acdream/src/AcDream.App/Rendering/ChargenPreviewRotationController.cs

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

namespace AcDream.App.Rendering;

/// <summary>
/// Retail's toggle direction enum
/// (<c>gmBarberUI::ERotateDirection</c>/<c>gmCGAppearancePage::ERotateDirection</c>
/// typedef alias, <c>acclient.h:6848-6852,6960</c>): <c>Invalid=0</c>,
/// <c>Clockwise=1</c>, <c>CounterClockwise=2</c>.
/// </summary>
internal enum ChargenRotateDirection
{
    Invalid = 0,
    Clockwise = 1,
    CounterClockwise = 2,
}

/// <summary>
/// Presentation-free port of <c>gmCGAppearancePage::Rotate</c>
/// (<c>0x0047CB50</c>) + <c>DoRotation</c> (<c>0x0047CA80</c>) — the
/// button-toggled continuous rotation retail applies to the preview
/// CHARACTER's heading (<c>CPhysicsObj::set_heading</c> inside
/// <c>gmCG3DView::Update</c>, pseudo-C ~0x0047eecf1), not the camera (see
/// <see cref="ChargenPreviewCamera"/>'s own doc comment on why rotation
/// lives here instead). Retail drives <see cref="Tick"/> once per frame from
/// a global-message-3 tick while <see cref="IsRotating"/> is set
/// (<c>gmCGAppearancePage::ListenToGlobalMessage @ 0x0047CED0</c>); the
/// CC6b page-mount half will bind the Rotate Clockwise/Counter-Clockwise
/// buttons to <see cref="Toggle"/> and the render loop to <see cref="Tick"/>.
/// </summary>
internal sealed class ChargenPreviewRotationController
{
    /// <summary>
    /// <c>Rotate</c>'s explicit sentinel write
    /// (<c>this->m_dLastRotateTime = -1.0</c>, pseudo-C ~0x0047cba7/0x0047cbb1
    /// — the high dword <c>0xbff00000</c> paired with a zero low dword is the
    /// exact IEEE-754 bit pattern for <c>-1.0</c>) — invalidates the
    /// timestamp so the very next <see cref="Tick"/> resets it to "now"
    /// (a zero-length first delta) instead of computing a huge jump from a
    /// stale or never-set value.
    /// </summary>
    private const double InvalidTimeSentinel = -1.0;

    private double _lastRotateTime = InvalidTimeSentinel;
    private ChargenRotateDirection _direction = ChargenRotateDirection.Invalid;
    private bool _rotating;

    public bool IsRotating => _rotating;
    public ChargenRotateDirection Direction => _direction;

    /// <summary>Retail's <c>m_fCurHeading</c>, degrees, ctor default 0 —
    /// applied to the preview entity via <c>MoveToMath.SetHeading</c>
    /// (<c>CPhysicsObj::set_heading</c>'s exact port).</summary>
    public float HeadingDegrees { get; private set; }

    /// <summary>
    /// <c>gmCGAppearancePage::Rotate @ 0x0047CB50</c>: pressing the SAME
    /// direction a second time while already rotating STOPS rotation
    /// (retail's button-toggle UX); any other press (opposite direction, or
    /// starting from stopped) sets that direction and (re)starts,
    /// invalidating <c>m_dLastRotateTime</c> per this class's own sentinel
    /// doc.
    /// </summary>
    public void Toggle(ChargenRotateDirection direction)
    {
        if (_rotating && direction == _direction)
        {
            _rotating = false;
            return;
        }
        _direction = direction;
        _lastRotateTime = InvalidTimeSentinel;
        _rotating = true;
    }

    /// <summary>
    /// <c>gmCGAppearancePage::DoRotation @ 0x0047CA80</c>: per-tick
    /// <c>deltaDegrees = ((now - lastRotateTime) / RotationSecondsPerRevolution)
    /// * 360</c>, added for <see cref="ChargenRotateDirection.Clockwise"/>
    /// and subtracted for every other direction (pseudo-C ~0x0047cacd:
    /// <c>if (m_eRotateDir != ECG_ROTATE_CLOCKWISE) heading -= delta; else
    /// heading += delta;</c>), then a SINGLE-PASS clamp back into
    /// <c>[0, 360)</c> — not a full modulo loop; retail's own tail only
    /// adds/subtracts 360 once (pseudo-C ~0x0047caf3-0x0047cb31), which is
    /// exactly enough for any realistic per-frame delta and is reproduced
    /// here verbatim rather than "improved" into a `%=`. Fix round F3: Binary
    /// Ninja literally renders <c>x87_r7_1 = x87_r6_3</c> at <c>0x0047CAEB</c>
    /// inside the counter-clockwise branch — reassigning the local that held
    /// the "now" timestamp to the just-computed delta-degrees value — which
    /// would make the <c>0x0047CB3D</c> store into <c>m_dLastRotateTime</c>
    /// write delta-degrees instead of the timestamp for CCW only; that is an
    /// x87-FPU-stack modeling artifact of the decompiler, not real retail
    /// behavior (a shipped feature where every counter-clockwise rotation
    /// visibly diverges from clockwise is implausible, and
    /// <c>claude-memory/feedback_bn_decomp_field_names.md</c> names exactly
    /// this x87-stack-register mislabeling as a known decompiler artifact
    /// class), so this port stores <c>now</c> into <c>_lastRotateTime</c>
    /// unconditionally in BOTH directions.
    /// </summary>
    public void Tick(double now)
    {
        if (!_rotating)
            return;
        if (_lastRotateTime <= 0d)
            _lastRotateTime = now;

        double deltaDegrees = ((now - _lastRotateTime) / ChargenPreviewCamera.RotationSecondsPerRevolution) * 360.0;
        HeadingDegrees = _direction == ChargenRotateDirection.Clockwise
            ? HeadingDegrees + (float)deltaDegrees
            : HeadingDegrees - (float)deltaDegrees;

        if (HeadingDegrees < 0f)
            HeadingDegrees += 360f;
        if (HeadingDegrees > 360f)
            HeadingDegrees -= 360f;

        _lastRotateTime = now;
    }

    /// <summary><c>CPhysicsObj::set_heading</c>'s exact quaternion
    /// construction — the SAME shared Core primitive retail movement already
    /// ports (<see cref="MoveToMath.SetHeading"/>).</summary>
    public Quaternion ToOrientation() =>
        MoveToMath.SetHeading(Quaternion.Identity, HeadingDegrees);
}