//! Arcball/orbit camera — Revit ViewCube style.
//!
//! Orbit with middle-mouse drag, zoom with scroll wheel.

use glam::{Mat4, Vec3};
use bytemuck::{Pod, Zeroable};

// ─── GPU uniform ─────────────────────────────────────────────────────────────

/// 64-byte view-projection matrix uploaded to the GPU once per frame.
#[repr(C)]
#[derive(Copy, Clone, Debug, Pod, Zeroable)]
pub struct CameraUniform {
    pub view_proj: [[f32; 4]; 4],
}

impl CameraUniform {
    pub fn identity() -> Self {
        Self { view_proj: Mat4::IDENTITY.to_cols_array_2d() }
    }
}

// ─── Camera ──────────────────────────────────────────────────────────────────

/// Standard axis-aligned views (Revit numpad convention).
#[derive(Debug, Clone, Copy)]
pub enum StandardView {
    Top,    // Numpad 7
    Front,  // Numpad 1
    Right,  // Numpad 3
    Left,   // Numpad 4 / Ctrl+Numpad3
    Iso,    // Home
}

/// Camera projection mode.
///
/// - `Perspective`: 원근 투영. 멀수록 작게 보임. 일반 3D 뷰.
/// - `Orthographic`: 평행 투영. 거리 무관 실측 크기. 치수 검증·도면 스타일 뷰.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Projection {
    Perspective,
    Orthographic,
}

/// Orbit camera — spherical coordinates around a fixed target point.
///
/// All distances in millimetres (scene units).
pub struct Camera {
    /// Point the camera orbits around.
    pub target:  Vec3,
    /// Distance from target [mm].
    pub radius:  f32,
    /// Horizontal rotation [radians].
    pub yaw:     f32,
    /// Vertical rotation [radians]. Clamped to avoid gimbal lock.
    pub pitch:   f32,
    pub fov_y:   f32,
    pub aspect:  f32,
    pub znear:   f32,
    pub zfar:    f32,
    /// 투영 모드 (원근 / 평행). 토글 O.
    pub projection: Projection,
}

impl Camera {
    /// Default view looking at a 40 m PSC-I girder from a comfortable angle.
    pub fn default_for_girder(span_mm: f32) -> Self {
        Self {
            target:  Vec3::new(300.0, 900.0, span_mm * 0.5),
            radius:  span_mm * 1.5,
            yaw:     std::f32::consts::FRAC_PI_4,   // 45°
            pitch:   0.35,                           // ~20°
            fov_y:   60.0_f32.to_radians(),
            aspect:  16.0 / 9.0,
            znear:   10.0,                           // 10 mm
            zfar:    10_000_000.0,                   // 10 km
            projection: Projection::Perspective,
        }
    }

    /// Eye position derived from orbit parameters.
    pub fn eye(&self) -> Vec3 {
        let sin_p = self.pitch.sin();
        let cos_p = self.pitch.cos();
        let sin_y = self.yaw.sin();
        let cos_y = self.yaw.cos();
        self.target + Vec3::new(
            self.radius * cos_p * sin_y,
            self.radius * sin_p,
            self.radius * cos_p * cos_y,
        )
    }

    /// View-projection matrix (right-handed, depth 0→1).
    pub fn view_proj(&self) -> Mat4 {
        let view = Mat4::look_at_rh(self.eye(), self.target, Vec3::Y);
        let proj = match self.projection {
            Projection::Perspective => {
                Mat4::perspective_rh(self.fov_y, self.aspect, self.znear, self.zfar)
            }
            Projection::Orthographic => {
                // Ortho 수직 반높이: 같은 radius·FOV 의 원근 뷰와 시각 스케일 일치 →
                //   target 평면에서 보이던 크기를 그대로 유지한 채 평행 투영.
                let half_h = self.radius * (self.fov_y * 0.5).tan();
                let half_w = half_h * self.aspect;
                Mat4::orthographic_rh(-half_w, half_w, -half_h, half_h, self.znear, self.zfar)
            }
        };
        proj * view
    }

    /// Perspective ↔ Orthographic 토글.
    pub fn toggle_projection(&mut self) {
        self.projection = match self.projection {
            Projection::Perspective  => Projection::Orthographic,
            Projection::Orthographic => Projection::Perspective,
        };
    }

    /// Build GPU uniform from current state.
    pub fn to_uniform(&self) -> CameraUniform {
        CameraUniform { view_proj: self.view_proj().to_cols_array_2d() }
    }

    // ── Interaction ────────────────────────────────────────────────────────

    /// Orbit by dragging (delta in pixels, scaled to radians).
    /// 사용자 요청: 회전 방향 반전 (yaw·pitch 양쪽 모두).
    pub fn orbit(&mut self, delta_x: f32, delta_y: f32) {
        self.yaw   -= delta_x * 0.005;
        self.pitch  = (self.pitch + delta_y * 0.005)
            .clamp(-std::f32::consts::FRAC_PI_2 + 0.05, std::f32::consts::FRAC_PI_2 - 0.05);
    }

    /// Zoom by scrolling (positive = closer, negative = farther).
    pub fn zoom(&mut self, delta: f32) {
        self.radius = (self.radius * (1.0 - delta * 0.1)).max(100.0);
    }

    /// Pan target by screen-space delta (Shift + middle mouse).
    ///
    /// Moves the orbit centre so the object stays under the cursor.
    pub fn pan(&mut self, delta_x: f32, delta_y: f32) {
        let eye      = self.eye();
        let view_dir = (self.target - eye).normalize();
        let right    = view_dir.cross(Vec3::Y).normalize();
        let up       = right.cross(view_dir).normalize();
        let scale    = self.radius * 0.001;   // pan speed proportional to zoom
        self.target -= right * delta_x * scale;
        self.target += up   * delta_y * scale;
    }

    /// Zoom-extents: fit the given bounding box into view.
    pub fn zoom_extents(&mut self, mn: [f32; 3], mx: [f32; 3]) {
        let c = Vec3::new(
            (mn[0] + mx[0]) * 0.5,
            (mn[1] + mx[1]) * 0.5,
            (mn[2] + mx[2]) * 0.5,
        );
        let diag = Vec3::new(mx[0]-mn[0], mx[1]-mn[1], mx[2]-mn[2]).length();
        self.target = c;
        self.radius = (diag * 0.75).max(1000.0);
    }

    /// Snap to a standard axis-aligned view (Revit numpad convention).
    pub fn set_standard_view(&mut self, view: StandardView) {
        match view {
            StandardView::Top   => { self.yaw = 0.0;  self.pitch =  std::f32::consts::FRAC_PI_2 - 0.01; }
            StandardView::Front => { self.yaw = std::f32::consts::PI; self.pitch = 0.0; }
            StandardView::Right => { self.yaw = std::f32::consts::FRAC_PI_2; self.pitch = 0.0; }
            StandardView::Left  => { self.yaw = -std::f32::consts::FRAC_PI_2; self.pitch = 0.0; }
            StandardView::Iso   => { self.yaw = std::f32::consts::FRAC_PI_4; self.pitch = 0.35; }
        }
    }

    /// Update aspect ratio on window resize.
    pub fn resize(&mut self, width: u32, height: u32) {
        self.aspect = width as f32 / height.max(1) as f32;
    }
}