Closing Thoughts

This tutorial should get you started with a basic understanding of the flow of a ratatui program. However, this is only one way to create a ratatui application. Because ratatui is relatively low level compared to other UI frameworks, almost any application model can be implemented. You can explore more of these in Concepts: Application Patterns and get some inspiration for what model will work best for your application.

Finished Files

You can find the finished project used for the tutorial on GitHub. The code is also shown at the bottom of this page.

You can test this application by yourself by running:

cargo run > test.json

and double checking the output.

Main.rs

use std::{error::Error, io};

use crossterm::{
    event::{self, DisableMouseCapture, EnableMouseCapture, Event, KeyCode, KeyEventKind},
    execute,
    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};
use ratatui::{
    backend::{Backend, CrosstermBackend},
    Terminal,
};

mod app;
mod ui;
use crate::{
    app::{App, CurrentScreen, CurrentlyEditing},
    ui::ui,
};

fn main() -> Result<(), Box<dyn Error>> {
    // setup terminal
    enable_raw_mode()?;
    let mut stderr = io::stderr(); // This is a special case. Normally using stdout is fine
    execute!(stderr, EnterAlternateScreen, EnableMouseCapture)?;
    let backend = CrosstermBackend::new(stderr);
    let mut terminal = Terminal::new(backend)?;

    // create app and run it
    let mut app = App::new();
    let res = run_app(&mut terminal, &mut app);


    // restore terminal
    disable_raw_mode()?;
    execute!(
        terminal.backend_mut(),
        LeaveAlternateScreen,
        DisableMouseCapture
    )?;
    terminal.show_cursor()?;

    if let Ok(do_print) = res {
        if do_print {
            app.print_json()?;
        }
    } else if let Err(err) = res {
        println!("{err:?}");
    }

    Ok(())
}

fn run_app<B: Backend>(terminal: &mut Terminal<B>, app: &mut App) -> io::Result<bool> {
    loop {
        terminal.draw(|f| ui(f, app))?;

        if let Event::Key(key) = event::read()? {
            if key.kind == event::KeyEventKind::Release {
                // Skip events that are not KeyEventKind::Press
                continue;
            }
            match app.current_screen {
                CurrentScreen::Main => match key.code {
                    KeyCode::Char('e') => {
                        app.current_screen = CurrentScreen::Editing;
                        app.currently_editing = Some(CurrentlyEditing::Key);
                    }
                    KeyCode::Char('q') => {
                        app.current_screen = CurrentScreen::Exiting;
                    }
                    _ => {}
                },
                CurrentScreen::Exiting => match key.code {
                    KeyCode::Char('y') => {
                        return Ok(true);
                    }
                    KeyCode::Char('n') | KeyCode::Char('q') => {
                        return Ok(false);
                    }
                    _ => {}
                },
                CurrentScreen::Editing if key.kind == KeyEventKind::Press => {
                    match key.code {
                        KeyCode::Enter => {
                            if let Some(editing) = &app.currently_editing {
                                match editing {
                                    CurrentlyEditing::Key => {
                                        app.currently_editing = Some(CurrentlyEditing::Value);
                                    }
                                    CurrentlyEditing::Value => {
                                        app.save_key_value();
                                        app.current_screen = CurrentScreen::Main;
                                    }
                                }
                            }
                        }
                        KeyCode::Backspace => {
                            if let Some(editing) = &app.currently_editing {
                                match editing {
                                    CurrentlyEditing::Key => {
                                        app.key_input.pop();
                                    }
                                    CurrentlyEditing::Value => {
                                        app.value_input.pop();
                                    }
                                }
                            }
                        }
                        KeyCode::Esc => {
                            app.current_screen = CurrentScreen::Main;
                            app.currently_editing = None;
                        }
                        KeyCode::Tab => {
                            app.toggle_editing();
                        }
                        KeyCode::Char(value) => {
                            if let Some(editing) = &app.currently_editing {
                                match editing {
                                    CurrentlyEditing::Key => {
                                        app.key_input.push(value);
                                    }
                                    CurrentlyEditing::Value => {
                                        app.value_input.push(value);
                                    }
                                }
                            }
                        }
                        _ => {}
                    }
                }
                _ => {}
            }
        }
    }
}

App.rs

use serde_json::Result;

pub enum CurrentScreen {
    Main,
    Editing,
    Exiting,
}

pub enum CurrentlyEditing {
    Key,
    Value,
}

pub struct App {
    pub key_input: String,              // the currently being edited json key.
    pub value_input: String,            // the currently being edited json value.
    pub pairs: HashMap<String, String>, // The representation of our key and value pairs with serde Serialize support
    pub current_screen: CurrentScreen, // the current screen the user is looking at, and will later determine what is rendered.
    pub currently_editing: Option<CurrentlyEditing>, // the optional state containing which of the key or value pair the user is editing. It is an option, because when the user is not directly editing a key-value pair, this will be set to `None`.
}

impl App {
    pub fn new() -> App {
        App {
            key_input: String::new(),
            value_input: String::new(),
            pairs: HashMap::new(),
            current_screen: CurrentScreen::Main,
            currently_editing: None,
        }
    }

    pub fn save_key_value(&mut self) {
        self.pairs
            .insert(self.key_input.clone(), self.value_input.clone());

        self.key_input = String::new();
        self.value_input = String::new();
        self.currently_editing = None;
    }

    pub fn toggle_editing(&mut self) {
        if let Some(edit_mode) = &self.currently_editing {
            match edit_mode {
                CurrentlyEditing::Key => self.currently_editing = Some(CurrentlyEditing::Value),
                CurrentlyEditing::Value => self.currently_editing = Some(CurrentlyEditing::Key),
            };
        } else {
            self.currently_editing = Some(CurrentlyEditing::Key);
        }
    }

    pub fn print_json(&self) -> Result<()> {
        let output = serde_json::to_string(&self.pairs)?;
        println!("{}", output);
        Ok(())
    }
}

UI.rs

use ratatui::{
    backend::Backend,
    layout::{Constraint, Direction, Layout, Rect},
    style::{Color, Style},
    text::{Line, Span, Text},
    widgets::{Block, Borders, Clear, List, ListItem, Paragraph, Wrap},
    Frame,
};

use crate::app::{App, CurrentScreen, CurrentlyEditing};

pub fn ui<B: Backend>(f: &mut Frame<B>, app: &App) {
    // Create the layout sections.
    let chunks = Layout::default()
        .direction(Direction::Vertical)
        .constraints([
            Constraint::Length(3),
            Constraint::Min(1),
            Constraint::Length(3),
        ])
        .split(f.size());

    let title_block = Block::default()
        .borders(Borders::ALL)
        .style(Style::default());

    let title = Paragraph::new(Text::styled(
        "Create New Json",
        Style::default().fg(Color::Green),
    ))
    .block(title_block);

    f.render_widget(title, chunks[0]);
    let mut list_items = Vec::<ListItem>::new();

    for key in app.pairs.keys() {
        list_items.push(ListItem::new(Line::from(Span::styled(
            format!("{: <25} : {}", key, app.pairs.get(key).unwrap()),
            Style::default().fg(Color::Yellow),
        ))));
    }

    let list = List::new(list_items);

    f.render_widget(list, chunks[1]);
    let current_navigation_text = vec![
        // The first half of the text
        match app.current_screen {
            CurrentScreen::Main => Span::styled("Normal Mode", Style::default().fg(Color::Green)),
            CurrentScreen::Editing => {
                Span::styled("Editing Mode", Style::default().fg(Color::Yellow))
            }
            CurrentScreen::Exiting => Span::styled("Exiting", Style::default().fg(Color::LightRed)),
        }
        .to_owned(),
        // A white divider bar to separate the two sections
        Span::styled(" | ", Style::default().fg(Color::White)),
        // The final section of the text, with hints on what the user is editing
        {
            if let Some(editing) = &app.currently_editing {
                match editing {
                    CurrentlyEditing::Key => {
                        Span::styled("Editing Json Key", Style::default().fg(Color::Green))
                    }
                    CurrentlyEditing::Value => {
                        Span::styled("Editing Json Value", Style::default().fg(Color::LightGreen))
                    }
                }
            } else {
                Span::styled("Not Editing Anything", Style::default().fg(Color::DarkGray))
            }
        },
    ];

    let mode_footer = Paragraph::new(Line::from(current_navigation_text))
        .block(Block::default().borders(Borders::ALL));

    let current_keys_hint = {
        match app.current_screen {
            CurrentScreen::Main => Span::styled(
                "(q) to quit / (e) to make new pair",
                Style::default().fg(Color::Red),
            ),
            CurrentScreen::Editing => Span::styled(
                "(ESC) to cancel/(Tab) to switch boxes/enter to complete",
                Style::default().fg(Color::Red),
            ),
            CurrentScreen::Exiting => Span::styled(
                "(q) to quit / (e) to make new pair",
                Style::default().fg(Color::Red),
            ),
        }
    };

    let key_notes_footer =
        Paragraph::new(Line::from(current_keys_hint)).block(Block::default().borders(Borders::ALL));

    let footer_chunks = Layout::default()
        .direction(Direction::Horizontal)
        .constraints([Constraint::Percentage(50), Constraint::Percentage(50)])
        .split(chunks[2]);

    f.render_widget(mode_footer, footer_chunks[0]);
    f.render_widget(key_notes_footer, footer_chunks[1]);

    if let Some(editing) = &app.currently_editing {
        let popup_block = Block::default()
            .title("Enter a new key-value pair")
            .borders(Borders::NONE)
            .style(Style::default().bg(Color::DarkGray));

        let area = centered_rect(60, 25, f.size());
        f.render_widget(popup_block, area);

        let popup_chunks = Layout::default()
            .direction(Direction::Horizontal)
            .margin(1)
            .constraints([Constraint::Percentage(50), Constraint::Percentage(50)])
            .split(area);

        let mut key_block = Block::default().title("Key").borders(Borders::ALL);
        let mut value_block = Block::default().title("Value").borders(Borders::ALL);

        let active_style = Style::default().bg(Color::LightYellow).fg(Color::Black);

        match editing {
            CurrentlyEditing::Key => key_block = key_block.style(active_style),
            CurrentlyEditing::Value => value_block = value_block.style(active_style),
        };

        let key_text = Paragraph::new(app.key_input.clone()).block(key_block);
        f.render_widget(key_text, popup_chunks[0]);

        let value_text = Paragraph::new(app.value_input.clone()).block(value_block);
        f.render_widget(value_text, popup_chunks[1]);
    }

    if let CurrentScreen::Exiting = app.current_screen {
        f.render_widget(Clear, f.size()); //this clears the entire screen and anything already drawn
        let popup_block = Block::default()
            .title("Y/N")
            .borders(Borders::NONE)
            .style(Style::default().bg(Color::DarkGray));

        let exit_text = Text::styled(
            "Would you like to output the buffer as json? (y/n)",
            Style::default().fg(Color::Red),
        );
        // the `trim: false` will stop the text from being cut off when over the edge of the block
        let exit_paragraph = Paragraph::new(exit_text)
            .block(popup_block)
            .wrap(Wrap { trim: false });

        let area = centered_rect(60, 25, f.size());
        f.render_widget(exit_paragraph, area);
    }
}

/// helper function to create a centered rect using up certain percentage of the available rect `r`
fn centered_rect(percent_x: u16, percent_y: u16, r: Rect) -> Rect {
    // Cut the given rectangle into three vertical pieces
    let popup_layout = Layout::default()
        .direction(Direction::Vertical)
        .constraints([
            Constraint::Percentage((100 - percent_y) / 2),
            Constraint::Percentage(percent_y),
            Constraint::Percentage((100 - percent_y) / 2),
        ])
        .split(r);

    // Then cut the middle vertical piece into three width-wise pieces
    Layout::default()
        .direction(Direction::Horizontal)
        .constraints([
            Constraint::Percentage((100 - percent_x) / 2),
            Constraint::Percentage(percent_x),
            Constraint::Percentage((100 - percent_x) / 2),
        ])
        .split(popup_layout[1])[1] // Return the middle chunk
}