use std::future::Future;
use winit::{
	event::{self, WindowEvent, DeviceEvent},
	event_loop::{ControlFlow, EventLoop},
};

#[allow(dead_code)]
pub fn cast_slice<T>(data: &[T]) -> &[u8] {
	use std::{mem::size_of, slice::from_raw_parts};

	unsafe { from_raw_parts(data.as_ptr() as *const u8, data.len() * size_of::<T>()) }
}

#[allow(dead_code)]
pub enum ShaderStage {
	Vertex,
	Fragment,
	Compute,
}

pub trait Example: '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 {
		wgpu::Limits::downlevel_webgl2_defaults() // These downlevel limits will allow the code to run on all possible hardware
	}
}

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,
}

async fn setup<E: Example>(title: &str) -> Setup {
	{
		env_logger::init();
	};

	let event_loop = EventLoop::new();
	let mut builder = winit::window::WindowBuilder::new();
	builder = builder.with_title(title);
	#[cfg(windows_OFF)] // TODO
	{
		use winit::platform::windows::WindowBuilderExtWindows;
		builder = builder.with_no_redirection_bitmap(true);
	}
	let window = builder.build(&event_loop).unwrap();


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

	let backends = wgpu::util::backend_bits_from_env().unwrap_or_else(wgpu::Backends::all);
	let dx12_shader_compiler = wgpu::util::dx12_shader_compiler_from_env().unwrap_or_default();

	let instance = wgpu::Instance::new(wgpu::InstanceDescriptor {
		backends,
		dx12_shader_compiler,
	});

	let size = window.inner_size();

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

	let adapter;

	let optional_features = E::optional_features();
	let required_features = E::required_features();

	//no helper function smh gotta write it myself
	let adapters = instance.enumerate_adapters(backends);

	let mut chosen_adapter = None;
	let mut chosen_adapter_score=0;
	for adapter in adapters {
		if !adapter.is_surface_supported(&surface) {
			continue;
		}

		let score=match adapter.get_info().device_type{
			wgpu::DeviceType::IntegratedGpu=>3,
			wgpu::DeviceType::DiscreteGpu=>4,
			wgpu::DeviceType::VirtualGpu=>2,
			wgpu::DeviceType::Other|wgpu::DeviceType::Cpu=>1,
		};

		let adapter_features = adapter.features();
		if chosen_adapter_score<score&&adapter_features.contains(required_features) {
			chosen_adapter_score=score;
			chosen_adapter=Some(adapter);
		}
	}

	if let Some(maybe_chosen_adapter) = chosen_adapter{
		adapter=maybe_chosen_adapter;
	}else{
		panic!("No suitable GPU adapters found on the system!");
	}


	let adapter_info = adapter.get_info();
	println!("Using {} ({:?})", adapter_info.name, adapter_info.backend);

	let required_downlevel_capabilities = E::required_downlevel_capabilities();
	let downlevel_capabilities = adapter.get_downlevel_capabilities();
	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 = E::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: Example>(
	Setup{
		window,
		event_loop,
		instance,
		size,
		surface,
		adapter,
		device,
		queue,
	}: Setup,
) {
	let spawner = Spawner::new();
	let mut config = surface
		.get_default_config(&adapter, size.width, size.height)
		.expect("Surface isn't supported by the adapter.");
	let surface_view_format = config.format.add_srgb_suffix();
	config.view_formats.push(surface_view_format);
	surface.configure(&device, &config);

	log::info!("Initializing the example...");
	let mut example=E::init();

	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::Event::RedrawEventsCleared => {
				spawner.run_until_stalled();

				window.request_redraw();
			}
			event::Event::WindowEvent {
				event:
					WindowEvent::Resized(size)
					| WindowEvent::ScaleFactorChanged {
						new_inner_size: &mut size,
						..
					},
				..
			} => {
				// Once winit is fixed, the detection conditions here can be removed.
				// https://github.com/rust-windowing/winit/issues/2876
				let max_dimension = adapter.limits().max_texture_dimension_2d;
				if size.width > max_dimension || size.height > max_dimension {
					log::warn!(
						"The resizing size {:?} exceeds the limit of {}.",
						size,
						max_dimension
					);
				} else {
					log::info!("Resizing to {:?}", size);
					config.width = size.width.max(1);
					config.height = size.height.max(1);
					example.resize(&config, &device, &queue);
					surface.configure(&device, &config);
				}
			}
			event::Event::WindowEvent { event, .. } => match event {
				WindowEvent::KeyboardInput {
					input:
						event::KeyboardInput {
							virtual_keycode: Some(event::VirtualKeyCode::Escape),
							state: event::ElementState::Pressed,
							..
						},
					..
				}
				| WindowEvent::CloseRequested => {
					*control_flow = ControlFlow::Exit;
				}
				WindowEvent::KeyboardInput {
					input:
						event::KeyboardInput {
							virtual_keycode: Some(event::VirtualKeyCode::Scroll),
							state: event::ElementState::Pressed,
							..
						},
					..
				} => {
					println!("{:#?}", instance.generate_report());
				}
				_ => {
					example.update(&window,&device,&queue,event);
				}
			},
			event::Event::DeviceEvent {
				event,
				..
			} => {
				example.device_event(&window,event);
			},
			event::Event::RedrawRequested(_) => {

				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 {
					format: Some(surface_view_format),
					..wgpu::TextureViewDescriptor::default()
				});

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

				frame.present();
			}
			_ => {}
		}
	});
}

pub struct Spawner<'a> {
	executor: async_executor::LocalExecutor<'a>,
}

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() {}
	}
}

pub fn run<E: Example>(title: &str) {
	let setup = pollster::block_on(setup::<E>(title));
	start::<E>(setup);
}