Tiny editor for GUI

src/tui.rs

@@ -1,11 +1,11 @@
 use anyhow::Result;
-use crossterm::event::{self, Event, KeyCode};
+use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyEventKind, KeyModifiers};
 use crossterm::execute;
 use crossterm::terminal::{
     disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen,
 };
 use ratatui::backend::CrosstermBackend;
-use ratatui::layout::Rect;
+use ratatui::layout::{Constraint, Direction, Layout, Rect};
 use ratatui::widgets::{Block, Borders, Paragraph, Wrap};
 use ratatui::{Frame, Terminal};
 use std::io::{stdout, Stdout};
@@ -14,15 +14,14 @@ use crate::levels::{self, Difficulty, Level};
 use crate::progress::{self, Progress};
 use crate::similarity;
 
+// -- State ------------------------------------------------------------------
+
 enum Screen {
     Welcome,
     TierSelect {
         cursor: u8,
     },
     Level,
-    Submit {
-        buf: String,
-    },
     Result {
         score: f64,
         passed: bool,
@@ -35,6 +34,110 @@ enum Screen {
     Completed,
 }
 
+#[derive(Copy, Clone, PartialEq, Eq)]
+enum Focus {
+    Game,
+    Editor,
+}
+
+/// Multi-line YAML editor backing the right column. Byte-indexed; assumes
+/// ASCII content (YAML is conventionally ASCII). Splitting at a multi-byte
+/// boundary would panic — that's flagged as risk R6.
+struct Editor {
+    buffer: Vec<String>,
+    cursor: (usize, usize), // (row, col)
+}
+
+impl Editor {
+    fn new() -> Self {
+        Self {
+            buffer: vec![String::new()],
+            cursor: (0, 0),
+        }
+    }
+
+    fn clear(&mut self) {
+        self.buffer = vec![String::new()];
+        self.cursor = (0, 0);
+    }
+
+    fn text(&self) -> String {
+        self.buffer.join("\n")
+    }
+
+    fn insert_char(&mut self, c: char) {
+        let (r, col) = self.cursor;
+        let line = &mut self.buffer[r];
+        let col = col.min(line.len());
+        line.insert(col, c);
+        self.cursor = (r, col + 1);
+    }
+
+    fn backspace(&mut self) {
+        let (r, col) = self.cursor;
+        if col > 0 {
+            self.buffer[r].remove(col - 1);
+            self.cursor = (r, col - 1);
+        } else if r > 0 {
+            let cur = self.buffer.remove(r);
+            let prev_len = self.buffer[r - 1].len();
+            self.buffer[r - 1].push_str(&cur);
+            self.cursor = (r - 1, prev_len);
+        }
+    }
+
+    fn newline(&mut self) {
+        let (r, col) = self.cursor;
+        let col = col.min(self.buffer[r].len());
+        let rest = self.buffer[r].split_off(col);
+        self.buffer.insert(r + 1, rest);
+        self.cursor = (r + 1, 0);
+    }
+
+    fn left(&mut self) {
+        let (r, col) = self.cursor;
+        if col > 0 {
+            self.cursor.1 = col - 1;
+        } else if r > 0 {
+            self.cursor = (r - 1, self.buffer[r - 1].len());
+        }
+    }
+
+    fn right(&mut self) {
+        let (r, col) = self.cursor;
+        let line_len = self.buffer[r].len();
+        if col < line_len {
+            self.cursor.1 = col + 1;
+        } else if r + 1 < self.buffer.len() {
+            self.cursor = (r + 1, 0);
+        }
+    }
+
+    fn up(&mut self) {
+        if self.cursor.0 > 0 {
+            let r = self.cursor.0 - 1;
+            self.cursor = (r, self.cursor.1.min(self.buffer[r].len()));
+        }
+    }
+
+    fn down(&mut self) {
+        if self.cursor.0 + 1 < self.buffer.len() {
+            let r = self.cursor.0 + 1;
+            self.cursor = (r, self.cursor.1.min(self.buffer[r].len()));
+        }
+    }
+
+    fn home(&mut self) {
+        self.cursor.1 = 0;
+    }
+
+    fn end(&mut self) {
+        self.cursor.1 = self.buffer[self.cursor.0].len();
+    }
+}
+
+// -- Entry ------------------------------------------------------------------
+
 pub fn run(prog: &mut Progress) -> Result<()> {
     install_panic_hook();
     let mut terminal = enter()?;
@@ -73,55 +176,132 @@ fn initial_screen(prog: &Progress, registry_len: usize) -> Screen {
     }
 }
 
+fn default_focus(screen: &Screen) -> Focus {
+    match screen {
+        Screen::Level | Screen::InvalidYaml { .. } => Focus::Editor,
+        _ => Focus::Game,
+    }
+}
+
+fn editor_active(screen: &Screen) -> bool {
+    matches!(
+        screen,
+        Screen::Level | Screen::Result { .. } | Screen::InvalidYaml { .. }
+    )
+}
+
+fn editor_interactive(screen: &Screen) -> bool {
+    matches!(screen, Screen::Level | Screen::InvalidYaml { .. })
+}
+
+// -- Main loop --------------------------------------------------------------
+
 fn main_loop(
     terminal: &mut Terminal<CrosstermBackend<Stdout>>,
     prog: &mut Progress,
 ) -> Result<()> {
     let registry = levels::registry();
     let mut screen = initial_screen(prog, registry.len());
+    let mut focus = default_focus(&screen);
+    let mut editor = Editor::new();
 
     loop {
-        terminal.draw(|frame| render(frame, &screen, prog, &registry))?;
+        terminal.draw(|frame| render(frame, &screen, prog, &registry, focus, &editor))?;
         let Event::Key(key) = event::read()? else {
             continue;
         };
+        if !matches!(key.kind, KeyEventKind::Press) {
+            continue;
+        }
 
-        // Swap `screen` out so we can match by value, then assign the new
-        // screen back. `Screen::Welcome` is just a placeholder during the
-        // swap; `step` never observes it.
-        let current = std::mem::replace(&mut screen, Screen::Welcome);
-        match step(current, key.code, prog, &registry)? {
-            Transition::To(next) => screen = next,
-            Transition::Quit => return Ok(()),
+        if step(&mut screen, &mut focus, &mut editor, key, prog, &registry)? {
+            return Ok(());
         }
     }
 }
 
-enum Transition {
-    To(Screen),
-    Quit,
-}
-
+/// Returns `true` when the user wants to quit.
 fn step(
-    screen: Screen,
-    key: KeyCode,
+    screen: &mut Screen,
+    focus: &mut Focus,
+    editor: &mut Editor,
+    key: KeyEvent,
     prog: &mut Progress,
     registry: &[Box<dyn Level>],
-) -> Result<Transition> {
-    use Transition::*;
+) -> Result<bool> {
+    let ctrl = key.modifiers.contains(KeyModifiers::CONTROL);
 
-    Ok(match (screen, key) {
-        // Welcome ------------------------------------------------------------
-        (Screen::Welcome, KeyCode::Enter) => To(Screen::TierSelect { cursor: 0 }),
-        (Screen::Welcome, KeyCode::Char('q')) => Quit,
+    // Global: Ctrl-Q quits from anywhere.
+    if ctrl && key.code == KeyCode::Char('q') {
+        return Ok(true);
+    }
 
-        // TierSelect ---------------------------------------------------------
-        (Screen::TierSelect { cursor }, KeyCode::Up) => To(Screen::TierSelect {
-            cursor: cursor.saturating_sub(1),
-        }),
-        (Screen::TierSelect { cursor }, KeyCode::Down) => To(Screen::TierSelect {
-            cursor: (cursor + 1).min(2),
-        }),
+    // Global: Ctrl-S grades when the editor is in play.
+    if ctrl && key.code == KeyCode::Char('s') && editor_interactive(screen) {
+        let next = grade(editor.text(), prog, registry)?;
+        *focus = default_focus(&next);
+        *screen = next;
+        return Ok(false);
+    }
+
+    // Tab toggles focus while the editor is interactive.
+    if key.code == KeyCode::Tab && editor_interactive(screen) {
+        *focus = match *focus {
+            Focus::Game => Focus::Editor,
+            Focus::Editor => Focus::Game,
+        };
+        return Ok(false);
+    }
+
+    // Editor keys (only when Editor is focused and screen is interactive).
+    if *focus == Focus::Editor && editor_interactive(screen) {
+        let was_invalid = matches!(screen, Screen::InvalidYaml { .. });
+        let mut consumed = true;
+        match key.code {
+            KeyCode::Char(c) if !ctrl => editor.insert_char(c),
+            KeyCode::Backspace => editor.backspace(),
+            KeyCode::Enter => editor.newline(),
+            KeyCode::Left => editor.left(),
+            KeyCode::Right => editor.right(),
+            KeyCode::Up => editor.up(),
+            KeyCode::Down => editor.down(),
+            KeyCode::Home => editor.home(),
+            KeyCode::End => editor.end(),
+            KeyCode::Esc => {
+                // Esc dismisses InvalidYaml (without retry) or returns focus
+                // to the Game column on Level.
+                if was_invalid {
+                    *screen = Screen::Level;
+                    *focus = default_focus(screen);
+                } else {
+                    *focus = Focus::Game;
+                }
+            }
+            _ => consumed = false,
+        }
+        if consumed && was_invalid {
+            // Any edit implicitly dismisses the error overlay.
+            *screen = Screen::Level;
+        }
+        return Ok(false);
+    }
+
+    // Game-focus keys.
+    match (&*screen, key.code) {
+        (Screen::Welcome, KeyCode::Enter) => {
+            *screen = Screen::TierSelect { cursor: 0 };
+            *focus = default_focus(screen);
+        }
+        (Screen::Welcome, KeyCode::Char('q')) => return Ok(true),
+
+        (Screen::TierSelect { cursor }, KeyCode::Up) => {
+            let c = cursor.saturating_sub(1);
+            *screen = Screen::TierSelect { cursor: c };
+        }
+        (Screen::TierSelect { cursor }, KeyCode::Down) => {
+            let c = (*cursor + 1).min(2);
+            *screen = Screen::TierSelect { cursor: c };
+        }
         (Screen::TierSelect { cursor }, KeyCode::Enter) => {
             let tier = match cursor {
                 0 => Difficulty::Easy,
@@ -134,71 +314,76 @@ fn step(
                 prog.current_seed = rand::random();
             }
             progress::save(prog)?;
-            To(Screen::Level)
+            editor.clear();
+            *screen = Screen::Level;
+            *focus = default_focus(screen);
         }
-        (Screen::TierSelect { .. }, KeyCode::Char('q')) => Quit,
+        (Screen::TierSelect { .. }, KeyCode::Char('q')) => return Ok(true),
 
-        // Level --------------------------------------------------------------
-        (Screen::Level, KeyCode::Char('s')) => To(Screen::Submit { buf: String::new() }),
-        (Screen::Level, KeyCode::Char('r')) => To(Screen::ResetConfirm),
-        (Screen::Level, KeyCode::Char('q')) => Quit,
-
-        // Submit -------------------------------------------------------------
-        (Screen::Submit { mut buf }, KeyCode::Char(c)) => {
-            buf.push(c);
-            To(Screen::Submit { buf })
+        (Screen::Level, KeyCode::Char('r')) => {
+            *screen = Screen::ResetConfirm;
+            *focus = default_focus(screen);
         }
-        (Screen::Submit { mut buf }, KeyCode::Backspace) => {
-            buf.pop();
-            To(Screen::Submit { buf })
-        }
-        (Screen::Submit { .. }, KeyCode::Esc) => To(Screen::Level),
-        (Screen::Submit { buf }, KeyCode::Enter) => To(grade(buf.trim(), prog, registry)?),
+        (Screen::Level, KeyCode::Char('q')) => return Ok(true),
 
-        // Result -------------------------------------------------------------
-        (Screen::Result { passed: true, .. }, _) => {
+        (Screen::Result { passed, .. }, KeyCode::Enter) => {
+            let pass = *passed;
+            if pass {
+                editor.clear();
                 if (prog.current_level as usize) > registry.len() {
-                To(Screen::Completed)
+                    *screen = Screen::Completed;
                 } else {
-                To(Screen::Level)
+                    *screen = Screen::Level;
                 }
+            } else {
+                *screen = Screen::Level;
+            }
+            *focus = default_focus(screen);
         }
-        (Screen::Result { passed: false, .. }, _) => To(Screen::Level),
 
-        // InvalidYaml --------------------------------------------------------
-        (Screen::InvalidYaml { .. }, _) => To(Screen::Submit { buf: String::new() }),
+        (Screen::InvalidYaml { .. }, KeyCode::Enter) => {
+            *screen = Screen::Level;
+            *focus = default_focus(screen);
+        }
+        (Screen::InvalidYaml { .. }, KeyCode::Esc) => {
+            *screen = Screen::Level;
+            *focus = default_focus(screen);
+        }
+        (Screen::InvalidYaml { .. }, KeyCode::Char('r')) => {
+            *screen = Screen::ResetConfirm;
+            *focus = default_focus(screen);
+        }
+        (Screen::InvalidYaml { .. }, KeyCode::Char('q')) => return Ok(true),
 
-        // ResetConfirm -------------------------------------------------------
         (Screen::ResetConfirm, KeyCode::Char('y')) => {
             let _ = std::fs::remove_file(progress::save_path());
             *prog = Progress::default();
-            To(Screen::Welcome)
+            editor.clear();
+            *screen = Screen::Welcome;
+            *focus = default_focus(screen);
+        }
+        (Screen::ResetConfirm, _) => {
+            *screen = Screen::Level;
+            *focus = default_focus(screen);
         }
-        (Screen::ResetConfirm, _) => To(Screen::Level),
 
-        // Completed ----------------------------------------------------------
-        (Screen::Completed, KeyCode::Char('q')) => Quit,
-        (Screen::Completed, KeyCode::Char('r')) => To(Screen::ResetConfirm),
+        (Screen::Completed, KeyCode::Char('q')) => return Ok(true),
+        (Screen::Completed, KeyCode::Char('r')) => {
+            *screen = Screen::ResetConfirm;
+            *focus = default_focus(screen);
+        }
 
-        // Anything else: stay where we are.
-        (other, _) => To(other),
-    })
+        _ => {}
+    }
+
+    Ok(false)
 }
 
-/// Read the player's file, parse it, score it, advance progress on a pass,
-/// and choose the next screen. Returns `Result` (`InvalidYaml` or `Result`).
-fn grade(path: &str, prog: &mut Progress, registry: &[Box<dyn Level>]) -> Result<Screen> {
-    let candidate = match std::fs::read_to_string(path) {
-        Ok(s) => s,
-        Err(e) => {
-            return Ok(Screen::InvalidYaml {
-                error: format!("could not read file: {e}"),
-            });
-        }
-    };
-
-    // Parse-first guard: invalid YAML is a wrong *format*, not a wrong
-    // *answer* — no scoring, no attempts bump.
+fn grade(
+    candidate: String,
+    prog: &mut Progress,
+    registry: &[Box<dyn Level>],
+) -> Result<Screen> {
     if let Err(e) = serde_yaml::from_str::<serde_yaml::Value>(&candidate) {
         return Ok(Screen::InvalidYaml { error: e.to_string() });
     }
@@ -231,28 +416,42 @@ fn grade(path: &str, prog: &mut Progress, registry: &[Box<dyn Level>]) -> Result
     })
 }
 
-// -- rendering --------------------------------------------------------------
+// -- Rendering --------------------------------------------------------------
 
 fn render(
     frame: &mut Frame,
     screen: &Screen,
     prog: &Progress,
     registry: &[Box<dyn Level>],
+    focus: Focus,
+    editor: &Editor,
 ) {
     let area = frame.size();
+    let chunks = Layout::default()
+        .direction(Direction::Horizontal)
+        .constraints([Constraint::Percentage(50), Constraint::Percentage(50)].as_ref())
+        .split(area);
+    let (left, right) = (chunks[0], chunks[1]);
+
     match screen {
-        Screen::Welcome => render_welcome(frame, area),
-        Screen::TierSelect { cursor } => render_tier_select(frame, area, *cursor),
-        Screen::Level => render_level(frame, area, prog, registry),
-        Screen::Submit { buf } => render_submit(frame, area, buf),
+        Screen::Welcome => render_welcome(frame, left),
+        Screen::TierSelect { cursor } => render_tier_select(frame, left, *cursor),
+        Screen::Level => render_level(frame, left, prog, registry),
         Screen::Result {
             score,
             passed,
             level_name,
-        } => render_result(frame, area, *score, *passed, level_name, prog),
-        Screen::InvalidYaml { error } => render_invalid_yaml(frame, area, error),
-        Screen::ResetConfirm => render_reset_confirm(frame, area),
-        Screen::Completed => render_completed(frame, area),
+        } => render_result(frame, left, *score, *passed, level_name, prog),
+        Screen::InvalidYaml { error } => render_invalid_yaml(frame, left, error),
+        Screen::ResetConfirm => render_reset_confirm(frame, left),
+        Screen::Completed => render_completed(frame, left),
+    }
+
+    if editor_active(screen) {
+        let editor_focused = focus == Focus::Editor && editor_interactive(screen);
+        render_editor(frame, right, editor, editor_focused);
+    } else {
+        render_editor_inactive(frame, right);
     }
 }
 
@@ -266,7 +465,7 @@ fn render_welcome(frame: &mut Frame, area: Rect) {
     let body = "\n\
         You stand at the entrance to the YAML labyrinth.\n\
         Within, broken syntax festers and dictionaries\n\
-        sprawl like vines. Reach the heart of it.\n\
+        sprawl like vines.\n\
         \n\
         [Enter] begin · [q] flee"
         .to_string();
@@ -305,19 +504,12 @@ fn render_level(
         tier_label
     );
     let body = format!(
-        "\n{}\n\n{}\nWrite your YAML answer in a file, then\n[s] submit · [r] reset · [q] flee",
+        "\n{}\n\n{}\n\n[Tab] swap focus · [Ctrl-S] grade · [r] reset · [q] quit",
         g.flavor, g.description
     );
     frame.render_widget(screen_widget(title, body), area);
 }
 
-fn render_submit(frame: &mut Frame, area: Rect, buf: &str) {
-    let body = format!(
-        "\nPath to your answer YAML:\n\n> {buf}_\n\n[Enter] grade · [Esc] cancel"
-    );
-    frame.render_widget(screen_widget(" Submit your answer ".to_string(), body), area);
-}
-
 fn render_result(
     frame: &mut Frame,
     area: Rect,
@@ -326,10 +518,7 @@ fn render_result(
     level_name: &str,
     prog: &Progress,
 ) {
-    let threshold = prog
-        .tier
-        .map(|t| t.threshold())
-        .unwrap_or(0.0);
+    let threshold = prog.tier.map(|t| t.threshold()).unwrap_or(0.0);
     let (title, narration) = if passed {
         (
             format!(" {level_name} cleared "),
@@ -352,7 +541,9 @@ fn render_result(
 
 fn render_invalid_yaml(frame: &mut Frame, area: Rect, error: &str) {
     let body = format!(
-        "\n{error}\n\nFix the syntax and try again.\n\n[Enter] back to submit"
+        "\n{error}\n\nFix the YAML in the editor (it's still there) and press\n\
+         [Ctrl-S] to retry. Attempts counter is not bumped.\n\n\
+         [Enter] dismiss · [r] reset · [q] quit"
     );
     frame.render_widget(
         screen_widget(" Couldn't parse your YAML ".to_string(), body),
@@ -361,11 +552,46 @@ fn render_invalid_yaml(frame: &mut Frame, area: Rect, error: &str) {
 }
 
 fn render_reset_confirm(frame: &mut Frame, area: Rect) {
-    let body = "\nWipe progress and start over?\n\n[y] yes, wipe · any other key cancels".to_string();
+    let body =
+        "\nWipe progress and start over?\n\n[y] yes, wipe · any other key cancels".to_string();
     frame.render_widget(screen_widget(" Reset? ".to_string(), body), area);
 }
 
 fn render_completed(frame: &mut Frame, area: Rect) {
-    let body = "\nYou cleared the YAML labyrinth.\n\n[r] reset and replay · [q] quit".to_string();
+    let body =
+        "\nYou cleared the YAML labyrinth.\n\n[r] reset and replay · [q] quit".to_string();
     frame.render_widget(screen_widget(" Labyrinth complete ".to_string(), body), area);
 }
+
+fn render_editor(frame: &mut Frame, area: Rect, editor: &Editor, focused: bool) {
+    let title = if focused {
+        " Your YAML * ".to_string()
+    } else {
+        " Your YAML ".to_string()
+    };
+    let body = if focused {
+        let (cr, cc) = editor.cursor;
+        let mut lines: Vec<String> = Vec::with_capacity(editor.buffer.len());
+        for (r, line) in editor.buffer.iter().enumerate() {
+            if r == cr {
+                let col = cc.min(line.len());
+                let mut with_cursor = String::with_capacity(line.len() + 1);
+                with_cursor.push_str(&line[..col]);
+                with_cursor.push('_');
+                with_cursor.push_str(&line[col..]);
+                lines.push(with_cursor);
+            } else {
+                lines.push(line.clone());
+            }
+        }
+        lines.join("\n")
+    } else {
+        editor.text()
+    };
+    frame.render_widget(screen_widget(title, body), area);
+}
+
+fn render_editor_inactive(frame: &mut Frame, area: Rect) {
+    let body = "\n  The editor opens when you start a level.".to_string();
+    frame.render_widget(screen_widget(" Editor (inactive) ".to_string(), body), area);
+}