#![doc = include_str!("../README.md")]

use std::future::Future;
#[cfg(not(target_arch = "wasm32"))]
use std::time::{Duration, Instant};
use winit::{
    event::{Event, WindowEvent},
    event_loop::{ControlFlow, EventLoop},
    window::Window,
};

pub use wgpu;
pub use winit;

pub mod projection;

pub trait Playground: 'static + Sized {
    fn optional_features() -> wgpu::Features {
        wgpu::Features::empty()
    }
    fn required_features() -> wgpu::Features {
        wgpu::Features::empty()
    }
    fn required_downlevel_capabilities() -> wgpu::DownlevelCapabilities {
        wgpu::DownlevelCapabilities {
            flags: wgpu::DownlevelFlags::empty(),
            shader_model: wgpu::ShaderModel::Sm5,
            ..wgpu::DownlevelCapabilities::default()
        }
    }
    fn required_limits() -> wgpu::Limits {
        #[cfg(target_arch = "wasm32")]
        {
            wgpu::Limits::downlevel_webgl2_defaults() // These downlevel limits will allow the code to run on all possible hardware
        }
        #[cfg(not(target_arch = "wasm32"))]
        {
            wgpu::Limits::downlevel_defaults()
        }
    }
    fn init(
        config: &wgpu::SurfaceConfiguration,
        adapter: &wgpu::Adapter,
        device: &wgpu::Device,
        queue: &wgpu::Queue,
    ) -> Self;
    fn resize(
        &mut self,
        config: &wgpu::SurfaceConfiguration,
        device: &wgpu::Device,
        queue: &wgpu::Queue,
    );
    fn update(&mut self, event: WindowEvent, control_flow: &mut ControlFlow) {
        if let WindowEvent::CloseRequested = event {
            *control_flow = ControlFlow::Exit;
        }
    }
    fn render(
        &mut self,
        view: &wgpu::TextureView,
        device: &wgpu::Device,
        queue: &wgpu::Queue,
        spawner: &Spawner,
    );
}

struct Setup {
    window: winit::window::Window,
    event_loop: EventLoop<()>,
    instance: wgpu::Instance,
    size: winit::dpi::PhysicalSize<u32>,
    surface: wgpu::Surface,
    adapter: wgpu::Adapter,
    device: wgpu::Device,
    queue: wgpu::Queue,
}

fn setup_logging(_window: &Window) {
    #[cfg(not(target_arch = "wasm32"))]
    {
        env_logger::init();
    }

    #[cfg(target_arch = "wasm32")]
    {
        use winit::platform::web::WindowExtWebSys;
        let query_string = web_sys::window().unwrap().location().search().unwrap();
        let level: log::Level = parse_url_query_string(&query_string, "RUST_LOG")
            .map(|x| x.parse().ok())
            .flatten()
            .unwrap_or(log::Level::Error);
        console_log::init_with_level(level).expect("could not initialize logger");
        std::panic::set_hook(Box::new(console_error_panic_hook::hook));
        // On wasm, append the canvas to the document body
        web_sys::window()
            .and_then(|win| win.document())
            .and_then(|doc| doc.body())
            .and_then(|body| {
                body.append_child(&web_sys::Element::from(_window.canvas()))
                    .ok()
            })
            .expect("couldn't append canvas to document body");
    }
}

async fn setup<P: Playground>(window: Window, event_loop: EventLoop<()>) -> Setup {
    setup_logging(&window);

    log::info!("Initializing the surface...");

    let backend = wgpu::util::backend_bits_from_env().unwrap_or_else(wgpu::Backends::all);

    let instance = wgpu::Instance::new(backend);
    let (size, surface) = unsafe {
        let size = window.inner_size();
        let surface = instance.create_surface(&window);
        (size, surface)
    };
    let adapter =
        wgpu::util::initialize_adapter_from_env_or_default(&instance, backend, Some(&surface))
            .await
            .expect("No suitable GPU adapters found on the system!");

    #[cfg(not(target_arch = "wasm32"))]
    {
        let adapter_info = adapter.get_info();
        println!("Using {} ({:?})", adapter_info.name, adapter_info.backend);
    }

    let optional_features = P::optional_features();
    let required_features = P::required_features();
    let adapter_features = adapter.features();
    assert!(
        adapter_features.contains(required_features),
        "Adapter does not support required features for this example: {:?}",
        required_features - adapter_features
    );

    let required_downlevel_capabilities = P::required_downlevel_capabilities();
    let downlevel_capabilities = adapter.get_downlevel_properties();
    assert!(
        downlevel_capabilities.shader_model >= required_downlevel_capabilities.shader_model,
        "Adapter does not support the minimum shader model required to run this example: {:?}",
        required_downlevel_capabilities.shader_model
    );
    assert!(
        downlevel_capabilities
            .flags
            .contains(required_downlevel_capabilities.flags),
        "Adapter does not support the downlevel capabilities required to run this example: {:?}",
        required_downlevel_capabilities.flags - downlevel_capabilities.flags
    );

    // Make sure we use the texture resolution limits from the adapter, so we can support images the size of the surface.
    let needed_limits = P::required_limits().using_resolution(adapter.limits());

    let trace_dir = std::env::var("WGPU_TRACE");
    let (device, queue) = adapter
        .request_device(
            &wgpu::DeviceDescriptor {
                label: None,
                features: (optional_features & adapter_features) | required_features,
                limits: needed_limits,
            },
            trace_dir.ok().as_ref().map(std::path::Path::new),
        )
        .await
        .expect("Unable to find a suitable GPU adapter!");

    Setup {
        window,
        event_loop,
        instance,
        size,
        surface,
        adapter,
        device,
        queue,
    }
}

fn start<E: Playground>(
    Setup {
        window,
        event_loop,
        instance,
        size,
        surface,
        adapter,
        device,
        queue,
    }: Setup,
) {
    let spawner = Spawner::new();
    let mut config = wgpu::SurfaceConfiguration {
        usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
        format: surface.get_preferred_format(&adapter).unwrap(),
        width: size.width,
        height: size.height,
        present_mode: wgpu::PresentMode::Mailbox,
    };
    surface.configure(&device, &config);

    log::info!("Initializing the example...");
    let mut playground = E::init(&config, &adapter, &device, &queue);

    #[cfg(not(target_arch = "wasm32"))]
    let mut last_update_inst = Instant::now();
    #[cfg(not(target_arch = "wasm32"))]
    let mut last_frame_inst = Instant::now();
    #[cfg(not(target_arch = "wasm32"))]
    let (mut frame_count, mut accum_time) = (0, 0.0);

    log::info!("Entering render loop...");
    event_loop.run(move |event, _, control_flow| {
        let _ = (&instance, &adapter); // force ownership by the closure
        *control_flow = if cfg!(feature = "metal-auto-capture") {
            ControlFlow::Exit
        } else {
            ControlFlow::Poll
        };
        match event {
            Event::NewEvents(_start_cause) => (),
            Event::WindowEvent { event, .. } => {
                match event {
                    WindowEvent::Resized(size)
                    | WindowEvent::ScaleFactorChanged {
                        new_inner_size: &mut size,
                        ..
                    } => {
                        log::info!("Resizing to {:?}", size);
                        config.width = size.width.max(1);
                        config.height = size.height.max(1);
                        playground.resize(&config, &device, &queue);
                        surface.configure(&device, &config);
                    }
                    _ => (),
                }
                playground.update(event, control_flow);
            }
            Event::DeviceEvent { .. } => (),
            Event::UserEvent(_event) => (),
            Event::Suspended => (),
            Event::Resumed => (),
            Event::MainEventsCleared => (),
            Event::RedrawRequested(_) => {
                #[cfg(not(target_arch = "wasm32"))]
                {
                    accum_time += last_frame_inst.elapsed().as_secs_f32();
                    last_frame_inst = Instant::now();
                    frame_count += 1;
                    if frame_count == 100 {
                        println!(
                            "Avg frame time {}ms",
                            accum_time * 1000.0 / frame_count as f32
                        );
                        accum_time = 0.0;
                        frame_count = 0;
                    }
                }

                let frame = match surface.get_current_texture() {
                    Ok(frame) => frame,
                    Err(_) => {
                        surface.configure(&device, &config);
                        surface
                            .get_current_texture()
                            .expect("Failed to acquire next surface texture!")
                    }
                };
                let view = frame
                    .texture
                    .create_view(&wgpu::TextureViewDescriptor::default());

                playground.render(&view, &device, &queue, &spawner);

                frame.present();
            }
            Event::RedrawEventsCleared => {
                #[cfg(not(target_arch = "wasm32"))]
                {
                    // Clamp to some max framerate to avoid busy-looping too much
                    // (we might be in wgpu::PresentMode::Mailbox, thus discarding superfluous frames)
                    //
                    // winit has window.current_monitor().video_modes() but that is a list of all full screen video modes.
                    // So without extra dependencies it's a bit tricky to get the max refresh rate we can run the window on.
                    // Therefore we just go with 60fps - sorry 120hz+ folks!
                    let target_frametime = Duration::from_secs_f64(1.0 / 60.0);
                    let now = Instant::now();
                    let time_since_last_frame = now.duration_since(last_update_inst);
                    if time_since_last_frame >= target_frametime {
                        window.request_redraw();
                        last_update_inst = now;
                    } else {
                        *control_flow =
                            ControlFlow::WaitUntil(now + target_frametime - time_since_last_frame);
                    }

                    spawner.run_until_stalled();
                }

                #[cfg(target_arch = "wasm32")]
                window.request_redraw();
            }

            Event::LoopDestroyed => (),
        }
    });
}

#[cfg(not(target_arch = "wasm32"))]
pub struct Spawner<'a> {
    executor: async_executor::LocalExecutor<'a>,
}

#[cfg(not(target_arch = "wasm32"))]
impl<'a> Spawner<'a> {
    fn new() -> Self {
        Self {
            executor: async_executor::LocalExecutor::new(),
        }
    }

    #[allow(dead_code)]
    pub fn spawn_local(&self, future: impl Future<Output = ()> + 'a) {
        self.executor.spawn(future).detach();
    }

    fn run_until_stalled(&self) {
        while self.executor.try_tick() {}
    }
}

#[cfg(target_arch = "wasm32")]
pub struct Spawner {}

#[cfg(target_arch = "wasm32")]
impl Spawner {
    fn new() -> Self {
        Self {}
    }

    #[allow(dead_code)]
    pub fn spawn_local(&self, future: impl Future<Output = ()> + 'static) {
        wasm_bindgen_futures::spawn_local(future);
    }
}

#[cfg(not(target_arch = "wasm32"))]
pub fn run<E: Playground>(window: Window, event_loop: EventLoop<()>) {
    let setup = pollster::block_on(setup::<E>(window, event_loop));
    start::<E>(setup);
}

#[cfg(target_arch = "wasm32")]
pub fn run<E: Playground>(window: Window, event_loop: EventLoop<()>) {
    use wasm_bindgen::{prelude::*, JsCast};

    wasm_bindgen_futures::spawn_local(async move {
        let setup = setup::<E>(window, event_loop).await;
        let start_closure = Closure::once_into_js(move || start::<E>(setup));

        // make sure to handle JS exceptions thrown inside start.
        // Otherwise wasm_bindgen_futures Queue would break and never handle any tasks again.
        // This is required, because winit uses JS exception for control flow to escape from `run`.
        if let Err(error) = call_catch(&start_closure) {
            let is_control_flow_exception = error.dyn_ref::<js_sys::Error>().map_or(false, |e| {
                e.message().includes("Using exceptions for control flow", 0)
            });

            if !is_control_flow_exception {
                web_sys::console::error_1(&error);
            }
        }

        #[wasm_bindgen]
        extern "C" {
            #[wasm_bindgen(catch, js_namespace = Function, js_name = "prototype.call.call")]
            fn call_catch(this: &JsValue) -> Result<(), JsValue>;
        }
    });
}

#[cfg(target_arch = "wasm32")]
/// Parse the query string as returned by `web_sys::window()?.location().search()?` and get a
/// specific key out of it.
pub fn parse_url_query_string<'a>(query: &'a str, search_key: &str) -> Option<&'a str> {
    let query_string = query.strip_prefix('?')?;

    for pair in query_string.split('&') {
        let mut pair = pair.split('=');
        let key = pair.next()?;
        let value = pair.next()?;

        if key == search_key {
            return Some(value);
        }
    }

    None
}