use std::num::NonZeroU32;

use thiserror::Error;
use winit::{
	dpi::{LogicalSize, PhysicalSize},
	error::OsError,
	event_loop::EventLoop,
	window::{Fullscreen, Window, WindowBuilder},
};

/// No device could be found which supports the given surface
#[derive(Clone, Copy, Debug, PartialEq, Eq, Error)]
#[error("No GPU could be found on this machine")]
pub struct NoGpuError {
	/// Prevents this type from being constructed
	_priv: (),
}

impl NoGpuError {
	/// Create a new error
	const fn new() -> Self {
		Self { _priv: () }
	}
}

#[derive(Debug, Error)]
pub enum NewRendererError {
	#[error(transparent)]
	NoGpu(#[from] NoGpuError),
	#[error(transparent)]
	WindowInitError(#[from] OsError),
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Resizable {
	pub min_width: Option<NonZeroU32>,
	pub min_height: Option<NonZeroU32>,
	pub max_width: Option<NonZeroU32>,
	pub max_height: Option<NonZeroU32>,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct WindowInfo {
	pub default_x: i32,
	pub default_y: i32,
	pub resizability: Option<Resizable>,
	pub default_maximized: bool,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum WindowMode {
	Windowed(WindowInfo),
	// TODO support choosing a monitor
	BorderlessFullscreen, // TODO exclusive fullscreen
}

#[derive(Clone, Debug, PartialEq, Eq)]
// TODO to consider: don't allow the x and y to be too big
// TODO window icon
pub struct RendererConfig {
	pub default_width: NonZeroU32,
	pub default_height: NonZeroU32,
	pub size: WindowMode,
	pub title: Option<Box<str>>,
	pub low_power: bool,
	pub vsync: bool,
}

pub struct Renderer {
	surface: wgpu::Surface,
	device: wgpu::Device,
	queue: wgpu::Queue,
	config: wgpu::SurfaceConfiguration,
	window: Window,
	event_loop: EventLoop<()>,
}

// TODO make this more complete
impl Renderer {
	/// Initializes the renderer
	///
	/// # Errors
	///
	/// Returns a [`NoGpu`] error if no device could be detected that can
	/// display to the window
	// TODO make it possible to use without winit (ie, use a bitmap in memory as a surface)
	// TODO make PowerPreference a configuration option
	// TODO check for zero size windows
	#[allow(clippy::missing_panics_doc)]
	pub async fn new(config: RendererConfig) -> Result<Self, NewRendererError> {
		let mut builder = WindowBuilder::new()
			.with_title(config.title.unwrap_or_else(|| "Alligator Game".into()))
			.with_inner_size(LogicalSize::new(
				config.default_width.get(),
				config.default_height.get(),
			));

		match config.size {
			WindowMode::Windowed(size) => {
				builder = builder.with_maximized(size.default_maximized);

				if let Some(resizing_options) = size.resizability {
					if resizing_options.max_height.is_some() || resizing_options.max_width.is_some()
					{
						builder = builder.with_max_inner_size(LogicalSize::new(
							resizing_options.max_width.unwrap_or(NonZeroU32::MAX).get(),
							resizing_options.max_height.unwrap_or(NonZeroU32::MAX).get(),
						));
					}

					if resizing_options.min_height.is_some() || resizing_options.min_width.is_some()
					{
						builder = builder.with_min_inner_size(LogicalSize::new(
							resizing_options.min_width.unwrap_or(NonZeroU32::MAX).get(),
							resizing_options.min_height.unwrap_or(NonZeroU32::MAX).get(),
						));
					}
				} else {
					builder = builder.with_resizable(false);
				}
			}
			WindowMode::BorderlessFullscreen => {
				builder = builder.with_fullscreen(Some(Fullscreen::Borderless(None)));
			}
		}

		let event_loop = EventLoop::new();
		let window = builder.build(&event_loop)?;

		// the instance's main purpose is to create an adapter and a surface
		let instance = wgpu::Instance::new(wgpu::Backends::all());

		// the surface is the part of the screen we'll draw to
		// TODO guarantee the window to stay open longer than the surface
		let surface = unsafe { instance.create_surface(&window) };

		let power_preference = if config.low_power {
			wgpu::PowerPreference::LowPower
		} else {
			wgpu::PowerPreference::HighPerformance
		};

		// the adapter is the handle to the GPU
		let adapter = instance
			.request_adapter(&wgpu::RequestAdapterOptions {
				power_preference,
				compatible_surface: Some(&surface),
				force_fallback_adapter: false,
			})
			.await;
		let adapter = adapter.or_else(|| {
			instance
				.enumerate_adapters(wgpu::Backends::all())
				.find(|adapter| !surface.get_supported_formats(adapter).is_empty())
		});
		let Some(adapter) = adapter else { return Err(NoGpuError::new().into()) };

		// gets a connection to the device, as well as a handle to its command queue
		// the options chosen here ensure that this is guaranteed to not panic
		let (device, queue) = adapter
			.request_device(
				&wgpu::DeviceDescriptor {
					label: None,
					features: wgpu::Features::empty(),
					limits: wgpu::Limits::default(),
				},
				None,
			)
			.await
			.unwrap();

		// configuration for the surface
		let config = wgpu::SurfaceConfiguration {
			usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
			format: surface.get_supported_formats(&adapter)[0], // TODO make this configurable
			width: config.default_width.get(),
			height: config.default_height.get(),
			present_mode: wgpu::PresentMode::Mailbox, // TODO make this configurable
		};

		surface.configure(&device, &config);

		Ok(Self {
			surface,
			device,
			queue,
			config,
			window,
			event_loop,
		})
	}

	pub const fn size(&self) -> PhysicalSize<u32> {
		PhysicalSize::new(self.config.width, self.config.height)
	}

	// TODO return error for zero-sized windows
	pub fn resize(&mut self, size: PhysicalSize<u32>) {
		if size.width > 0 && size.height > 0 {
			self.config.height = size.height;
			self.config.width = size.width;
			self.surface.configure(&self.device, &self.config);
		}
	}

	/// Renders a new frame to the window
	///
	/// # Errors
	///
	/// A number of problems could occur here. A timeout could occur while
	/// trying to acquire the next frame. There may also be no more memory left
	/// that can be used for the new frame.
	pub fn render(&mut self) -> Result<(), wgpu::SurfaceError> {
		// the new texture we can render to
		let output = self.surface.get_current_texture()?;
		let view = output
			.texture
			.create_view(&wgpu::TextureViewDescriptor::default());

		// this will allow us to send commands to the gpu
		let mut encoder = self
			.device
			.create_command_encoder(&wgpu::CommandEncoderDescriptor {
				label: Some("Render Encoder"),
			});

		{
			let _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::BLACK),
						store: true,
					},
				})],
				depth_stencil_attachment: None,
			});
		}
		// the encoder can't finish building the command buffer until the
		// render pass is dropped

		// submit the command buffer to the GPU
		self.queue.submit(std::iter::once(encoder.finish()));
		output.present();

		Ok(())
	}
}