mod chat;
mod euph;
mod input;
mod rooms;
mod util;
mod widgets;

use std::convert::Infallible;
use std::sync::{Arc, Weak};
use std::time::{Duration, Instant};

use crossterm::event::{Event, KeyCode, MouseEvent};
use parking_lot::FairMutex;
use tokio::sync::mpsc::error::TryRecvError;
use tokio::sync::mpsc::{self, UnboundedReceiver, UnboundedSender};
use tokio::task;
use toss::terminal::Terminal;

use crate::logger::{LogMsg, Logger};
use crate::vault::Vault;

pub use self::chat::ChatMsg;
use self::chat::ChatState;
use self::input::{key, KeyBindingsList, KeyEvent};
use self::rooms::Rooms;
use self::widgets::layer::Layer;
use self::widgets::list::ListState;
use self::widgets::BoxedWidget;

/// Time to spend batch processing events before redrawing the screen.
const EVENT_PROCESSING_TIME: Duration = Duration::from_millis(1000 / 15); // 15 fps

#[derive(Debug)]
pub enum UiEvent {
    Redraw,
    Term(Event),
}

enum EventHandleResult {
    Continue,
    Stop,
}

enum Mode {
    Main,
    Log,
}

pub struct Ui {
    event_tx: UnboundedSender<UiEvent>,

    mode: Mode,

    rooms: Rooms,
    log_chat: ChatState<LogMsg, Logger>,
    key_bindings_list: Option<ListState<Infallible>>,
}

impl Ui {
    const POLL_DURATION: Duration = Duration::from_millis(100);

    pub async fn run(
        terminal: &mut Terminal,
        vault: Vault,
        logger: Logger,
        logger_rx: UnboundedReceiver<()>,
    ) -> anyhow::Result<()> {
        let (event_tx, event_rx) = mpsc::unbounded_channel();
        let crossterm_lock = Arc::new(FairMutex::new(()));

        // Prepare and start crossterm event polling task
        let weak_crossterm_lock = Arc::downgrade(&crossterm_lock);
        let event_tx_clone = event_tx.clone();
        let crossterm_event_task = task::spawn_blocking(|| {
            Self::poll_crossterm_events(event_tx_clone, weak_crossterm_lock)
        });

        // Run main UI.
        //
        // If the run_main method exits at any point or if this `run` method is
        // not awaited any more, the crossterm_lock Arc should be deallocated,
        // meaning the crossterm_event_task will also stop after at most
        // `Self::POLL_DURATION`.
        //
        // On the other hand, if the crossterm_event_task stops for any reason,
        // the rest of the UI is also shut down and the client stops.
        let mut ui = Self {
            event_tx: event_tx.clone(),
            mode: Mode::Main,
            rooms: Rooms::new(vault, event_tx.clone()),
            log_chat: ChatState::new(logger),
            key_bindings_list: None,
        };
        tokio::select! {
            e = ui.run_main(terminal, event_rx, crossterm_lock) => Ok(e),
            _ = Self::update_on_log_event(logger_rx, &event_tx) => Ok(Ok(())),
            e = crossterm_event_task => e,
        }?
    }

    fn poll_crossterm_events(
        tx: UnboundedSender<UiEvent>,
        lock: Weak<FairMutex<()>>,
    ) -> anyhow::Result<()> {
        while let Some(lock) = lock.upgrade() {
            let _guard = lock.lock();
            if crossterm::event::poll(Self::POLL_DURATION)? {
                let event = crossterm::event::read()?;
                tx.send(UiEvent::Term(event))?;
            }
        }
        Ok(())
    }

    async fn update_on_log_event(
        mut logger_rx: UnboundedReceiver<()>,
        event_tx: &UnboundedSender<UiEvent>,
    ) {
        while let Some(()) = logger_rx.recv().await {
            if event_tx.send(UiEvent::Redraw).is_err() {
                break;
            }
        }
    }

    async fn run_main(
        &mut self,
        terminal: &mut Terminal,
        mut event_rx: UnboundedReceiver<UiEvent>,
        crossterm_lock: Arc<FairMutex<()>>,
    ) -> anyhow::Result<()> {
        // Initial render so we don't show a blank screen until the first event
        terminal.autoresize()?;
        terminal.frame().reset();
        self.widget().await.render(terminal.frame()).await;
        terminal.present()?;

        loop {
            // 1. Measure grapheme widths if required
            if terminal.measuring_required() {
                let _guard = crossterm_lock.lock();
                terminal.measure_widths()?;
                self.event_tx.send(UiEvent::Redraw)?;
            }

            // 2. Handle events (in batches)
            let mut event = match event_rx.recv().await {
                Some(event) => event,
                None => return Ok(()),
            };
            let end_time = Instant::now() + EVENT_PROCESSING_TIME;
            loop {
                // Render in-between events so the next event is handled in an
                // up-to-date state. The results of these intermediate renders
                // will be thrown away before the final render.
                terminal.autoresize()?;
                self.widget().await.render(terminal.frame()).await;

                let result = match event {
                    UiEvent::Redraw => EventHandleResult::Continue,
                    UiEvent::Term(Event::Key(event)) => {
                        self.handle_key_event(event.into(), terminal, &crossterm_lock)
                            .await
                    }
                    UiEvent::Term(Event::Mouse(event)) => self.handle_mouse_event(event).await?,
                    UiEvent::Term(_) => EventHandleResult::Continue,
                };
                match result {
                    EventHandleResult::Continue => {}
                    EventHandleResult::Stop => return Ok(()),
                }
                if Instant::now() >= end_time {
                    break;
                }
                event = match event_rx.try_recv() {
                    Ok(event) => event,
                    Err(TryRecvError::Empty) => break,
                    Err(TryRecvError::Disconnected) => return Ok(()),
                };
            }

            // 3. Render and present final state
            terminal.autoresize()?;
            terminal.frame().reset();
            self.widget().await.render(terminal.frame()).await;
            terminal.present()?;
        }
    }

    async fn widget(&mut self) -> BoxedWidget {
        let widget = match self.mode {
            Mode::Main => self.rooms.widget().await,
            Mode::Log => self.log_chat.widget(String::new()).into(),
        };

        if let Some(key_bindings_list) = &self.key_bindings_list {
            let mut bindings = KeyBindingsList::new(key_bindings_list);
            self.list_key_bindings(&mut bindings).await;
            Layer::new(vec![widget, bindings.widget()]).into()
        } else {
            widget
        }
    }

    fn show_key_bindings(&mut self) {
        if self.key_bindings_list.is_none() {
            self.key_bindings_list = Some(ListState::new())
        }
    }

    async fn list_key_bindings(&self, bindings: &mut KeyBindingsList) {
        bindings.binding("ctrl+c", "quit cove");
        bindings.binding("F1, ?", "show this menu");
        bindings.binding("F12", "toggle log");
        bindings.empty();
        match self.mode {
            Mode::Main => self.rooms.list_key_bindings(bindings).await,
            Mode::Log => self.log_chat.list_key_bindings(bindings, false).await,
        }
    }

    async fn handle_key_event(
        &mut self,
        event: KeyEvent,
        terminal: &mut Terminal,
        crossterm_lock: &Arc<FairMutex<()>>,
    ) -> EventHandleResult {
        if let key!(Ctrl + 'c') = event {
            // Exit unconditionally on ctrl+c. Previously, shift+q would also
            // unconditionally exit, but that interfered with typing text in
            // inline editors.
            return EventHandleResult::Stop;
        }

        // Key bindings list overrides any other bindings if visible
        if let Some(key_bindings_list) = &mut self.key_bindings_list {
            match event {
                key!(Esc) | key!(F 1) | key!('?') => self.key_bindings_list = None,
                key!('k') | key!(Up) => key_bindings_list.scroll_up(1),
                key!('j') | key!(Down) => key_bindings_list.scroll_down(1),
                _ => {}
            }
            return EventHandleResult::Continue;
        }

        match event {
            key!(F 1) => {
                self.key_bindings_list = Some(ListState::new());
                return EventHandleResult::Continue;
            }
            key!(F 12) => {
                self.mode = match self.mode {
                    Mode::Main => Mode::Log,
                    Mode::Log => Mode::Main,
                };
                return EventHandleResult::Continue;
            }
            _ => {}
        }

        let handled = match self.mode {
            Mode::Main => {
                self.rooms
                    .handle_key_event(terminal, crossterm_lock, event)
                    .await
            }
            Mode::Log => self
                .log_chat
                .handle_key_event(terminal, crossterm_lock, event, false)
                .await
                .handled(),
        };

        // Pressing '?' should only open the key bindings list if it doesn't
        // interfere with any part of the main UI, such as entering text in a
        // text editor.
        if !handled {
            if let key!('?') = event {
                self.show_key_bindings();
            }
        }

        EventHandleResult::Continue
    }

    async fn handle_mouse_event(
        &mut self,
        _event: MouseEvent,
    ) -> anyhow::Result<EventHandleResult> {
        Ok(EventHandleResult::Continue)
    }
}