Add typewriter effect

game.ini

@@ -0,0 +1,10 @@
+# YAMLabyrinth — game configuration.
+# Delete this file to use defaults. Keys are case-insensitive; spaces
+# and underscores in keys are equivalent.
+
+# Animate level prompts character-by-character in the log.
+typewriter_effect = true
+
+# Typing speed in characters per minute. Higher = faster.
+# Defaults: 1000 cpm (~60 ms per character).
+typewriter_speed_cpm = 1000

src/config.rs

@@ -0,0 +1,130 @@
+//! Game configuration, loaded from `./game.ini`.
+//!
+//! Two settings today:
+//! - `typewriter_effect` (bool, default `true`) — animate level prompts
+//!   character-by-character as they appear in the log.
+//! - `typewriter_speed_cpm` (u32, default `1000`) — typing speed in
+//!   characters per minute (~60 ms per character).
+//!
+//! Missing keys fall back to defaults. Missing file falls back to all
+//! defaults. Comments (`#` or `;`) and `[sections]` are ignored.
+
+use std::path::PathBuf;
+use std::time::Duration;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct GameConfig {
+    pub typewriter_enabled: bool,
+    pub typewriter_speed_cpm: u32,
+}
+
+impl Default for GameConfig {
+    fn default() -> Self {
+        Self {
+            typewriter_enabled: true,
+            typewriter_speed_cpm: 1000,
+        }
+    }
+}
+
+impl GameConfig {
+    /// How long each character takes to appear during the typewriter
+    /// animation. Falls back to the default speed if `speed_cpm` is 0.
+    pub fn char_duration(&self) -> Duration {
+        let cpm = if self.typewriter_speed_cpm == 0 {
+            Self::default().typewriter_speed_cpm
+        } else {
+            self.typewriter_speed_cpm
+        };
+        Duration::from_millis(60_000 / cpm as u64)
+    }
+}
+
+pub fn config_path() -> PathBuf {
+    PathBuf::from("game.ini")
+}
+
+pub fn load() -> GameConfig {
+    match std::fs::read_to_string(config_path()) {
+        Ok(content) => parse(&content),
+        Err(_) => GameConfig::default(),
+    }
+}
+
+pub fn parse(content: &str) -> GameConfig {
+    let mut cfg = GameConfig::default();
+    for line in content.lines() {
+        let line = line.trim();
+        if line.is_empty()
+            || line.starts_with('#')
+            || line.starts_with(';')
+            || line.starts_with('[')
+        {
+            continue;
+        }
+        let Some((key, value)) = line.split_once('=') else {
+            continue;
+        };
+        let key = key.trim().to_lowercase().replace(' ', "_");
+        let value = value.trim();
+        match key.as_str() {
+            "typewriter_effect" | "typewriter_enabled" => {
+                if let Ok(b) = value.parse::<bool>() {
+                    cfg.typewriter_enabled = b;
+                }
+            }
+            "typewriter_speed" | "typewriter_speed_cpm" => {
+                if let Ok(n) = value.parse::<u32>() {
+                    cfg.typewriter_speed_cpm = n;
+                }
+            }
+            _ => {}
+        }
+    }
+    cfg
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn defaults() {
+        let cfg = GameConfig::default();
+        assert!(cfg.typewriter_enabled);
+        assert_eq!(cfg.typewriter_speed_cpm, 1000);
+        // 1000 cpm = 60 ms per char
+        assert_eq!(cfg.char_duration().as_millis(), 60);
+    }
+
+    #[test]
+    fn parser_reads_both_underscored_and_spaced_keys() {
+        let ini = "\
+            # comment\n\
+            ; another comment\n\
+            [section]\n\
+            typewriter effect = false\n\
+            typewriter_speed_cpm = 240\n\
+        ";
+        let cfg = parse(ini);
+        assert!(!cfg.typewriter_enabled);
+        assert_eq!(cfg.typewriter_speed_cpm, 240);
+        // 240 cpm = 250 ms per char
+        assert_eq!(cfg.char_duration().as_millis(), 250);
+    }
+
+    #[test]
+    fn parser_keeps_defaults_on_garbage() {
+        let cfg = parse("typewriter_effect = maybe\ntypewriter_speed_cpm = fast\n");
+        assert_eq!(cfg, GameConfig::default());
+    }
+
+    #[test]
+    fn zero_speed_falls_back_to_default_duration() {
+        let cfg = GameConfig {
+            typewriter_enabled: true,
+            typewriter_speed_cpm: 0,
+        };
+        assert_eq!(cfg.char_duration().as_millis(), 60);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+pub mod config;
 pub mod describe;
 pub mod levels;
 pub mod progress;

src/tui.rs

@@ -9,7 +9,9 @@ use ratatui::layout::{Constraint, Direction, Layout, Rect};
 use ratatui::widgets::{Block, Borders, Paragraph, Wrap};
 use ratatui::{Frame, Terminal};
 use std::io::{stdout, Stdout};
+use std::time::{Duration, Instant};
 
+use crate::config;
 use crate::levels::{self, Difficulty, Level};
 use crate::progress::{self, Progress};
 use crate::similarity;
@@ -93,6 +95,45 @@ impl HistoryLog {
     }
 }
 
+/// Drives the character-by-character reveal of the latest `LevelPrompt`.
+/// `entry_idx` is the index into `HistoryLog::entries` being animated.
+struct Typewriter {
+    entry_idx: usize,
+    chars_shown: usize,
+    total_chars: usize,
+    char_duration: Duration,
+    next_tick_at: Instant,
+}
+
+impl Typewriter {
+    fn new(entry_idx: usize, total_chars: usize, char_duration: Duration) -> Self {
+        Self {
+            entry_idx,
+            chars_shown: 0,
+            total_chars,
+            char_duration,
+            next_tick_at: Instant::now() + char_duration,
+        }
+    }
+
+    fn is_done(&self) -> bool {
+        self.chars_shown >= self.total_chars
+    }
+
+    fn tick(&mut self) {
+        let now = Instant::now();
+        while self.next_tick_at <= now && self.chars_shown < self.total_chars {
+            self.chars_shown += 1;
+            self.next_tick_at += self.char_duration;
+        }
+    }
+
+    fn time_to_next_tick(&self) -> Duration {
+        let now = Instant::now();
+        self.next_tick_at.saturating_duration_since(now)
+    }
+}
+
 /// Multi-line YAML editor. Byte-indexed; ASCII-only (see risk R6).
 struct Editor {
     buffer: Vec<String>,
@@ -279,21 +320,37 @@ fn main_loop(
     prog: &mut Progress,
 ) -> Result<()> {
     let registry = levels::registry();
+    let cfg = config::load();
     let (mut screen, mut log) = initial_state(prog, &registry);
     let mut focus = default_focus(&screen);
     let mut editor = Editor::new();
 
+    // If resume put a LevelPrompt at the bottom, typewriter it from scratch.
+    let mut typewriter = if cfg.typewriter_enabled {
+        start_typewriter(&log, &cfg)
+    } else {
+        None
+    };
+    let mut prev_log_len = log.entries.len();
+
     loop {
         terminal.draw(|frame| {
-            render(frame, &screen, focus, &editor, &log);
+            render(frame, &screen, focus, &editor, &log, typewriter.as_ref());
         })?;
+
+        let poll_timeout = typewriter
+            .as_ref()
+            .filter(|tw| !tw.is_done())
+            .map(|tw| tw.time_to_next_tick())
+            .unwrap_or_else(|| Duration::from_secs(3600));
+
+        if event::poll(poll_timeout)? {
             let Event::Key(key) = event::read()? else {
                 continue;
             };
             if !matches!(key.kind, KeyEventKind::Press) {
                 continue;
             }
-
             if step(
                 &mut screen,
                 &mut focus,
@@ -305,7 +362,38 @@ fn main_loop(
             )? {
                 return Ok(());
             }
+            if cfg.typewriter_enabled && log.entries.len() > prev_log_len {
+                if let Some(tw) = start_typewriter(&log, &cfg) {
+                    if tw.entry_idx >= prev_log_len {
+                        typewriter = Some(tw);
                     }
+                }
+            }
+            prev_log_len = log.entries.len();
+        } else if let Some(tw) = typewriter.as_mut() {
+            tw.tick();
+            if tw.is_done() {
+                typewriter = None;
+            }
+        }
+    }
+}
+
+/// Build a `Typewriter` for the most recent `LevelPrompt` entry in the log,
+/// if any.
+fn start_typewriter(log: &HistoryLog, cfg: &config::GameConfig) -> Option<Typewriter> {
+    let idx = log.entries.iter().enumerate().rev().find_map(|(i, e)| {
+        if matches!(e, LogEntry::LevelPrompt { .. }) {
+            Some(i)
+        } else {
+            None
+        }
+    })?;
+    let total = entry_lines(&log.entries[idx])
+        .join("\n")
+        .chars()
+        .count();
+    Some(Typewriter::new(idx, total, cfg.char_duration()))
 }
 
 /// Returns `true` to quit the loop.
@@ -515,6 +603,7 @@ fn render(
     focus: Focus,
     editor: &Editor,
     log: &HistoryLog,
+    typewriter: Option<&Typewriter>,
 ) {
     let area = frame.size();
     let chunks = Layout::default()
@@ -524,11 +613,17 @@ fn render(
     let (left, right) = (chunks[0], chunks[1]);
 
     match screen {
-        Screen::Welcome => render_log(frame, left, log, Some(&welcome_prompt_lines())),
-        Screen::TierSelect { cursor } => {
-            render_log(frame, left, log, Some(&tier_picker_lines(*cursor)))
+        Screen::Welcome => {
+            render_log(frame, left, log, Some(&welcome_prompt_lines()), typewriter)
         }
-        Screen::Game | Screen::Completed => render_log(frame, left, log, None),
+        Screen::TierSelect { cursor } => render_log(
+            frame,
+            left,
+            log,
+            Some(&tier_picker_lines(*cursor)),
+            typewriter,
+        ),
+        Screen::Game | Screen::Completed => render_log(frame, left, log, None, typewriter),
         Screen::ResetConfirm => render_reset_confirm(frame, left),
     }
 
@@ -579,6 +674,7 @@ fn render_log(
     area: Rect,
     log: &HistoryLog,
     trailing_prompt: Option<&[String]>,
+    typewriter: Option<&Typewriter>,
 ) {
     // Flatten log entries into a single line stream, blank line between each.
     let mut all_lines: Vec<String> = Vec::new();
@@ -586,7 +682,13 @@ fn render_log(
         if i > 0 {
             all_lines.push(String::new());
         }
-        all_lines.extend(entry_lines(entry));
+        let entry_view = match typewriter {
+            Some(tw) if tw.entry_idx == i && !tw.is_done() => {
+                truncate_entry_to_chars(entry, tw.chars_shown)
+            }
+            _ => entry_lines(entry),
+        };
+        all_lines.extend(entry_view);
     }
     // Append the transient prompt (Welcome / TierSelect) as the bottom block.
     // It's part of the bottom-anchored view but not part of the log itself.
@@ -620,6 +722,15 @@ fn render_log(
     frame.render_widget(screen_widget(title, body), area);
 }
 
+fn truncate_entry_to_chars(entry: &LogEntry, max_chars: usize) -> Vec<String> {
+    if max_chars == 0 {
+        return Vec::new();
+    }
+    let full = entry_lines(entry).join("\n");
+    let truncated: String = full.chars().take(max_chars).collect();
+    truncated.split('\n').map(str::to_string).collect()
+}
+
 fn entry_lines(entry: &LogEntry) -> Vec<String> {
     match entry {
         LogEntry::Intro => vec![