use crate::{Backend, Color, Error, Renderer, Settings, Viewport};

use futures::stream::{self, StreamExt};

use iced_graphics::compositor;
use iced_native::futures;
use raw_window_handle::{HasRawDisplayHandle, HasRawWindowHandle};

use std::marker::PhantomData;

/// A window graphics backend for iced powered by `wgpu`.
#[allow(missing_debug_implementations)]
pub struct Compositor<Theme> {
    settings: Settings,
    instance: wgpu::Instance,
    adapter: wgpu::Adapter,
    device: wgpu::Device,
    queue: wgpu::Queue,
    staging_belt: wgpu::util::StagingBelt,
    format: wgpu::TextureFormat,
    theme: PhantomData<Theme>,
}

impl<Theme> Compositor<Theme> {
    const CHUNK_SIZE: u64 = 10 * 1024;

    /// Requests a new [`Compositor`] with the given [`Settings`].
    ///
    /// Returns `None` if no compatible graphics adapter could be found.
    pub async fn request<W: HasRawWindowHandle + HasRawDisplayHandle>(
        settings: Settings,
        compatible_window: Option<&W>,
    ) -> Option<Self> {
        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor {
            backends: settings.internal_backend,
            ..Default::default()
        });

        log::info!("{:#?}", settings);

        #[cfg(not(target_arch = "wasm32"))]
        if log::max_level() >= log::LevelFilter::Info {
            let available_adapters: Vec<_> = instance
                .enumerate_adapters(settings.internal_backend)
                .map(|adapter| adapter.get_info())
                .collect();
            log::info!("Available adapters: {:#?}", available_adapters);
        }

        #[allow(unsafe_code)]
        let compatible_surface = compatible_window
            .and_then(|window| unsafe { instance.create_surface(window).ok() });

        let adapter = instance
            .request_adapter(&wgpu::RequestAdapterOptions {
                power_preference: if settings.antialiasing.is_none() {
                    wgpu::PowerPreference::LowPower
                } else {
                    wgpu::PowerPreference::HighPerformance
                },
                compatible_surface: compatible_surface.as_ref(),
                force_fallback_adapter: false,
            })
            .await?;

        log::info!("Selected: {:#?}", adapter.get_info());

        let format = compatible_surface.as_ref().and_then(|surface| {
            surface
                .get_capabilities(&adapter)
                .formats
                .iter()
                .filter(|format| format.describe().srgb)
                .copied()
                .next()
                .or_else(|| {
                    log::warn!("No sRGB format found!");

                    surface.get_capabilities(&adapter).formats.first().copied()
                })
        })?;

        log::info!("Selected format: {:?}", format);

        #[cfg(target_arch = "wasm32")]
        let limits = [wgpu::Limits::downlevel_webgl2_defaults()
            .using_resolution(adapter.limits())];

        #[cfg(not(target_arch = "wasm32"))]
        let limits =
            [wgpu::Limits::default(), wgpu::Limits::downlevel_defaults()];

        let limits = limits.into_iter().map(|limits| wgpu::Limits {
            max_bind_groups: 2,
            ..limits
        });

        let (device, queue) = stream::iter(limits)
            .filter_map(|limits| async {
                adapter.request_device(
                    &wgpu::DeviceDescriptor {
                        label: Some(
                            "iced_wgpu::window::compositor device descriptor",
                        ),
                        features: wgpu::Features::empty(),
                        limits,
                    },
                    None,
                ).await.ok()
            })
            .boxed()
            .next()
            .await?;

        let staging_belt = wgpu::util::StagingBelt::new(Self::CHUNK_SIZE);

        Some(Compositor {
            instance,
            settings,
            adapter,
            device,
            queue,
            staging_belt,
            format,
            theme: PhantomData,
        })
    }

    /// Creates a new rendering [`Backend`] for this [`Compositor`].
    pub fn create_backend(&self) -> Backend {
        Backend::new(&self.device, self.settings, self.format)
    }
}

impl<Theme> iced_graphics::window::Compositor for Compositor<Theme> {
    type Settings = Settings;
    type Renderer = Renderer<Theme>;
    type Surface = wgpu::Surface;

    fn new<W: HasRawWindowHandle + HasRawDisplayHandle>(
        settings: Self::Settings,
        compatible_window: Option<&W>,
    ) -> Result<(Self, Self::Renderer), Error> {
        let compositor = futures::executor::block_on(Self::request(
            settings,
            compatible_window,
        ))
        .ok_or(Error::GraphicsAdapterNotFound)?;

        let backend = compositor.create_backend();

        Ok((compositor, Renderer::new(backend)))
    }

    fn create_surface<W: HasRawWindowHandle + HasRawDisplayHandle>(
        &mut self,
        window: &W,
    ) -> wgpu::Surface {
        #[allow(unsafe_code)]
        unsafe {
            self.instance
                .create_surface(window)
                .expect("Create surface")
        }
    }

    fn configure_surface(
        &mut self,
        surface: &mut Self::Surface,
        width: u32,
        height: u32,
    ) {
        surface.configure(
            &self.device,
            &wgpu::SurfaceConfiguration {
                usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
                format: self.format,
                present_mode: self.settings.present_mode,
                width,
                height,
                alpha_mode: wgpu::CompositeAlphaMode::Auto,
                view_formats: vec![],
            },
        );
    }

    fn fetch_information(&self) -> compositor::Information {
        let information = self.adapter.get_info();

        compositor::Information {
            adapter: information.name,
            backend: format!("{:?}", information.backend),
        }
    }

    fn present<T: AsRef<str>>(
        &mut self,
        renderer: &mut Self::Renderer,
        surface: &mut Self::Surface,
        viewport: &Viewport,
        background_color: Color,
        overlay: &[T],
    ) -> Result<(), compositor::SurfaceError> {
        match surface.get_current_texture() {
            Ok(frame) => {
                let mut encoder = self.device.create_command_encoder(
                    &wgpu::CommandEncoderDescriptor {
                        label: Some("iced_wgpu encoder"),
                    },
                );

                let view = &frame
                    .texture
                    .create_view(&wgpu::TextureViewDescriptor::default());

                let _ =
                    encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                        label: Some(
                            "iced_wgpu::window::Compositor render pass",
                        ),
                        color_attachments: &[Some(
                            wgpu::RenderPassColorAttachment {
                                view,
                                resolve_target: None,
                                ops: wgpu::Operations {
                                    load: wgpu::LoadOp::Clear({
                                        let [r, g, b, a] =
                                            background_color.into_linear();

                                        wgpu::Color {
                                            r: f64::from(r),
                                            g: f64::from(g),
                                            b: f64::from(b),
                                            a: f64::from(a),
                                        }
                                    }),
                                    store: true,
                                },
                            },
                        )],
                        depth_stencil_attachment: None,
                    });

                renderer.with_primitives(|backend, primitives| {
                    backend.present(
                        &self.device,
                        &mut self.staging_belt,
                        &mut encoder,
                        view,
                        primitives,
                        viewport,
                        overlay,
                    );
                });

                // Submit work
                self.staging_belt.finish();
                let _submission = self.queue.submit(Some(encoder.finish()));
                frame.present();

                // Recall staging buffers
                self.staging_belt.recall();

                Ok(())
            }
            Err(error) => match error {
                wgpu::SurfaceError::Timeout => {
                    Err(compositor::SurfaceError::Timeout)
                }
                wgpu::SurfaceError::Outdated => {
                    Err(compositor::SurfaceError::Outdated)
                }
                wgpu::SurfaceError::Lost => Err(compositor::SurfaceError::Lost),
                wgpu::SurfaceError::OutOfMemory => {
                    Err(compositor::SurfaceError::OutOfMemory)
                }
            },
        }
    }
}