use std::ops::Range;
use std::path::Path;

use crate::texture;

pub trait Vertex {
    fn desc<'a>() -> wgpu::VertexBufferDescriptor<'a>;
}

#[repr(C)]
#[derive(Copy, Clone, Debug)]
pub struct ModelVertex {
    position: cgmath::Vector3<f32>,
    tex_coords: cgmath::Vector2<f32>,
    normal: cgmath::Vector3<f32>,
    tangent: cgmath::Vector3<f32>,
    bitangent: cgmath::Vector3<f32>,
}

unsafe impl bytemuck::Zeroable for ModelVertex {}
unsafe impl bytemuck::Pod for ModelVertex {}

impl Vertex for ModelVertex {
    fn desc<'a>() -> wgpu::VertexBufferDescriptor<'a> {
        use std::mem;
        wgpu::VertexBufferDescriptor {
            stride: mem::size_of::<ModelVertex>() as wgpu::BufferAddress,
            step_mode: wgpu::InputStepMode::Vertex,
            attributes: &[
                wgpu::VertexAttributeDescriptor {
                    offset: 0,
                    shader_location: 0,
                    format: wgpu::VertexFormat::Float3,
                },
                wgpu::VertexAttributeDescriptor {
                    offset: mem::size_of::<[f32; 3]>() as wgpu::BufferAddress,
                    shader_location: 1,
                    format: wgpu::VertexFormat::Float2,
                },
                wgpu::VertexAttributeDescriptor {
                    offset: mem::size_of::<[f32; 5]>() as wgpu::BufferAddress,
                    shader_location: 2,
                    format: wgpu::VertexFormat::Float3,
                },
                // Tangent and bitangent
                wgpu::VertexAttributeDescriptor {
                    offset: mem::size_of::<[f32; 8]>() as wgpu::BufferAddress,
                    shader_location: 3,
                    format: wgpu::VertexFormat::Float3,
                },
                wgpu::VertexAttributeDescriptor {
                    offset: mem::size_of::<[f32; 11]>() as wgpu::BufferAddress,
                    shader_location: 4,
                    format: wgpu::VertexFormat::Float3,
                },
            ],
        }
    }
}

pub struct Material {
    pub name: String,
    pub diffuse_texture: texture::Texture,
    pub normal_texture: texture::Texture,
    pub bind_group: wgpu::BindGroup,
}

impl Material {
    pub fn new(
        device: &wgpu::Device,
        name: &str,
        diffuse_texture: texture::Texture,
        normal_texture: texture::Texture,
        layout: &wgpu::BindGroupLayout,
    ) -> Self {
        let bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
            layout,
            bindings: &[
                wgpu::Binding {
                    binding: 0,
                    resource: wgpu::BindingResource::TextureView(&diffuse_texture.view),
                },
                wgpu::Binding {
                    binding: 1,
                    resource: wgpu::BindingResource::Sampler(&diffuse_texture.sampler),
                },
                wgpu::Binding {
                    binding: 2,
                    resource: wgpu::BindingResource::TextureView(&normal_texture.view),
                },
                wgpu::Binding {
                    binding: 3,
                    resource: wgpu::BindingResource::Sampler(&normal_texture.sampler),
                },
            ],
            label: Some(name),
        });

        Self {
            name: String::from(name),
            diffuse_texture,
            normal_texture,
            bind_group,
        }
    }
}

pub struct Mesh {
    pub name: String,
    pub vertex_buffer: wgpu::Buffer,
    pub index_buffer: wgpu::Buffer,
    pub num_elements: u32,
    pub material: usize,
}

pub struct Model {
    pub meshes: Vec<Mesh>,
    pub materials: Vec<Material>,
}

impl Model {
    pub fn load<P: AsRef<Path>>(
        device: &wgpu::Device,
        layout: &wgpu::BindGroupLayout,
        path: P,
    ) -> Result<(Self, Vec<wgpu::CommandBuffer>), failure::Error> {
        let (obj_models, obj_materials) = tobj::load_obj(path.as_ref())?;

        // We're assuming that the texture files are stored with the obj file
        let containing_folder = path.as_ref().parent().unwrap();

        // Our `Texure` struct currently returns a `CommandBuffer` when it's created so we need to collect those and return them.
        let mut command_buffers = Vec::new();

        let mut materials = Vec::new();
        for mat in obj_materials {
            let diffuse_path = mat.diffuse_texture;
            let (diffuse_texture, cmds) =
                texture::Texture::load(device, containing_folder.join(diffuse_path), false)?;
            command_buffers.push(cmds);

            let normal_path = match mat.unknown_param.get("map_Bump") {
                Some(v) => Ok(v),
                None => Err(failure::err_msg("Unable to find normal map")),
            };
            let (normal_texture, cmds) =
                texture::Texture::load(device, containing_folder.join(normal_path?), true)?;
            command_buffers.push(cmds);

            materials.push(Material::new(
                device,
                &mat.name,
                diffuse_texture,
                normal_texture,
                layout,
            ));
        }

        let mut meshes = Vec::new();
        for m in obj_models {
            let mut vertices = Vec::new();
            for i in 0..m.mesh.positions.len() / 3 {
                vertices.push(ModelVertex {
                    position: [
                        m.mesh.positions[i * 3],
                        m.mesh.positions[i * 3 + 1],
                        m.mesh.positions[i * 3 + 2],
                    ]
                    .into(),
                    tex_coords: [m.mesh.texcoords[i * 2], m.mesh.texcoords[i * 2 + 1]].into(),
                    normal: [
                        m.mesh.normals[i * 3],
                        m.mesh.normals[i * 3 + 1],
                        m.mesh.normals[i * 3 + 2],
                    ]
                    .into(),
                    // We'll calculate these later
                    tangent: [0.0; 3].into(),
                    bitangent: [0.0; 3].into(),
                });
            }

            let indices = &m.mesh.indices;

            // Calculate tangents and bitangets. We're going to
            // use the triangles, so we need to loop through the
            // indices in chunks of 3
            for c in indices.chunks(3) {
                let v0 = vertices[c[0] as usize];
                let v1 = vertices[c[1] as usize];
                let v2 = vertices[c[2] as usize];

                let pos0 = v0.position;
                let pos1 = v1.position;
                let pos2 = v2.position;

                let uv0 = v0.tex_coords;
                let uv1 = v1.tex_coords;
                let uv2 = v2.tex_coords;

                // Calculate the edges of the triangle
                let delta_pos1 = pos1 - pos0;
                let delta_pos2 = pos2 - pos0;

                // This will give us a direction to calculate the
                // tangent and bitangent
                let delta_uv1 = uv1 - uv0;
                let delta_uv2 = uv2 - uv0;

                // Solving the following system of equations will
                // give us the tangent and bitangent.
                //     delta_pos1 = delta_uv1.x * T + delta_u.y * B
                //     delta_pos2 = delta_uv2.x * T + delta_uv2.y * B
                // Luckily, the place I found this equation provided
                // the solution!
                let r = 1.0 / (delta_uv1.x * delta_uv2.y - delta_uv1.y * delta_uv2.x);
                let tangent = (delta_pos1 * delta_uv2.y - delta_pos2 * delta_uv1.y) * r;
                let bitangent = (delta_pos2 * delta_uv1.x - delta_pos1 * delta_uv2.x) * r;

                // We'll use the same tangent/bitangent for each vertex in the triangle
                vertices[c[0] as usize].tangent = tangent;
                vertices[c[1] as usize].tangent = tangent;
                vertices[c[2] as usize].tangent = tangent;

                vertices[c[0] as usize].bitangent = bitangent;
                vertices[c[1] as usize].bitangent = bitangent;
                vertices[c[2] as usize].bitangent = bitangent;
            }

            let vertex_buffer = device.create_buffer_with_data(
                bytemuck::cast_slice(&vertices),
                wgpu::BufferUsage::VERTEX,
            );

            let index_buffer = device
                .create_buffer_with_data(bytemuck::cast_slice(indices), wgpu::BufferUsage::INDEX);

            meshes.push(Mesh {
                name: m.name,
                vertex_buffer,
                index_buffer,
                num_elements: m.mesh.indices.len() as u32,
                material: m.mesh.material_id.unwrap_or(0),
            });
        }

        Ok((Self { meshes, materials }, command_buffers))
    }
}

pub trait DrawModel<'a, 'b>
where
    'b: 'a,
{
    fn draw_mesh(
        &mut self,
        mesh: &'b Mesh,
        material: &'b Material,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );
    fn draw_mesh_instanced(
        &mut self,
        mesh: &'b Mesh,
        material: &'b Material,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );

    fn draw_model(
        &mut self,
        model: &'b Model,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );
    fn draw_model_instanced(
        &mut self,
        model: &'b Model,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );
    fn draw_model_instanced_with_material(
        &mut self,
        model: &'b Model,
        material: &'b Material,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );
}

impl<'a, 'b> DrawModel<'a, 'b> for wgpu::RenderPass<'a>
where
    'b: 'a,
{
    fn draw_mesh(
        &mut self,
        mesh: &'b Mesh,
        material: &'b Material,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.draw_mesh_instanced(mesh, material, 0..1, uniforms, light);
    }

    fn draw_mesh_instanced(
        &mut self,
        mesh: &'b Mesh,
        material: &'b Material,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.set_vertex_buffer(0, &mesh.vertex_buffer, 0, 0);
        self.set_index_buffer(&mesh.index_buffer, 0, 0);
        self.set_bind_group(0, &material.bind_group, &[]);
        self.set_bind_group(1, &uniforms, &[]);
        self.set_bind_group(2, &light, &[]);
        self.draw_indexed(0..mesh.num_elements, 0, instances);
    }

    fn draw_model(
        &mut self,
        model: &'b Model,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.draw_model_instanced(model, 0..1, uniforms, light);
    }

    fn draw_model_instanced(
        &mut self,
        model: &'b Model,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        for mesh in &model.meshes {
            let material = &model.materials[mesh.material];
            self.draw_mesh_instanced(mesh, material, instances.clone(), uniforms, light);
        }
    }

    fn draw_model_instanced_with_material(
        &mut self,
        model: &'b Model,
        material: &'b Material,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        for mesh in &model.meshes {
            self.draw_mesh_instanced(mesh, material, instances.clone(), uniforms, light);
        }
    }
}

pub trait DrawLight<'a, 'b>
where
    'b: 'a,
{
    fn draw_light_mesh(
        &mut self,
        mesh: &'b Mesh,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );
    fn draw_light_mesh_instanced(
        &mut self,
        mesh: &'b Mesh,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) where
        'b: 'a;

    fn draw_light_model(
        &mut self,
        model: &'b Model,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );
    fn draw_light_model_instanced(
        &mut self,
        model: &'b Model,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    );
}

impl<'a, 'b> DrawLight<'a, 'b> for wgpu::RenderPass<'a>
where
    'b: 'a,
{
    fn draw_light_mesh(
        &mut self,
        mesh: &'b Mesh,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.draw_light_mesh_instanced(mesh, 0..1, uniforms, light);
    }

    fn draw_light_mesh_instanced(
        &mut self,
        mesh: &'b Mesh,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.set_vertex_buffer(0, &mesh.vertex_buffer, 0, 0);
        self.set_index_buffer(&mesh.index_buffer, 0, 0);
        self.set_bind_group(0, uniforms, &[]);
        self.set_bind_group(1, light, &[]);
        self.draw_indexed(0..mesh.num_elements, 0, instances);
    }

    fn draw_light_model(
        &mut self,
        model: &'b Model,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.draw_light_model_instanced(model, 0..1, uniforms, light);
    }
    fn draw_light_model_instanced(
        &mut self,
        model: &'b Model,
        instances: Range<u32>,
        uniforms: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        for mesh in &model.meshes {
            self.draw_light_mesh_instanced(mesh, instances.clone(), uniforms, light);
        }
    }
}