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use crate::math::*;
use crate::definition::*;
use crate::core::*;
use crate::camera::*;

///
/// A light which shines from the given position and in the given direction.
/// The light will cast shadows if you [generate a shadow map](SpotLight::generate_shadow_map).
///
pub struct SpotLight {
    context: Context,
    light_buffer: UniformBuffer,
    shadow_texture: DepthTargetTexture2D,
    shadow_camera: Option<Camera>
}

impl SpotLight {

    pub fn new(context: &Context, intensity: f32, color: &Vec3, position: &Vec3, direction: &Vec3, cutoff: f32,
               attenuation_constant: f32, attenuation_linear: f32, attenuation_exponential: f32) -> Result<SpotLight, Error>
    {
        let uniform_sizes = [3u32, 1, 1, 1, 1, 1, 3, 1, 3, 1, 16];
        let mut light = SpotLight {
            context: context.clone(),
            light_buffer: UniformBuffer::new(context, &uniform_sizes)?,
            shadow_texture: DepthTargetTexture2D::new(context, 1, 1, Wrapping::ClampToEdge, Wrapping::ClampToEdge, DepthFormat::Depth32F)?,
            shadow_camera: None
        };
        light.set_intensity(intensity);
        light.set_color(color);
        light.set_cutoff(cutoff);
        light.set_direction(direction);
        light.set_position(position);
        light.set_attenuation(attenuation_constant, attenuation_linear, attenuation_exponential);
        Ok(light)
    }

    pub fn set_color(&mut self, color: &Vec3)
    {
        self.light_buffer.update(0, &color.to_slice()).unwrap();
    }

    pub fn set_intensity(&mut self, intensity: f32)
    {
        self.light_buffer.update(1, &[intensity]).unwrap();
    }

    pub fn set_attenuation(&mut self, constant: f32, linear: f32, exponential: f32)
    {
        self.light_buffer.update(2, &[constant]).unwrap();
        self.light_buffer.update(3, &[linear]).unwrap();
        self.light_buffer.update(4, &[exponential]).unwrap();
    }

    pub fn set_position(&mut self, position: &Vec3)
    {
        self.light_buffer.update(6, &position.to_slice()).unwrap();
    }

    pub fn position(&self) -> Vec3
    {
        let p = self.light_buffer.get(6).unwrap();
        vec3(p[0], p[1], p[2])
    }

    pub fn set_cutoff(&mut self, cutoff: f32)
    {
        self.light_buffer.update(7, &[cutoff]).unwrap();
    }

    pub fn set_direction(&mut self, direction: &Vec3)
    {
        self.light_buffer.update(8, &direction.normalize().to_slice()).unwrap();
    }

    pub fn direction(&self) -> Vec3
    {
        let d = self.light_buffer.get(8).unwrap();
        vec3(d[0], d[1], d[2])
    }

    pub fn clear_shadow_map(&mut self)
    {
        self.shadow_camera = None;
        self.shadow_texture = DepthTargetTexture2D::new(&self.context, 1, 1, Wrapping::ClampToEdge, Wrapping::ClampToEdge, DepthFormat::Depth32F).unwrap();
        self.light_buffer.update(9, &[0.0]).unwrap();
    }

    pub fn generate_shadow_map<F: FnOnce(Viewport, &Camera) -> Result<(), Error>>(&mut self, frustrum_depth: f32, texture_size: usize, render_scene: F) -> Result<(), Error>
    {
        let position = self.position();
        let direction = self.direction();
        let up = compute_up_direction(direction);
        let cutoff = self.light_buffer.get(7).unwrap()[0];

        self.shadow_camera = Some(Camera::new_perspective(&self.context, position, position + direction, up,
                                                          degrees(cutoff), 1.0, 0.1, frustrum_depth)?);
        self.light_buffer.update(10, &shadow_matrix(self.shadow_camera.as_ref().unwrap()).to_slice())?;

        self.shadow_texture = DepthTargetTexture2D::new(&self.context, texture_size, texture_size,Wrapping::ClampToEdge, Wrapping::ClampToEdge, DepthFormat::Depth32F)?;
        RenderTarget::new_depth(&self.context, &self.shadow_texture)?.write( &ClearState::depth(1.0), || {
                render_scene(Viewport::new_at_origo(texture_size, texture_size), self.shadow_camera.as_ref().unwrap())?;
                Ok(())
            })?;
        self.light_buffer.update(9, &[1.0])?;
        Ok(())
    }

    pub fn shadow_map(&self) -> &dyn Texture
    {
        &self.shadow_texture
    }

    pub fn buffer(&self) -> &UniformBuffer
    {
        &self.light_buffer
    }
}

fn shadow_matrix(camera: &Camera) -> Mat4
{
    let bias_matrix = crate::Mat4::new(
                         0.5, 0.0, 0.0, 0.0,
                         0.0, 0.5, 0.0, 0.0,
                         0.0, 0.0, 0.5, 0.0,
                         0.5, 0.5, 0.5, 1.0);
    bias_matrix * camera.projection() * camera.view()
}

fn compute_up_direction(direction: Vec3) -> Vec3
{
    if vec3(1.0, 0.0, 0.0).dot(direction).abs() > 0.9
    {
        (vec3(0.0, 1.0, 0.0).cross(direction)).normalize()
    }
    else {
        (vec3(1.0, 0.0, 0.0).cross(direction)).normalize()
    }
}