//! Main camera

use cgmath::{prelude::*, AbsDiffEq, Matrix4, Point2, Point3, Rad, Vector2, Vector3, Vector4};

use crate::util::{
    math::{bounds_from_points, Aabb2, Aabb3, Plane},
    SignificantlyDifferent,
};

#[rustfmt::skip]
pub const OPENGL_TO_WGPU_MATRIX: Matrix4<f64> = Matrix4::new(
    1.0, 0.0, 0.0, 0.0,
    0.0, 1.0, 0.0, 0.0,
    0.0, 0.0, 0.5, 0.0,
    0.0, 0.0, 0.5, 1.0,
);

#[rustfmt::skip]
pub const FLIP_Y: Matrix4<f64> = Matrix4::new(
    1.0, 0.0, 0.0, 0.0, 
    0.0, -1.0, 0.0, 0.0, 
    0.0, 0.0, 1.0, 0.0, 
    0.0, 0.0, 0.0, 1.0,
);

#[derive(Debug)]
pub struct ViewProjection(Matrix4<f64>);

impl ViewProjection {
    #[tracing::instrument(skip_all)]
    pub fn invert(&self) -> InvertedViewProjection {
        InvertedViewProjection(self.0.invert().expect("Unable to invert view projection"))
    }

    pub fn project(&self, vector: Vector4<f64>) -> Vector4<f64> {
        self.0 * vector
    }

    #[tracing::instrument(skip_all)]
    pub fn to_model_view_projection(&self, projection: Matrix4<f64>) -> ModelViewProjection {
        ModelViewProjection(self.0 * projection)
    }

    pub fn downcast(&self) -> Matrix4<f32> {
        self.0
            .cast::<f32>()
            .expect("Unable to cast view projection to f32")
    }
}

pub struct InvertedViewProjection(Matrix4<f64>);

impl InvertedViewProjection {
    pub fn project(&self, vector: Vector4<f64>) -> Vector4<f64> {
        self.0 * vector
    }
}

pub struct ModelViewProjection(Matrix4<f64>);

impl ModelViewProjection {
    pub fn downcast(&self) -> Matrix4<f32> {
        self.0
            .cast::<f32>()
            .expect("Unable to cast view projection to f32")
    }
}

const MIN_PITCH: Rad<f64> = Rad(-0.5);
const MAX_PITCH: Rad<f64> = Rad(0.5);

#[derive(Debug, Clone)]
pub struct Camera {
    position: Point3<f64>, // The z axis never changes, the zoom is used instead
    yaw: Rad<f64>,
    pitch: Rad<f64>,

    width: f64,
    height: f64,
}

impl SignificantlyDifferent for Camera {
    type Epsilon = f64;

    fn ne(&self, other: &Self, epsilon: Self::Epsilon) -> bool {
        self.position.abs_diff_ne(&other.position, epsilon)
            || self.yaw.abs_diff_ne(&other.yaw, epsilon)
            || self.pitch.abs_diff_ne(&other.pitch, epsilon)
    }
}

impl Camera {
    pub fn new<V: Into<Point3<f64>>, Y: Into<Rad<f64>>, P: Into<Rad<f64>>>(
        position: V,
        yaw: Y,
        pitch: P,
        width: u32,
        height: u32,
    ) -> Self {
        Self {
            position: position.into(),
            yaw: yaw.into(),
            pitch: pitch.into(),
            width: width as f64,
            height: height as f64,
        }
    }

    pub fn resize(&mut self, width: u32, height: u32) {
        self.width = width as f64;
        self.height = height as f64;
    }

    fn calc_matrix(&self) -> Matrix4<f64> {
        Matrix4::look_to_rh(
            self.position,
            Vector3::new(self.yaw.cos(), self.pitch.sin(), self.yaw.sin()).normalize(),
            Vector3::unit_y(),
        )
    }

    #[tracing::instrument(skip_all)]
    pub fn calc_view_proj(&self, perspective: &Perspective) -> ViewProjection {
        ViewProjection(FLIP_Y * perspective.current_projection * self.calc_matrix())
    }

    /// A transform which can be used to transform between clip and window space.
    /// Adopted from [here](https://docs.microsoft.com/en-us/windows/win32/direct3d9/viewports-and-clipping#viewport-rectangle) (Direct3D).
    fn clip_to_window_transform(&self) -> Matrix4<f64> {
        let min_depth = 0.0;
        let max_depth = 1.0;
        let x = 0.0;
        let y = 0.0;
        let ox = x + self.width / 2.0;
        let oy = y + self.height / 2.0;
        let oz = min_depth;
        let pz = max_depth - min_depth;
        Matrix4::from_cols(
            Vector4::new(self.width / 2.0, 0.0, 0.0, 0.0),
            Vector4::new(0.0, -self.height / 2.0, 0.0, 0.0),
            Vector4::new(0.0, 0.0, pz, 0.0),
            Vector4::new(ox, oy, oz, 1.0),
        )
    }

    /// Transforms coordinates in clip space to window coordinates.
    ///
    /// Adopted from [here](https://docs.microsoft.com/en-us/windows/win32/dxtecharts/the-direct3d-transformation-pipeline) (Direct3D).
    fn clip_to_window(&self, clip: &Vector4<f64>) -> Vector4<f64> {
        #[rustfmt::skip]
            let ndc = Vector4::new(
            clip.x / clip.w,
            clip.y / clip.w,
            clip.z / clip.w,
            1.0
        );

        self.clip_to_window_transform() * ndc
    }
    /// Alternative implementation to `clip_to_window`. Transforms coordinates in clip space to
    /// window coordinates.
    ///
    /// Adopted from [here](https://www.khronos.org/registry/vulkan/specs/1.2-extensions/man/html/VkViewport.html)
    /// and [here](https://matthewwellings.com/blog/the-new-vulkan-coordinate-system/) (Vulkan).
    fn clip_to_window_vulkan(&self, clip: &Vector4<f64>) -> Vector3<f64> {
        #[rustfmt::skip]
            let ndc = Vector4::new(
            clip.x / clip.w,
            clip.y / clip.w,
            clip.z / clip.w,
            1.0
        );

        let min_depth = 0.0;
        let max_depth = 1.0;

        let x = 0.0;
        let y = 0.0;
        let ox = x + self.width / 2.0;
        let oy = y + self.height / 2.0;
        let oz = min_depth;
        let px = self.width;
        let py = self.height;
        let pz = max_depth - min_depth;
        let xd = ndc.x;
        let yd = ndc.y;
        let zd = ndc.z;
        Vector3::new(px / 2.0 * xd + ox, py / 2.0 * yd + oy, pz * zd + oz)
    }

    /// Order of transformations reversed: https://computergraphics.stackexchange.com/questions/6087/screen-space-coordinates-to-eye-space-conversion/6093
    /// `w` is lost.
    ///
    /// OpenGL explanation: https://www.khronos.org/opengl/wiki/Compute_eye_space_from_window_space#From_window_to_ndc
    fn window_to_world(
        &self,
        window: &Vector3<f64>,
        inverted_view_proj: &InvertedViewProjection,
    ) -> Vector3<f64> {
        #[rustfmt::skip]
        let fixed_window = Vector4::new(
            window.x,
            window.y,
            window.z,
            1.0
        );

        let ndc = self.clip_to_window_transform().invert().unwrap() * fixed_window;
        let unprojected = inverted_view_proj.project(ndc);

        Vector3::new(
            unprojected.x / unprojected.w,
            unprojected.y / unprojected.w,
            unprojected.z / unprojected.w,
        )
    }

    /// Alternative implementation to `window_to_world`
    ///
    /// Adopted from [here](https://docs.rs/nalgebra-glm/latest/src/nalgebra_glm/ext/matrix_projection.rs.html#164-181).
    fn window_to_world_nalgebra(
        window: &Vector3<f64>,
        inverted_view_proj: &InvertedViewProjection,
        width: f64,
        height: f64,
    ) -> Vector3<f64> {
        let pt = Vector4::new(
            2.0 * (window.x - 0.0) / width - 1.0,
            2.0 * (height - window.y - 0.0) / height - 1.0,
            window.z,
            1.0,
        );
        let unprojected = inverted_view_proj.project(pt);

        Vector3::new(
            unprojected.x / unprojected.w,
            unprojected.y / unprojected.w,
            unprojected.z / unprojected.w,
        )
    }

    /// Gets the world coordinates for the specified `window` coordinates on the `z=0` plane.
    pub fn window_to_world_at_ground(
        &self,
        window: &Vector2<f64>,
        inverted_view_proj: &InvertedViewProjection,
        bound: bool,
    ) -> Option<Vector3<f64>> {
        let near_world =
            self.window_to_world(&Vector3::new(window.x, window.y, 0.0), inverted_view_proj);

        let far_world =
            self.window_to_world(&Vector3::new(window.x, window.y, 1.0), inverted_view_proj);

        // for z = 0 in world coordinates
        // Idea comes from: https://dondi.lmu.build/share/cg/unproject-explained.pdf
        let u = -near_world.z / (far_world.z - near_world.z);
        if !bound || (0.0..=1.0).contains(&u) {
            Some(near_world + u * (far_world - near_world))
        } else {
            None
        }
    }

    /// Calculates an [`Aabb2`] bounding box which contains at least the visible area on the `z=0`
    /// plane. One can think of it as being the bounding box of the geometry which forms the
    /// intersection between the viewing frustum and the `z=0` plane.
    ///
    /// This implementation works in the world 3D space. It casts rays from the corners of the
    /// window to calculate intersections points with the `z=0` plane. Then a bounding box is
    /// calculated.
    ///
    /// *Note:* It is possible that no such bounding box exists. This is the case if the `z=0` plane
    /// is not in view.
    pub fn view_region_bounding_box(
        &self,
        inverted_view_proj: &InvertedViewProjection,
    ) -> Option<Aabb2<f64>> {
        let screen_bounding_box = [
            Vector2::new(0.0, 0.0),
            Vector2::new(self.width, 0.0),
            Vector2::new(self.width, self.height),
            Vector2::new(0.0, self.height),
        ]
        .map(|point| self.window_to_world_at_ground(&point, inverted_view_proj, false));

        let (min, max) = bounds_from_points(
            screen_bounding_box
                .into_iter()
                .flatten()
                .map(|point| [point.x, point.y]),
        )?;

        Some(Aabb2::new(Point2::from(min), Point2::from(max)))
    }
    /// An alternative implementation for `view_bounding_box`.
    ///
    /// This implementation works in the NDC space. We are creating a plane in the world 3D space.
    /// Then we are transforming it to the NDC space. In NDC space it is easy to calculate
    /// the intersection points between an Aabb3 and a plane. The resulting Aabb2 is returned.
    pub fn view_region_bounding_box_ndc(&self, perspective: &Perspective) -> Option<Aabb2<f64>> {
        let view_proj = self.calc_view_proj(perspective);
        let a = view_proj.project(Vector4::new(0.0, 0.0, 0.0, 1.0));
        let b = view_proj.project(Vector4::new(1.0, 0.0, 0.0, 1.0));
        let c = view_proj.project(Vector4::new(1.0, 1.0, 0.0, 1.0));

        let a_ndc = self.clip_to_window(&a).truncate();
        let b_ndc = self.clip_to_window(&b).truncate();
        let c_ndc = self.clip_to_window(&c).truncate();
        let to_ndc = Vector3::new(1.0 / self.width, 1.0 / self.height, 1.0);
        let plane: Plane<f64> = Plane::from_points(
            Point3::from_vec(a_ndc.mul_element_wise(to_ndc)),
            Point3::from_vec(b_ndc.mul_element_wise(to_ndc)),
            Point3::from_vec(c_ndc.mul_element_wise(to_ndc)),
        )?;

        let points = plane.intersection_points_aabb3(&Aabb3::new(
            Point3::new(0.0, 0.0, 0.0),
            Point3::new(1.0, 1.0, 1.0),
        ));

        let inverted_view_proj = view_proj.invert();

        let from_ndc = Vector3::new(self.width, self.height, 1.0);
        let vec = points
            .iter()
            .map(|point| {
                self.window_to_world(&point.mul_element_wise(from_ndc), &inverted_view_proj)
            })
            .collect::<Vec<_>>();

        let min_x = vec
            .iter()
            .map(|point| point.x)
            .min_by(|a, b| a.partial_cmp(b).unwrap())?;
        let min_y = vec
            .iter()
            .map(|point| point.y)
            .min_by(|a, b| a.partial_cmp(b).unwrap())?;
        let max_x = vec
            .iter()
            .map(|point| point.x)
            .max_by(|a, b| a.partial_cmp(b).unwrap())?;
        let max_y = vec
            .iter()
            .map(|point| point.y)
            .max_by(|a, b| a.partial_cmp(b).unwrap())?;
        Some(Aabb2::new(
            Point2::new(min_x, min_y),
            Point2::new(max_x, max_y),
        ))
    }

    pub fn position(&self) -> Point3<f64> {
        self.position
    }

    pub fn yaw(&self) -> Rad<f64> {
        self.yaw
    }

    pub fn rotate<P: Into<Rad<f64>>>(&mut self, delta: P) {
        self.yaw += delta.into();
    }

    pub fn pitch(&self) -> Rad<f64> {
        self.pitch
    }

    pub fn tilt<P: Into<Rad<f64>>>(&mut self, delta: P) {
        let new_pitch = self.pitch + delta.into();

        if new_pitch <= MAX_PITCH && new_pitch >= MIN_PITCH {
            self.pitch = new_pitch;
        }
    }

    pub fn move_relative(&mut self, delta: Vector3<f64>) {
        self.position += delta;
    }

    pub fn move_to(&mut self, new_position: Point3<f64>) {
        self.position = new_position;
    }

    pub fn position_vector(&self) -> Vector3<f64> {
        self.position.to_vec()
    }

    pub fn homogenous_position(&self) -> Vector4<f64> {
        self.position.to_homogeneous()
    }
}

pub struct Perspective {
    fovy: Rad<f64>,
    znear: f64,
    zfar: f64,

    current_projection: Matrix4<f64>,
}

impl Perspective {
    pub fn new<F: Into<Rad<f64>>>(width: u32, height: u32, fovy: F, znear: f64, zfar: f64) -> Self {
        let rad = fovy.into();
        Self {
            current_projection: Self::calc_matrix(width as f64 / height as f64, rad, znear, zfar),
            fovy: rad,
            znear,
            zfar,
        }
    }

    pub fn resize(&mut self, width: u32, height: u32) {
        self.current_projection = Self::calc_matrix(
            width as f64 / height as f64,
            self.fovy,
            self.znear,
            self.zfar,
        );
    }

    fn calc_matrix(aspect: f64, fovy: Rad<f64>, znear: f64, zfar: f64) -> Matrix4<f64> {
        OPENGL_TO_WGPU_MATRIX * cgmath::perspective(fovy, aspect, znear, zfar)
    }
}

#[cfg(test)]
mod tests {
    use cgmath::{AbsDiffEq, Vector2, Vector3, Vector4};

    use super::{Camera, Perspective};
    use crate::render::camera::{InvertedViewProjection, ViewProjection};

    #[test]
    fn test() {
        let width = 1920.0;
        let height = 1080.0;
        let camera = Camera::new(
            (0.0, 5.0, 5000.0),
            cgmath::Deg(-90.0),
            cgmath::Deg(45.0),
            width as u32,
            height as u32,
        );
        // 4732.561319582916
        let perspective = Perspective::new(
            width as u32,
            height as u32,
            cgmath::Deg(45.0),
            0.1,
            100000.0,
        );
        let view_proj: ViewProjection = camera.calc_view_proj(&perspective);
        let inverted_view_proj: InvertedViewProjection = view_proj.invert();

        let world_pos: Vector4<f64> = Vector4::new(0.0, 0.0, 0.0, 1.0);
        let clip = view_proj.project(world_pos);

        let origin_clip_space = view_proj.project(Vector4::new(0.0, 0.0, 0.0, 1.0));
        println!("origin w in clip space: {:?}", origin_clip_space.w);

        println!("world_pos: {world_pos:?}");
        println!("clip: {clip:?}");
        println!("world_pos: {:?}", view_proj.invert().project(clip));

        println!("window: {:?}", camera.clip_to_window_vulkan(&clip));
        let window = camera.clip_to_window(&clip);
        println!("window (matrix): {window:?}");

        // --------- nalgebra

        println!(
            "r world (nalgebra): {:?}",
            Camera::window_to_world_nalgebra(
                &window.truncate(),
                &inverted_view_proj,
                width,
                height
            )
        );

        // -------- far vs. near plane trick

        let near_world = Camera::window_to_world_nalgebra(
            &Vector3::new(window.x, window.y, 0.0),
            &inverted_view_proj,
            width,
            height,
        );

        let far_world = Camera::window_to_world_nalgebra(
            &Vector3::new(window.x, window.y, 1.0),
            &inverted_view_proj,
            width,
            height,
        );

        // for z = 0 in world coordinates
        let u = -near_world.z / (far_world.z - near_world.z);
        println!("u: {u:?}");
        let unprojected = near_world + u * (far_world - near_world);
        println!("unprojected: {unprojected:?}");
        assert!(Vector3::new(world_pos.x, world_pos.y, world_pos.z).abs_diff_eq(&unprojected, 0.05));

        // ---- test for unproject

        let window = Vector2::new(960.0, 631.0); // 0, 4096: passt nicht
                                                 //let window = Vector2::new(962.0, 1.0); // 0, 300: passt nicht
                                                 //let window = Vector2::new(960.0, 540.0); // 0, 0 passt
        let near_world =
            camera.window_to_world(&Vector3::new(window.x, window.y, 0.0), &inverted_view_proj);

        let far_world =
            camera.window_to_world(&Vector3::new(window.x, window.y, 1.0), &inverted_view_proj);

        // for z = 0 in world coordinates
        let u = -near_world.z / (far_world.z - near_world.z);
        println!("u: {u:?}");
        let unprojected = near_world + u * (far_world - near_world);
        println!("unprojected: {unprojected:?}");
        // ----

        //assert!(reverse_world.abs_diff_eq(&world_pos, 0.05))
    }
}