First one-shot pass

src/engine/scoring.rs

@@ -0,0 +1,45 @@
+use crate::session::result::LessonResult;
+
+pub fn compute_score(result: &LessonResult, complexity: f64) -> f64 {
+    let speed = result.cpm;
+    let errors = result.incorrect as f64;
+    let length = result.total_chars as f64;
+    (speed * complexity) / (errors + 1.0) * (length / 50.0)
+}
+
+pub fn compute_complexity(unlocked_count: usize) -> f64 {
+    (unlocked_count as f64 / 26.0).max(0.1)
+}
+
+pub fn level_from_score(total_score: f64) -> u32 {
+    let level = (total_score / 100.0).sqrt() as u32;
+    level.max(1)
+}
+
+#[allow(dead_code)]
+pub fn score_to_next_level(total_score: f64) -> f64 {
+    let current_level = level_from_score(total_score);
+    let next_level_score = ((current_level + 1) as f64).powi(2) * 100.0;
+    next_level_score - total_score
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_level_starts_at_one() {
+        assert_eq!(level_from_score(0.0), 1);
+    }
+
+    #[test]
+    fn test_level_increases_with_score() {
+        assert!(level_from_score(1000.0) > level_from_score(100.0));
+    }
+
+    #[test]
+    fn test_complexity_scales_with_letters() {
+        assert!(compute_complexity(26) > compute_complexity(6));
+        assert!((compute_complexity(26) - 1.0).abs() < 0.001);
+    }
+}