use std::{
    io::{self, Read},
    sync::{Arc, RwLock},
    time::Duration,
};

use crossterm::event::{self, Event, KeyCode, KeyEventKind};
use portable_pty::{CommandBuilder, NativePtySystem, PtySize, PtySystem};
use ratatui::{
    DefaultTerminal, Frame,
    layout::Alignment,
    style::{Modifier, Style},
    text::Line,
    widgets::{Block, Borders, Paragraph},
};
use tui_term::widget::PseudoTerminal;
use vt100::Screen;

fn main() -> std::io::Result<()> {
    let mut terminal = ratatui::init();
    let result = run_app(&mut terminal);
    ratatui::restore();
    result
}

fn run_app(terminal: &mut DefaultTerminal) -> std::io::Result<()> {
    let pty_system = NativePtySystem::default();
    let cwd = std::env::current_dir().unwrap();
    let mut cmd = CommandBuilder::new("top");
    cmd.cwd(cwd);

    let pair = pty_system
        .openpty(PtySize {
            rows: 24,
            cols: 80,
            pixel_width: 0,
            pixel_height: 0,
        })
        .unwrap();
    // Wait for the child to complete
    std::thread::spawn(move || {
        let mut child = pair.slave.spawn_command(cmd).unwrap();
        let _child_exit_status = child.wait().unwrap();
        drop(pair.slave);
    });

    let mut reader = pair.master.try_clone_reader().unwrap();
    let parser = Arc::new(RwLock::new(vt100::Parser::new(24, 80, 0)));

    {
        let parser = parser.clone();
        std::thread::spawn(move || {
            // Consume the output from the child
            // Can't read the full buffer, since that would wait for EOF
            let mut buf = [0u8; 8192];
            let mut processed_buf = Vec::new();
            loop {
                let size = reader.read(&mut buf).unwrap();
                if size == 0 {
                    break;
                }
                if size > 0 {
                    processed_buf.extend_from_slice(&buf[..size]);
                    let mut parser = parser.write().unwrap();
                    parser.process(&processed_buf);

                    // Clear the processed portion of the buffer
                    processed_buf.clear();
                }
            }
        });
    }

    {
        // Drop writer on purpose
        let _writer = pair.master.take_writer().unwrap();
    }
    drop(pair.master);

    run(terminal, parser)
}

fn run(terminal: &mut DefaultTerminal, parser: Arc<RwLock<vt100::Parser>>) -> io::Result<()> {
    loop {
        terminal.draw(|f| ui(f, parser.read().unwrap().screen()))?;

        // Event read is blocking
        if event::poll(Duration::from_millis(10))? {
            // It's guaranteed that the `read()` won't block when the `poll()`
            // function returns `true`
            if let Event::Key(key) = event::read()? {
                if key.kind == KeyEventKind::Press {
                    if let KeyCode::Char('q') = key.code {
                        return Ok(());
                    }
                }
            }
        }
    }
}

fn ui(f: &mut Frame, screen: &Screen) {
    let chunks = ratatui::layout::Layout::default()
        .direction(ratatui::layout::Direction::Vertical)
        .margin(1)
        .constraints(
            [
                ratatui::layout::Constraint::Percentage(0),
                ratatui::layout::Constraint::Percentage(100),
                ratatui::layout::Constraint::Min(1),
            ]
            .as_ref(),
        )
        .split(f.area());
    let title = Line::from("[ Running: top ]");
    let block = Block::default()
        .borders(Borders::ALL)
        .title(title)
        .style(Style::default().add_modifier(Modifier::BOLD));
    let pseudo_term = PseudoTerminal::new(screen).block(block);
    f.render_widget(pseudo_term, chunks[1]);
    let block = Block::default().borders(Borders::ALL);
    f.render_widget(block, f.area());
    let explanation = "Press q to exit".to_string();
    let explanation = Paragraph::new(explanation)
        .style(Style::default().add_modifier(Modifier::BOLD | Modifier::REVERSED))
        .alignment(Alignment::Center);
    f.render_widget(explanation, chunks[2]);
}
