use crate::{
    app::{App, AppExit},
    plugin::Plugin,
    PluginsState,
};
use bevy_utils::{Duration, Instant};

#[cfg(target_arch = "wasm32")]
use std::{cell::RefCell, rc::Rc};
#[cfg(target_arch = "wasm32")]
use wasm_bindgen::{prelude::*, JsCast};

/// Determines the method used to run an [`App`]'s [`Schedule`](bevy_ecs::schedule::Schedule).
///
/// It is used in the [`ScheduleRunnerPlugin`].
#[derive(Copy, Clone, Debug)]
pub enum RunMode {
    /// Indicates that the [`App`]'s schedule should run repeatedly.
    Loop {
        /// The minimum [`Duration`] to wait after a [`Schedule`](bevy_ecs::schedule::Schedule)
        /// has completed before repeating. A value of [`None`] will not wait.
        wait: Option<Duration>,
    },
    /// Indicates that the [`App`]'s schedule should run only once.
    Once,
}

impl Default for RunMode {
    fn default() -> Self {
        RunMode::Loop { wait: None }
    }
}

/// Configures an [`App`] to run its [`Schedule`](bevy_ecs::schedule::Schedule) according to a given
/// [`RunMode`].
///
/// [`ScheduleRunnerPlugin`] is included in the
/// [`MinimalPlugins`](https://docs.rs/bevy/latest/bevy/struct.MinimalPlugins.html) plugin group.
///
/// [`ScheduleRunnerPlugin`] is *not* included in the
/// [`DefaultPlugins`](https://docs.rs/bevy/latest/bevy/struct.DefaultPlugins.html) plugin group
/// which assumes that the [`Schedule`](bevy_ecs::schedule::Schedule) will be executed by other means:
/// typically, the `winit` event loop
/// (see [`WinitPlugin`](https://docs.rs/bevy/latest/bevy/winit/struct.WinitPlugin.html))
/// executes the schedule making [`ScheduleRunnerPlugin`] unnecessary.
#[derive(Default)]
pub struct ScheduleRunnerPlugin {
    /// Determines whether the [`Schedule`](bevy_ecs::schedule::Schedule) is run once or repeatedly.
    pub run_mode: RunMode,
}

impl ScheduleRunnerPlugin {
    /// See [`RunMode::Once`].
    pub fn run_once() -> Self {
        ScheduleRunnerPlugin {
            run_mode: RunMode::Once,
        }
    }

    /// See [`RunMode::Loop`].
    pub fn run_loop(wait_duration: Duration) -> Self {
        ScheduleRunnerPlugin {
            run_mode: RunMode::Loop {
                wait: Some(wait_duration),
            },
        }
    }
}

impl Plugin for ScheduleRunnerPlugin {
    fn build(&self, app: &mut App) {
        let run_mode = self.run_mode;
        app.set_runner(move |mut app: App| {
            let plugins_state = app.plugins_state();
            if plugins_state != PluginsState::Cleaned {
                while app.plugins_state() == PluginsState::Adding {
                    #[cfg(not(target_arch = "wasm32"))]
                    bevy_tasks::tick_global_task_pools_on_main_thread();
                }
                app.finish();
                app.cleanup();
            }

            match run_mode {
                RunMode::Once => {
                    app.update();

                    if let Some(exit) = app.should_exit() {
                        return exit;
                    }

                    AppExit::Success
                }
                RunMode::Loop { wait } => {
                    let tick = move |app: &mut App,
                                     wait: Option<Duration>|
                          -> Result<Option<Duration>, AppExit> {
                        let start_time = Instant::now();

                        app.update();

                        if let Some(exit) = app.should_exit() {
                            return Err(exit);
                        };

                        let end_time = Instant::now();

                        if let Some(wait) = wait {
                            let exe_time = end_time - start_time;
                            if exe_time < wait {
                                return Ok(Some(wait - exe_time));
                            }
                        }

                        Ok(None)
                    };

                    #[cfg(not(target_arch = "wasm32"))]
                    {
                        loop {
                            match tick(&mut app, wait) {
                                Ok(Some(delay)) => std::thread::sleep(delay),
                                Ok(None) => continue,
                                Err(exit) => return exit,
                            }
                        }
                    }

                    #[cfg(target_arch = "wasm32")]
                    {
                        fn set_timeout(callback: &Closure<dyn FnMut()>, dur: Duration) {
                            web_sys::window()
                                .unwrap()
                                .set_timeout_with_callback_and_timeout_and_arguments_0(
                                    callback.as_ref().unchecked_ref(),
                                    dur.as_millis() as i32,
                                )
                                .expect("Should register `setTimeout`.");
                        }
                        let asap = Duration::from_millis(1);

                        let exit = Rc::new(RefCell::new(AppExit::Success));
                        let closure_exit = exit.clone();

                        let mut app = Rc::new(app);
                        let moved_tick_closure = Rc::new(RefCell::new(None));
                        let base_tick_closure = moved_tick_closure.clone();

                        let tick_app = move || {
                            let app = Rc::get_mut(&mut app).unwrap();
                            let delay = tick(app, wait);
                            match delay {
                                Ok(delay) => set_timeout(
                                    moved_tick_closure.borrow().as_ref().unwrap(),
                                    delay.unwrap_or(asap),
                                ),
                                Err(code) => {
                                    closure_exit.replace(code);
                                }
                            }
                        };
                        *base_tick_closure.borrow_mut() =
                            Some(Closure::wrap(Box::new(tick_app) as Box<dyn FnMut()>));
                        set_timeout(base_tick_closure.borrow().as_ref().unwrap(), asap);

                        exit.take()
                    }
                }
            }
        });
    }
}