use std::iter;

use wgpu::util::DeviceExt;
use winit::{
    event::*,
    event_loop::{ControlFlow, EventLoop},
    window::{Window, WindowBuilder},
};

#[repr(C)]
#[derive(Copy, Clone, Debug, bytemuck::Pod, bytemuck::Zeroable)]
struct Vertex {
    position: [f32; 3],
    color: [f32; 3],
}

impl Vertex {
    fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
        wgpu::VertexBufferLayout {
            array_stride: std::mem::size_of::<Vertex>() as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: &[
                wgpu::VertexAttribute {
                    offset: 0,
                    shader_location: 0,
                    format: wgpu::VertexFormat::Float32x3,
                },
                wgpu::VertexAttribute {
                    offset: std::mem::size_of::<[f32; 3]>() as wgpu::BufferAddress,
                    shader_location: 1,
                    format: wgpu::VertexFormat::Float32x3,
                },
            ],
        }
    }
}

const VERTICES: &[Vertex] = &[
    Vertex {
        position: [-0.0868241, 0.49240386, 0.0],
        color: [0.5, 0.0, 0.5],
    }, // A
    Vertex {
        position: [-0.49513406, 0.06958647, 0.0],
        color: [0.5, 0.0, 0.5],
    }, // B
    Vertex {
        position: [-0.21918549, -0.44939706, 0.0],
        color: [0.5, 0.0, 0.5],
    }, // C
    Vertex {
        position: [0.35966998, -0.3473291, 0.0],
        color: [0.5, 0.0, 0.5],
    }, // D
    Vertex {
        position: [0.44147372, 0.2347359, 0.0],
        color: [0.5, 0.0, 0.5],
    }, // E
];

const INDICES: &[u16] = &[0, 1, 4, 1, 2, 4, 2, 3, 4];

struct State {
    surface: wgpu::Surface,
    device: wgpu::Device,
    queue: wgpu::Queue,
    config: wgpu::SurfaceConfiguration,

    render_pipeline: wgpu::RenderPipeline,

    vertex_buffer: wgpu::Buffer,
    index_buffer: wgpu::Buffer,
    num_indices: u32,

    challenge_vertex_buffer: wgpu::Buffer,
    challenge_index_buffer: wgpu::Buffer,
    num_challenge_indices: u32,
    use_complex: bool,

    size: winit::dpi::PhysicalSize<u32>,
}

impl State {
    async fn new(window: &Window) -> Self {
        let size = window.inner_size();

        // The instance is a handle to our GPU
        // BackendBit::PRIMARY => Vulkan + Metal + DX12 + Browser WebGPU
        let instance = wgpu::Instance::new(wgpu::Backends::all());
        let surface = unsafe { instance.create_surface(window) };
        let adapter = instance
            .request_adapter(&wgpu::RequestAdapterOptions {
                power_preference: wgpu::PowerPreference::default(),
                compatible_surface: Some(&surface),
                force_fallback_adapter: false,
            })
            .await
            .unwrap();

        let (device, queue) = adapter
            .request_device(
                &wgpu::DeviceDescriptor {
                    label: None,
                    features: wgpu::Features::empty(),
                    // WebGL doesn't support all of wgpu's features, so if
                    // we're building for the web we'll have to disable some.
                    limits: if cfg!(target_arch = "wasm32") {
                        wgpu::Limits::downlevel_webgl2_defaults()
                    } else {
                        wgpu::Limits::default()
                    },
                },
                None, // Trace path
            )
            .await
            .unwrap();

        let config = wgpu::SurfaceConfiguration {
            usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
            format: surface.get_supported_formats(&adapter)[0],
            width: size.width,
            height: size.height,
            present_mode: wgpu::PresentMode::Fifo,
            alpha_mode: wgpu::CompositeAlphaMode::Auto,
        };
        surface.configure(&device, &config);

        let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
            label: Some("Shader"),
            source: wgpu::ShaderSource::Wgsl(include_str!("shader.wgsl").into()),
        });

        let render_pipeline_layout =
            device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
                label: Some("Render Pipeline Layout"),
                bind_group_layouts: &[],
                push_constant_ranges: &[],
            });

        let render_pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
            label: Some("Render Pipeline"),
            layout: Some(&render_pipeline_layout),
            vertex: wgpu::VertexState {
                module: &shader,
                entry_point: "vs_main",
                buffers: &[Vertex::desc()],
            },
            fragment: Some(wgpu::FragmentState {
                module: &shader,
                entry_point: "fs_main",
                targets: &[Some(wgpu::ColorTargetState {
                    format: config.format,
                    blend: Some(wgpu::BlendState {
                        color: wgpu::BlendComponent::REPLACE,
                        alpha: wgpu::BlendComponent::REPLACE,
                    }),
                    write_mask: wgpu::ColorWrites::ALL,
                })],
            }),
            primitive: wgpu::PrimitiveState {
                topology: wgpu::PrimitiveTopology::TriangleList,
                strip_index_format: None,
                front_face: wgpu::FrontFace::Ccw,
                cull_mode: Some(wgpu::Face::Back),
                // Setting this to anything other than Fill requires Features::POLYGON_MODE_LINE
                // or Features::POLYGON_MODE_POINT
                polygon_mode: wgpu::PolygonMode::Fill,
                // Requires Features::DEPTH_CLIP_CONTROL
                unclipped_depth: false,
                // Requires Features::CONSERVATIVE_RASTERIZATION
                conservative: false,
            },
            depth_stencil: None,
            multisample: wgpu::MultisampleState {
                count: 1,
                mask: !0,
                alpha_to_coverage_enabled: false,
            },
            // If the pipeline will be used with a multiview render pass, this
            // indicates how many array layers the attachments will have.
            multiview: None,
        });

        let vertex_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Vertex Buffer"),
            contents: bytemuck::cast_slice(VERTICES),
            usage: wgpu::BufferUsages::VERTEX,
        });
        let index_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Index Buffer"),
            contents: bytemuck::cast_slice(INDICES),
            usage: wgpu::BufferUsages::INDEX,
        });
        let num_indices = INDICES.len() as u32;

        let num_vertices = 16;
        let angle = std::f32::consts::PI * 2.0 / num_vertices as f32;
        let challenge_verts = (0..num_vertices)
            .map(|i| {
                let theta = angle * i as f32;
                Vertex {
                    position: [0.5 * theta.cos(), -0.5 * theta.sin(), 0.0],
                    color: [(1.0 + theta.cos()) / 2.0, (1.0 + theta.sin()) / 2.0, 1.0],
                }
            })
            .collect::<Vec<_>>();

        let num_triangles = num_vertices - 2;
        let challenge_indices = (1u16..num_triangles + 1)
            .into_iter()
            .flat_map(|i| vec![i + 1, i, 0])
            .collect::<Vec<_>>();
        let num_challenge_indices = challenge_indices.len() as u32;

        let challenge_vertex_buffer =
            device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
                label: Some("Challenge Vertex Buffer"),
                contents: bytemuck::cast_slice(&challenge_verts),
                usage: wgpu::BufferUsages::VERTEX,
            });
        let challenge_index_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Challenge Index Buffer"),
            contents: bytemuck::cast_slice(&challenge_indices),
            usage: wgpu::BufferUsages::INDEX,
        });

        let use_complex = false;

        Self {
            surface,
            device,
            queue,
            config,
            render_pipeline,
            vertex_buffer,
            index_buffer,
            num_indices,
            challenge_vertex_buffer,
            challenge_index_buffer,
            num_challenge_indices,
            use_complex,
            size,
        }
    }

    pub fn resize(&mut self, new_size: winit::dpi::PhysicalSize<u32>) {
        if new_size.width > 0 && new_size.height > 0 {
            self.size = new_size;
            self.config.width = new_size.width;
            self.config.height = new_size.height;
            self.surface.configure(&self.device, &self.config);
        }
    }

    fn input(&mut self, event: &WindowEvent) -> bool {
        match event {
            WindowEvent::KeyboardInput {
                input:
                    KeyboardInput {
                        state,
                        virtual_keycode: Some(VirtualKeyCode::Space),
                        ..
                    },
                ..
            } => {
                self.use_complex = *state == ElementState::Pressed;
                true
            }
            _ => false,
        }
    }

    fn update(&mut self) {}

    fn render(&mut self) -> Result<(), wgpu::SurfaceError> {
        let output = self.surface.get_current_texture()?;
        let view = output
            .texture
            .create_view(&wgpu::TextureViewDescriptor::default());

        let mut encoder = self
            .device
            .create_command_encoder(&wgpu::CommandEncoderDescriptor {
                label: Some("Render Encoder"),
            });

        {
            let mut render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                label: Some("Render Pass"),
                color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                    view: &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,
            });

            render_pass.set_pipeline(&self.render_pipeline);

            let data = if self.use_complex {
                (
                    &self.challenge_vertex_buffer,
                    &self.challenge_index_buffer,
                    self.num_challenge_indices,
                )
            } else {
                (&self.vertex_buffer, &self.index_buffer, self.num_indices)
            };
            render_pass.set_vertex_buffer(0, data.0.slice(..));
            render_pass.set_index_buffer(data.1.slice(..), wgpu::IndexFormat::Uint16);

            render_pass.draw_indexed(0..data.2, 0, 0..1);
        }

        self.queue.submit(iter::once(encoder.finish()));
        output.present();

        Ok(())
    }
}

fn main() {
    pollster::block_on(run());
}

async fn run() {
    env_logger::init();
    let event_loop = EventLoop::new();
    let window = WindowBuilder::new().build(&event_loop).unwrap();

    // State::new uses async code, so we're going to wait for it to finish
    let mut state = State::new(&window).await;

    event_loop.run(move |event, _, control_flow| {
        match event {
            Event::WindowEvent {
                ref event,
                window_id,
            } if window_id == window.id() => {
                if !state.input(event) {
                    match event {
                        WindowEvent::CloseRequested
                        | WindowEvent::KeyboardInput {
                            input:
                                KeyboardInput {
                                    state: ElementState::Pressed,
                                    virtual_keycode: Some(VirtualKeyCode::Escape),
                                    ..
                                },
                            ..
                        } => *control_flow = ControlFlow::Exit,
                        WindowEvent::Resized(physical_size) => {
                            state.resize(*physical_size);
                        }
                        WindowEvent::ScaleFactorChanged { new_inner_size, .. } => {
                            // new_inner_size is &mut so w have to dereference it twice
                            state.resize(**new_inner_size);
                        }
                        _ => {}
                    }
                }
            }
            Event::RedrawRequested(window_id) if window_id == window.id() => {
                state.update();
                match state.render() {
                    Ok(_) => {}
                    // Reconfigure the surface if it's lost or outdated
                    Err(wgpu::SurfaceError::Lost | wgpu::SurfaceError::Outdated) => state.resize(state.size),
                    // The system is out of memory, we should probably quit
                    Err(wgpu::SurfaceError::OutOfMemory) => *control_flow = ControlFlow::Exit,
                    // We're ignoring timeouts
                    Err(wgpu::SurfaceError::Timeout) => log::warn!("Surface timeout"),
                }
            }
            Event::MainEventsCleared => {
                // RedrawRequested will only trigger once, unless we manually
                // request it.
                window.request_redraw();
            }
            _ => {}
        }
    });
}