/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! Application entry point, runs the event loop.

use std::cell::{Cell, RefCell, RefMut};
use std::collections::HashMap;
use std::rc::Rc;
use std::time::Instant;
use std::{env, fs};

use gleam::gl;
use log::{info, trace, warn};
use servo::compositing::windowing::EmbedderEvent;
use servo::compositing::CompositeTarget;
use servo::config::{opts, set_pref};
use servo::servo_config::pref;
use servo::Servo;
use surfman::GLApi;
use webxr::glwindow::GlWindowDiscovery;
#[cfg(target_os = "windows")]
use webxr::openxr::{AppInfo, OpenXrDiscovery};
use winit::event::WindowEvent;
use winit::event_loop::EventLoopWindowTarget;
use winit::window::WindowId;

use super::events_loop::{EventsLoop, WakerEvent};
use super::minibrowser::Minibrowser;
use super::webview::WebViewManager;
use super::{headed_window, headless_window};
use crate::desktop::embedder::{EmbedderCallbacks, XrDiscovery};
use crate::desktop::tracing::trace_winit_event;
use crate::desktop::window_trait::WindowPortsMethods;
use crate::parser::get_default_url;

pub struct App {
    servo: Option<Servo<dyn WindowPortsMethods>>,
    webviews: RefCell<WebViewManager<dyn WindowPortsMethods>>,
    event_queue: RefCell<Vec<EmbedderEvent>>,
    suspended: Cell<bool>,
    windows: HashMap<WindowId, Rc<dyn WindowPortsMethods>>,
    minibrowser: Option<RefCell<Minibrowser>>,
}

enum Present {
    Immediate,
    Deferred,
    None,
}

/// Action to be taken by the caller of [`App::handle_events`].
enum PumpResult {
    /// The caller should shut down Servo and its related context.
    Shutdown,
    Continue {
        update: bool,
        present: Present,
    },
}

impl App {
    pub fn run(
        no_native_titlebar: bool,
        device_pixel_ratio_override: Option<f32>,
        user_agent: Option<String>,
        url: Option<String>,
    ) {
        let events_loop = EventsLoop::new(opts::get().headless, opts::get().output_file.is_some())
            .expect("Failed to create events loop");

        // Implements window methods, used by compositor.
        let window = if opts::get().headless {
            // GL video rendering is not supported on headless windows.
            set_pref!(media.glvideo.enabled, false);
            headless_window::Window::new(
                opts::get().initial_window_size,
                device_pixel_ratio_override,
            )
        } else {
            Rc::new(headed_window::Window::new(
                opts::get().initial_window_size,
                &events_loop,
                no_native_titlebar,
                device_pixel_ratio_override,
            ))
        };

        // Handle browser state.
        let webviews = WebViewManager::new(window.clone());
        let initial_url = get_default_url(url.as_deref(), env::current_dir().unwrap(), |path| {
            fs::metadata(path).is_ok()
        });

        let mut app = App {
            event_queue: RefCell::new(vec![]),
            webviews: RefCell::new(webviews),
            servo: None,
            suspended: Cell::new(false),
            windows: HashMap::new(),
            minibrowser: None,
        };

        if opts::get().minibrowser && window.winit_window().is_some() {
            // Make sure the gl context is made current.
            let rendering_context = window.rendering_context();
            let webrender_gl = match rendering_context.connection().gl_api() {
                GLApi::GL => unsafe {
                    gl::GlFns::load_with(|s| rendering_context.get_proc_address(s))
                },
                GLApi::GLES => unsafe {
                    gl::GlesFns::load_with(|s| rendering_context.get_proc_address(s))
                },
            };
            rendering_context.make_gl_context_current().unwrap();
            debug_assert_eq!(webrender_gl.get_error(), gleam::gl::NO_ERROR);

            app.minibrowser = Some(
                Minibrowser::new(&rendering_context, &events_loop, initial_url.clone()).into(),
            );
        }

        if let Some(mut minibrowser) = app.minibrowser() {
            // Servo is not yet initialised, so there is no `servo_framebuffer_id`.
            minibrowser.update(
                window.winit_window().unwrap(),
                &mut app.webviews.borrow_mut(),
                None,
                "init",
            );
            window.set_toolbar_height(minibrowser.toolbar_height);
        }

        let t_start = Instant::now();
        let mut t = t_start;
        let ev_waker = events_loop.create_event_loop_waker();
        events_loop.run_forever(move |event, w, control_flow| {
            let now = Instant::now();
            trace_winit_event!(event, "@{:?} (+{:?}) {event:?}", now - t_start, now - t);
            t = now;
            if let winit::event::Event::NewEvents(winit::event::StartCause::Init) = event {
                let surfman = window.rendering_context();

                let openxr_discovery = if pref!(dom.webxr.openxr.enabled) && !opts::get().headless {
                    #[cfg(target_os = "windows")]
                    let openxr = {
                        let app_info = AppInfo::new("Servoshell", 0, "Servo", 0);
                        Some(XrDiscovery::OpenXr(OpenXrDiscovery::new(None, app_info)))
                    };
                    #[cfg(not(target_os = "windows"))]
                    let openxr = None;

                    openxr
                } else {
                    None
                };

                let glwindow_discovery =
                    if pref!(dom.webxr.glwindow.enabled) && !opts::get().headless {
                        let window = window.clone();
                        // This should be safe because run_forever does, in fact,
                        // run forever. The event loop window target doesn't get
                        // moved, and does outlast this closure, and we won't
                        // ever try to make use of it once shutdown begins and
                        // it stops being valid.
                        let w = unsafe {
                            std::mem::transmute::<
                                &EventLoopWindowTarget<WakerEvent>,
                                &'static EventLoopWindowTarget<WakerEvent>,
                            >(w.unwrap())
                        };
                        let factory = Box::new(move || Ok(window.new_glwindow(w)));
                        Some(XrDiscovery::GlWindow(GlWindowDiscovery::new(
                            surfman.connection(),
                            surfman.adapter(),
                            surfman.context_attributes(),
                            factory,
                        )))
                    } else {
                        None
                    };

                let xr_discovery = openxr_discovery.or(glwindow_discovery);

                let window = window.clone();
                // Implements embedder methods, used by libservo and constellation.
                let embedder = Box::new(EmbedderCallbacks::new(ev_waker.clone(), xr_discovery));

                let composite_target = if app.minibrowser.is_some() {
                    CompositeTarget::Fbo
                } else {
                    CompositeTarget::Window
                };
                let servo_data = Servo::new(
                    embedder,
                    window.clone(),
                    user_agent.clone(),
                    composite_target,
                );
                let mut servo = servo_data.servo;

                servo.handle_events(vec![EmbedderEvent::NewWebView(
                    initial_url.to_owned(),
                    servo_data.browser_id,
                )]);
                servo.setup_logging();

                app.windows.insert(window.id(), window.clone());
                app.servo = Some(servo);
            }

            // If self.servo is None here, it means that we're in the process of shutting down,
            // let's ignore events.
            if app.servo.is_none() {
                return;
            }

            if let winit::event::Event::WindowEvent {
                window_id: _,
                event: winit::event::WindowEvent::RedrawRequested,
            } = event
            {
                // We need to redraw the window for some reason.
                trace!("RedrawRequested");

                // WARNING: do not defer painting or presenting to some later tick of the event
                // loop or servoshell may become unresponsive! (servo#30312)
                if let Some(mut minibrowser) = app.minibrowser() {
                    minibrowser.update(
                        window.winit_window().unwrap(),
                        &mut app.webviews.borrow_mut(),
                        app.servo.as_ref().unwrap().offscreen_framebuffer_id(),
                        "RedrawRequested",
                    );
                    minibrowser.paint(window.winit_window().unwrap());
                }

                app.servo.as_mut().unwrap().present();
            }

            // Handle the event
            let mut consumed = false;
            if let Some(mut minibrowser) = app.minibrowser() {
                match event {
                    winit::event::Event::WindowEvent {
                        event: WindowEvent::ScaleFactorChanged { scale_factor, .. },
                        ..
                    } => {
                        // Intercept any ScaleFactorChanged events away from EguiGlow::on_window_event, so
                        // we can use our own logic for calculating the scale factor and set egui’s
                        // scale factor to that value manually.
                        let effective_scale_factor = window.hidpi_factor().get();
                        info!(
                            "window scale factor changed to {}, setting scale factor to {}",
                            scale_factor, effective_scale_factor
                        );
                        minibrowser
                            .context
                            .egui_ctx
                            .set_pixels_per_point(effective_scale_factor);

                        // Request a winit redraw event, so we can recomposite, update and paint
                        // the minibrowser, and present the new frame.
                        window.winit_window().unwrap().request_redraw();
                    },
                    winit::event::Event::WindowEvent {
                        ref event,
                        window_id: _,
                    } => {
                        let response =
                            minibrowser.on_window_event(window.winit_window().unwrap(), event);
                        // Update minibrowser if there's resize event to sync up with window.
                        if let WindowEvent::Resized(_) = event {
                            minibrowser.update(
                                window.winit_window().unwrap(),
                                &mut app.webviews.borrow_mut(),
                                app.servo.as_ref().unwrap().offscreen_framebuffer_id(),
                                "Sync WebView size with Window Resize event",
                            );
                        }
                        if response.repaint {
                            // Request a winit redraw event, so we can recomposite, update and paint
                            // the minibrowser, and present the new frame.
                            window.winit_window().unwrap().request_redraw();
                        }

                        // TODO how do we handle the tab key? (see doc for consumed)
                        // Note that servo doesn’t yet support tabbing through links and inputs
                        consumed = response.consumed;
                    },
                    _ => {},
                }
            }
            if !consumed {
                app.queue_embedder_events_for_winit_event(event);
            }

            let animating = app.is_animating();

            // Block until the window gets an event
            if !animating || app.suspended.get() {
                control_flow.set_wait();
            } else {
                control_flow.set_poll();
            }

            // Consume and handle any events from the Minibrowser.
            if let Some(minibrowser) = app.minibrowser() {
                let webviews = &mut app.webviews.borrow_mut();
                let app_event_queue = &mut app.event_queue.borrow_mut();
                minibrowser.queue_embedder_events_for_minibrowser_events(webviews, app_event_queue);
            }

            match app.handle_events() {
                PumpResult::Shutdown => {
                    control_flow.set_exit();
                    app.servo.take().unwrap().deinit();
                    if let Some(mut minibrowser) = app.minibrowser() {
                        minibrowser.context.destroy();
                    }
                },
                PumpResult::Continue { update, present } => {
                    if update {
                        if let Some(mut minibrowser) = app.minibrowser() {
                            let webviews = &mut app.webviews.borrow_mut();
                            if minibrowser.update_webview_data(webviews) {
                                // Update the minibrowser immediately. While we could update by requesting a
                                // redraw, doing so would delay the location update by two frames.
                                minibrowser.update(
                                    window.winit_window().unwrap(),
                                    webviews,
                                    app.servo.as_ref().unwrap().offscreen_framebuffer_id(),
                                    "update_location_in_toolbar",
                                );
                            }
                        }
                    }
                    match present {
                        Present::Immediate => {
                            // The window was resized.
                            trace!("PumpResult::Present::Immediate");

                            // If we had resized any of the viewports in response to this, we would need to
                            // call Servo::repaint_synchronously. At the moment we don’t, so there won’t be
                            // any paint scheduled, and calling it would hang the compositor forever.
                            if let Some(mut minibrowser) = app.minibrowser() {
                                minibrowser.update(
                                    window.winit_window().unwrap(),
                                    &mut app.webviews.borrow_mut(),
                                    app.servo.as_ref().unwrap().offscreen_framebuffer_id(),
                                    "PumpResult::Present::Immediate",
                                );
                                minibrowser.paint(window.winit_window().unwrap());
                            }
                            app.servo.as_mut().unwrap().present();
                        },
                        Present::Deferred => {
                            // The compositor has painted to this frame.
                            trace!("PumpResult::Present::Deferred");

                            // Request a winit redraw event, so we can paint the minibrowser and present.
                            // Otherwise, it's in headless mode and we present directly.
                            if let Some(window) = window.winit_window() {
                                window.request_redraw();
                            } else {
                                app.servo.as_mut().unwrap().present();
                            }
                        },
                        Present::None => {},
                    }
                },
            }
        });
    }

    fn is_animating(&self) -> bool {
        self.windows.iter().any(|(_, window)| window.is_animating())
    }

    fn get_events(&self) -> Vec<EmbedderEvent> {
        std::mem::take(&mut *self.event_queue.borrow_mut())
    }

    /// Processes the given winit Event, possibly converting it to an [EmbedderEvent] and
    /// routing that to the App or relevant Window event queues.
    fn queue_embedder_events_for_winit_event(&self, event: winit::event::Event<WakerEvent>) {
        match event {
            // App level events
            winit::event::Event::Suspended => {
                self.suspended.set(true);
            },
            winit::event::Event::Resumed => {
                self.suspended.set(false);
                self.event_queue.borrow_mut().push(EmbedderEvent::Idle);
            },
            winit::event::Event::UserEvent(_) => {
                self.event_queue.borrow_mut().push(EmbedderEvent::Idle);
            },
            winit::event::Event::DeviceEvent { .. } => {},

            // Window level events
            winit::event::Event::WindowEvent {
                window_id, event, ..
            } => match self.windows.get(&window_id) {
                None => {
                    warn!("Got an event from unknown window");
                },
                Some(window) => {
                    if event == winit::event::WindowEvent::RedrawRequested {
                        self.event_queue.borrow_mut().push(EmbedderEvent::Idle);
                    }

                    window.queue_embedder_events_for_winit_event(event);
                },
            },

            winit::event::Event::LoopExiting |
            winit::event::Event::AboutToWait |
            winit::event::Event::MemoryWarning |
            winit::event::Event::NewEvents(..) => {},
        }
    }

    /// Pumps events and messages between the embedder and Servo, where embedder events flow
    /// towards Servo and embedder messages flow away from Servo, and also runs the compositor.
    ///
    /// As the embedder, we push embedder events through our event queues, from the App queue and
    /// Window queues to the WebViewManager queue, and from the WebViewManager queue to Servo. We
    /// receive and collect embedder messages from the various Servo components, then take them out
    /// of the Servo interface so that the WebViewManager can handle them.
    fn handle_events(&mut self) -> PumpResult {
        let mut webviews = self.webviews.borrow_mut();

        // Take any outstanding embedder events from the App and its Windows.
        let mut embedder_events = self.get_events();
        for window in self.windows.values() {
            embedder_events.extend(window.get_events());
        }

        // Catch some keyboard events, and push the rest onto the WebViewManager event queue.
        webviews.handle_window_events(embedder_events);

        // If the Gamepad API is enabled, handle gamepad events from GilRs.
        // Checking for focused_webview_id should ensure we'll have a valid browsing context.
        if pref!(dom.gamepad.enabled) && webviews.focused_webview_id().is_some() {
            webviews.handle_gamepad_events();
        }

        // Take any new embedder messages from Servo itself.
        let mut embedder_messages = self.servo.as_mut().unwrap().get_events();
        let mut need_resize = false;
        let mut need_present = false;
        let mut need_update = false;
        loop {
            // Consume and handle those embedder messages.
            let servo_event_response = webviews.handle_servo_events(embedder_messages);
            need_present |= servo_event_response.need_present;
            need_update |= servo_event_response.need_update;

            // Route embedder events from the WebViewManager to the relevant Servo components,
            // receives and collects embedder messages from various Servo components,
            // and runs the compositor.
            need_resize |= self
                .servo
                .as_mut()
                .unwrap()
                .handle_events(webviews.get_events());
            if webviews.shutdown_requested() {
                return PumpResult::Shutdown;
            }

            // Take any new embedder messages from Servo itself.
            embedder_messages = self.servo.as_mut().unwrap().get_events();
            if embedder_messages.len() == 0 {
                break;
            }
        }

        let present = if need_resize {
            Present::Immediate
        } else if need_present {
            Present::Deferred
        } else {
            Present::None
        };

        PumpResult::Continue {
            update: need_update,
            present,
        }
    }

    fn minibrowser(&self) -> Option<RefMut<Minibrowser>> {
        self.minibrowser.as_ref().map(|x| x.borrow_mut())
    }
}