//! Backdrops (docs/backgrounds.md): the quiet, moving pictures behind

//! some of OxygenHub's pages, in Rust compiled to WebAssembly and drawn

//! with WebGL2. `sky` is the scene and its motion, with no browser in it;

//! `gl` draws it; this module is the browser around them: the frame loop,

//! the cursor, the window's size, the page's colours and when to stop.

pub mod gl;

pub mod sky;

use sky::{Colours, Event, Kind, Repo, Sky};

use std::cell::RefCell;

use std::rc::Rc;

use wasm_bindgen::prelude::*;

use wasm_bindgen::JsCast;

use web_sys::{HtmlCanvasElement, HtmlElement, WebGl2RenderingContext, Window};

/// The highest device pixel ratio drawn at: sharp enough, and cheap.

const MAX_DPR: f64 = 1.5;

/// After this long without input a moving backdrop draws its last frame

/// and stops until the next movement (§6).

const STOP_AFTER_S: f64 = 120.0;

/// A still cursor drops the frame rate to half after this long.

const HALF_RATE_AFTER_S: f64 = 3.0;

struct Engine {

    window: Window,

    canvas: HtmlCanvasElement,

    renderer: gl::Renderer,

    sky: Sky,

    colours: Colours,

    colours_at: f64,

    probe: HtmlElement,

    label: HtmlElement,

    label_text: String,

    inst: Vec<f32>,

    lines: Vec<f32>,

    last: Option<f64>,

    frame: u64,

    running: bool,

    input_at: f64,

    pw: i32,

    ph: i32,

}

type Frame = Rc<RefCell<Option<Closure<dyn FnMut(f64)>>>>;

impl Engine {

    fn now(&self) -> f64 {

        self.window.performance().map(|p| p.now()).unwrap_or(0.0)

    }

    /// Fit the canvas to the window.

    fn fit(&mut self) {

        let w = self.window.inner_width().ok().and_then(|v| v.as_f64()).unwrap_or(0.0);

        let h = self.window.inner_height().ok().and_then(|v| v.as_f64()).unwrap_or(0.0);

        let dpr = self.window.device_pixel_ratio().clamp(1.0, MAX_DPR);

        self.pw = (w * dpr).round() as i32;

        self.ph = (h * dpr).round() as i32;

        self.canvas.set_width(self.pw.max(1) as u32);

        self.canvas.set_height(self.ph.max(1) as u32);

        self.sky.resize(w as f32, h as f32);

    }

    /// The page's backdrop tokens, as the browser computes them, so a

    /// theme switch shows within a second.

    fn read_colours(&mut self) {

        let read = |token: &str, fallback: sky::Rgba| -> sky::Rgba {

            let _ = self.probe.style().set_property("color", &format!("var({token})"));

            self.window

                .get_computed_style(&self.probe)

                .ok()

                .flatten()

                .and_then(|s| s.get_property_value("color").ok())

                .and_then(|c| sky::parse_colour(&c))

                .unwrap_or(fallback)

        };

        self.colours = Colours {

            mark: read("--bd-mark", [0.5, 0.5, 0.55, 0.16]),

            lit: read("--bd-lit", [0.04, 0.41, 0.85, 0.7]),

            link: read("--bd-link", [0.04, 0.41, 0.85, 0.22]),

        };

    }

    /// One animation frame at time `t`; whether another is wanted.

    fn tick(&mut self, t: f64) -> bool {

        if self.window.document().is_some_and(|d| d.hidden()) {

            self.last = None;

            return false;

        }

        let idle = (t - self.input_at) / 1000.0;

        self.frame += 1;

        if !self.sky.still && idle > HALF_RATE_AFTER_S && self.frame % 2 == 1 {

            return true;

        }

        let dt = self.last.map(|l| ((t - l) / 1000.0) as f32).unwrap_or(0.0);

        self.last = Some(t);

        if t - self.colours_at > 1000.0 {

            self.read_colours();

            self.colours_at = t;

        }

        self.sky.step(dt);

        self.sky.instances(&self.colours, &mut self.inst);

        self.sky.links(&self.colours, &mut self.lines);

        self.renderer.draw(self.sky.w, self.sky.h, self.pw, self.ph, &self.inst, &self.lines);

        self.show_label();

        if self.sky.still {

            self.sky.busy()

        } else {

            idle < STOP_AFTER_S || self.sky.busy()

        }

    }

    /// The name above the cluster a cursor rests by (§4): faded in and out

    /// by CSS, which centres it on `left` and sets its foot on `top`.

    fn show_label(&mut self) {

        let next = self.sky.label().map(|(name, x, y)| (name.to_string(), x, y));

        let style = self.label.style();

        match next {

            Some((name, x, y)) => {

                if name != self.label_text {

                    self.label.set_text_content(Some(&name));

                    self.label_text = name;

                }

                let _ = style.set_property("left", &format!("{}px", x as i32));

                let _ = style.set_property("top", &format!("{}px", y as i32));

                let _ = style.set_property("opacity", "1");

            }

            None => {

                let _ = style.set_property("opacity", "0");

            }

        }

    }

}

/// Ask for a frame unless the loop is already running.

fn wake(engine: &Rc<RefCell<Engine>>, frame: &Frame) {

    let mut e = engine.borrow_mut();

    if e.running {

        return;

    }

    e.running = true;

    if let Some(f) = frame.borrow().as_ref() {

        let _ = e.window.request_animation_frame(f.as_ref().unchecked_ref());

    }

}

fn get(v: &JsValue, key: &str) -> JsValue {

    js_sys::Reflect::get(v, &JsValue::from_str(key)).unwrap_or(JsValue::UNDEFINED)

}

/// The page's data (§5): `{now, repos: [name], events: [[repo, kind, at_ms, n]]}`.

fn read_data(data: &JsValue) -> (Vec<Repo>, Vec<Event>) {

    let now = get(data, "now").as_f64().unwrap_or(0.0);

    let repos: Vec<Repo> =

        js_sys::Array::from(&get(data, "repos")).iter().filter_map(|v| v.as_string()).map(|name| Repo { name }).collect();

    let events: Vec<Event> = js_sys::Array::from(&get(data, "events"))

        .iter()

        .filter_map(|v| {

            let e = js_sys::Array::from(&v);

            let repo = e.get(0).as_f64()? as usize;

            let kind = Kind::from_code(e.get(1).as_f64()? as u32);

            let at = e.get(2).as_f64()?;

            let n = e.get(3).as_f64().unwrap_or(1.0).max(1.0) as u32;

            Some(Event { repo, kind, age_days: ((now - at) / 86_400_000.0).max(0.0) as f32, n })

        })

        .collect();

    (repos, events)

}

/// Start the dashboard's sky on `canvas` with the page's `data`. `still`

/// is the viewer's choice of a still backdrop; reduced motion asks for

/// one too. Without WebGL2 there is no backdrop, and nothing breaks.

#[wasm_bindgen]

pub fn start(canvas: HtmlCanvasElement, data: JsValue, still: bool) -> Result<(), JsValue> {

    let window = web_sys::window().ok_or("no window")?;

    let document = window.document().ok_or("no document")?;

    let reduced = window.match_media("(prefers-reduced-motion: reduce)").ok().flatten().is_some_and(|m| m.matches());

    let still = still || reduced;

    let options = js_sys::Object::new();

    js_sys::Reflect::set(&options, &"alpha".into(), &true.into())?;

    js_sys::Reflect::set(&options, &"premultipliedAlpha".into(), &true.into())?;

    js_sys::Reflect::set(&options, &"antialias".into(), &false.into())?;

    js_sys::Reflect::set(&options, &"powerPreference".into(), &"low-power".into())?;

    let gl: WebGl2RenderingContext = canvas.get_context_with_context_options("webgl2", &options)?.ok_or("no WebGL2")?.dyn_into()?;

    let renderer = gl::Renderer::new(gl)?;

    let body = document.body().ok_or("no body")?;

    let probe: HtmlElement = document.create_element("span")?.dyn_into()?;

    probe.set_attribute("style", "position:fixed;visibility:hidden;pointer-events:none")?;

    probe.set_attribute("aria-hidden", "true")?;

    body.append_child(&probe)?;

    let label: HtmlElement = document.create_element("div")?.dyn_into()?;

    label.set_class_name("bd-label");

    label.set_attribute("aria-hidden", "true")?;

    body.append_child(&label)?;

    let (repos, events) = read_data(&data);

    let sky = Sky::new(&repos, &events, 0.0, 0.0, still);

    let colours = Colours { mark: [0.0; 4], lit: [0.0; 4], link: [0.0; 4] };

    let engine = Rc::new(RefCell::new(Engine {

        window: window.clone(),

        canvas,

        renderer,

        sky,

        colours,

        colours_at: f64::NEG_INFINITY,

        probe,

        label,

        label_text: String::new(),

        inst: Vec::new(),

        lines: Vec::new(),

        last: None,

        frame: 0,

        running: false,

        input_at: 0.0,

        pw: 0,

        ph: 0,

    }));

    {

        let mut e = engine.borrow_mut();

        e.fit();

        e.input_at = e.now();

    }

    // The frame loop: each frame asks for the next while it is wanted.

    let frame: Frame = Rc::new(RefCell::new(None));

    {

        let (engine, again) = (engine.clone(), frame.clone());

        *frame.borrow_mut() = Some(Closure::new(move |t: f64| {

            let more = engine.borrow_mut().tick(t);

            let mut e = engine.borrow_mut();

            if more {

                if let Some(f) = again.borrow().as_ref() {

                    let _ = e.window.request_animation_frame(f.as_ref().unchecked_ref());

                }

            } else {

                e.running = false;

            }

        }));

    }

    // The cursor lights marks; it never moves them.

    {

        let (engine, frame) = (engine.clone(), frame.clone());

        let moved = Closure::<dyn FnMut(web_sys::MouseEvent)>::new(move |ev: web_sys::MouseEvent| {

            {

                let mut e = engine.borrow_mut();

                e.sky.point(Some((ev.client_x() as f32, ev.client_y() as f32)));

                e.input_at = e.now();

            }

            wake(&engine, &frame);

        });

        window.add_event_listener_with_callback("mousemove", moved.as_ref().unchecked_ref())?;

        moved.forget();

    }

    {

        let (engine, frame) = (engine.clone(), frame.clone());

        let left = Closure::<dyn FnMut(web_sys::MouseEvent)>::new(move |ev: web_sys::MouseEvent| {

            if ev.related_target().is_none() {

                engine.borrow_mut().sky.point(None);

                wake(&engine, &frame);

            }

        });

        document.add_event_listener_with_callback("mouseout", left.as_ref().unchecked_ref())?;

        left.forget();

    }

    {

        let (engine, frame) = (engine.clone(), frame.clone());

        let resized = Closure::<dyn FnMut()>::new(move || {

            engine.borrow_mut().fit();

            wake(&engine, &frame);

        });

        window.add_event_listener_with_callback("resize", resized.as_ref().unchecked_ref())?;

        resized.forget();

    }

    {

        let (engine, frame) = (engine.clone(), frame.clone());

        let shown = Closure::<dyn FnMut()>::new(move || {

            let visible = engine.borrow().window.document().is_some_and(|d| !d.hidden());

            if visible {

                engine.borrow_mut().last = None;

                wake(&engine, &frame);

            }

        });

        document.add_event_listener_with_callback("visibilitychange", shown.as_ref().unchecked_ref())?;

        shown.forget();

    }

    wake(&engine, &frame);

    Ok(())

}