use anyhow::*;
use cgmath::InnerSpace;
use std::ops::Range;
use std::path::Path;
use tobj::LoadOptions;
use wgpu::util::DeviceExt;

use crate::texture;

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

#[repr(C)]
#[derive(Copy, Clone, Debug, bytemuck::Pod, bytemuck::Zeroable)]
pub struct ModelVertex {
    position: [f32; 3],
    tex_coords: [f32; 2],
    normal: [f32; 3],
    tangent: [f32; 3],
    bitangent: [f32; 3],
}

impl Vertex for ModelVertex {
    fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
        use std::mem;
        wgpu::VertexBufferLayout {
            array_stride: mem::size_of::<ModelVertex>() as wgpu::BufferAddress,
            step_mode: wgpu::InputStepMode::Vertex,
            attributes: &[
                wgpu::VertexAttribute {
                    offset: 0,
                    shader_location: 0,
                    format: wgpu::VertexFormat::Float32x3,
                },
                wgpu::VertexAttribute {
                    offset: mem::size_of::<[f32; 3]>() as wgpu::BufferAddress,
                    shader_location: 1,
                    format: wgpu::VertexFormat::Float32x2,
                },
                wgpu::VertexAttribute {
                    offset: mem::size_of::<[f32; 5]>() as wgpu::BufferAddress,
                    shader_location: 2,
                    format: wgpu::VertexFormat::Float32x3,
                },
                // Tangent and bitangent
                wgpu::VertexAttribute {
                    offset: mem::size_of::<[f32; 8]>() as wgpu::BufferAddress,
                    shader_location: 3,
                    format: wgpu::VertexFormat::Float32x3,
                },
                wgpu::VertexAttribute {
                    offset: mem::size_of::<[f32; 11]>() as wgpu::BufferAddress,
                    shader_location: 4,
                    format: wgpu::VertexFormat::Float32x3,
                },
            ],
        }
    }
}

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,
            entries: &[
                wgpu::BindGroupEntry {
                    binding: 0,
                    resource: wgpu::BindingResource::TextureView(&diffuse_texture.view),
                },
                wgpu::BindGroupEntry {
                    binding: 1,
                    resource: wgpu::BindingResource::Sampler(&diffuse_texture.sampler),
                },
                wgpu::BindGroupEntry {
                    binding: 2,
                    resource: wgpu::BindingResource::TextureView(&normal_texture.view),
                },
                wgpu::BindGroupEntry {
                    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,
        queue: &wgpu::Queue,
        layout: &wgpu::BindGroupLayout,
        path: P,
    ) -> Result<Self> {
        let (obj_models, obj_materials) = tobj::load_obj(
            path.as_ref(),
            &LoadOptions {
                triangulate: true,
                single_index: true,
                ..Default::default()
            },
        )?;

        let obj_materials = obj_materials?;

        // We're assuming that the texture files are stored with the obj file
        let containing_folder = path.as_ref().parent().context("Directory has no parent")?;

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

            let normal_path = mat.normal_texture;
            let normal_texture =
                texture::Texture::load(device, queue, containing_folder.join(normal_path), true)?;

            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;
            let mut triangles_included = (0..vertices.len()).collect::<Vec<_>>();

            // 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: cgmath::Vector3<_> = v0.position.into();
                let pos1: cgmath::Vector3<_> = v1.position.into();
                let pos2: cgmath::Vector3<_> = v2.position.into();

                let uv0: cgmath::Vector2<_> = v0.tex_coords.into();
                let uv1: cgmath::Vector2<_> = v1.tex_coords.into();
                let uv2: cgmath::Vector2<_> = v2.tex_coords.into();

                // 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 + cgmath::Vector3::from(vertices[c[0] as usize].tangent)).into();
                vertices[c[1] as usize].tangent =
                    (tangent + cgmath::Vector3::from(vertices[c[1] as usize].tangent)).into();
                vertices[c[2] as usize].tangent =
                    (tangent + cgmath::Vector3::from(vertices[c[2] as usize].tangent)).into();
                vertices[c[0] as usize].bitangent =
                    (bitangent + cgmath::Vector3::from(vertices[c[0] as usize].bitangent)).into();
                vertices[c[1] as usize].bitangent =
                    (bitangent + cgmath::Vector3::from(vertices[c[1] as usize].bitangent)).into();
                vertices[c[2] as usize].bitangent =
                    (bitangent + cgmath::Vector3::from(vertices[c[2] as usize].bitangent)).into();

                // Used to average the tangents/bitangents
                triangles_included[c[0] as usize] += 1;
                triangles_included[c[1] as usize] += 1;
                triangles_included[c[2] as usize] += 1;
            }

            // Average the tangents/bitangents
            for (i, n) in triangles_included.into_iter().enumerate() {
                let denom = 1.0 / n as f32;
                let mut v = &mut vertices[i];
                v.tangent = (cgmath::Vector3::from(v.tangent) * denom)
                    .normalize()
                    .into();
                v.bitangent = (cgmath::Vector3::from(v.bitangent) * denom)
                    .normalize()
                    .into();
            }

            let vertex_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
                label: Some(&format!("{:?} Vertex Buffer", path.as_ref())),
                contents: bytemuck::cast_slice(&vertices),
                usage: wgpu::BufferUsage::VERTEX,
            });
            let index_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
                label: Some(&format!("{:?} Index Buffer", path.as_ref())),
                contents: bytemuck::cast_slice(&m.mesh.indices),
                usage: 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 })
    }
}

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

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

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

    fn draw_mesh_instanced(
        &mut self,
        mesh: &'b Mesh,
        material: &'b Material,
        instances: Range<u32>,
        camera: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.set_vertex_buffer(0, mesh.vertex_buffer.slice(..));
        self.set_index_buffer(mesh.index_buffer.slice(..), wgpu::IndexFormat::Uint32);
        self.set_bind_group(0, &material.bind_group, &[]);
        self.set_bind_group(1, camera, &[]);
        self.set_bind_group(2, light, &[]);
        self.draw_indexed(0..mesh.num_elements, 0, instances);
    }

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

    fn draw_model_instanced(
        &mut self,
        model: &'b Model,
        instances: Range<u32>,
        camera: &'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(), camera, light);
        }
    }

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

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

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

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

    fn draw_light_mesh_instanced(
        &mut self,
        mesh: &'b Mesh,
        instances: Range<u32>,
        camera: &'b wgpu::BindGroup,
        light: &'b wgpu::BindGroup,
    ) {
        self.set_vertex_buffer(0, mesh.vertex_buffer.slice(..));
        self.set_index_buffer(mesh.index_buffer.slice(..), wgpu::IndexFormat::Uint32);
        self.set_bind_group(0, camera, &[]);
        self.set_bind_group(1, light, &[]);
        self.draw_indexed(0..mesh.num_elements, 0, instances);
    }

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