First one-shot pass

src/engine/key_stats.rs

@@ -0,0 +1,120 @@
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+
+const EMA_ALPHA: f64 = 0.1;
+const DEFAULT_TARGET_CPM: f64 = 175.0;
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct KeyStat {
+    pub filtered_time_ms: f64,
+    pub best_time_ms: f64,
+    pub confidence: f64,
+    pub sample_count: usize,
+    pub recent_times: Vec<f64>,
+}
+
+impl Default for KeyStat {
+    fn default() -> Self {
+        Self {
+            filtered_time_ms: 1000.0,
+            best_time_ms: f64::MAX,
+            confidence: 0.0,
+            sample_count: 0,
+            recent_times: Vec::new(),
+        }
+    }
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct KeyStatsStore {
+    pub stats: HashMap<char, KeyStat>,
+    pub target_cpm: f64,
+}
+
+impl Default for KeyStatsStore {
+    fn default() -> Self {
+        Self {
+            stats: HashMap::new(),
+            target_cpm: DEFAULT_TARGET_CPM,
+        }
+    }
+}
+
+impl KeyStatsStore {
+    pub fn update_key(&mut self, key: char, time_ms: f64) {
+        let stat = self.stats.entry(key).or_default();
+        stat.sample_count += 1;
+
+        if stat.sample_count == 1 {
+            stat.filtered_time_ms = time_ms;
+        } else {
+            stat.filtered_time_ms =
+                EMA_ALPHA * time_ms + (1.0 - EMA_ALPHA) * stat.filtered_time_ms;
+        }
+
+        stat.best_time_ms = stat.best_time_ms.min(stat.filtered_time_ms);
+
+        let target_time_ms = 60000.0 / self.target_cpm;
+        stat.confidence = target_time_ms / stat.filtered_time_ms;
+
+        stat.recent_times.push(time_ms);
+        if stat.recent_times.len() > 30 {
+            stat.recent_times.remove(0);
+        }
+    }
+
+    pub fn get_confidence(&self, key: char) -> f64 {
+        self.stats
+            .get(&key)
+            .map(|s| s.confidence)
+            .unwrap_or(0.0)
+    }
+
+    #[allow(dead_code)]
+    pub fn get_stat(&self, key: char) -> Option<&KeyStat> {
+        self.stats.get(&key)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_initial_confidence_is_zero() {
+        let store = KeyStatsStore::default();
+        assert_eq!(store.get_confidence('a'), 0.0);
+    }
+
+    #[test]
+    fn test_update_key_creates_stat() {
+        let mut store = KeyStatsStore::default();
+        store.update_key('e', 300.0);
+        assert!(store.get_confidence('e') > 0.0);
+        assert_eq!(store.stats.get(&'e').unwrap().sample_count, 1);
+    }
+
+    #[test]
+    fn test_ema_converges() {
+        let mut store = KeyStatsStore::default();
+        // Type key fast many times - confidence should increase
+        for _ in 0..50 {
+            store.update_key('t', 200.0);
+        }
+        let conf = store.get_confidence('t');
+        // At 175 CPM target, target_time = 60000/175 = 342.8ms
+        // With 200ms typing time, confidence = 342.8/200 = 1.71
+        assert!(conf > 1.0, "confidence should be > 1.0 for fast typing, got {conf}");
+    }
+
+    #[test]
+    fn test_slow_typing_low_confidence() {
+        let mut store = KeyStatsStore::default();
+        for _ in 0..50 {
+            store.update_key('a', 1000.0);
+        }
+        let conf = store.get_confidence('a');
+        // target_time = 342.8ms, typing at 1000ms -> conf = 342.8/1000 = 0.34
+        assert!(conf < 1.0, "confidence should be < 1.0 for slow typing, got {conf}");
+    }
+}