【完結】Rust × Ratatuiで作るTUIツール：基礎編の総まとめと実践サンプル

use crossterm::{
    event::{self, Event, KeyCode, KeyEventKind, KeyModifiers},
    execute,
    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};
use ratatui::{
    backend::CrosstermBackend,
    layout::{Constraint, Direction, Layout},
    style::{Color, Style},
    widgets::{Block, Borders, Paragraph},
    Terminal,
};
use std::{error::Error, io};

#[derive(PartialEq)]
enum Focus {
    Left,
    Right,
}

fn main() -> Result<(), Box<dyn Error>> {
    // セットアップ
    enable_raw_mode()?;
    let mut stdout = io::stdout();
    execute!(stdout, EnterAlternateScreen)?;
    let mut terminal = Terminal::new(CrosstermBackend::new(stdout))?;

    // 状態管理
    let mut current_focus = Focus::Left;
    let mut left_input = String::new();
    let mut right_input = String::new();

    loop {
        terminal.draw(|f| {
            // レイアウト：上下に分割し、上を左右に分割
            let chunks = Layout::default()
                .direction(Direction::Vertical)
                .constraints([Constraint::Min(0), Constraint::Length(3)])
                .split(f.area());

            let top_chunks = Layout::default()
                .direction(Direction::Horizontal)
                .constraints([Constraint::Percentage(50), Constraint::Percentage(50)])
                .split(chunks[0]);

            let get_style = |focus: Focus| {
                if current_focus == focus { Style::default().fg(Color::Yellow) }
                else { Style::default().fg(Color::White) }
            };

            // 各パネルの描画
            f.render_widget(
                Paragraph::new(left_input.as_str())
                    .block(Block::default().title(" Left Panel ").borders(Borders::ALL).style(get_style(Focus::Left))),
                top_chunks[0],
            );
            f.render_widget(
                Paragraph::new(right_input.as_str())
                    .block(Block::default().title(" Right Panel ").borders(Borders::ALL).style(get_style(Focus::Right))),
                top_chunks[1],
            );
            f.render_widget(
                Paragraph::new(" [Tab] Switch Focus | [Ctrl+Q] Quit ")
                    .block(Block::default().title(" Help ").borders(Borders::ALL)),
                chunks[1],
            );
        })?;

        // イベント処理
        if let Event::Key(key) = event::read()? {
            if key.kind == KeyEventKind::Press {
                match key.code {
                    // 終了コンボ
                    KeyCode::Char('q') if key.modifiers.contains(KeyModifiers::CONTROL) => break,
                    // フォーカス切り替え
                    KeyCode::Tab => {
                        current_focus = if current_focus == Focus::Left { Focus::Right } else { Focus::Left };
                    }
                    // 入力振り分け
                    KeyCode::Char(c) if !key.modifiers.contains(KeyModifiers::CONTROL) => {
                        match current_focus {
                            Focus::Left => left_input.push(c),
                            Focus::Right => right_input.push(c),
                        }
                    }
                    KeyCode::Backspace => {
                        match current_focus {
                            Focus::Left => { left_input.pop(); },
                            Focus::Right => { right_input.pop(); },
                        }
                    }
                    _ => {}
                }
            }
        }
    }

    // クリーンアップ
    disable_raw_mode()?;
    execute!(terminal.backend_mut(), LeaveAlternateScreen)?;
    Ok(())
}