#![deny(missing_docs)]

//! Dioxus WebSys
//!
//! ## Overview
//! ------------
//! This crate implements a renderer of the Dioxus Virtual DOM for the web browser using WebSys. This web render for
//! Dioxus is one of the more advanced renderers, supporting:
//! - idle work
//! - animations
//! - jank-free rendering
//! - controlled components
//! - hydration
//! - and more.
//!
//! The actual implementation is farily thin, with the heavy lifting happening inside the Dioxus Core crate.
//!
//! To purview the examples, check of the root Dioxus crate - the examples in this crate are mostly meant to provide
//! validation of websys-specific features and not the general use of Dioxus.

// ## RequestAnimationFrame and RequestIdleCallback
// ------------------------------------------------
// React implements "jank free rendering" by deliberately not blocking the browser's main thread. For large diffs, long
// running work, and integration with things like React-Three-Fiber, it's extremeley important to avoid blocking the
// main thread.
//
// React solves this problem by breaking up the rendering process into a "diff" phase and a "render" phase. In Dioxus,
// the diff phase is non-blocking, using "work_with_deadline" to allow the browser to process other events. When the diff phase
// is  finally complete, the VirtualDOM will return a set of "Mutations" for this crate to apply.
//
// Here, we schedule the "diff" phase during the browser's idle period, achieved by calling RequestIdleCallback and then
// setting a timeout from the that completes when the idleperiod is over. Then, we call requestAnimationFrame
//
//     From Google's guide on rAF and rIC:
//     -----------------------------------
//
//     If the callback is fired at the end of the frame, it will be scheduled to go after the current frame has been committed,
//     which means that style changes will have been applied, and, importantly, layout calculated. If we make DOM changes inside
//      of the idle callback, those layout calculations will be invalidated. If there are any kind of layout reads in the next
//      frame, e.g. getBoundingClientRect, clientWidth, etc, the browser will have to perform a Forced Synchronous Layout,
//      which is a potential performance bottleneck.
//
//     Another reason not trigger DOM changes in the idle callback is that the time impact of changing the DOM is unpredictable,
//     and as such we could easily go past the deadline the browser provided.
//
//     The best practice is to only make DOM changes inside of a requestAnimationFrame callback, since it is scheduled by the
//     browser with that type of work in mind. That means that our code will need to use a document fragment, which can then
//     be appended in the next requestAnimationFrame callback. If you are using a VDOM library, you would use requestIdleCallback
//     to make changes, but you would apply the DOM patches in the next requestAnimationFrame callback, not the idle callback.
//
//     Essentially:
//     ------------
//     - Do the VDOM work during the idlecallback
//     - Do DOM work in the next requestAnimationFrame callback

pub use crate::cfg::Config;
use dioxus_core::{Element, Scope, VirtualDom};
use futures_util::{
    future::{select, Either},
    pin_mut, FutureExt, StreamExt,
};

mod cache;
mod cfg;
mod dom;
#[cfg(feature = "eval")]
mod eval;
#[cfg(feature = "file_engine")]
mod file_engine;
#[cfg(all(feature = "hot_reload", debug_assertions))]
mod hot_reload;
#[cfg(feature = "hydrate")]
mod rehydrate;

// Currently disabled since it actually slows down immediate rendering
// todo: only schedule non-immediate renders through ric/raf
// mod ric_raf;
// mod rehydrate;

/// Launch the VirtualDOM given a root component and a configuration.
///
/// This function expects the root component to not have root props. To launch the root component with root props, use
/// `launch_with_props` instead.
///
/// This method will block the thread with `spawn_local` from wasm_bindgen_futures.
///
/// If you need to run the VirtualDOM in its own thread, use `run_with_props` instead and await the future.
///
/// # Example
///
/// ```rust, ignore
/// fn main() {
///     dioxus_web::launch(App);
/// }
///
/// static App: Component = |cx| {
///     render!(div {"hello world"})
/// }
/// ```
pub fn launch(root_component: fn(Scope) -> Element) {
    launch_with_props(root_component, (), Config::default());
}

/// Launch your app and run the event loop, with configuration.
///
/// This function will start your web app on the main web thread.
///
/// You can configure the WebView window with a configuration closure
///
/// ```rust, ignore
/// use dioxus::prelude::*;
///
/// fn main() {
///     dioxus_web::launch_with_props(App, Config::new().pre_render(true));
/// }
///
/// fn app(cx: Scope) -> Element {
///     cx.render(rsx!{
///         h1 {"hello world!"}
///     })
/// }
/// ```
pub fn launch_cfg(root: fn(Scope) -> Element, config: Config) {
    launch_with_props(root, (), config)
}

/// Launches the VirtualDOM from the specified component function and props.
///
/// This method will block the thread with `spawn_local`
///
/// # Example
///
/// ```rust, ignore
/// fn main() {
///     dioxus_web::launch_with_props(
///         App,
///         RootProps { name: String::from("joe") },
///         Config::new()
///     );
/// }
///
/// #[derive(ParitalEq, Props)]
/// struct RootProps {
///     name: String
/// }
///
/// static App: Component<RootProps> = |cx| {
///     render!(div {"hello {cx.props.name}"})
/// }
/// ```
pub fn launch_with_props<T: 'static>(
    root_component: fn(Scope<T>) -> Element,
    root_properties: T,
    config: Config,
) {
    wasm_bindgen_futures::spawn_local(run_with_props(root_component, root_properties, config));
}

/// Runs the app as a future that can be scheduled around the main thread.
///
/// Polls futures internal to the VirtualDOM, hence the async nature of this function.
///
/// # Example
///
/// ```ignore
/// fn main() {
///     let app_fut = dioxus_web::run_with_props(App, RootProps { name: String::from("joe") });
///     wasm_bindgen_futures::spawn_local(app_fut);
/// }
/// ```
pub async fn run_with_props<T: 'static>(root: fn(Scope<T>) -> Element, root_props: T, cfg: Config) {
    log::info!("Starting up");

    let mut dom = VirtualDom::new_with_props(root, root_props);

    #[cfg(feature = "eval")]
    {
        // Eval
        let cx = dom.base_scope();
        eval::init_eval(cx);
    }

    #[cfg(feature = "panic_hook")]
    if cfg.default_panic_hook {
        console_error_panic_hook::set_once();
    }

    #[cfg(all(feature = "hot_reload", debug_assertions))]
    let mut hotreload_rx = hot_reload::init();

    for s in crate::cache::BUILTIN_INTERNED_STRINGS {
        wasm_bindgen::intern(s);
    }
    for s in &cfg.cached_strings {
        wasm_bindgen::intern(s);
    }

    let (tx, mut rx) = futures_channel::mpsc::unbounded();

    #[cfg(feature = "hydrate")]
    let should_hydrate = cfg.hydrate;
    #[cfg(not(feature = "hydrate"))]
    let should_hydrate = false;

    let mut websys_dom = dom::WebsysDom::new(cfg, tx);

    log::info!("rebuilding app");

    if should_hydrate {
        #[cfg(feature = "hydrate")]
        {
            // todo: we need to split rebuild and initialize into two phases
            // it's a waste to produce edits just to get the vdom loaded

            let templates = dom.rebuild().templates;
            websys_dom.load_templates(&templates);

            if let Err(err) = websys_dom.rehydrate(&dom) {
                log::error!(
                    "Rehydration failed {:?}. Rebuild DOM into element from scratch",
                    &err
                );
                websys_dom.root.set_text_content(None);

                let edits = dom.rebuild();

                websys_dom.load_templates(&edits.templates);
                websys_dom.apply_edits(edits.edits);
            }
        }
    } else {
        let edits = dom.rebuild();

        websys_dom.load_templates(&edits.templates);
        websys_dom.apply_edits(edits.edits);
    }

    // the mutations come back with nothing - we need to actually mount them
    websys_dom.mount();

    loop {
        log::trace!("waiting for work");

        // if virtualdom has nothing, wait for it to have something before requesting idle time
        // if there is work then this future resolves immediately.
        let (mut res, template) = {
            let work = dom.wait_for_work().fuse();
            pin_mut!(work);

            #[cfg(all(feature = "hot_reload", debug_assertions))]
            // futures_util::select! {
            //     _ = work => (None, None),
            //     new_template = hotreload_rx.next() => {
            //         (None, new_template)
            //     }
            //     evt = rx.next() =>
            // }
            match select(work, select(hotreload_rx.next(), rx.next())).await {
                Either::Left((_, _)) => (None, None),
                Either::Right((Either::Left((new_template, _)), _)) => (None, new_template),
                Either::Right((Either::Right((evt, _)), _)) => (evt, None),
            }
            #[cfg(not(all(feature = "hot_reload", debug_assertions)))]
            match select(work, rx.next()).await {
                Either::Left((_, _)) => (None, None),
                Either::Right((evt, _)) => (evt, None),
            }
        };

        if let Some(template) = template {
            dom.replace_template(template);
        }

        // Dequeue all of the events from the channel in send order
        // todo: we should re-order these if possible
        while let Some(evt) = res {
            dom.handle_event(evt.name.as_str(), evt.data, evt.element, evt.bubbles);
            res = rx.try_next().transpose().unwrap().ok();
        }

        // Todo: This is currently disabled because it has a negative impact on response times for events but it could be re-enabled for tasks
        // Jank free rendering
        //
        // 1. wait for the browser to give us "idle" time
        // 2. During idle time, diff the dom
        // 3. Stop diffing if the deadline is exceded
        // 4. Wait for the animation frame to patch the dom

        // wait for the mainthread to schedule us in
        // let deadline = work_loop.wait_for_idle_time().await;

        // run the virtualdom work phase until the frame deadline is reached
        let edits = dom.render_immediate();

        // wait for the animation frame to fire so we can apply our changes
        // work_loop.wait_for_raf().await;

        websys_dom.load_templates(&edits.templates);
        websys_dom.apply_edits(edits.edits);
    }
}
