PlayerDescription gives us the server's real
        // skill, this default is the right "feels like retail" baseline.
        int runSkill  = int.TryParse(Environment.GetEnvironmentVariable("ACDREAM_RUN_SKILL"),  out var rs) ? rs : 200;
        int jumpSkill = int.TryParse(Environment.GetEnvironmentVariable("ACDREAM_JUMP_SKILL"), out var jsv) ? jsv : 300;
        _weenie = new PlayerWeenie(runSkill: runSkill, jumpSkill: jumpSkill);
        _motion = new MotionInterpreter(_body, _weenie);
    }

    public void SetCharacterSkills(int runSkill, int jumpSkill)
    {
        _weenie.SetSkills(runSkill, jumpSkill);
    }

    /// <summary>
    /// Wire the player's AnimationSequencer current cycle velocity into
    /// <see cref="MotionInterpreter.GetCycleVelocity"/>.  When attached,
    /// <c>get_state_velocity</c> uses <c>MotionData.Velocity * speedMod</c>
    /// as the primary forward-axis drive, keeping the body's world velocity
    /// locked to the animation's baked-in root-motion velocity.
    ///
    /// <para>
    /// Without this accessor, the decompiled constant path
    /// (<c>RunAnimSpeed * ForwardSpeed</c>) is used — matches retail only
    /// when the character's MotionTable happens to bake Velocity=4.0 on
    /// RunForward, which is true for Humanoid but not for arbitrary
    /// creatures. See <see cref="MotionInterpreter.GetCycleVelocity"/>
    /// for the full rationale.
    /// </para>
    ///
    /// <para>
    /// Called once from <c>GameWindow.CreateAnimatedEntity</c> after the
    /// player's <c>AnimatedEntity.Sequencer</c> is constructed.
    /// </para>
    /// </summary>
    public void AttachCycleVelocityAccessor(Func<Vector3> accessor)
    {
        if (accessor is null) throw new ArgumentNullException(nameof(accessor));
        _motion.GetCycleVelocity = accessor;
    }

    /// <summary>
    /// Apply a server-echoed run rate (ForwardSpeed from UpdateMotion) to the
    /// player's MotionInterpreter. The server broadcasts the real RunRate
    /// derived from the character's Run skill; wiring it here ensures
    /// get_state_velocity produces the correct speed instead of the default 1.0.
    /// </summary>
    public void ApplyServerRunRate(float forwardSpeed)
    {
        _motion.InterpretedState.ForwardSpeed = forwardSpeed;
        _motion.apply_current_movement(cancelMoveTo: false, allowJump: false);
    }

    public void SetPosition(Vector3 pos, uint cellId)
    {
        _body.Position = pos;
        CellId = cellId;

        // Treat as grounded after a server-side position snap.
        _body.TransientState = TransientStateFlags.Contact | TransientStateFlags.OnWalkable;
        _body.Velocity = Vector3.Zero;

        // Reset physics clock so any subsequent update_object calls start fresh.
        _body.LastUpdateTime = 0.0;
    }

    public MovementResult Update(float dt, MovementInput input)
    {
        // Portal-space guard: while teleporting, no input is processed and
        // no physics is resolved. Return a zero-movement result so the caller
        // can detect the frozen state (MotionStateChanged = false, no commands).
        if (State == PlayerState.PortalSpace)
        {
            return new MovementResult(
                Position: Position,
                CellId: CellId,
                IsOnGround: _body.OnWalkable,
                MotionStateChanged: false,
                ForwardCommand: null,
                SidestepCommand: null,
                TurnCommand: null,
                ForwardSpeed: null,
                SidestepSpeed: null,
                TurnSpeed: null);
        }

        // ── 1. Apply turning from keyboard + mouse ────────────────────────────
        if (input.TurnRight)
            Yaw -= MotionInterpreter.WalkAnimSpeed * 0.5f * dt;  // ~90°/s
        if (input.TurnLeft)
            Yaw += MotionInterpreter.WalkAnimSpeed * 0.5f * dt;
        Yaw -= input.MouseDeltaX * MouseTurnSensitivity;
        // Wrap yaw to [-PI, PI] so it doesn't grow unbounded.
        while (Yaw > MathF.PI)  Yaw -= 2f * MathF.PI;
        while (Yaw < -MathF.PI) Yaw += 2f * MathF.PI;

        // Sync the body's orientation quaternion with our Yaw (rotation about Z).
        // Convention: Yaw=0 faces +X.  Local body +Y is "forward", so we rotate
        // by (Yaw - PI/2) about Z to map local +Y → world (cos Yaw, sin Yaw, 0).
        _body.Orientation = Quaternion.CreateFromAxisAngle(Vector3.UnitZ, Yaw - MathF.PI / 2f);

        // ── 2. Set velocity via MotionInterpreter state machine ───────────────
        // Determine the dominant forward/backward command and speed.
        uint forwardCmd;
        float forwardCmdSpeed;
        if (input.Forward)
        {
            forwardCmd = input.Run ? MotionCommand.RunForward : MotionCommand.WalkForward;
            // When running, use the PlayerWeenie's RunRate as ForwardSpeed.
            // The retail server computes this from Run skill + encumbrance and
            // broadcasts it in UpdateMotion, but it doesn't echo to the sender.
            // We compute locally using the same formula.
            if (input.Run && _weenie.InqRunRate(out float runRate))
                forwardCmdSpeed = runRate;
            else
                forwardCmdSpeed = 1.0f;
        }
        else if (input.Backward)
        {
            forwardCmd = MotionCommand.WalkBackward;
            // K-fix3 (2026-04-26): backward also honors Run. Without
            // this, holding X with Run=true (default) still produced
            // walk-tier backward speed because forwardCmdSpeed was
            // hardcoded to 1.0. Now scale by runRate the same way
            // RunForward does.
            if (input.Run && _weenie.InqRunRate(out float runRateBack))
                forwardCmdSpeed = runRateBack;
            else
                forwardCmdSpeed = 1.0f;
        }
        else
        {
            forwardCmd      = MotionCommand.Ready;
            forwardCmdSpeed = 1.0f;
        }

        // Update interpreted motion state (needed for animation + server messages).
        _motion.DoMotion(forwardCmd, forwardCmdSpeed);

        // Sidestep.
        if (input.StrafeRight)
            _motion.DoInterpretedMotion(MotionCommand.SideStepRight, 1.0f, modifyInterpretedState: true);
        else if (input.StrafeLeft)
            _motion.DoInterpretedMotion(MotionCommand.SideStepLeft, 1.0f, modifyInterpretedState: true);
        else
        {
            _motion.StopInterpretedMotion(MotionCommand.SideStepRight, modifyInterpretedState: true);
            _motion.StopInterpretedMotion(MotionCommand.SideStepLeft,  modifyInterpretedState: true);
        }

        // Only replace velocity with motion interpreter output when grounded.
        // While airborne, the physics body's integrated velocity (from LeaveGround)
        // persists — gravity pulls Z down, horizontal momentum is preserved.
        // Retail AC works this way: you maintain momentum in the air.
        if (_body.OnWalkable)
        {
            float savedWorldVz = _body.Velocity.Z;
            var stateVel = _motion.get_state_velocity();

            float localY = 0f;
            float localX = 0f;

            // K-fix3 (2026-04-26): unified run-multiplier for backward
            // + strafe. Forward already scales correctly because it uses
            // stateVel.Y (which the motion state machine fed runRate
            // into via DoMotion). Backward + strafe bypass the state
            // machine and hardcoded speed; previously they capped at
            // walk speed regardless of Run, which made the ~2.4×
            // forward-vs-back/strafe ratio feel wrong. Now both scale
            // with the same runRate the forward branch uses.
            float runMul = 1.0f;
            if (input.Run && _weenie.InqRunRate(out float vrr))
                runMul = vrr;

            if (input.Forward)
                localY =  stateVel.Y;
            else if (input.Backward)
                localY = -(MotionInterpreter.WalkAnimSpeed * 0.65f * runMul);

            // Strafe scales with the same runMul so sidestep matches
            // the forward pace at run speed (retail uses speed=1.0 for
            // SideStep + the same hold-key-driven run/walk multiplier).
            if (input.StrafeRight)
                localX =  MotionInterpreter.SidestepAnimSpeed * runMul;
            else if (input.StrafeLeft)
                localX = -MotionInterpreter.SidestepAnimSpeed * runMul;

            _body.set_local_velocity(new Vector3(localX, localY, savedWorldVz));
        }

        // ── 3. Jump (charged) ─────────────────────────────────────────────────
        // Hold spacebar to charge (0→1 over JumpChargeRate seconds).
        // Release to execute: jump(extent) validates + sets JumpExtent,
        // then LeaveGround() applies the scaled velocity via get_leave_ground_velocity.
        float? outJumpExtent = null;
        Vector3? outJumpVelocity = null;

        if (input.Jump && _body.OnWalkable)
        {
            // Spacebar held and on the ground — accumulate charge.
            if (!_jumpCharging)
            {
                _jumpCharging = true;
                _jumpExtent   = 0f;
            }
            _jumpExtent = MathF.Min(_jumpExtent + dt * JumpChargeRate, 1.0f);
        }
        else if (_jumpCharging)
        {
            // Spacebar released (or left ground during charge) — fire jump.
            var jumpResult = _motion.jump(_jumpExtent);
            if (jumpResult == WeenieError.None)
            {
                _motion.LeaveGround();
                outJumpExtent = _jumpExtent;
                outJumpVelocity = _body.Velocity; // capture after LeaveGround applies it
            }
            _jumpCharging = false;
            _jumpExtent   = 0f;
        }

        // ── 4. Integrate physics (gravity, friction, sub-stepping) ────────────
        var preIntegratePos = _body.Position;
        _body.calc_acceleration();
        _body.UpdatePhysicsInternal(dt);
        var postIntegratePos = _body.Position;

        // ── 5. Collision resolution via CTransition sphere-sweep ─────────────
        // The Transition system subdivides the movement from pre→post into
        // sphere-radius steps, testing terrain collision at each step.
        // Falls back to simple Z-snap if transition fails.
        var resolveResult = _physics.ResolveWithTransition(
            preIntegratePos, postIntegratePos, CellId,
            sphereRadius: 0.48f,    // human player radius from Setup
            sphereHeight: 1.2f,     // human player height from Setup
            stepUpHeight: StepUpHeight,
            stepDownHeight: StepDownHeight,  // L.2.3a: from Setup.StepDownHeight
            isOnGround: _body.OnWalkable,
            body: _body,           // persist ContactPlane across frames for slope tracking
            // L.2c 2026-04-30: retail PhysicsGlobals.DefaultState includes
            // EdgeSlide, and PhysicsObj.get_object_info copies that bit into
            // OBJECTINFO. Keep it explicit here so edge/cliff handling runs
            // under the same flag profile as retail player movement.
            //
            // Commit C 2026-04-29 — local player is always IsPlayer.
            // The PK/PKLite/Impenetrable bits come from PlayerDescription's
            // PlayerKillerStatus property; not yet parsed (non-PK pair → walks
            // through other non-PK players, which is retail's default for
            // ACE's character creation defaults too).
            moverFlags: AcDream.Core.Physics.ObjectInfoState.IsPlayer
                      | AcDream.Core.Physics.ObjectInfoState.EdgeSlide);

        // L.4-diag (2026-04-30): trace position transitions so we can see
        // whether the body is actually moving frame-to-frame on the steep
        // roof, or whether it's frozen at the impact point.
        if (Environment.GetEnvironmentVariable("ACDREAM_DUMP_STEEP_ROOF") == "1"
            && resolveResult.CollisionNormalValid)
        {
            Console.WriteLine(
                $"[steep-roof] FRAME pre=({preIntegratePos.X:F2},{preIntegratePos.Y:F2},{preIntegratePos.Z:F2}) " +
                $"post=({postIntegratePos.X:F2},{postIntegratePos.Y:F2},{postIntegratePos.Z:F2}) " +
                $"resolved=({resolveResult.Position.X:F2},{resolveResult.Position.Y:F2},{resolveResult.Position.Z:F2}) " +
                $"isOnGround={resolveResult.IsOnGround}");
        }

        // Apply resolved position.
        _body.Position = resolveResult.Position;

        // L.3a (2026-04-30): retail wall-bounce / velocity reflection.
        //
        // Retail's CPhysicsObj::handle_all_collisions runs after every
        // SetPositionInternal. It reads the wall normal that the
        // transition's slide computed and reflects the body's velocity:
        //
        //     v_new = v - (1 + elasticity) * dot(v, n) * n
        //
        // This is what gives retail its "bouncy" feel — fast head-on
        // jumps push the player back from the wall, glancing angles
        // produce a small deflection. acdream's transition resolver
        // SLID position correctly but never updated velocity, so the
        // player kept driving into walls until the controller's input
        // changed direction. Felt sticky / fragile.
        //
        // Suppression rule (apply_bounce): grounded movement on a wall
        // SHOULDN'T bounce — sliding along a corridor is expected. Only
        // airborne wall hits reflect. Mirrors retail's `var_10_1` guard
        // and ACE PhysicsObj.cs:2656-2660 `apply_bounce`.
        //
        // Inelastic flag (spell projectiles, missiles) zeros velocity
        // entirely instead of reflecting. The player never has it set.
        //
        // Sources:
        //   acclient_2013_pseudo_c.txt:282699-282715 (handle_all_collisions)
        //   acclient.h:2834                          (INELASTIC_PS = 0x20000)
        //   ACE PhysicsObj.cs:2656-2721              (line-for-line port)
        //   PhysicsGlobals.DefaultElasticity = 0.05f, MaxElasticity = 0.1f
        if (resolveResult.CollisionNormalValid)
        {
            bool prevOnWalkable = _body.OnWalkable;
            bool nowOnWalkable  = resolveResult.IsOnGround;

            // apply_bounce: bounce ONLY when the body stays airborne both
            // before and after this step. That is: jumping into a wall
            // mid-flight, hitting a ceiling, etc. Specifically NOT:
            //
            //  - prev grounded + now grounded → wall-slide along corridor
            //    (bounce would feel sticky on every wall touch).
            //  - prev airborne + now grounded → terrain landing
            //    (terrain normal is mostly +Z; reflecting downward velocity
            //    would push the body upward and prevent the landing snap
            //    from firing — player perpetually micro-bouncing on the
            //    floor instead of resting).
            //  - prev grounded + now airborne → walked off cliff
            //    (gravity should take over, not lateral bounce).
            //
            // Sledding mode reverts to retail's broader rule (bounce
            // unless both grounded), since sledding intentionally bounces
            // off ramps.
            //
            // This is more conservative than retail's strict
            // `!(prev && now && !sledding)` rule — retail bounces on
            // landing too, but at elasticity 0.05 the visual effect is
            // imperceptible there. acdream's per-frame architecture
            // amplifies the artifact (the post-reflection upward Z
            // defeats the controller's `Velocity.Z <= 0` landing-snap
            // gate), so we suppress it on landing to avoid the
            // micro-bounce death spiral.
            bool applyBounce = _body.State.HasFlag(PhysicsStateFlags.Sledding)
                ? !(prevOnWalkable && nowOnWalkable)
                : (!prevOnWalkable && !nowOnWalkable);

            // L.4-steep-landing-bounce (2026-04-30): also bounce on
            // landing IF the contact surface is upward-facing but
            // steeper than walkable (FloorZ ≈ 49°). Per retail and the
            // user's expectation: jumping onto a steep roof should NOT
            // result in a landing — the player should bounce off, keep
            // the falling animation, and slide off.
            //
            // Without this: the L.3a base rule suppresses the bounce on
            // landing transitions (prev air → now ground) to avoid
            // micro-bounce on flat terrain, but that suppression also
            // sticks the player to too-steep roofs they shouldn't land
            // on. This carve-out re-enables the bounce specifically for
            // steep upward-facing surfaces.
            //
            // Range `0 < N.Z < FloorZ` means "facing upward but too
            // steep" — excludes walls (N.Z ≈ 0) which are handled by the
            // existing prevAirborne+nowAirborne rule, and ceilings
            // (N.Z < 0) which the body shouldn't bounce off the same way.
            if (!applyBounce
                && resolveResult.CollisionNormalValid
                && resolveResult.CollisionNormal.Z > 0f
                && resolveResult.CollisionNormal.Z < PhysicsGlobals.FloorZ)
            {
                applyBounce = true;
            }

            // L.4-diag (2026-04-30): per-frame bounce trace for steep-roof bug.
            bool diagSteep = Environment.GetEnvironmentVariable("ACDREAM_DUMP_STEEP_ROOF") == "1";
            if (diagSteep && resolveResult.CollisionNormalValid)
            {
                var n0 = resolveResult.CollisionNormal;
                var v0 = _body.Velocity;
                Console.WriteLine(
                    $"[steep-roof] BOUNCE-CHECK applyBounce={applyBounce} " +
                    $"prevWalk={prevOnWalkable} nowWalk={nowOnWalkable} " +
                    $"N=({n0.X:F2},{n0.Y:F2},{n0.Z:F2}) FloorZ={PhysicsGlobals.FloorZ:F2} " +
                    $"V=({v0.X:F2},{v0.Y:F2},{v0.Z:F2}) " +
                    $"dot={Vector3.Dot(v0, n0):F3} " +
                    $"isOnGround={resolveResult.IsOnGround}");
            }

            if (applyBounce)
            {
                if (_body.State.HasFlag(PhysicsStateFlags.Inelastic))
                {
                    // Full stop on impact. Spell projectiles / missiles.
                    _body.Velocity = Vector3.Zero;
                }
                else
                {
                    var v = _body.Velocity;
                    var n = resolveResult.CollisionNormal;
                    float dotVN = Vector3.Dot(v, n);
                    if (dotVN < 0f)
                    {
                        // Reflect the into-wall component back out.
                        // Player elasticity is 0.05 → 105% of perpendicular
                        // velocity reflects (subtle bounce).
                        float k = -(dotVN * (_body.Elasticity + 1f));
                        _body.Velocity = v + n * k;

                        if (diagSteep)
                        {
                            var v1 = _body.Velocity;
                            Console.WriteLine(
                                $"[steep-roof] BOUNCE-APPLIED V_after=({v1.X:F2},{v1.Y:F2},{v1.Z:F2}) k={k:F3}");
                        }
                    }
                }
            }
        }

        bool justLanded = false;
        if (resolveResult.IsOnGround)
        {
            if (_body.Velocity.Z <= 0f)
            {
                // Grounded — snap to resolved position and land.
                bool wasAirborne = !_body.OnWalkable;
                _body.TransientState |= TransientStateFlags.Contact | TransientStateFlags.OnWalkable;
                _body.calc_acceleration();

                if (_body.Velocity.Z < 0f)
                    _body.Velocity = new Vector3(_body.Velocity.X, _body.Velocity.Y, 0f);

                if (wasAirborne)
                {
                    _motion.HitGround();
                    justLanded = true;
                }
            }
            else
            {
                // Moving upward (jump) — stay airborne even though terrain is below.
                _body.TransientState &= ~(TransientStateFlags.Contact | TransientStateFlags.OnWalkable);
                _body.calc_acceleration();
            }
        }
        else
        {
            // No ground found — airborne.
            _body.TransientState &= ~(TransientStateFlags.Contact | TransientStateFlags.OnWalkable);
            _body.calc_acceleration();
        }


        _wasAirborneLastFrame = !_body.OnWalkable;
        CellId = resolveResult.CellId;

        // ── 6. Determine outbound motion commands ─────────────────────────────
        uint? outForwardCmd = null;
        float? outForwardSpeed = null;
        uint? outSidestepCmd = null;
        float? outSidestepSpeed = null;
        uint? outTurnCmd = null;
        float? outTurnSpeed = null;

        // Retail-faithful wire commands. ACE's MovementData constructor only
        // computes interpState.ForwardSpeed for WalkForward / WalkBackwards
        // (Network/Motion/MovementData.cs:104-119) — for any other command
        // the else-branch passes through without setting speed, so observers
        // dead-reckon at speed=0. The wire therefore must be:
        //   - Forward (walk): WalkForward  @ 1.0
        //   - Forward (run):  WalkForward  @ run_rate  + HoldKey.Run
        //                     (ACE auto-upgrades to RunForward for observers)
        //   - Backward:       WalkBackward @ 1.0
        // Our own local animation still wants the actual RunForward cycle
        // though — that's carried separately in LocalAnimationCommand below.
        uint? localAnimCmd = null;
        if (input.Forward)
        {
            outForwardCmd = MotionCommand.WalkForward;
            if (input.Run && _weenie.InqRunRate(out float runRate))
            {
                outForwardSpeed  = runRate;
                localAnimCmd     = MotionCommand.RunForward;   // local cycle is RunForward
            }
            else
            {
                outForwardSpeed  = 1.0f;
                localAnimCmd     = MotionCommand.WalkForward;
            }
        }
        else if (input.Backward)
        {
            outForwardCmd    = MotionCommand.WalkBackward;
            outForwardSpeed  = 1.0f;
            localAnimCmd     = MotionCommand.WalkBackward;
        }

        // Strafe: retail uses speed=1.0 for SideStep (see holtburger
        // common.rs::locomotion_command_for_state). 0.5 was our earlier guess
        // and made strafing feel lethargic; the retail feel is full-speed
        // sidestep matching the walk forward pace.
        if (input.StrafeRight)
        {
            outSidestepCmd   = MotionCommand.SideStepRight;
            outSidestepSpeed = 1.0f;
        }
        else if (input.StrafeLeft)
        {
            outSidestepCmd   = MotionCommand.SideStepLeft;
            outSidestepSpeed = 1.0f;
        }

        // Turn commands from KEYBOARD only (A/D). Mouse turning is applied
        // directly to Yaw above and doesn't generate a turn command — if it
        // did, mouse jitter would flip turnCmd between TurnRight/TurnLeft
        // every frame, causing stateChanged=True on every frame and flooding
        // the server with MoveToState spam.
        if (input.TurnRight)
        {
            outTurnCmd   = MotionCommand.TurnRight;
            outTurnSpeed = 1.0f;
        }
        else if (input.TurnLeft)
        {
            outTurnCmd   = MotionCommand.TurnLeft;
            outTurnSpeed = 1.0f;
        }

        // ── 7. Detect motion state change ─────────────────────────────────────
        // Bug fix: ForwardCommand can stay the same (WalkForward) while ONLY
        // ForwardSpeed or the run-hold bit changes. If the user is already
        // walking (W held), then presses Shift, the outbound wire still has
        // ForwardCommand=WalkForward but outForwardSpeed jumps from 1.0 to
        // runRate. Without also tracking speed + hold-key here, no new
        // MoveToState is sent — the server keeps thinking the player walks,
        // and retail observers render walking animation despite the local
        // player's RunForward cycle.
        //
        // Similarly LocalAnimationCommand change (Walk→Run on local cycle)
        // must force a fresh outbound so ACE's BroadcastMovement re-runs
        // MovementData(this, moveToState) which only reads ForwardCommand +
        // ForwardSpeed + HoldKey to pick between WalkForward vs RunForward
        // for remote observers.
        bool runHold = input.Run;
        bool changed = outForwardCmd    != _prevForwardCmd
                    || outSidestepCmd   != _prevSidestepCmd
                    || outTurnCmd       != _prevTurnCmd
                    || !FloatsEqual(outForwardSpeed, _prevForwardSpeed)
                    || runHold          != _prevRunHold
                    || localAnimCmd     != _prevLocalAnimCmd;
        _prevForwardCmd    = outForwardCmd;
        _prevSidestepCmd   = outSidestepCmd;
        _prevTurnCmd       = outTurnCmd;
        _prevForwardSpeed  = outForwardSpeed;
        _prevRunHold       = runHold;
        _prevLocalAnimCmd  = localAnimCmd;

        static bool FloatsEqual(float? a, float? b)
        {
            if (a.HasValue != b.HasValue) return false;
            if (!a.HasValue || !b.HasValue) return true;
            return System.Math.Abs(a.Value - b.Value) < 1e-4f;
        }

        // ── 8. Heartbeat timer (only while moving) ────────────────────────────
        bool isMoving = outForwardCmd is not null
                     || outSidestepCmd is not null
                     || outTurnCmd is not null;
        if (isMoving)
        {
            _heartbeatAccum += dt;
            HeartbeatDue = _heartbeatAccum >= HeartbeatInterval;
            if (HeartbeatDue) _heartbeatAccum = 0f;
        }
        else
        {
            _heartbeatAccum = 0f;
            HeartbeatDue = false;
        }

        // K-fix5 (2026-04-26): local-animation-cycle pacing. Visual rate
        // should match the actual movement speed. For Forward+Run this is
        // already runRate (it equals ForwardSpeed). For Backward+Run and
        // Strafe+Run it must be runRate too even though the wire keeps
        // those at 1.0. Picking runMul (already computed above) keeps the
        // math in one place.
        bool anyDirectional = input.Forward || input.Backward
                            || input.StrafeLeft || input.StrafeRight;
        float localAnimSpeed = (input.Run && anyDirectional)
            ? (_weenie.InqRunRate(out float vrrAnim) ? vrrAnim : 1f)
            : 1f;

        return new MovementResult(
            Position: Position,
            CellId: CellId,
            IsOnGround: _body.OnWalkable,
            MotionStateChanged: changed,
            ForwardCommand: outForwardCmd,
            SidestepCommand: outSidestepCmd,
            TurnCommand: outTurnCmd,
            ForwardSpeed: outForwardSpeed,
            SidestepSpeed: outSidestepSpeed,
            TurnSpeed: outTurnSpeed,
            IsRunning: input.Run && input.Forward,
            LocalAnimationCommand: localAnimCmd,
            LocalAnimationSpeed: localAnimSpeed,
            JustLanded: justLanded,
            JumpExtent: outJumpExtent,
            JumpVelocity: outJumpVelocity);
    }
}