use crate::task::RequestRedraw;
use iris_core::{FrameParts, UiData, UiRenderNode, UiRenderState, util::Vec2};
use pollster::FutureExt;
use std::sync::Arc;
use std::time::Instant;
use wgpu::*;
use winit::{dpi::PhysicalSize, window::Window};

pub const CLEAR_COLOR: Color = Color::BLACK;

impl RequestRedraw for Window {
    fn request_redraw(&self) {
        Window::request_redraw(self);
    }
}

pub struct UiRenderer {
    window: Arc<Window>,
    surface: Surface<'static>,
    device: Device,
    queue: Queue,
    config: SurfaceConfiguration,
    encoder: CommandEncoder,
    pub ui: UiRenderNode,
}

impl UiRenderer {
    pub fn update(&mut self, ui: &mut UiData, render: &mut UiRenderState) {
        self.ui.update(&self.device, &self.queue, ui, render);
    }

    /// The two waits, so a desktop frame divides up the same way an
    /// Android one does -- see `AndroidRenderer::draw` for why the
    /// swapchain acquire is measured apart from the work.
    pub fn draw(&mut self) -> FrameParts {
        let acquire_start = Instant::now();
        let output = match self.surface.get_current_texture() {
            CurrentSurfaceTexture::Success(texture)
            | CurrentSurfaceTexture::Suboptimal(texture) => texture,
            // wgpu 30 turned this Result into an enum; every arm here was an
            // `Err` the previous `.unwrap()` panicked on, except `Occluded`,
            // which is new. Named rather than swallowed: a window that stops
            // presenting silently is the state this file's `pre_present_notify`
            // comment was written about.
            other => panic!("no surface texture to draw into: {other:?}"),
        };
        let acquire = acquire_start.elapsed();
        let view = output
            .texture
            .create_view(&TextureViewDescriptor::default());

        let mut encoder = std::mem::replace(&mut self.encoder, Self::create_encoder(&self.device));
        {
            let render_pass = &mut encoder.begin_render_pass(&RenderPassDescriptor {
                color_attachments: &[Some(RenderPassColorAttachment {
                    view: &view,
                    resolve_target: None,
                    ops: Operations {
                        load: LoadOp::Clear(CLEAR_COLOR),
                        store: StoreOp::Store,
                    },
                    depth_slice: None,
                })],
                ..Default::default()
            });
            self.ui.draw(render_pass);
        }

        let submit_start = Instant::now();
        self.queue.submit(std::iter::once(encoder.finish()));
        // Immediately before presenting, so the windowing system can schedule
        // the frame. On Wayland this is what ties the commit to the surface's
        // frame callback; without it a frame drawn when nothing else follows
        // could sit unpresented, and the window kept the layout it had before
        // the compositor's first resize -- intermittently, on about a fifth of
        // starts, with nothing left to flush it.
        self.window.pre_present_notify();
        self.queue.present(output);
        FrameParts::waits(acquire, submit_start.elapsed())
    }

    pub fn resize(&mut self, size: &PhysicalSize<u32>) {
        self.config.width = size.width;
        self.config.height = size.height;
        self.surface.configure(&self.device, &self.config);
        // Physical, matching `new`'s own seed -- see the comment there.
        self.ui.resize(
            Vec2::new(size.width as f32, size.height as f32),
            &self.queue,
        );
    }

    fn create_encoder(device: &Device) -> CommandEncoder {
        device.create_command_encoder(&CommandEncoderDescriptor {
            label: Some("Render Encoder"),
        })
    }

    pub fn new(window: Arc<Window>) -> Self {
        let size = window.inner_size();

        // `force-gles` on the desktop too, not just on Android: the
        // GLES backend has behaviour of its own (a one-layer array
        // texture is a `GL_TEXTURE_2D` -- see
        // `GpuTextures::create_array_texture`), and a machine with a
        // real GPU is where that is cheap to reproduce and screenshot.
        let mut backends = if cfg!(feature = "force-gles") {
            Backends::GL
        } else {
            Backends::PRIMARY
        };
        // The display handle comes from the window rather than being left
        // out: wgpu 30 asks for it whenever a GLES surface is going to be
        // presented on Wayland, which is exactly what the fallback below
        // produces on this machine.
        let mut instance = Instance::new(InstanceDescriptor {
            backends,
            ..InstanceDescriptor::new_with_display_handle(Box::new(window.clone()))
        });
        // The same fallback the Android backend grew in 85869d0, and for
        // the same reason: a machine can advertise a Vulkan ICD with no
        // device behind it, and refusing to draw at all because the only
        // usable adapter is a GLES one is iris's bug rather than the
        // machine's. On this VM the Vulkan device disappears whenever
        // the host refuses a virtio-gpu context, so `run-headless.sh` --
        // layer 2 of the test rig -- aborted with `Could not get
        // adapter!` while GL was sitting there working. Probed before the
        // surface exists, matching Android, where an instance carrying
        // both backends fails worse than one carrying the wrong one.
        if backends != Backends::GL && instance.enumerate_adapters(backends).block_on().is_empty() {
            log::warn!(
                "iris renderer: no {backends:?} adapter on this machine, falling back to GLES"
            );
            backends = Backends::GL;
            instance = Instance::new(InstanceDescriptor {
                backends,
                ..InstanceDescriptor::new_with_display_handle(Box::new(window.clone()))
            });
        }

        let surface = instance
            .create_surface(window.clone())
            .expect("Could not create window surface!");

        let adapter = instance
            .request_adapter(&RequestAdapterOptions {
                power_preference: PowerPreference::default(),
                compatible_surface: Some(&surface),
                force_fallback_adapter: false,
                ..Default::default()
            })
            .block_on()
            .unwrap_or_else(|error| {
                panic!("No usable GPU adapter for backends {backends:?}: {error}")
            });

        // Say which adapter won, in the same words the Android backend
        // uses. Without it a layer-2 screenshot or frame time from this
        // window carries no record of what drew it, and the two cases that
        // matter look identical in the PNG: the host's real GPU, and
        // llvmpipe after this VM lost its virtio-gpu contexts. That
        // happened on 2026-09-08, and the only reason anyone noticed is
        // that the fallback above did not exist yet and the app aborted
        // instead. A silent fallback needs this line to stay honest.
        {
            let info = adapter.get_info();
            log::info!(
                "iris renderer: {name} ({backend:?}, {driver}{driver_info}) on {backends:?}",
                name = info.name,
                backend = info.backend,
                driver = info.driver,
                driver_info = if info.driver_info.is_empty() {
                    String::new()
                } else {
                    format!(" {}", info.driver_info)
                },
            );
        }

        // No features beyond what wgpu asks for by default, and no
        // binding-array limits: the atlas is one texture_2d_array and a
        // standalone image is its own ordinary bind group, neither of which
        // needs descriptor indexing. See TEXTURES.md's "Recommended shape"
        // for why the old binding array asked for
        // VK_EXT_descriptor_indexing unconditionally and did not survive a
        // real share of Android GPUs. `iris_core::device_limits()` is
        // shared with the Android backend; see its own doc for why it is
        // not simply `Limits::default()`.
        let (device, queue) = adapter
            .request_device(&DeviceDescriptor {
                required_limits: iris_core::device_limits(),
                ..Default::default()
            })
            .block_on()
            .expect("Could not get device!");

        let surface_caps = surface.get_capabilities(&adapter);
        let surface_format = surface_caps
            .formats
            .iter()
            .copied()
            .find(|f| f.is_srgb())
            .unwrap_or(surface_caps.formats[0]);

        let config = SurfaceConfiguration {
            usage: TextureUsages::RENDER_ATTACHMENT,
            format: surface_format,
            // wgpu 30's new field; `Auto` is what every earlier version did.
            color_space: SurfaceColorSpace::Auto,
            width: size.width,
            height: size.height,
            // Vsync, because a toolkit aiming at battery life must not present
            // frames a display will never show: AutoNoVsync accepts them as
            // fast as the GPU will take them, so a redraw burst costs whatever
            // the hardware can be made to do rather than one frame.
            // AutoVsync picks Fifo, which every backend supports.
            present_mode: PresentMode::AutoVsync,
            alpha_mode: surface_caps.alpha_modes[0],
            desired_maximum_frame_latency: 2,
            view_formats: vec![],
        };

        surface.configure(&device, &config);

        let encoder = Self::create_encoder(&device);

        // Unlike the Android backend, the desktop backend has no on-screen
        // fallback to show a diagnostic through, so a renderer-creation
        // failure still panics here -- but now with wgpu's full "Caused
        // by:" chain as the message, since `UiRenderNode::new` returns it
        // rather than letting wgpu's own default handler panic first (see
        // that function's doc comment).
        // Physical size, the same units the swapchain, `WindowEvent::
        // Resized`, the pointer and the widget tree all use -- see
        // `default::content_scale` for why this backend stopped dividing
        // into a separate logical space, and what disagreed while it did.
        let physical_size = Vec2::new(size.width as f32, size.height as f32);
        let ui = UiRenderNode::new(&device, &queue, &config, physical_size)
            .expect("Could not create iris render node!");

        Self {
            surface,
            device,
            queue,
            config,
            encoder,
            ui,
            window,
        }
    }

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