hello_world.rs

use std::{
    io::{self, Stdout},
    time::Duration,
};

use anyhow::{Context, Result};
use crossterm::{
    event::{self, Event, KeyCode},
    execute,
    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};
use ratatui::{prelude::*, widgets::*};

/// This is a bare minimum example. There are many approaches to running an application loop, so
/// this is not meant to be prescriptive. It is only meant to demonstrate the basic setup and
/// teardown of a terminal application.
///
/// A more robust application would probably want to handle errors and ensure that the terminal is
/// restored to a sane state before exiting. This example does not do that. It also does not handle
/// events or update the application state. It just draws a greeting and exits when the user
/// presses 'q'.
fn main() -> Result<()> {
    let mut terminal = setup_terminal().context("setup failed")?;
    run(&mut terminal).context("app loop failed")?;
    restore_terminal(&mut terminal).context("restore terminal failed")?;
    Ok(())
}

/// Setup the terminal. This is where you would enable raw mode, enter the alternate screen, and
/// hide the cursor. This example does not handle errors. A more robust application would probably
/// want to handle errors and ensure that the terminal is restored to a sane state before exiting.
fn setup_terminal() -> Result<Terminal<CrosstermBackend<Stdout>>> {
    let mut stdout = io::stdout();
    enable_raw_mode().context("failed to enable raw mode")?;
    execute!(stdout, EnterAlternateScreen).context("unable to enter alternate screen")?;
    Terminal::new(CrosstermBackend::new(stdout)).context("creating terminal failed")
}

/// Restore the terminal. This is where you disable raw mode, leave the alternate screen, and show
/// the cursor.
fn restore_terminal(terminal: &mut Terminal<CrosstermBackend<Stdout>>) -> Result<()> {
    disable_raw_mode().context("failed to disable raw mode")?;
    execute!(terminal.backend_mut(), LeaveAlternateScreen)
        .context("unable to switch to main screen")?;
    terminal.show_cursor().context("unable to show cursor")
}

/// Run the application loop. This is where you would handle events and update the application
/// state. This example exits when the user presses 'q'. Other styles of application loops are
/// possible, for example, you could have multiple application states and switch between them based
/// on events, or you could have a single application state and update it based on events.
fn run(terminal: &mut Terminal<CrosstermBackend<Stdout>>) -> Result<()> {
    loop {
        terminal.draw(crate::render_app)?;
        if should_quit()? {
            break;
        }
    }
    Ok(())
}

/// Render the application. This is where you would draw the application UI. This example just
/// draws a greeting.
fn render_app(frame: &mut ratatui::Frame<CrosstermBackend<Stdout>>) {
    let greeting = Paragraph::new("Hello World! (press 'q' to quit)");
    frame.render_widget(greeting, frame.size());
}

/// Check if the user has pressed 'q'. This is where you would handle events. This example just
/// checks if the user has pressed 'q' and returns true if they have. It does not handle any other
/// events. There is a 250ms timeout on the event poll so that the application can exit in a timely
/// manner, and to ensure that the terminal is rendered at least once every 250ms.
fn should_quit() -> Result<bool> {
    if event::poll(Duration::from_millis(250)).context("event poll failed")? {
        if let Event::Key(key) = event::read().context("event read failed")? {
            return Ok(KeyCode::Char('q') == key.code);
        }
    }
    Ok(false)
}