use std::cmp::max;
use std::sync::{Arc, RwLock};
use std::thread;
use std::time::Duration;
use cgmath::num_traits::ToPrimitive;
use cgmath::Rotation3;
use pollster::FutureExt;
use wgpu::util::DeviceExt;
use wgpu::{Adapter, Device, Instance, PresentMode, Queue, Surface, SurfaceCapabilities};
use winit::application::ApplicationHandler;
use winit::dpi::PhysicalSize;
use winit::event::WindowEvent;
use winit::event_loop::{ActiveEventLoop, EventLoop};
use winit::window::{Window, WindowId};
use solar_engine::{Body, Simulator};

pub async fn run() {
    let event_loop = EventLoop::new().unwrap();

    let mut window_state = StateApplication::new();
    let _ = event_loop.run_app(&mut window_state);
}

struct RenderInstance {
    position: cgmath::Vector3<f32>,
    rotation: cgmath::Quaternion<f32>,
}

impl RenderInstance {
    fn to_raw(&self) -> InstanceRaw {
        let model = cgmath::Matrix4::from_translation(self.position) * cgmath::Matrix4::from(self.rotation);
        InstanceRaw { model: model.into() }
    }
}

#[repr(C)]
#[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
struct InstanceRaw {
    model: [[f32; 4]; 4],
}

impl InstanceRaw {
    fn desc() -> wgpu::VertexBufferLayout<'static> {
        wgpu::VertexBufferLayout {
            array_stride: size_of::<InstanceRaw>() as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Instance,
            attributes: &[
                wgpu::VertexAttribute { offset: 0, shader_location: 5, format: wgpu::VertexFormat::Float32x4 },
                wgpu::VertexAttribute { offset: size_of::<[f32; 4]>() as wgpu::BufferAddress, shader_location: 6, format: wgpu::VertexFormat::Float32x4 },
                wgpu::VertexAttribute { offset: size_of::<[f32; 8]>() as wgpu::BufferAddress, shader_location: 7, format: wgpu::VertexFormat::Float32x4 },
                wgpu::VertexAttribute { offset: size_of::<[f32; 12]>() as wgpu::BufferAddress, shader_location: 8, format: wgpu::VertexFormat::Float32x4 },
            ],
        }
    }
}

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

impl Vertex {
    const ATTRIBS: [wgpu::VertexAttribute; 2] =
        wgpu::vertex_attr_array![0 => Float32x3, 1 => Float32x3];

    fn desc() -> wgpu::VertexBufferLayout<'static> {
        wgpu::VertexBufferLayout {
            array_stride: size_of::<Self>() as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: &Self::ATTRIBS,
        }
    }
}

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

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

struct StateApplication<'a> {
    state: Option<State<'a>>,
}

impl<'a> StateApplication<'a> {
    pub fn new() -> Self {
        Self {
            state: None,
        }
    }
}

impl<'a> ApplicationHandler for StateApplication<'a>{
    fn resumed(&mut self, event_loop: &ActiveEventLoop) {
        let window = event_loop.create_window(Window::default_attributes().with_title("Hello!")).unwrap();
        self.state = Some(State::new(window));
    }

    fn window_event(&mut self, event_loop: &ActiveEventLoop, window_id: WindowId, event: WindowEvent) {
        let window = self.state.as_ref().unwrap().window();

        if window.id() == window_id {
            match event {
                WindowEvent::CloseRequested => {
                    event_loop.exit();
                }
                WindowEvent::Resized(physical_size) => {
                    self.state.as_mut().unwrap().resize(physical_size);
                }
                WindowEvent::RedrawRequested => {
                    self.state.as_mut().unwrap().update();
                    self.state.as_mut().unwrap().render().unwrap();
                }
                WindowEvent::KeyboardInput { .. } => {
                    if let Some(state) = self.state.as_mut() {
                        if state.input(&event) {
                            return;
                        }
                    }
                }
                _ => {}
            }
        }
    }

    fn about_to_wait(&mut self, _event_loop: &ActiveEventLoop) {
        let window = self.state.as_ref().unwrap().window();
        window.request_redraw();
    }
}

struct State<'a> {
    surface: Surface<'a>,
    device: Device,
    queue: Queue,
    config: wgpu::SurfaceConfiguration,

    size: PhysicalSize<u32>,
    window: Arc<Window>,
    
    render_pipeline: wgpu::RenderPipeline,
    vertex_buffer: wgpu::Buffer,
    index_buffer: wgpu::Buffer,

    instances: Vec<RenderInstance>,
    instance_buffer: wgpu::Buffer,

    num_vertices: u32,
    num_indices: u32,

    simulator: Arc<RwLock<Simulator>>,
}

impl<'a> State<'a> {
    pub fn new (window: Window) -> Self {
        let window_arc = Arc::new(window);
        let size = window_arc.inner_size();
        let instance = Self::create_gpu_instance();
        let surface = instance.create_surface(window_arc.clone()).unwrap();
        let adapter = Self::create_adapter(instance, &surface);
        let (device, queue) = Self::create_device(&adapter);
        let surface_caps = surface.get_capabilities(&adapter);
        let config = Self::create_surface_config(size, surface_caps);
        surface.configure(&device, &config);

        let render_pipeline = Self::create_render_pipeline(&device, &config);
        let vertex_buffer = Self::create_vertex_buffer(&device);
        let index_buffer = Self::create_index_buffer(&device);

        let num_vertices = VERTICES.len() as u32;
        let num_indices = INDICES.len() as u32;

        let mut sim = Simulator::new(60.0 * 60.0 * 24.0);
        sim.add_body(Body {
            name: "Sun".to_string(),
            position: [0.0, 0.0],
            velocity: [0.0, 0.0],
            mass: 1.989e30,
        });
        sim.add_body(Body {
            name: "Earth".to_string(),
            position: [1.496e11, 0.0],
            velocity: [0.0, 29780.0],
            mass: 5.972e24,
        });
        
        let simulator = Arc::new(RwLock::new(sim));

        let sim_clone = simulator.clone();
        thread::spawn(move || {
            loop {
                {
                    let mut sim = sim_clone.write().unwrap();
                    sim.step();
                }
                thread::sleep(Duration::from_millis(16));
            }
        });

        let instances = {
            let sim = simulator.read().unwrap();
            sim.bodies.iter().map(|b| RenderInstance {
                position: cgmath::Vector3::new(
                    (b.position[0] / 1.496e11) as f32,
                    (b.position[1] / 1.496e11) as f32,
                    0.0,
                ),
                rotation: cgmath::Quaternion::from_angle_z(cgmath::Deg(0.0)),
            }).collect::<Vec<_>>()
        };

        let instance_data: Vec<InstanceRaw> = instances.iter().map(RenderInstance::to_raw).collect();
        let instance_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Instance Buffer"),
            contents: bytemuck::cast_slice(&instance_data),
            usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
        });

        Self {
            surface,
            device,
            queue,
            config,
            size,
            window: window_arc,
            
            render_pipeline,
            vertex_buffer,
            index_buffer,

            instances,
            instance_buffer,
            
            num_vertices,
            num_indices,

            simulator,
        }
    }

    pub fn input(&mut self, event: &WindowEvent) -> bool {
        false
    }

    fn update(&mut self) {
        let updated_instances: Vec<RenderInstance> = {
            let sim = self.simulator.read().unwrap();
            sim.bodies.iter().map(|b| RenderInstance {
                position: cgmath::Vector3::new((b.position[0] / 1.496e11) as f32, (b.position[1] / 1.496e11) as f32, 0.0),
                rotation: cgmath::Quaternion::from_angle_z(cgmath::Deg(0.0)),
            }).collect()
        };

        let instance_data: Vec<InstanceRaw> = updated_instances.iter().map(RenderInstance::to_raw).collect();
        self.queue.write_buffer(&self.instance_buffer, 0, bytemuck::cast_slice(&instance_data));
        self.instances = updated_instances;
    }
    
    fn create_index_buffer(device: &Device) -> wgpu::Buffer {
        device.create_buffer_init(
            &wgpu::util::BufferInitDescriptor {
                label: Some("Index Buffer"),
                contents: bytemuck::cast_slice(INDICES),
                usage: wgpu::BufferUsages::INDEX,
            }
        )
    }
    
    fn create_vertex_buffer(device: &Device) -> wgpu::Buffer {
        device.create_buffer_init(
            &wgpu::util::BufferInitDescriptor {
                label: Some("Vertex Buffer"),
                contents: bytemuck::cast_slice(VERTICES),
                usage: wgpu::BufferUsages::VERTEX,
            }
        )
    }
    
    fn create_render_pipeline(device: &Device, config: &wgpu::SurfaceConfiguration) -> wgpu::RenderPipeline {
        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: &[],
            });

        device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
            label: Some("Render Pipeline"),
            layout: Some(&render_pipeline_layout),
            vertex: wgpu::VertexState {
                module: &shader,
                entry_point: Some("vs_main"),
                buffers: &[Vertex::desc(), InstanceRaw::desc()],
                compilation_options: Default::default(),
            },
            fragment: Some(wgpu::FragmentState {
                module: &shader,
                entry_point: Some("fs_main"),
                targets: &[Some(wgpu::ColorTargetState {
                    format: config.format,
                    blend: Some(wgpu::BlendState::REPLACE),
                    write_mask: wgpu::ColorWrites::ALL,
                })],
                compilation_options: wgpu::PipelineCompilationOptions::default(),
            }),
            primitive: wgpu::PrimitiveState {
                topology: wgpu::PrimitiveTopology::TriangleList, // 1.
                strip_index_format: None,
                front_face: wgpu::FrontFace::Ccw,
                cull_mode: Some(wgpu::Face::Back),
                // Setting this to anything other than Fill requires Features::NON_FILL_POLYGON_MODE
                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,
            },
            multiview: None,
            cache: None,
        })
    }

    fn create_surface_config(size: PhysicalSize<u32>, capabilities: SurfaceCapabilities) -> wgpu::SurfaceConfiguration {
        let surface_format = capabilities.formats.iter()
            .find(|f| f.is_srgb())
            .copied()
            .unwrap_or(capabilities.formats[0]);

        wgpu::SurfaceConfiguration {
            usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
            format: surface_format,
            width: size.width,
            height: size.height,
            present_mode: PresentMode::AutoNoVsync,
            alpha_mode: capabilities.alpha_modes[0],
            view_formats: vec![],
            desired_maximum_frame_latency: 2,
        }
    }

    fn create_device(adapter: &Adapter) -> (Device, Queue) {
        adapter.request_device(
            &wgpu::DeviceDescriptor {
                required_features: wgpu::Features::empty(),
                required_limits: wgpu::Limits::default(),
                memory_hints: Default::default(),
                label: None,
                trace: Default::default(),
            }).block_on().unwrap()
    }

    fn create_adapter(instance: Instance, surface: &Surface) -> Adapter {
        instance.request_adapter(
            &wgpu::RequestAdapterOptions {
                power_preference: wgpu::PowerPreference::default(),
                compatible_surface: Some(&surface),
                force_fallback_adapter: false,
            }
        ).block_on().unwrap()
    }

    fn create_gpu_instance() -> Instance {
        Instance::new(&wgpu::InstanceDescriptor {
            backends: wgpu::Backends::PRIMARY,
            ..Default::default()
        })
    }

    pub fn resize(&mut self, new_size: PhysicalSize<u32>) {
        self.size = new_size;

        self.config.width = max(new_size.width, 1);
        self.config.height = max(new_size.height, 1);

        self.surface.configure(&self.device, &self.config);

        println!("Resized to {:?} from state!", new_size);
    }

    pub 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: 1.0,
                            g: 0.2,
                            b: 0.3,
                            a: 1.0,
                        }),
                        store: wgpu::StoreOp::Store,
                    }
                })],
                depth_stencil_attachment: None,
                occlusion_query_set: None,
                timestamp_writes: None,
            });

            render_pass.set_pipeline(&self.render_pipeline);
            render_pass.set_vertex_buffer(0, self.vertex_buffer.slice(..));
            render_pass.set_index_buffer(self.index_buffer.slice(..), wgpu::IndexFormat::Uint16);
            if !self.instances.is_empty() {
                render_pass.set_vertex_buffer(1, self.instance_buffer.slice(..));
                render_pass.draw_indexed(0..self.num_indices, 0, 0..self.instances.len() as u32);
            }
        }

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

        Ok(())
    }

    pub fn window(&self) -> &Window {
        &self.window
    }
}

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