using System.Numerics;

namespace AcDream.App.Rendering;

/// <summary>
/// Retail portal-space camera from <c>gmSmartBoxUI::PostInit</c>
/// (<c>0x004D6D8A</c>) and <c>CreatureMode::SetCameraDirection_Degrees</c>
/// (<c>0x00453760</c>). Identity looks along AC +Y with +Z up; the animated
/// angle rolls that view around its own +Y forward axis.
/// </summary>
public sealed class PortalTunnelCamera : ICamera
{
    public static readonly Vector3 RetailEye = new(0.24f, -2.7f, 0.88f);

    public float DirectionDegrees { get; set; }
    public float FovRadians { get; set; } = MathF.PI / 4f;
    public float Near { get; set; } = 0.1f;
    // Render::zfar defaults to 4000 in retail (0x0081EC88). CreatureMode::Render
    // does not install a private far plane: PrimD3DRender::SetFOVInternal
    // (0x0059AB40) rebuilds the portal projection with that shared value.
    public float Far { get; set; } = 4000f;
    public float Aspect { get; set; } = 1f;

    /// <summary>
    /// Retail <c>CreatureMode::UseSmartboxFOV</c> reads the active SmartBox
    /// projection each draw. Recover its vertical field of view and near
    /// and far planes from that perspective matrix. Retail's CreatureMode
    /// changes the FOV through the SmartBox path while retaining the renderer's
    /// shared near/far clip range.
    /// </summary>
    public void UseSmartBoxFov(Matrix4x4 smartBoxProjection)
    {
        float verticalScale = smartBoxProjection.M22;
        if (!float.IsFinite(verticalScale) || verticalScale <= 0f)
            return;

        float fov = 2f * MathF.Atan(1f / verticalScale);
        if (float.IsFinite(fov) && fov > 0f && fov < MathF.PI)
            FovRadians = fov;

        // System.Numerics perspective matrices encode near as M43/M33.
        // During teleport fades this carries Render::set_vdst's
        // max(0.1, viewPlaneDistance * 0.25) result.
        float near = smartBoxProjection.M33 != 0f
            ? smartBoxProjection.M43 / smartBoxProjection.M33
            : float.NaN;
        float far = smartBoxProjection.M33 != -1f
            ? smartBoxProjection.M43 / (smartBoxProjection.M33 + 1f)
            : float.NaN;
        if (float.IsFinite(far) && far > 0f)
            Far = far;
        if (float.IsFinite(near) && near > 0f && near < Far)
            Near = near;
    }

    public Matrix4x4 View
    {
        get
        {
            float radians = DirectionDegrees * (MathF.PI / 180f);
            // CreatureMode::SetCameraDirection_Degrees (0x00453760) resets
            // the Frame to identity, converts (0, angle, 0) to radians, and
            // passes that rotation vector to Frame::rotate (0x004525B0).
            // Frame::rotate interprets the vector as axis * angle, so this is
            // a roll around AC +Y -- the identity camera's FORWARD axis --
            // not a yaw around world +Z. The passage therefore stays ahead
            // while the authored tunnel rolls around the viewer.
            Quaternion rotation = Quaternion.CreateFromAxisAngle(Vector3.UnitY, radians);
            Vector3 forward = Vector3.UnitY;
            Vector3 up = Vector3.Transform(Vector3.UnitZ, rotation);
            return Matrix4x4.CreateLookAt(RetailEye, RetailEye + forward, up);
        }
    }

    public Matrix4x4 Projection => Matrix4x4.CreatePerspectiveFieldOfView(
        FovRadians,
        Aspect <= 0f ? 1f : Aspect,
        Near,
        Far);
}