use std::cell::{Cell, RefCell};
use std::rc::Rc;

use wasm_bindgen::prelude::wasm_bindgen;

use crate::gpu::Wgpu;
use crate::gpu_resource::{profiler, GpuPass, ProfileMap};
use crate::graph::{ColorAttachment, DepthAttachment};
use crate::render_data::RenderData;
use crate::store::{Loadout, Store};

#[wasm_bindgen(inline_js = r#"
const channel = new MessageChannel();
const ready = [];
channel.port1.onmessage = () => ready.shift()?.();

export function nextFrame() {
    return new Promise(resolve => requestAnimationFrame(resolve));
}

export function yieldTask() {
    return new Promise(resolve => {
        ready.push(resolve);
        channel.port2.postMessage(0);
    });
}
"#)]
extern "C" {
    #[wasm_bindgen(js_name = nextFrame)]
    async fn next_frame();
    #[wasm_bindgen(js_name = yieldTask)]
    async fn yield_task();
}

pub struct RenderLoop {
    playing: Cell<bool>,
    fps: Cell<u32>,
    started: Cell<bool>,
    frame: Cell<u32>,
    elapsed: Cell<f64>,
    last: Cell<f64>,
    active_loadout: Loadout,
    profile_state: RefCell<profiler::ProfileState>,
}

impl RenderLoop {
    pub fn new() -> Self {
        Self {
            playing: Cell::new(true),
            fps: Cell::new(0),
            started: Cell::new(false),
            frame: Cell::new(0),
            elapsed: Cell::new(0.0),
            last: Cell::new(js_sys::Date::now()),
            active_loadout: todo!(),
            profile_state: RefCell::new(profiler::ProfileState::Detached),
        }
    }

    pub fn play(&self) {
        self.last.set(js_sys::Date::now());
        self.playing.set(true);
    }

    pub fn pause(&self) {
        self.playing.set(false);
    }

    pub fn set_fps(&self, fps: u32) -> Result<(), &'static str> {
        if fps > 1000 {
            return Err("FPS");
        }
        self.fps.set(fps);
        Ok(())
    }

    pub fn set_profiling(&mut self) {
        self.profile_state = RefCell::new(profiler::ProfileState::Attached);
    }

    pub fn take_profile(&self) -> Option<String> {
        if let profiler::ProfileState::Ready(data) = self.profile_state.get_mut().take() {
            Some(data)
        } else {
            None
        }
    }

    pub fn start(self: &Rc<Self>, gpu: &Wgpu, data: Rc<RefCell<RenderData>>) {
        if self.started.replace(true) {
            return;
        }
        let control = self.clone();
        wasm_bindgen_futures::spawn_local(async move {
            loop {
                next_frame().await;
                if !control.playing.get() {
                    continue;
                }

                let started = js_sys::Date::now();
                let fps = control.fps.get();
                if fps != 0 && started - control.last.get() < 900.0 / f64::from(fps) {
                    continue;
                }
                let delta = (started - control.last.replace(started)) / 1000.0;
                let elapsed = control.elapsed.get() + delta;
                control.elapsed.set(elapsed);
                let frame = control.frame.get().wrapping_add(1);
                control.frame.set(frame);
                {
                    let mut data = data.borrow_mut();
                    data.update_signals(delta as f32, frame, elapsed as f32, control.fps.get());
                }

                // returns false when no render is pending
                if !data.borrow_mut().begin_render() {
                    continue;
                }

                let should_profile = matches!(
                    *control.profile_state.borrow(),
                    profiler::ProfileState::Attached
                );

                gpu.render(&mut self.active_loadout, &data.borrow(), should_profile)
                    .and_then(|profile_metadata| {
                        // we are done with render loop but we got a profile data for this
                        // frame, so we need to process that

                        control.profile_state
                    });

                if let Some((profile, adapter, width, height)) = submission {
                    control.profile_pending.set(true);
                    control.profile_after.set(started + 250.0);
                    let control = control.clone();
                    wasm_bindgen_futures::spawn_local(async move {
                        while profile.state() == 0 {
                            yield_task().await;
                        }
                        if profile.state() == 1 {
                            let passes = profile
                                .read()
                                .into_iter()
                                .map(|(name, milliseconds)| profiler::Pass { name, milliseconds })
                                .collect::<Vec<_>>();
                            let milliseconds =
                                passes.iter().map(|pass| pass.milliseconds).sum::<f64>();
                            if control.profiling.get() {
                                *control.profile_state.borrow_mut() = Some(
                                    profiler::FrameData {
                                        frame,
                                        milliseconds,
                                        readback_milliseconds: js_sys::Date::now() - started,
                                        adapter,
                                        canvas: profiler::Canvas { width, height },
                                        passes,
                                    }
                                    .to_string(),
                                );
                            }
                        }
                        control.profile_pending.set(false);
                    });
                }
            }
        });
    }
}

impl Wgpu {
    fn render(
        &mut self,
        loadout: &mut Loadout,
        data: &RenderData,
        profile: bool,
    ) -> Result<ProfileMap, String> {
        for buffer in loadout.resources.buffers.values() {
            if !buffer.sync_each_frame {
                continue;
            }
            self.queue.write_buffer(
                &buffer.buffer,
                0,
                data.bytes(&buffer.source).ok_or("ROWS_UNKNOWN")?,
            );
        }

        let output = match self.surface.get_current_texture() {
            Ok(output) => output,
            Err(wgpu::SurfaceError::Lost | wgpu::SurfaceError::Outdated) => {
                self.surface.configure(&self.device, &self.config);
                self.surface.get_current_texture().map_err(|_| "SURFACE")?
            }
            Err(wgpu::SurfaceError::Timeout) => return Err("SURFACE".into()),
            Err(_) => return Err("SURFACE".into()),
        };

        let surface_view = output
            .texture
            .create_view(&wgpu::TextureViewDescriptor::default());

        // profiler is used only when enabled
        // the presence of a profiler means:
        // - profiler is available and
        // - we want to profile this frame
        let profiler = if profile {
            loadout.resources.profiler
        } else {
            None
        };

        let mut encoder = self
            .device
            .create_command_encoder(&wgpu::CommandEncoderDescriptor {
                label: Some("frame"),
            });
        for (pass_index, compiled) in loadout.resources.passes.iter().enumerate() {
            match compiled {
                GpuPass::Compute {
                    pass,
                    pipeline,
                    bind_groups,
                    ..
                } => {
                    let pass = &loadout.graph.passes[*pass];
                    let timestamp_writes = profiler.and(|p| wgpu::ComputePassTimestampWrites {
                        query_set: &p.query_set,
                        beginning_of_pass_write_index: Some(pass_index as u32 * 2),
                        end_of_pass_write_index: Some(pass_index as u32 + 1),
                    });

                    let mut command = encoder.begin_compute_pass(&wgpu::ComputePassDescriptor {
                        label: Some(&pass.id),
                        timestamp_writes,
                    });
                    command.set_pipeline(pipeline);
                    for (group, bind_group) in bind_groups {
                        command.set_bind_group(*group, bind_group, &[]);
                    }
                    command.dispatch_workgroups(
                        pass.dispatch[0],
                        pass.dispatch[1],
                        pass.dispatch[2],
                    );
                }
                GpuPass::Render {
                    first,
                    last,
                    bundle,
                    ..
                } => {
                    let pass = &loadout.graph.passes[*first];
                    let last = &loadout.graph.passes[*last];
                    let colors = pass
                        .color
                        .iter()
                        .zip(&last.color)
                        .map(|(attachment, final_attachment)| {
                            Ok(Some(wgpu::RenderPassColorAttachment {
                                view: view(
                                    &loadout.resources,
                                    &surface_view,
                                    &attachment.resource,
                                )?,
                                depth_slice: None,
                                resolve_target: None,
                                ops: color_ops(attachment, final_attachment)?,
                            }))
                        })
                        .collect::<Result<Vec<_>, String>>()?;
                    let depth = pass
                        .depth
                        .as_ref()
                        .zip(last.depth.as_ref())
                        .map(|(attachment, final_attachment)| {
                            Ok::<_, String>(wgpu::RenderPassDepthStencilAttachment {
                                view: view(
                                    &loadout.resources,
                                    &surface_view,
                                    &attachment.resource,
                                )?,
                                depth_ops: Some(depth_ops(attachment, final_attachment)?),
                                stencil_ops: None,
                            })
                        })
                        .transpose()?;

                    let timestamp_writes = profiler.and(|p| wgpu::RenderPassTimestampWrites {
                        query_set: &p.query_set,
                        beginning_of_pass_write_index: Some(pass_index as u32 * 2),
                        end_of_pass_write_index: Some(pass_index as u32 * 2 + 1),
                    });

                    let mut command = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                        label: Some(&pass.id),
                        color_attachments: &colors,
                        depth_stencil_attachment: depth,
                        timestamp_writes,
                        occlusion_query_set: None,
                    });
                    command.execute_bundles([bundle]);
                }
            }
        }

        profiler.as_ref().map(|p| p.encode_query_set(&mut encoder));
        self.queue.submit([encoder.finish()]);

        output.present();

        profiler
            .and_then(|p| p.map_profile(self.queue.get_timestamp_period()))
            .flatten();
    }
}

fn view<'a>(
    resources: &'a crate::gpu_resource::GpuResources,
    surface: &'a wgpu::TextureView,
    id: &str,
) -> Result<&'a wgpu::TextureView, String> {
    if id == "canvas" {
        Ok(surface)
    } else {
        resources
            .texture_view(id)
            .ok_or_else(|| "GRAPH_ATTACHMENT".into())
    }
}

fn color_ops(
    attachment: &ColorAttachment,
    final_attachment: &ColorAttachment,
) -> Result<wgpu::Operations<wgpu::Color>, String> {
    let clear = attachment.clear.as_slice();
    Ok(wgpu::Operations {
        load: match attachment.load.as_str() {
            "load" => wgpu::LoadOp::Load,
            "clear" => wgpu::LoadOp::Clear(wgpu::Color {
                r: f64::from(clear.first().copied().unwrap_or(0.0)),
                g: f64::from(clear.get(1).copied().unwrap_or(0.0)),
                b: f64::from(clear.get(2).copied().unwrap_or(0.0)),
                a: f64::from(clear.get(3).copied().unwrap_or(1.0)),
            }),
            _ => return Err("GRAPH_LOAD_OP".into()),
        },
        store: store_op(&final_attachment.store)?,
    })
}

fn depth_ops(
    attachment: &DepthAttachment,
    final_attachment: &DepthAttachment,
) -> Result<wgpu::Operations<f32>, String> {
    Ok(wgpu::Operations {
        load: match attachment.load.as_str() {
            "load" => wgpu::LoadOp::Load,
            "clear" => wgpu::LoadOp::Clear(attachment.clear),
            _ => return Err("GRAPH_LOAD_OP".into()),
        },
        store: store_op(&final_attachment.store)?,
    })
}

fn store_op(value: &str) -> Result<wgpu::StoreOp, String> {
    match value {
        "store" => Ok(wgpu::StoreOp::Store),
        "discard" => Ok(wgpu::StoreOp::Discard),
        _ => Err("GRAPH_STORE_OP".into()),
    }
}