lib.rs

//! [`egui`] bindings for web apps (compiling to WASM).
//!
//! This library is an [`epi`] backend.
//!
//! If you are writing an app, you may want to look at [`eframe`](https://docs.rs/eframe) instead.
//!
//! ## Specifying the size of the egui canvas
//! For performance reasons (on some browsers) the egui canvas does not, by default,
//! fill the whole width of the browser.
//! This can be changed by overriding [`epi::App::max_size_points`].

// Forbid warnings in release builds:
#![cfg_attr(not(debug_assertions), deny(warnings))]
#![forbid(unsafe_code)]
#![warn(clippy::all, missing_crate_level_docs, rust_2018_idioms)]

pub mod backend;
mod painter;
pub mod screen_reader;
pub mod webgl1;
pub mod webgl2;

pub use backend::*;

use egui::mutex::Mutex;
pub use wasm_bindgen;
pub use web_sys;

pub use painter::Painter;
use std::cell::Cell;
use std::rc::Rc;
use std::sync::Arc;
use wasm_bindgen::prelude::*;

static AGENT_ID: &str = "egui_text_agent";

// ----------------------------------------------------------------------------
// Helpers to hide some of the verbosity of web_sys

/// Log some text to the developer console (`console.log(…)` in JS)
pub fn console_log(s: impl Into<JsValue>) {
    web_sys::console::log_1(&s.into());
}

/// Log a warning to the developer console (`console.warn(…)` in JS)
pub fn console_warn(s: impl Into<JsValue>) {
    web_sys::console::warn_1(&s.into());
}

/// Log an error to the developer console (`console.error(…)` in JS)
pub fn console_error(s: impl Into<JsValue>) {
    web_sys::console::error_1(&s.into());
}

/// Current time in seconds (since undefined point in time)
pub fn now_sec() -> f64 {
    web_sys::window()
        .expect("should have a Window")
        .performance()
        .expect("should have a Performance")
        .now()
        / 1000.0
}

pub fn screen_size_in_native_points() -> Option<egui::Vec2> {
    let window = web_sys::window()?;
    Some(egui::Vec2::new(
        window.inner_width().ok()?.as_f64()? as f32,
        window.inner_height().ok()?.as_f64()? as f32,
    ))
}

pub fn native_pixels_per_point() -> f32 {
    let pixels_per_point = web_sys::window().unwrap().device_pixel_ratio() as f32;
    if pixels_per_point > 0.0 && pixels_per_point.is_finite() {
        pixels_per_point
    } else {
        1.0
    }
}

pub fn prefer_dark_mode() -> Option<bool> {
    Some(
        web_sys::window()?
            .match_media("(prefers-color-scheme: dark)")
            .ok()??
            .matches(),
    )
}

pub fn canvas_element(canvas_id: &str) -> Option<web_sys::HtmlCanvasElement> {
    use wasm_bindgen::JsCast;
    let document = web_sys::window()?.document()?;
    let canvas = document.get_element_by_id(canvas_id)?;
    canvas.dyn_into::<web_sys::HtmlCanvasElement>().ok()
}

pub fn canvas_element_or_die(canvas_id: &str) -> web_sys::HtmlCanvasElement {
    crate::canvas_element(canvas_id)
        .unwrap_or_else(|| panic!("Failed to find canvas with id '{}'", canvas_id))
}

pub fn pos_from_mouse_event(canvas_id: &str, event: &web_sys::MouseEvent) -> egui::Pos2 {
    let canvas = canvas_element(canvas_id).unwrap();
    let rect = canvas.get_bounding_client_rect();
    egui::Pos2 {
        x: event.client_x() as f32 - rect.left() as f32,
        y: event.client_y() as f32 - rect.top() as f32,
    }
}

pub fn button_from_mouse_event(event: &web_sys::MouseEvent) -> Option<egui::PointerButton> {
    match event.button() {
        0 => Some(egui::PointerButton::Primary),
        1 => Some(egui::PointerButton::Middle),
        2 => Some(egui::PointerButton::Secondary),
        _ => None,
    }
}

/// A single touch is translated to a pointer movement. When a second touch is added, the pointer
/// should not jump to a different position. Therefore, we do not calculate the average position
/// of all touches, but we keep using the same touch as long as it is available.
///
/// `touch_id_for_pos` is the `TouchId` of the `Touch` we previously used to determine the
/// pointer position.
pub fn pos_from_touch_event(
    canvas_id: &str,
    event: &web_sys::TouchEvent,
    touch_id_for_pos: &mut Option<egui::TouchId>,
) -> egui::Pos2 {
    let touch_for_pos;
    if let Some(touch_id_for_pos) = touch_id_for_pos {
        // search for the touch we previously used for the position
        // (unfortunately, `event.touches()` is not a rust collection):
        touch_for_pos = (0..event.touches().length())
            .into_iter()
            .map(|i| event.touches().get(i).unwrap())
            .find(|touch| egui::TouchId::from(touch.identifier()) == *touch_id_for_pos);
    } else {
        touch_for_pos = None;
    }
    // Use the touch found above or pick the first, or return a default position if there is no
    // touch at all. (The latter is not expected as the current method is only called when there is
    // at least one touch.)
    touch_for_pos
        .or_else(|| event.touches().get(0))
        .map_or(Default::default(), |touch| {
            *touch_id_for_pos = Some(egui::TouchId::from(touch.identifier()));
            pos_from_touch(canvas_origin(canvas_id), &touch)
        })
}

fn pos_from_touch(canvas_origin: egui::Pos2, touch: &web_sys::Touch) -> egui::Pos2 {
    egui::Pos2 {
        x: touch.page_x() as f32 - canvas_origin.x as f32,
        y: touch.page_y() as f32 - canvas_origin.y as f32,
    }
}

fn canvas_origin(canvas_id: &str) -> egui::Pos2 {
    let rect = canvas_element(canvas_id)
        .unwrap()
        .get_bounding_client_rect();
    egui::Pos2::new(rect.left() as f32, rect.top() as f32)
}

fn push_touches(runner: &mut AppRunner, phase: egui::TouchPhase, event: &web_sys::TouchEvent) {
    let canvas_origin = canvas_origin(runner.canvas_id());
    for touch_idx in 0..event.changed_touches().length() {
        if let Some(touch) = event.changed_touches().item(touch_idx) {
            runner.input.raw.events.push(egui::Event::Touch {
                device_id: egui::TouchDeviceId(0),
                id: egui::TouchId::from(touch.identifier()),
                phase,
                pos: pos_from_touch(canvas_origin, &touch),
                force: touch.force(),
            });
        }
    }
}

pub fn canvas_size_in_points(canvas_id: &str) -> egui::Vec2 {
    let canvas = canvas_element(canvas_id).unwrap();
    let pixels_per_point = native_pixels_per_point();
    egui::vec2(
        canvas.width() as f32 / pixels_per_point,
        canvas.height() as f32 / pixels_per_point,
    )
}

pub fn resize_canvas_to_screen_size(canvas_id: &str, max_size_points: egui::Vec2) -> Option<()> {
    let canvas = canvas_element(canvas_id)?;

    let screen_size_points = screen_size_in_native_points()?;
    let pixels_per_point = native_pixels_per_point();

    let max_size_pixels = pixels_per_point * max_size_points;

    let canvas_size_pixels = pixels_per_point * screen_size_points;
    let canvas_size_pixels = canvas_size_pixels.min(max_size_pixels);
    let canvas_size_points = canvas_size_pixels / pixels_per_point;

    // Make sure that the height and width are always even numbers.
    // otherwise, the page renders blurry on some platforms.
    // See https://github.com/emilk/egui/issues/103
    fn round_to_even(v: f32) -> f32 {
        (v / 2.0).round() * 2.0
    }

    canvas
        .style()
        .set_property(
            "width",
            &format!("{}px", round_to_even(canvas_size_points.x)),
        )
        .ok()?;
    canvas
        .style()
        .set_property(
            "height",
            &format!("{}px", round_to_even(canvas_size_points.y)),
        )
        .ok()?;
    canvas.set_width(round_to_even(canvas_size_pixels.x) as u32);
    canvas.set_height(round_to_even(canvas_size_pixels.y) as u32);

    Some(())
}

// ----------------------------------------------------------------------------

pub fn local_storage() -> Option<web_sys::Storage> {
    web_sys::window()?.local_storage().ok()?
}

pub fn local_storage_get(key: &str) -> Option<String> {
    local_storage().map(|storage| storage.get_item(key).ok())??
}

pub fn local_storage_set(key: &str, value: &str) {
    local_storage().map(|storage| storage.set_item(key, value));
}

pub fn local_storage_remove(key: &str) {
    local_storage().map(|storage| storage.remove_item(key));
}

#[cfg(feature = "persistence")]
pub fn load_memory(ctx: &egui::Context) {
    if let Some(memory_string) = local_storage_get("egui_memory_ron") {
        match ron::from_str(&memory_string) {
            Ok(memory) => {
                *ctx.memory() = memory;
            }
            Err(err) => {
                console_error(format!("Failed to parse memory RON: {}", err));
            }
        }
    }
}

#[cfg(not(feature = "persistence"))]
pub fn load_memory(_: &egui::Context) {}

#[cfg(feature = "persistence")]
pub fn save_memory(ctx: &egui::Context) {
    match ron::to_string(&*ctx.memory()) {
        Ok(ron) => {
            local_storage_set("egui_memory_ron", &ron);
        }
        Err(err) => {
            console_error(format!("Failed to serialize memory as RON: {}", err));
        }
    }
}

#[cfg(not(feature = "persistence"))]
pub fn save_memory(_: &egui::Context) {}

#[derive(Default)]
pub struct LocalStorage {}

impl epi::Storage for LocalStorage {
    fn get_string(&self, key: &str) -> Option<String> {
        local_storage_get(key)
    }
    fn set_string(&mut self, key: &str, value: String) {
        local_storage_set(key, &value);
    }
    fn flush(&mut self) {}
}

// ----------------------------------------------------------------------------

pub fn handle_output(output: &egui::Output, runner: &mut AppRunner) {
    let egui::Output {
        cursor_icon,
        open_url,
        copied_text,
        needs_repaint: _, // handled elsewhere
        events: _,        // we ignore these (TODO: accessibility screen reader)
        mutable_text_under_cursor,
        text_cursor_pos,
    } = output;

    set_cursor_icon(*cursor_icon);
    if let Some(open) = open_url {
        crate::open_url(&open.url, open.new_tab);
    }

    #[cfg(web_sys_unstable_apis)]
    if !copied_text.is_empty() {
        set_clipboard_text(copied_text);
    }

    #[cfg(not(web_sys_unstable_apis))]
    let _ = copied_text;

    runner.mutable_text_under_cursor = *mutable_text_under_cursor;

    if &runner.text_cursor_pos != text_cursor_pos {
        move_text_cursor(text_cursor_pos, runner.canvas_id());
        runner.text_cursor_pos = *text_cursor_pos;
    }
}

pub fn set_cursor_icon(cursor: egui::CursorIcon) -> Option<()> {
    let document = web_sys::window()?.document()?;
    document
        .body()?
        .style()
        .set_property("cursor", cursor_web_name(cursor))
        .ok()
}

#[cfg(web_sys_unstable_apis)]
pub fn set_clipboard_text(s: &str) {
    if let Some(window) = web_sys::window() {
        if let Some(clipboard) = window.navigator().clipboard() {
            let promise = clipboard.write_text(s);
            let future = wasm_bindgen_futures::JsFuture::from(promise);
            let future = async move {
                if let Err(err) = future.await {
                    console_error(format!("Copy/cut action denied: {:?}", err));
                }
            };
            wasm_bindgen_futures::spawn_local(future);
        }
    }
}

pub fn spawn_future<F>(future: F)
where
    F: std::future::Future<Output = ()> + 'static,
{
    wasm_bindgen_futures::spawn_local(future);
}

fn cursor_web_name(cursor: egui::CursorIcon) -> &'static str {
    match cursor {
        egui::CursorIcon::Alias => "alias",
        egui::CursorIcon::AllScroll => "all-scroll",
        egui::CursorIcon::Cell => "cell",
        egui::CursorIcon::ContextMenu => "context-menu",
        egui::CursorIcon::Copy => "copy",
        egui::CursorIcon::Crosshair => "crosshair",
        egui::CursorIcon::Default => "default",
        egui::CursorIcon::Grab => "grab",
        egui::CursorIcon::Grabbing => "grabbing",
        egui::CursorIcon::Help => "help",
        egui::CursorIcon::Move => "move",
        egui::CursorIcon::NoDrop => "no-drop",
        egui::CursorIcon::None => "none",
        egui::CursorIcon::NotAllowed => "not-allowed",
        egui::CursorIcon::PointingHand => "pointer",
        egui::CursorIcon::Progress => "progress",
        egui::CursorIcon::ResizeHorizontal => "ew-resize",
        egui::CursorIcon::ResizeNeSw => "nesw-resize",
        egui::CursorIcon::ResizeNwSe => "nwse-resize",
        egui::CursorIcon::ResizeVertical => "ns-resize",
        egui::CursorIcon::Text => "text",
        egui::CursorIcon::VerticalText => "vertical-text",
        egui::CursorIcon::Wait => "wait",
        egui::CursorIcon::ZoomIn => "zoom-in",
        egui::CursorIcon::ZoomOut => "zoom-out",
    }
}

pub fn open_url(url: &str, new_tab: bool) -> Option<()> {
    let name = if new_tab { "_blank" } else { "_self" };

    web_sys::window()?
        .open_with_url_and_target(url, name)
        .ok()?;
    Some(())
}

/// e.g. "#fragment" part of "www.example.com/index.html#fragment"
pub fn location_hash() -> Option<String> {
    web_sys::window()?.location().hash().ok()
}

/// Web sends all keys as strings, so it is up to us to figure out if it is
/// a real text input or the name of a key.
fn should_ignore_key(key: &str) -> bool {
    let is_function_key = key.starts_with('F') && key.len() > 1;
    is_function_key
        || matches!(
            key,
            "Alt"
                | "ArrowDown"
                | "ArrowLeft"
                | "ArrowRight"
                | "ArrowUp"
                | "Backspace"
                | "CapsLock"
                | "ContextMenu"
                | "Control"
                | "Delete"
                | "End"
                | "Enter"
                | "Esc"
                | "Escape"
                | "Help"
                | "Home"
                | "Insert"
                | "Meta"
                | "NumLock"
                | "PageDown"
                | "PageUp"
                | "Pause"
                | "ScrollLock"
                | "Shift"
                | "Tab"
        )
}

/// Web sends all all keys as strings, so it is up to us to figure out if it is
/// a real text input or the name of a key.
pub fn translate_key(key: &str) -> Option<egui::Key> {
    match key {
        "ArrowDown" => Some(egui::Key::ArrowDown),
        "ArrowLeft" => Some(egui::Key::ArrowLeft),
        "ArrowRight" => Some(egui::Key::ArrowRight),
        "ArrowUp" => Some(egui::Key::ArrowUp),

        "Esc" | "Escape" => Some(egui::Key::Escape),
        "Tab" => Some(egui::Key::Tab),
        "Backspace" => Some(egui::Key::Backspace),
        "Enter" => Some(egui::Key::Enter),
        "Space" | " " => Some(egui::Key::Space),

        "Help" | "Insert" => Some(egui::Key::Insert),
        "Delete" => Some(egui::Key::Delete),
        "Home" => Some(egui::Key::Home),
        "End" => Some(egui::Key::End),
        "PageUp" => Some(egui::Key::PageUp),
        "PageDown" => Some(egui::Key::PageDown),

        "0" => Some(egui::Key::Num0),
        "1" => Some(egui::Key::Num1),
        "2" => Some(egui::Key::Num2),
        "3" => Some(egui::Key::Num3),
        "4" => Some(egui::Key::Num4),
        "5" => Some(egui::Key::Num5),
        "6" => Some(egui::Key::Num6),
        "7" => Some(egui::Key::Num7),
        "8" => Some(egui::Key::Num8),
        "9" => Some(egui::Key::Num9),

        "a" | "A" => Some(egui::Key::A),
        "b" | "B" => Some(egui::Key::B),
        "c" | "C" => Some(egui::Key::C),
        "d" | "D" => Some(egui::Key::D),
        "e" | "E" => Some(egui::Key::E),
        "f" | "F" => Some(egui::Key::F),
        "g" | "G" => Some(egui::Key::G),
        "h" | "H" => Some(egui::Key::H),
        "i" | "I" => Some(egui::Key::I),
        "j" | "J" => Some(egui::Key::J),
        "k" | "K" => Some(egui::Key::K),
        "l" | "L" => Some(egui::Key::L),
        "m" | "M" => Some(egui::Key::M),
        "n" | "N" => Some(egui::Key::N),
        "o" | "O" => Some(egui::Key::O),
        "p" | "P" => Some(egui::Key::P),
        "q" | "Q" => Some(egui::Key::Q),
        "r" | "R" => Some(egui::Key::R),
        "s" | "S" => Some(egui::Key::S),
        "t" | "T" => Some(egui::Key::T),
        "u" | "U" => Some(egui::Key::U),
        "v" | "V" => Some(egui::Key::V),
        "w" | "W" => Some(egui::Key::W),
        "x" | "X" => Some(egui::Key::X),
        "y" | "Y" => Some(egui::Key::Y),
        "z" | "Z" => Some(egui::Key::Z),

        _ => None,
    }
}

// ----------------------------------------------------------------------------

#[derive(Clone)]
pub struct AppRunnerRef(Arc<Mutex<AppRunner>>);

fn paint_and_schedule(runner_ref: AppRunnerRef) -> Result<(), JsValue> {
    fn paint_if_needed(runner_ref: &AppRunnerRef) -> Result<(), JsValue> {
        let mut runner_lock = runner_ref.0.lock();
        if runner_lock.needs_repaint.fetch_and_clear() {
            let (output, clipped_meshes) = runner_lock.logic()?;
            runner_lock.paint(clipped_meshes)?;
            if output.needs_repaint {
                runner_lock.needs_repaint.set_true();
            }
            runner_lock.auto_save();
        }

        Ok(())
    }

    fn request_animation_frame(runner_ref: AppRunnerRef) -> Result<(), JsValue> {
        use wasm_bindgen::JsCast;
        let window = web_sys::window().unwrap();
        let closure = Closure::once(move || paint_and_schedule(runner_ref));
        window.request_animation_frame(closure.as_ref().unchecked_ref())?;
        closure.forget(); // We must forget it, or else the callback is canceled on drop
        Ok(())
    }

    paint_if_needed(&runner_ref)?;
    request_animation_frame(runner_ref)
}

fn text_agent() -> web_sys::HtmlInputElement {
    use wasm_bindgen::JsCast;
    web_sys::window()
        .unwrap()
        .document()
        .unwrap()
        .get_element_by_id(AGENT_ID)
        .unwrap()
        .dyn_into()
        .unwrap()
}

fn install_document_events(runner_ref: &AppRunnerRef) -> Result<(), JsValue> {
    use wasm_bindgen::JsCast;
    let window = web_sys::window().unwrap();
    let document = window.document().unwrap();

    {
        // keydown
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::KeyboardEvent| {
            if event.is_composing() || event.key_code() == 229 {
                // https://www.fxsitecompat.dev/en-CA/docs/2018/keydown-and-keyup-events-are-now-fired-during-ime-composition/
                return;
            }

            let mut runner_lock = runner_ref.0.lock();
            let modifiers = modifiers_from_event(&event);
            runner_lock.input.raw.modifiers = modifiers;

            let key = event.key();

            if let Some(key) = translate_key(&key) {
                runner_lock.input.raw.events.push(egui::Event::Key {
                    key,
                    pressed: true,
                    modifiers,
                });
            }
            if !modifiers.ctrl
                && !modifiers.command
                && !should_ignore_key(&key)
                // When text agent is shown, it sends text event instead.
                && text_agent().hidden()
            {
                runner_lock.input.raw.events.push(egui::Event::Text(key));
            }
            runner_lock.needs_repaint.set_true();

            let egui_wants_keyboard = runner_lock.egui_ctx().wants_keyboard_input();

            let prevent_default = if matches!(event.key().as_str(), "Tab") {
                // Always prevent moving cursor to url bar.
                // egui wants to use tab to move to the next text field.
                true
            } else if egui_wants_keyboard {
                matches!(
                    event.key().as_str(),
                    "Backspace" // so we don't go back to previous page when deleting text
                | "ArrowDown" | "ArrowLeft" | "ArrowRight" | "ArrowUp" // cmd-left is "back" on Mac (https://github.com/emilk/egui/issues/58)
                )
            } else {
                // We never want to prevent:
                // * F5 / cmd-R (refresh)
                // * cmd-shift-C (debug tools)
                // * cmd/ctrl-c/v/x (or we stop copy/past/cut events)
                false
            };

            // console_log(format!(
            //     "On key-down {:?}, egui_wants_keyboard: {}, prevent_default: {}",
            //     event.key().as_str(),
            //     egui_wants_keyboard,
            //     prevent_default
            // ));

            if prevent_default {
                event.prevent_default();
            }
        }) as Box<dyn FnMut(_)>);
        document.add_event_listener_with_callback("keydown", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        // keyup
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::KeyboardEvent| {
            let mut runner_lock = runner_ref.0.lock();
            let modifiers = modifiers_from_event(&event);
            runner_lock.input.raw.modifiers = modifiers;
            if let Some(key) = translate_key(&event.key()) {
                runner_lock.input.raw.events.push(egui::Event::Key {
                    key,
                    pressed: false,
                    modifiers,
                });
            }
            runner_lock.needs_repaint.set_true();
        }) as Box<dyn FnMut(_)>);
        document.add_event_listener_with_callback("keyup", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    #[cfg(web_sys_unstable_apis)]
    {
        // paste
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::ClipboardEvent| {
            if let Some(data) = event.clipboard_data() {
                if let Ok(text) = data.get_data("text") {
                    let mut runner_lock = runner_ref.0.lock();
                    runner_lock
                        .input
                        .raw
                        .events
                        .push(egui::Event::Text(text.replace("\r\n", "\n")));
                    runner_lock.needs_repaint.set_true();
                    event.stop_propagation();
                    event.prevent_default();
                }
            }
        }) as Box<dyn FnMut(_)>);
        document.add_event_listener_with_callback("paste", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    #[cfg(web_sys_unstable_apis)]
    {
        // cut
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |_: web_sys::ClipboardEvent| {
            let mut runner_lock = runner_ref.0.lock();
            runner_lock.input.raw.events.push(egui::Event::Cut);
            runner_lock.needs_repaint.set_true();
        }) as Box<dyn FnMut(_)>);
        document.add_event_listener_with_callback("cut", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    #[cfg(web_sys_unstable_apis)]
    {
        // copy
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |_: web_sys::ClipboardEvent| {
            let mut runner_lock = runner_ref.0.lock();
            runner_lock.input.raw.events.push(egui::Event::Copy);
            runner_lock.needs_repaint.set_true();
        }) as Box<dyn FnMut(_)>);
        document.add_event_listener_with_callback("copy", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    for event_name in &["load", "pagehide", "pageshow", "resize"] {
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move || {
            runner_ref.0.lock().needs_repaint.set_true();
        }) as Box<dyn FnMut()>);
        window.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    Ok(())
}

/// Repaint at least every `ms` milliseconds.
fn repaint_every_ms(runner_ref: &AppRunnerRef, milliseconds: i32) -> Result<(), JsValue> {
    assert!(milliseconds >= 0);
    use wasm_bindgen::JsCast;
    let window = web_sys::window().unwrap();
    let runner_ref = runner_ref.clone();
    let closure = Closure::wrap(Box::new(move || {
        runner_ref.0.lock().needs_repaint.set_true();
    }) as Box<dyn FnMut()>);
    window.set_interval_with_callback_and_timeout_and_arguments_0(
        closure.as_ref().unchecked_ref(),
        milliseconds,
    )?;
    closure.forget();
    Ok(())
}

fn modifiers_from_event(event: &web_sys::KeyboardEvent) -> egui::Modifiers {
    egui::Modifiers {
        alt: event.alt_key(),
        ctrl: event.ctrl_key(),
        shift: event.shift_key(),

        // Ideally we should know if we are running or mac or not,
        // but this works good enough for now.
        mac_cmd: event.meta_key(),

        // Ideally we should know if we are running or mac or not,
        // but this works good enough for now.
        command: event.ctrl_key() || event.meta_key(),
    }
}

///
/// Text event handler,
fn install_text_agent(runner_ref: &AppRunnerRef) -> Result<(), JsValue> {
    use wasm_bindgen::JsCast;
    let window = web_sys::window().unwrap();
    let document = window.document().unwrap();
    let body = document.body().expect("document should have a body");
    let input = document
        .create_element("input")?
        .dyn_into::<web_sys::HtmlInputElement>()?;
    let input = std::rc::Rc::new(input);
    input.set_id(AGENT_ID);
    let is_composing = Rc::new(Cell::new(false));
    {
        let style = input.style();
        // Transparent
        style.set_property("opacity", "0").unwrap();
        // Hide under canvas
        style.set_property("z-index", "-1").unwrap();
    }
    // Set size as small as possible, in case user may click on it.
    input.set_size(1);
    input.set_autofocus(true);
    input.set_hidden(true);
    {
        // When IME is off
        let input_clone = input.clone();
        let runner_ref = runner_ref.clone();
        let is_composing = is_composing.clone();
        let on_input = Closure::wrap(Box::new(move |_event: web_sys::InputEvent| {
            let text = input_clone.value();
            if !text.is_empty() && !is_composing.get() {
                input_clone.set_value("");
                let mut runner_lock = runner_ref.0.lock();
                runner_lock.input.raw.events.push(egui::Event::Text(text));
                runner_lock.needs_repaint.set_true();
            }
        }) as Box<dyn FnMut(_)>);
        input.add_event_listener_with_callback("input", on_input.as_ref().unchecked_ref())?;
        on_input.forget();
    }
    {
        // When IME is on, handle composition event
        let input_clone = input.clone();
        let runner_ref = runner_ref.clone();
        let on_compositionend = Closure::wrap(Box::new(move |event: web_sys::CompositionEvent| {
            let mut runner_lock = runner_ref.0.lock();
            let opt_event = match event.type_().as_ref() {
                "compositionstart" => {
                    is_composing.set(true);
                    input_clone.set_value("");
                    Some(egui::Event::CompositionStart)
                }
                "compositionend" => {
                    is_composing.set(false);
                    input_clone.set_value("");
                    event.data().map(egui::Event::CompositionEnd)
                }
                "compositionupdate" => event.data().map(egui::Event::CompositionUpdate),
                s => {
                    console_error(format!("Unknown composition event type: {:?}", s));
                    None
                }
            };
            if let Some(event) = opt_event {
                runner_lock.input.raw.events.push(event);
                runner_lock.needs_repaint.set_true();
            }
        }) as Box<dyn FnMut(_)>);
        let f = on_compositionend.as_ref().unchecked_ref();
        input.add_event_listener_with_callback("compositionstart", f)?;
        input.add_event_listener_with_callback("compositionupdate", f)?;
        input.add_event_listener_with_callback("compositionend", f)?;
        on_compositionend.forget();
    }
    {
        // When input lost focus, focus on it again.
        // It is useful when user click somewhere outside canvas.
        let on_focusout = Closure::wrap(Box::new(move |_event: web_sys::MouseEvent| {
            // Delay 10 ms, and focus again.
            let func = js_sys::Function::new_no_args(&format!(
                "document.getElementById('{}').focus()",
                AGENT_ID
            ));
            window
                .set_timeout_with_callback_and_timeout_and_arguments_0(&func, 10)
                .unwrap();
        }) as Box<dyn FnMut(_)>);
        input.add_event_listener_with_callback("focusout", on_focusout.as_ref().unchecked_ref())?;
        on_focusout.forget();
    }
    body.append_child(&input)?;
    Ok(())
}

fn install_canvas_events(runner_ref: &AppRunnerRef) -> Result<(), JsValue> {
    use wasm_bindgen::JsCast;
    let canvas = canvas_element(runner_ref.0.lock().canvas_id()).unwrap();

    {
        // By default, right-clicks open a context menu.
        // We don't want to do that (right clicks is handled by egui):
        let event_name = "contextmenu";
        let closure = Closure::wrap(Box::new(move |event: web_sys::MouseEvent| {
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "mousedown";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::MouseEvent| {
            if let Some(button) = button_from_mouse_event(&event) {
                let mut runner_lock = runner_ref.0.lock();
                let pos = pos_from_mouse_event(runner_lock.canvas_id(), &event);
                let modifiers = runner_lock.input.raw.modifiers;
                runner_lock
                    .input
                    .raw
                    .events
                    .push(egui::Event::PointerButton {
                        pos,
                        button,
                        pressed: true,
                        modifiers,
                    });
                runner_lock.needs_repaint.set_true();
            }
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "mousemove";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::MouseEvent| {
            let mut runner_lock = runner_ref.0.lock();
            let pos = pos_from_mouse_event(runner_lock.canvas_id(), &event);
            runner_lock
                .input
                .raw
                .events
                .push(egui::Event::PointerMoved(pos));
            runner_lock.needs_repaint.set_true();
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "mouseup";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::MouseEvent| {
            if let Some(button) = button_from_mouse_event(&event) {
                let mut runner_lock = runner_ref.0.lock();
                let pos = pos_from_mouse_event(runner_lock.canvas_id(), &event);
                let modifiers = runner_lock.input.raw.modifiers;
                runner_lock
                    .input
                    .raw
                    .events
                    .push(egui::Event::PointerButton {
                        pos,
                        button,
                        pressed: false,
                        modifiers,
                    });
                runner_lock.needs_repaint.set_true();

                update_text_agent(&runner_lock);
            }
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "mouseleave";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::MouseEvent| {
            let mut runner_lock = runner_ref.0.lock();
            runner_lock.input.raw.events.push(egui::Event::PointerGone);
            runner_lock.needs_repaint.set_true();
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "touchstart";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::TouchEvent| {
            let mut runner_lock = runner_ref.0.lock();
            let mut latest_touch_pos_id = runner_lock.input.latest_touch_pos_id;
            let pos =
                pos_from_touch_event(runner_lock.canvas_id(), &event, &mut latest_touch_pos_id);
            runner_lock.input.latest_touch_pos_id = latest_touch_pos_id;
            runner_lock.input.latest_touch_pos = Some(pos);
            let modifiers = runner_lock.input.raw.modifiers;
            runner_lock
                .input
                .raw
                .events
                .push(egui::Event::PointerButton {
                    pos,
                    button: egui::PointerButton::Primary,
                    pressed: true,
                    modifiers,
                });

            push_touches(&mut *runner_lock, egui::TouchPhase::Start, &event);
            runner_lock.needs_repaint.set_true();
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "touchmove";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::TouchEvent| {
            let mut runner_lock = runner_ref.0.lock();
            let mut latest_touch_pos_id = runner_lock.input.latest_touch_pos_id;
            let pos =
                pos_from_touch_event(runner_lock.canvas_id(), &event, &mut latest_touch_pos_id);
            runner_lock.input.latest_touch_pos_id = latest_touch_pos_id;
            runner_lock.input.latest_touch_pos = Some(pos);
            runner_lock
                .input
                .raw
                .events
                .push(egui::Event::PointerMoved(pos));

            push_touches(&mut *runner_lock, egui::TouchPhase::Move, &event);
            runner_lock.needs_repaint.set_true();
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "touchend";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::TouchEvent| {
            let mut runner_lock = runner_ref.0.lock();

            if let Some(pos) = runner_lock.input.latest_touch_pos {
                let modifiers = runner_lock.input.raw.modifiers;
                // First release mouse to click:
                runner_lock
                    .input
                    .raw
                    .events
                    .push(egui::Event::PointerButton {
                        pos,
                        button: egui::PointerButton::Primary,
                        pressed: false,
                        modifiers,
                    });
                // Then remove hover effect:
                runner_lock.input.raw.events.push(egui::Event::PointerGone);

                push_touches(&mut *runner_lock, egui::TouchPhase::End, &event);
                runner_lock.needs_repaint.set_true();
                event.stop_propagation();
                event.prevent_default();
            }

            // Finally, focus or blur text agent to toggle mobile keyboard:
            update_text_agent(&runner_lock);
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "touchcancel";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::TouchEvent| {
            let mut runner_lock = runner_ref.0.lock();
            push_touches(&mut *runner_lock, egui::TouchPhase::Cancel, &event);
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "wheel";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::WheelEvent| {
            let mut runner_lock = runner_ref.0.lock();

            let scroll_multiplier = match event.delta_mode() {
                web_sys::WheelEvent::DOM_DELTA_PAGE => {
                    canvas_size_in_points(runner_ref.0.lock().canvas_id()).y
                }
                web_sys::WheelEvent::DOM_DELTA_LINE => {
                    #[allow(clippy::let_and_return)]
                    let points_per_scroll_line = 8.0; // Note that this is intentionally different from what we use in egui_glium / winit.
                    points_per_scroll_line
                }
                _ => 1.0,
            };

            let delta = -scroll_multiplier
                * egui::Vec2::new(event.delta_x() as f32, event.delta_y() as f32);

            // Report a zoom event in case CTRL (on Windows or Linux) or CMD (on Mac) is pressed.
            // This if-statement is equivalent to how `Modifiers.command` is determined in
            // `modifiers_from_event()`, but we cannot directly use that fn for a `WheelEvent`.
            if event.ctrl_key() || event.meta_key() {
                runner_lock.input.raw.zoom_delta *= (delta.y / 200.0).exp();
            } else {
                runner_lock.input.raw.scroll_delta += delta;
            }

            runner_lock.needs_repaint.set_true();
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "dragover";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::DragEvent| {
            if let Some(data_transfer) = event.data_transfer() {
                let mut runner_lock = runner_ref.0.lock();
                runner_lock.input.raw.hovered_files.clear();
                for i in 0..data_transfer.items().length() {
                    if let Some(item) = data_transfer.items().get(i) {
                        runner_lock.input.raw.hovered_files.push(egui::HoveredFile {
                            mime: item.type_(),
                            ..Default::default()
                        });
                    }
                }
                runner_lock.needs_repaint.set_true();
                event.stop_propagation();
                event.prevent_default();
            }
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "dragleave";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::DragEvent| {
            let mut runner_lock = runner_ref.0.lock();
            runner_lock.input.raw.hovered_files.clear();
            runner_lock.needs_repaint.set_true();
            event.stop_propagation();
            event.prevent_default();
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    {
        let event_name = "drop";
        let runner_ref = runner_ref.clone();
        let closure = Closure::wrap(Box::new(move |event: web_sys::DragEvent| {
            if let Some(data_transfer) = event.data_transfer() {
                {
                    let mut runner_lock = runner_ref.0.lock();
                    runner_lock.input.raw.hovered_files.clear();
                    runner_lock.needs_repaint.set_true();
                }

                if let Some(files) = data_transfer.files() {
                    for i in 0..files.length() {
                        if let Some(file) = files.get(i) {
                            let name = file.name();
                            let last_modified = std::time::UNIX_EPOCH
                                + std::time::Duration::from_millis(file.last_modified() as u64);

                            console_log(format!("Loading {:?} ({} bytes)…", name, file.size()));

                            let future = wasm_bindgen_futures::JsFuture::from(file.array_buffer());

                            let runner_ref = runner_ref.clone();
                            let future = async move {
                                match future.await {
                                    Ok(array_buffer) => {
                                        let bytes = js_sys::Uint8Array::new(&array_buffer).to_vec();
                                        console_log(format!(
                                            "Loaded {:?} ({} bytes).",
                                            name,
                                            bytes.len()
                                        ));

                                        let mut runner_lock = runner_ref.0.lock();
                                        runner_lock.input.raw.dropped_files.push(
                                            egui::DroppedFile {
                                                name,
                                                last_modified: Some(last_modified),
                                                bytes: Some(bytes.into()),
                                                ..Default::default()
                                            },
                                        );
                                        runner_lock.needs_repaint.set_true();
                                    }
                                    Err(err) => {
                                        console_error(format!("Failed to read file: {:?}", err));
                                    }
                                }
                            };
                            wasm_bindgen_futures::spawn_local(future);
                        }
                    }
                }
                event.stop_propagation();
                event.prevent_default();
            }
        }) as Box<dyn FnMut(_)>);
        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    Ok(())
}

/// Focus or blur text agent to toggle mobile keyboard.
fn update_text_agent(runner: &AppRunner) -> Option<()> {
    use wasm_bindgen::JsCast;
    use web_sys::HtmlInputElement;
    let window = web_sys::window()?;
    let document = window.document()?;
    let input: HtmlInputElement = document.get_element_by_id(AGENT_ID)?.dyn_into().unwrap();
    let canvas_style = canvas_element(runner.canvas_id())?.style();

    if runner.mutable_text_under_cursor {
        let is_already_editing = input.hidden();
        if is_already_editing {
            input.set_hidden(false);
            input.focus().ok()?;

            // Move up canvas so that text edit is shown at ~30% of screen height.
            // Only on touch screens, when keyboard popups.
            if let Some(latest_touch_pos) = runner.input.latest_touch_pos {
                let window_height = window.inner_height().ok()?.as_f64()? as f32;
                let current_rel = latest_touch_pos.y / window_height;

                // estimated amount of screen covered by keyboard
                let keyboard_fraction = 0.5;

                if current_rel > keyboard_fraction {
                    // below the keyboard

                    let target_rel = 0.3;

                    // Note: `delta` is negative, since we are moving the canvas UP
                    let delta = target_rel - current_rel;

                    let delta = delta.max(-keyboard_fraction); // Don't move it crazy much

                    let new_pos_percent = (delta * 100.0).round().to_string() + "%";

                    canvas_style.set_property("position", "absolute").ok()?;
                    canvas_style.set_property("top", &new_pos_percent).ok()?;
                }
            }
        }
    } else {
        input.blur().ok()?;
        input.set_hidden(true);
        canvas_style.set_property("position", "absolute").ok()?;
        canvas_style.set_property("top", "0%").ok()?; // move back to normal position
    }
    Some(())
}

const MOBILE_DEVICE: [&str; 6] = ["Android", "iPhone", "iPad", "iPod", "webOS", "BlackBerry"];
/// If context is running under mobile device?
fn is_mobile() -> Option<bool> {
    let user_agent = web_sys::window()?.navigator().user_agent().ok()?;
    let is_mobile = MOBILE_DEVICE.iter().any(|&name| user_agent.contains(name));
    Some(is_mobile)
}

// Move text agent to text cursor's position, on desktop/laptop,
// candidate window moves following text element (agent),
// so it appears that the IME candidate window moves with text cursor.
// On mobile devices, there is no need to do that.
fn move_text_cursor(cursor: &Option<egui::Pos2>, canvas_id: &str) -> Option<()> {
    let style = text_agent().style();
    // Note: movint agent on mobile devices will lead to unpredictable scroll.
    if is_mobile() == Some(false) {
        cursor.as_ref().and_then(|&egui::Pos2 { x, y }| {
            let canvas = canvas_element(canvas_id)?;
            let bounding_rect = text_agent().get_bounding_client_rect();
            let y = (y + (canvas.scroll_top() + canvas.offset_top()) as f32)
                .min(canvas.client_height() as f32 - bounding_rect.height() as f32);
            let x = x + (canvas.scroll_left() + canvas.offset_left()) as f32;
            // Canvas is translated 50% horizontally in html.
            let x = (x - canvas.offset_width() as f32 / 2.0)
                .min(canvas.client_width() as f32 - bounding_rect.width() as f32);
            style.set_property("position", "absolute").ok()?;
            style.set_property("top", &(y.to_string() + "px")).ok()?;
            style.set_property("left", &(x.to_string() + "px")).ok()
        })
    } else {
        style.set_property("position", "absolute").ok()?;
        style.set_property("top", "0px").ok()?;
        style.set_property("left", "0px").ok()
    }
}