using System;
using System.Numerics;

namespace AcDream.App.Rendering;

/// <summary>
/// Fixed camera for the paperdoll mini-scene — retail-exact, ported from the gmPaperDollUI viewport
/// setup (decomp 0x004a5a39–0x004a5a69). The viewport (element <c>0x100001d5</c>) is configured by
/// <c>UIElement_Viewport::SetCamera(position, direction)</c> with:
/// <list type="bullet">
///   <item>position  = (0.12, −2.4, 0.88)  [hex 0x3df5c28f, 0xc019999a, 0x3f6147ae]</item>
///   <item>direction = (0, 0, 0) ⇒ <c>CreatureMode::SetCameraDirection</c> resets the view frame to
///         IDENTITY (<c>euler_set_rotate(0,0,0)</c> then <c>rotate(0,0,0)</c>), so the camera looks
///         straight down +Y with +Z up — NO yaw, NO pitch.</item>
/// </list>
/// The doll is framed purely by camera POSITION + FOV, NOT by aiming at the body: at distance 2.4 with
/// a π/4 (45°) vertical FOV the visible vertical band is z≈[−0.11, 1.87], which covers the whole ~1.6 m
/// figure even though the model origin sits at the FEET (z=0). FOV π/4 is <c>CreatureMode</c>'s default
/// <c>m_fFOVRadians</c> (ctor 0x004543cf, hex 0x3f490fdb); default ambient is (0.3,0.3,0.3); the
/// paperdoll uses <c>UseSharpMode</c> (not SmartboxFOV) so <c>Render::SetFOVRad(m_fFOVRadians)</c> applies.
///
/// <para>An earlier hand-tune aimed the camera at mid-body to "fit the figure", which introduced a
/// spurious yaw (Target.x ≠ Eye.x) that rotated the view and turned the doll's face away from the
/// viewer. This restores retail's zero-yaw frame, where full-body framing comes from the eye height +
/// FOV, not from aiming.</para>
///
/// Uses the same <see cref="Matrix4x4.CreateLookAt"/> / <see cref="Matrix4x4.CreatePerspectiveFieldOfView"/>
/// convention as <see cref="ChaseCamera"/> so the doll's triangle winding + back-face culling match the
/// world render pass. AC up-axis = +Z.
/// </summary>
public sealed class DollCamera : ICamera
{
    // Retail paperdoll camera origin (decomp 0x004a5a51–0x004a5a61).
    private static readonly Vector3 Eye    = new(0.12f, -2.4f, 0.88f);
    // Identity view orientation ⇒ look straight down +Y (no yaw/pitch). Target = Eye + (0,1,0).
    private static readonly Vector3 Target = new(0.12f, -1.4f, 0.88f);
    private static readonly Vector3 Up     = Vector3.UnitZ;   // AC up-axis = +Z, same as ChaseCamera

    /// <summary>Vertical field of view — retail <c>CreatureMode</c> default <c>m_fFOVRadians</c> = π/4 (45°).</summary>
    public float FovRadians { get; set; } = MathF.PI / 4f;

    public float Near   { get; set; } = 0.1f;    // same near plane as ChaseCamera / retail znear
    public float Far    { get; set; } = 50f;     // doll scene is small; 50 m is ample
    public float Aspect { get; set; } = 1f;

    /// <inheritdoc/>
    public Matrix4x4 View =>
        Matrix4x4.CreateLookAt(Eye, Target, Up);

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