use bytemuck::{Pod, Zeroable};
use imgui::*;
use imgui_wgpu::{Renderer, RendererConfig, Texture, TextureConfig};
use pollster::block_on;
use std::time::Instant;
use wgpu::{include_wgsl, util::DeviceExt, Extent3d};
use winit::{
    dpi::LogicalSize,
    event::{ElementState, Event, KeyboardInput, VirtualKeyCode, WindowEvent},
    event_loop::{ControlFlow, EventLoop},
    window::Window,
};

const OPENGL_TO_WGPU_MATRIX: cgmath::Matrix4<f32> = cgmath::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,
);

// Example code modified from https://github.com/gfx-rs/wgpu-rs/tree/master/examples/cube
#[repr(C)]
#[derive(Clone, Copy, Pod, Zeroable)]
struct Vertex {
    _pos: [f32; 4],
    _tex_coord: [f32; 2],
}

fn vertex(pos: [i8; 3], tc: [i8; 2]) -> Vertex {
    Vertex {
        _pos: [pos[0] as f32, pos[1] as f32, pos[2] as f32, 1.0],
        _tex_coord: [tc[0] as f32, tc[1] as f32],
    }
}

fn create_vertices() -> (Vec<Vertex>, Vec<u16>) {
    let vertex_data = [
        // top (0, 0, 1)
        vertex([-1, -1, 1], [0, 0]),
        vertex([1, -1, 1], [1, 0]),
        vertex([1, 1, 1], [1, 1]),
        vertex([-1, 1, 1], [0, 1]),
        // bottom (0, 0, -1)
        vertex([-1, 1, -1], [1, 0]),
        vertex([1, 1, -1], [0, 0]),
        vertex([1, -1, -1], [0, 1]),
        vertex([-1, -1, -1], [1, 1]),
        // right (1, 0, 0)
        vertex([1, -1, -1], [0, 0]),
        vertex([1, 1, -1], [1, 0]),
        vertex([1, 1, 1], [1, 1]),
        vertex([1, -1, 1], [0, 1]),
        // left (-1, 0, 0)
        vertex([-1, -1, 1], [1, 0]),
        vertex([-1, 1, 1], [0, 0]),
        vertex([-1, 1, -1], [0, 1]),
        vertex([-1, -1, -1], [1, 1]),
        // front (0, 1, 0)
        vertex([1, 1, -1], [1, 0]),
        vertex([-1, 1, -1], [0, 0]),
        vertex([-1, 1, 1], [0, 1]),
        vertex([1, 1, 1], [1, 1]),
        // back (0, -1, 0)
        vertex([1, -1, 1], [0, 0]),
        vertex([-1, -1, 1], [1, 0]),
        vertex([-1, -1, -1], [1, 1]),
        vertex([1, -1, -1], [0, 1]),
    ];

    let index_data: &[u16] = &[
        0, 1, 2, 2, 3, 0, // top
        4, 5, 6, 6, 7, 4, // bottom
        8, 9, 10, 10, 11, 8, // right
        12, 13, 14, 14, 15, 12, // left
        16, 17, 18, 18, 19, 16, // front
        20, 21, 22, 22, 23, 20, // back
    ];

    (vertex_data.to_vec(), index_data.to_vec())
}

fn create_texels(size: usize) -> Vec<u8> {
    (0..size * size)
        .map(|id| {
            // get high five for recognizing this ;)
            let cx = 3.0 * (id % size) as f32 / (size - 1) as f32 - 2.0;
            let cy = 2.0 * (id / size) as f32 / (size - 1) as f32 - 1.0;
            let (mut x, mut y, mut count) = (cx, cy, 0);
            while count < 0xFF && x * x + y * y < 4.0 {
                let old_x = x;
                x = x * x - y * y + cx;
                y = 2.0 * old_x * y + cy;
                count += 1;
            }
            count
        })
        .collect()
}

struct Example {
    vertex_buf: wgpu::Buffer,
    index_buf: wgpu::Buffer,
    index_count: usize,
    bind_group: wgpu::BindGroup,
    uniform_buf: wgpu::Buffer,
    pipeline: wgpu::RenderPipeline,
    time: f32,
}

impl Example {
    fn generate_matrix(aspect_ratio: f32) -> cgmath::Matrix4<f32> {
        let mx_projection = cgmath::perspective(cgmath::Deg(45f32), aspect_ratio, 1.0, 10.0);
        let mx_view = cgmath::Matrix4::look_at_rh(
            cgmath::Point3::new(1.5f32, -5.0, 3.0),
            cgmath::Point3::new(0f32, 0.0, 0.0),
            cgmath::Vector3::unit_z(),
        );
        let mx_correction = OPENGL_TO_WGPU_MATRIX;
        mx_correction * mx_projection * mx_view
    }
}

impl Example {
    fn init(
        config: &wgpu::SurfaceConfiguration,
        device: &wgpu::Device,
        queue: &wgpu::Queue,
    ) -> Self {
        use std::mem;

        // Create the vertex and index buffers
        let vertex_size = mem::size_of::<Vertex>();
        let (vertex_data, index_data) = create_vertices();

        let vertex_buf = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Vertex Buffer"),
            contents: bytemuck::cast_slice(&vertex_data),
            usage: wgpu::BufferUsages::VERTEX,
        });

        let index_buf = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Index Buffer"),
            contents: bytemuck::cast_slice(&index_data),
            usage: wgpu::BufferUsages::INDEX,
        });

        // Create pipeline layout
        let bind_group_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
            label: None,
            entries: &[
                wgpu::BindGroupLayoutEntry {
                    binding: 0,
                    visibility: wgpu::ShaderStages::VERTEX,
                    ty: wgpu::BindingType::Buffer {
                        ty: wgpu::BufferBindingType::Uniform,
                        has_dynamic_offset: false,
                        min_binding_size: wgpu::BufferSize::new(64),
                    },
                    count: None,
                },
                wgpu::BindGroupLayoutEntry {
                    binding: 1,
                    visibility: wgpu::ShaderStages::FRAGMENT,
                    ty: wgpu::BindingType::Texture {
                        multisampled: false,
                        sample_type: wgpu::TextureSampleType::Uint,
                        view_dimension: wgpu::TextureViewDimension::D2,
                    },
                    count: None,
                },
            ],
        });
        let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
            label: None,
            bind_group_layouts: &[&bind_group_layout],
            push_constant_ranges: &[],
        });

        // Create the texture
        let size = 256u32;
        let texels = create_texels(size as usize);
        let texture_extent = wgpu::Extent3d {
            width: size,
            height: size,
            depth_or_array_layers: 1,
        };
        let texture = device.create_texture(&wgpu::TextureDescriptor {
            label: None,
            size: texture_extent,
            mip_level_count: 1,
            sample_count: 1,
            dimension: wgpu::TextureDimension::D2,
            format: wgpu::TextureFormat::R8Uint,
            usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
            view_formats: &[wgpu::TextureFormat::R8Uint],
        });
        let texture_view = texture.create_view(&wgpu::TextureViewDescriptor::default());
        queue.write_texture(
            texture.as_image_copy(),
            &texels,
            wgpu::ImageDataLayout {
                offset: 0,
                bytes_per_row: Some(size),
                rows_per_image: None,
            },
            texture_extent,
        );

        // Create other resources
        let mx_total = Self::generate_matrix(config.width as f32 / config.height as f32);
        let mx_ref: &[f32; 16] = mx_total.as_ref();
        let uniform_buf = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Uniform Buffer"),
            contents: bytemuck::cast_slice(mx_ref),
            usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
        });

        // Create bind group
        let bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
            layout: &bind_group_layout,
            entries: &[
                wgpu::BindGroupEntry {
                    binding: 0,
                    resource: uniform_buf.as_entire_binding(),
                },
                wgpu::BindGroupEntry {
                    binding: 1,
                    resource: wgpu::BindingResource::TextureView(&texture_view),
                },
            ],
            label: None,
        });

        let shader = device.create_shader_module(include_wgsl!("../resources/cube.wgsl"));

        let vertex_buffers = [wgpu::VertexBufferLayout {
            array_stride: vertex_size as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: &[
                wgpu::VertexAttribute {
                    format: wgpu::VertexFormat::Float32x4,
                    offset: 0,
                    shader_location: 0,
                },
                wgpu::VertexAttribute {
                    format: wgpu::VertexFormat::Float32x2,
                    offset: 4 * 4,
                    shader_location: 1,
                },
            ],
        }];

        let pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
            label: None,
            layout: Some(&pipeline_layout),
            vertex: wgpu::VertexState {
                module: &shader,
                entry_point: "vs_main",
                buffers: &vertex_buffers,
            },
            fragment: Some(wgpu::FragmentState {
                module: &shader,
                entry_point: "fs_main",
                targets: &[Some(config.format.into())],
            }),
            primitive: wgpu::PrimitiveState {
                cull_mode: Some(wgpu::Face::Back),
                ..Default::default()
            },
            depth_stencil: None,
            multisample: wgpu::MultisampleState::default(),
            multiview: None,
        });

        // Done
        Example {
            vertex_buf,
            index_buf,
            index_count: index_data.len(),
            bind_group,
            uniform_buf,
            pipeline,
            time: 0.0,
        }
    }

    fn update(&mut self, delta_time: f32) {
        self.time += delta_time;
    }

    fn setup_camera(&mut self, queue: &wgpu::Queue, size: [f32; 2]) {
        let mx_total = Self::generate_matrix(size[0] / size[1]);
        let mx_ref: &[f32; 16] = mx_total.as_ref();
        queue.write_buffer(&self.uniform_buf, 0, bytemuck::cast_slice(mx_ref));
    }

    fn render(&mut self, view: &wgpu::TextureView, device: &wgpu::Device, queue: &wgpu::Queue) {
        let mut encoder =
            device.create_command_encoder(&wgpu::CommandEncoderDescriptor { label: None });
        {
            let mut rpass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                label: None,
                color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                    view,
                    resolve_target: None,
                    ops: wgpu::Operations {
                        load: wgpu::LoadOp::Clear(wgpu::Color {
                            r: 0.1,
                            g: 0.2,
                            b: 0.3,
                            a: 1.0,
                        }),
                        store: true,
                    },
                })],
                depth_stencil_attachment: None,
            });
            rpass.push_debug_group("Prepare data for draw.");
            rpass.set_pipeline(&self.pipeline);
            rpass.set_bind_group(0, &self.bind_group, &[]);
            rpass.set_index_buffer(self.index_buf.slice(..), wgpu::IndexFormat::Uint16);
            rpass.set_vertex_buffer(0, self.vertex_buf.slice(..));
            rpass.pop_debug_group();
            rpass.insert_debug_marker("Draw!");
            rpass.draw_indexed(0..self.index_count as u32, 0, 0..1);
        }

        queue.submit(Some(encoder.finish()));
    }
}

fn main() {
    env_logger::init();

    // Set up window and GPU
    let event_loop = EventLoop::new();

    let instance = wgpu::Instance::new(wgpu::InstanceDescriptor {
        backends: wgpu::Backends::PRIMARY,
        ..Default::default()
    });

    let (window, size, surface) = {
        let version = env!("CARGO_PKG_VERSION");

        let window = Window::new(&event_loop).unwrap();
        window.set_inner_size(LogicalSize {
            width: 1280.0,
            height: 720.0,
        });
        window.set_title(&format!("imgui-wgpu {version}"));
        let size = window.inner_size();

        let surface = unsafe { instance.create_surface(&window) }.unwrap();

        (window, size, surface)
    };

    let hidpi_factor = window.scale_factor();

    let adapter = block_on(instance.request_adapter(&wgpu::RequestAdapterOptions {
        power_preference: wgpu::PowerPreference::HighPerformance,
        compatible_surface: Some(&surface),
        force_fallback_adapter: false,
    }))
    .unwrap();

    let (device, queue) =
        block_on(adapter.request_device(&wgpu::DeviceDescriptor::default(), None)).unwrap();

    // Set up swap chain
    let surface_desc = wgpu::SurfaceConfiguration {
        usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
        format: wgpu::TextureFormat::Bgra8UnormSrgb,
        width: size.width,
        height: size.height,
        present_mode: wgpu::PresentMode::Fifo,
        alpha_mode: wgpu::CompositeAlphaMode::Auto,
        view_formats: vec![wgpu::TextureFormat::Bgra8Unorm],
    };

    surface.configure(&device, &surface_desc);

    // Set up dear imgui
    let mut imgui = imgui::Context::create();
    let mut platform = imgui_winit_support::WinitPlatform::init(&mut imgui);
    platform.attach_window(
        imgui.io_mut(),
        &window,
        imgui_winit_support::HiDpiMode::Default,
    );
    imgui.set_ini_filename(None);

    let font_size = (13.0 * hidpi_factor) as f32;
    imgui.io_mut().font_global_scale = (1.0 / hidpi_factor) as f32;

    imgui.fonts().add_font(&[FontSource::DefaultFontData {
        config: Some(imgui::FontConfig {
            oversample_h: 1,
            pixel_snap_h: true,
            size_pixels: font_size,
            ..Default::default()
        }),
    }]);

    //
    // Set up dear imgui wgpu renderer
    //
    // let clear_color = wgpu::Color {
    //     r: 0.1,
    //     g: 0.2,
    //     b: 0.3,
    //     a: 1.0,
    // };

    let renderer_config = RendererConfig {
        texture_format: surface_desc.format,
        ..Default::default()
    };

    let mut renderer = Renderer::new(&mut imgui, &device, &queue, renderer_config);

    let mut last_frame = Instant::now();

    let mut last_cursor = None;

    let mut example_size: [f32; 2] = [640.0, 480.0];
    let mut example = Example::init(&surface_desc, &device, &queue);

    // Stores a texture for displaying with imgui::Image(),
    // also as a texture view for rendering into it

    let texture_config = TextureConfig {
        size: wgpu::Extent3d {
            width: example_size[0] as u32,
            height: example_size[1] as u32,
            ..Default::default()
        },
        usage: wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::TEXTURE_BINDING,
        ..Default::default()
    };

    let texture = Texture::new(&device, &renderer, texture_config);
    let example_texture_id = renderer.textures.insert(texture);

    // Event loop
    event_loop.run(move |event, _, control_flow| {
        *control_flow = if cfg!(feature = "metal-auto-capture") {
            ControlFlow::Exit
        } else {
            ControlFlow::Poll
        };
        match event {
            Event::WindowEvent {
                event: WindowEvent::Resized(size),
                ..
            } => {
                let surface_desc = wgpu::SurfaceConfiguration {
                    usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
                    format: wgpu::TextureFormat::Bgra8UnormSrgb,
                    width: size.width,
                    height: size.height,
                    present_mode: wgpu::PresentMode::Fifo,
                    alpha_mode: wgpu::CompositeAlphaMode::Auto,
                    view_formats: vec![wgpu::TextureFormat::Bgra8Unorm],
                };

                surface.configure(&device, &surface_desc);
            }
            Event::WindowEvent {
                event:
                    WindowEvent::KeyboardInput {
                        input:
                            KeyboardInput {
                                virtual_keycode: Some(VirtualKeyCode::Escape),
                                state: ElementState::Pressed,
                                ..
                            },
                        ..
                    },
                ..
            }
            | Event::WindowEvent {
                event: WindowEvent::CloseRequested,
                ..
            } => {
                *control_flow = ControlFlow::Exit;
            }
            Event::MainEventsCleared => window.request_redraw(),
            Event::RedrawEventsCleared => {
                let now = Instant::now();
                imgui.io_mut().update_delta_time(now - last_frame);
                last_frame = now;

                let frame = match surface.get_current_texture() {
                    Ok(frame) => frame,
                    Err(e) => {
                        eprintln!("dropped frame: {e:?}");
                        return;
                    }
                };
                platform
                    .prepare_frame(imgui.io_mut(), &window)
                    .expect("Failed to prepare frame");
                let ui = imgui.frame();

                let view = frame
                    .texture
                    .create_view(&wgpu::TextureViewDescriptor::default());

                // Render example normally at background
                example.update(ui.io().delta_time);
                example.setup_camera(&queue, ui.io().display_size);
                example.render(&view, &device, &queue);

                // Store the new size of Image() or None to indicate that the window is collapsed.
                let mut new_example_size: Option<[f32; 2]> = None;

                ui.window("Cube")
                    .size([512.0, 512.0], Condition::FirstUseEver)
                    .build(|| {
                        new_example_size = Some(ui.content_region_avail());
                        imgui::Image::new(example_texture_id, new_example_size.unwrap()).build(ui);
                    });

                if let Some(size) = new_example_size {
                    // Resize render target, which is optional
                    if size != example_size && size[0] >= 1.0 && size[1] >= 1.0 {
                        example_size = size;
                        let scale = &ui.io().display_framebuffer_scale;
                        let texture_config = TextureConfig {
                            size: Extent3d {
                                width: (example_size[0] * scale[0]) as u32,
                                height: (example_size[1] * scale[1]) as u32,
                                ..Default::default()
                            },
                            usage: wgpu::TextureUsages::RENDER_ATTACHMENT
                                | wgpu::TextureUsages::TEXTURE_BINDING,
                            ..Default::default()
                        };
                        renderer.textures.replace(
                            example_texture_id,
                            Texture::new(&device, &renderer, texture_config),
                        );
                    }

                    // Only render example to example_texture if thw window is not collapsed
                    example.setup_camera(&queue, size);
                    example.render(
                        renderer.textures.get(example_texture_id).unwrap().view(),
                        &device,
                        &queue,
                    );
                }

                let mut encoder: wgpu::CommandEncoder =
                    device.create_command_encoder(&wgpu::CommandEncoderDescriptor { label: None });

                if last_cursor != Some(ui.mouse_cursor()) {
                    last_cursor = Some(ui.mouse_cursor());
                    platform.prepare_render(ui, &window);
                }

                let mut rpass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                    label: None,
                    color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                        view: &view,
                        resolve_target: None,
                        ops: wgpu::Operations {
                            load: wgpu::LoadOp::Load, // Do not clear
                            // load: wgpu::LoadOp::Clear(clear_color),
                            store: true,
                        },
                    })],
                    depth_stencil_attachment: None,
                });

                renderer
                    .render(imgui.render(), &queue, &device, &mut rpass)
                    .expect("Rendering failed");

                drop(rpass);

                queue.submit(Some(encoder.finish()));
                frame.present();
            }
            _ => (),
        }

        platform.handle_event(imgui.io_mut(), &window, &event);
    });
}