kiln/kiln-tui/src/main.rs

//! `kiln-tui` — a terminal "player" for kiln boards.
//!
//! Pass a `.toml` map file as the single command-line argument; kiln-tui loads
//! that board and lets you walk the player around it with the arrow keys
//! (or HJKL). There is no editor — this is a play-only front-end.
//!
//! Rendering is text-based: kiln's bitmap-font tile indices are reinterpreted
//! as characters (see [`cp437`]) and drawn with each cell's RGB colors.

mod cp437;
mod render;
mod term;

use kiln_core::game::GameState;
use kiln_core::log::LogLine;
use kiln_core::map_file;
use ratatui::Frame;
use ratatui::crossterm::event::{
    self, DisableMouseCapture, EnableMouseCapture, Event, KeyCode, KeyEventKind, MouseEventKind,
};
use ratatui::crossterm::execute;
use ratatui::layout::{Constraint, Layout, Spacing};
use ratatui::style::{Color, Style};
use ratatui::text::{Line, Span};
use ratatui::widgets::{Block, Paragraph, Wrap};
use render::{BoardWidget, logline_to_line};
use std::io;
use std::process::ExitCode;
use std::time::{Duration, Instant};
use ratatui::symbols::merge::MergeStrategy;
use term::TerminalCaps;

/// View-only UI state for the log panel. This is presentation state, so it lives
/// in the front-end rather than on the engine's [`GameState`].
struct Ui {
    /// Whether the bottom log panel is open.
    log_open: bool,
    /// Height (in terminal rows, borders included) of the log panel when open.
    log_height: u16,
    /// Vertical scroll offset of the log panel, in lines from the top (newest).
    scroll: u16,
}

impl Default for Ui {
    fn default() -> Self {
        Self {
            log_open: false,
            log_height: 10,
            scroll: 0,
        }
    }
}

/// Entry point: parse the map path, load the board, then run the play loop with
/// the terminal in raw/alternate-screen mode (restored on every exit path).
fn main() -> ExitCode {
    // The single positional argument is the map file to play.
    let Some(path) = std::env::args().nth(1) else {
        eprintln!("usage: kiln-tui <map.toml>");
        return ExitCode::from(2);
    };

    // Load before touching the terminal so load errors print to a normal screen.
    let board = match map_file::load(&path) {
        Ok(board) => board,
        Err(e) => {
            eprintln!("error loading {path}: {e}");
            return ExitCode::FAILURE;
        }
    };

    let mut game = GameState::new(board);

    // `init` enters the alternate screen and raw mode; `restore` always undoes it.
    let mut terminal = ratatui::init();

    // Capture mouse events so the log panel can be scrolled with the wheel and
    // resized by dragging its divider. Disabled again before restoring.
    let _ = execute!(io::stdout(), EnableMouseCapture);

    // Detect terminal capabilities (now that we're in raw mode) and enable the
    // Kitty keyboard protocol when it's available, so scripts can rely on the
    // richer bindings it provides. Disabled again before restoring the terminal.
    let caps = TerminalCaps::detect();
    if caps.keyboard_enhancement {
        let _ = term::push_kitty_flags();
    }

    // Seed the log: the terminal-capabilities badge plus a couple of test
    // messages (temporary, just to exercise the panel).
    // Note these will appear in reverse order, latest on top
    game.log(LogLine::raw("Press 'q' to exit."));
    game.log(LogLine::raw("Welcome to kiln - ").append(caps.status_logline()));

    let mut ui = Ui::default();
    let result = run(&mut terminal, &mut game, &mut ui);

    if caps.keyboard_enhancement {
        let _ = term::pop_kitty_flags();
    }
    let _ = execute!(io::stdout(), DisableMouseCapture);
    ratatui::restore();

    if let Err(e) = result {
        eprintln!("error: {e}");
        return ExitCode::FAILURE;
    }
    ExitCode::SUCCESS
}

/// The target frame interval: 30 frames per second.
const FRAME: Duration = Duration::from_nanos(1_000_000_000 / 30);

/// Real-time draw / input / update loop at ~30 FPS. Returns once the user quits.
///
/// Unlike a turn-based loop, this never blocks indefinitely: it waits for input
/// only until the next frame deadline (`event::poll`), then advances the game by
/// the real time elapsed since the last tick. `poll` returns the instant a key
/// arrives, so input stays responsive while the game keeps ticking on its own.
fn run(
    terminal: &mut ratatui::DefaultTerminal,
    game: &mut GameState,
    ui: &mut Ui,
) -> std::io::Result<()> {
    let mut last_tick = Instant::now();
    loop {
        // Redraw every iteration; ratatui diffs against the previous frame so
        // only changed cells are actually written to the terminal.
        terminal.draw(|frame| draw(frame, game, ui))?;

        // Wait for input only up to the next frame deadline so the loop wakes to
        // tick even with no keypresses.
        let timeout = FRAME.saturating_sub(last_tick.elapsed());
        if event::poll(timeout)? {
            match event::read()? {
                // Act on Press and Repeat so holding a key moves the player
                // continuously (the Kitty protocol emits Repeat events while a key
                // is held). Ignore Release, which that protocol also emits and
                // which would otherwise fire a second, spurious move per keypress.
                Event::Key(key) if key.kind != KeyEventKind::Release => match key.code {
                    KeyCode::Char('q') | KeyCode::Esc => return Ok(()),
                    KeyCode::Up => game.try_move(0, -1),
                    KeyCode::Down => game.try_move(0, 1),
                    KeyCode::Left => game.try_move(-1, 0),
                    // Right arrow moves right; 'l' is the log panel.
                    KeyCode::Right => game.try_move(1, 0),
                    // 'l' toggles the log panel; reset scroll to newest.
                    KeyCode::Char('l') => {
                        ui.log_open = !ui.log_open;
                        ui.scroll = 0;
                    }
                    // PageUp/PageDown scroll the log when it's open.
                    KeyCode::PageUp if ui.log_open => scroll_log(ui, game, -5),
                    KeyCode::PageDown if ui.log_open => scroll_log(ui, game, 5),
                    _ => {}
                },
                // Wheel scrolls the open log; dragging the divider resizes it.
                Event::Mouse(m) if ui.log_open => match m.kind {
                    MouseEventKind::ScrollUp => scroll_log(ui, game, -1),
                    MouseEventKind::ScrollDown => scroll_log(ui, game, 1),
                    MouseEventKind::Drag(_) => {
                        // The divider sits at row `total - log_height`; dragging
                        // it up (smaller row) grows the panel. Keep both usable.
                        let total = terminal.size()?.height;
                        let target = total.saturating_sub(m.row);
                        ui.log_height = target.clamp(3, total.saturating_sub(3).max(3));
                    }
                    _ => {}
                },
                _ => {}
            }
        }

        // Advance the game by the real time elapsed since the last tick. Only
        // resetting `last_tick` when we actually tick means time spent waiting on
        // input (or skipped Release events) is preserved in the next `dt`.
        if last_tick.elapsed() >= FRAME {
            let dt = last_tick.elapsed();
            last_tick = Instant::now();
            game.tick(dt);
        }
    }
}

/// Adjusts the log scroll offset by `delta` lines, clamped so it can neither go
/// above the newest message nor scroll past the oldest.
fn scroll_log(ui: &mut Ui, game: &GameState, delta: i32) {
    let max = game.log.len().saturating_sub(1) as i32;
    ui.scroll = (ui.scroll as i32 + delta).clamp(0, max) as u16;
}

/// Render a single frame: the board in a bordered block, and — when open — a log
/// panel across the bottom. When the panel is closed the latest log message is
/// previewed in the board's bottom-left border after a `[l]og:` label.
fn draw(frame: &mut Frame, game: &GameState, ui: &Ui) {
    let board = &game.board;

    if ui.log_open {
        // Split the screen: board on top, log panel of `log_height` at the bottom.
        let [board_area, log_area] =
            Layout::vertical([Constraint::Min(3), Constraint::Length(ui.log_height)])
                .spacing(Spacing::Overlap(1))
                .areas(frame.area());

        let block = Block::bordered().title(format!(" {} ", board.name)).merge_borders(MergeStrategy::Exact);
        let inner = block.inner(board_area);
        frame.render_widget(block, board_area);
        frame.render_widget(BoardWidget::new(board), inner);

        // Newest message on top: reverse the log into ratatui lines.
        let log_block = Block::bordered()
            .title(Span::styled(" [l]og: ", Style::default().fg(Color::DarkGray)))
            .merge_borders(MergeStrategy::Exact);
        let lines: Vec<Line> = game.log.iter().rev().map(logline_to_line).collect();
        let paragraph = Paragraph::new(lines)
            .block(log_block)
            .scroll((ui.scroll, 0))
            .wrap(Wrap { trim: false });
        frame.render_widget(paragraph, log_area);
    } else {
        // Panel closed: board fills the screen, latest message in the border.
        let mut block =
            Block::bordered().title(format!(" {} ", board.name));
        block = block.title_bottom(log_preview(game).left_aligned());
        let inner = block.inner(frame.area());
        frame.render_widget(block, frame.area());
        frame.render_widget(BoardWidget::new(board), inner);
    }
}

/// Builds the `[l]og: <latest message>` preview shown in the board's bottom-left
/// border when the log panel is closed.
fn log_preview(game: &GameState) -> Line<'static> {
    let mut spans = vec![Span::styled(
        " [l]og: ",
        Style::default().fg(Color::DarkGray),
    )];
    if let Some(latest) = game.log.last() {
        spans.extend(logline_to_line(latest).spans);
    }
    spans.push(Span::raw(" "));
    Line::from(spans)
}