feat(engine): add StatsPlugin with persistent stats and toggleable overlay

StatsPlugin loads stats on startup, persists them on every GameWonEvent
and abandoned NewGameRequestEvent (>=1 move, not won), and provides a
full-window overlay toggled with `S` showing games played/won, win rate,
streak, best score, fastest win, and average win time.

The storage path is configurable via StatsPlugin::storage_path: the
default ctor uses dirs::data_dir(); StatsPlugin::headless() disables
I/O entirely so tests don't read or overwrite the user's real
stats.json. record_abandoned runs before GameMutation so it reads
move_count before handle_new_game clobbers it.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/src/stats_plugin.rs

@@ -0,0 +1,325 @@
+//! Loads, updates, and persists `StatsSnapshot` in response to game events,
+//! and provides a toggleable full-window stats overlay (press `S`).
+//!
+//! The persistence path is configurable via `StatsPlugin::storage_path`.
+//! In production, `StatsPlugin::default()` loads/saves from the platform
+//! data dir. In tests, use `StatsPlugin::headless()` to disable all file
+//! I/O so the user's real stats file is neither read nor overwritten.
+
+use std::path::PathBuf;
+
+use bevy::input::ButtonInput;
+use bevy::prelude::*;
+use solitaire_data::{load_stats_from, save_stats_to, stats_file_path, StatsSnapshot};
+
+use crate::events::{GameWonEvent, NewGameRequestEvent};
+use crate::game_plugin::GameMutation;
+use crate::resources::GameStateResource;
+
+/// Bevy resource wrapping the current stats.
+#[derive(Resource, Debug, Clone)]
+pub struct StatsResource(pub StatsSnapshot);
+
+/// Persistence path for `StatsResource`. `None` disables I/O.
+#[derive(Resource, Debug, Clone)]
+pub struct StatsStoragePath(pub Option<PathBuf>);
+
+/// Marker component on the stats overlay root node.
+#[derive(Component, Debug)]
+pub struct StatsScreen;
+
+/// Registers stats resources, update systems, and the UI toggle.
+pub struct StatsPlugin {
+    /// Where to persist stats. `None` disables all file I/O (for tests).
+    pub storage_path: Option<PathBuf>,
+}
+
+impl Default for StatsPlugin {
+    fn default() -> Self {
+        Self {
+            storage_path: stats_file_path(),
+        }
+    }
+}
+
+impl StatsPlugin {
+    /// Plugin configured with no persistence. Use in tests and headless apps
+    /// where touching `~/.local/share/solitaire_quest/stats.json` would be
+    /// incorrect.
+    pub fn headless() -> Self {
+        Self { storage_path: None }
+    }
+}
+
+impl Plugin for StatsPlugin {
+    fn build(&self, app: &mut App) {
+        let loaded = match &self.storage_path {
+            Some(path) => load_stats_from(path),
+            None => StatsSnapshot::default(),
+        };
+        app.insert_resource(StatsResource(loaded))
+            .insert_resource(StatsStoragePath(self.storage_path.clone()))
+            .add_event::<GameWonEvent>()
+            .add_event::<NewGameRequestEvent>()
+            // record_abandoned must read `move_count` BEFORE handle_new_game
+            // clobbers it with a fresh game.
+            .add_systems(Update, update_stats_on_new_game.before(GameMutation))
+            .add_systems(
+                Update,
+                (update_stats_on_win, toggle_stats_screen).after(GameMutation),
+            );
+    }
+}
+
+fn persist(path: &StatsStoragePath, stats: &StatsSnapshot, context: &str) {
+    let Some(target) = &path.0 else {
+        return;
+    };
+    if let Err(e) = save_stats_to(target, stats) {
+        warn!("failed to save stats after {context}: {e}");
+    }
+}
+
+fn update_stats_on_win(
+    mut events: EventReader<GameWonEvent>,
+    game: Res<GameStateResource>,
+    mut stats: ResMut<StatsResource>,
+    path: Res<StatsStoragePath>,
+) {
+    for ev in events.read() {
+        stats
+            .0
+            .update_on_win(ev.score, ev.time_seconds, &game.0.draw_mode);
+        persist(&path, &stats.0, "win");
+    }
+}
+
+fn update_stats_on_new_game(
+    mut events: EventReader<NewGameRequestEvent>,
+    game: Res<GameStateResource>,
+    mut stats: ResMut<StatsResource>,
+    path: Res<StatsStoragePath>,
+) {
+    for _ in events.read() {
+        if game.0.move_count > 0 && !game.0.is_won {
+            stats.0.record_abandoned();
+            persist(&path, &stats.0, "abandoned game");
+        }
+    }
+}
+
+fn toggle_stats_screen(
+    mut commands: Commands,
+    keys: Res<ButtonInput<KeyCode>>,
+    stats: Res<StatsResource>,
+    screens: Query<Entity, With<StatsScreen>>,
+) {
+    if !keys.just_pressed(KeyCode::KeyS) {
+        return;
+    }
+    if let Ok(entity) = screens.get_single() {
+        commands.entity(entity).despawn_recursive();
+    } else {
+        spawn_stats_screen(&mut commands, &stats.0);
+    }
+}
+
+fn spawn_stats_screen(commands: &mut Commands, stats: &StatsSnapshot) {
+    let win_rate = stats
+        .win_rate()
+        .map_or("N/A".to_string(), |r| format!("{r:.1}%"));
+    let fastest = if stats.fastest_win_seconds == u64::MAX {
+        "N/A".to_string()
+    } else {
+        format_duration(stats.fastest_win_seconds)
+    };
+    let avg = if stats.games_won == 0 {
+        "N/A".to_string()
+    } else {
+        format_duration(stats.avg_time_seconds)
+    };
+
+    let lines = [
+        "=== Statistics ===".to_string(),
+        format!("Games Played:  {}", stats.games_played),
+        format!("Games Won:     {}", stats.games_won),
+        format!("Win Rate:      {win_rate}"),
+        format!(
+            "Win Streak:    {} (Best: {})",
+            stats.win_streak_current, stats.win_streak_best
+        ),
+        format!("Best Score:    {}", stats.best_single_score),
+        format!("Fastest Win:   {fastest}"),
+        format!("Avg Win Time:  {avg}"),
+        String::new(),
+        "Press S to close".to_string(),
+    ];
+
+    commands
+        .spawn((
+            StatsScreen,
+            Node {
+                position_type: PositionType::Absolute,
+                left: Val::Percent(0.0),
+                top: Val::Percent(0.0),
+                width: Val::Percent(100.0),
+                height: Val::Percent(100.0),
+                flex_direction: FlexDirection::Column,
+                justify_content: JustifyContent::Center,
+                align_items: AlignItems::Center,
+                row_gap: Val::Px(6.0),
+                ..default()
+            },
+            BackgroundColor(Color::srgba(0.0, 0.0, 0.0, 0.88)),
+            ZIndex(200),
+        ))
+        .with_children(|b| {
+            for line in lines {
+                b.spawn((
+                    Text::new(line),
+                    TextFont {
+                        font_size: 24.0,
+                        ..default()
+                    },
+                    TextColor(Color::srgb(0.95, 0.95, 0.90)),
+                ));
+            }
+        });
+}
+
+fn format_duration(secs: u64) -> String {
+    let m = secs / 60;
+    let s = secs % 60;
+    format!("{m}m {s:02}s")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::game_plugin::GamePlugin;
+    use crate::table_plugin::TablePlugin;
+
+    fn headless_app() -> App {
+        let mut app = App::new();
+        app.add_plugins(MinimalPlugins)
+            .add_plugins(GamePlugin)
+            .add_plugins(TablePlugin)
+            .add_plugins(StatsPlugin::headless());
+        // MinimalPlugins doesn't register keyboard input — add it so the
+        // toggle system can read ButtonInput<KeyCode> in tests.
+        app.init_resource::<ButtonInput<KeyCode>>();
+        app.update();
+        app
+    }
+
+    #[test]
+    fn stats_resource_exists_after_startup() {
+        let app = headless_app();
+        assert!(app.world().get_resource::<StatsResource>().is_some());
+    }
+
+    #[test]
+    fn headless_plugin_starts_with_default_stats() {
+        let app = headless_app();
+        let stats = &app.world().resource::<StatsResource>().0;
+        assert_eq!(stats, &StatsSnapshot::default());
+    }
+
+    #[test]
+    fn win_event_increments_games_won() {
+        let mut app = headless_app();
+        app.world_mut().send_event(GameWonEvent {
+            score: 1000,
+            time_seconds: 120,
+        });
+        app.update();
+
+        let stats = &app.world().resource::<StatsResource>().0;
+        assert_eq!(stats.games_won, 1);
+        assert_eq!(stats.games_played, 1);
+    }
+
+    #[test]
+    fn new_game_after_moves_records_abandoned() {
+        let mut app = headless_app();
+
+        app.world_mut()
+            .resource_mut::<crate::resources::GameStateResource>()
+            .0
+            .move_count = 3;
+
+        app.world_mut()
+            .send_event(NewGameRequestEvent { seed: Some(999) });
+        app.update();
+
+        let stats = &app.world().resource::<StatsResource>().0;
+        assert_eq!(stats.games_played, 1);
+        assert_eq!(stats.games_lost, 1);
+        assert_eq!(stats.win_streak_current, 0);
+    }
+
+    #[test]
+    fn new_game_without_moves_does_not_record_abandoned() {
+        let mut app = headless_app();
+        app.world_mut()
+            .send_event(NewGameRequestEvent { seed: Some(42) });
+        app.update();
+
+        let stats = &app.world().resource::<StatsResource>().0;
+        assert_eq!(stats.games_played, 0);
+    }
+
+    #[test]
+    fn pressing_s_spawns_stats_screen() {
+        let mut app = headless_app();
+        assert_eq!(
+            app.world_mut()
+                .query::<&StatsScreen>()
+                .iter(app.world())
+                .count(),
+            0
+        );
+
+        app.world_mut()
+            .resource_mut::<ButtonInput<KeyCode>>()
+            .press(KeyCode::KeyS);
+        app.update();
+
+        assert_eq!(
+            app.world_mut()
+                .query::<&StatsScreen>()
+                .iter(app.world())
+                .count(),
+            1
+        );
+    }
+
+    #[test]
+    fn pressing_s_twice_closes_stats_screen() {
+        let mut app = headless_app();
+
+        app.world_mut()
+            .resource_mut::<ButtonInput<KeyCode>>()
+            .press(KeyCode::KeyS);
+        app.update();
+
+        // Release + clear + press: `press()` is a no-op if the key is already
+        // in `pressed`, and MinimalPlugins doesn't include bevy_input's
+        // per-frame updater to drain `just_pressed`, so we cycle manually.
+        {
+            let mut input = app.world_mut().resource_mut::<ButtonInput<KeyCode>>();
+            input.release(KeyCode::KeyS);
+            input.clear();
+            input.press(KeyCode::KeyS);
+        }
+        app.update();
+
+        assert_eq!(
+            app.world_mut()
+                .query::<&StatsScreen>()
+                .iter(app.world())
+                .count(),
+            0
+        );
+    }
+}