fix: UTF-8 char boundary panic in extract_title (#12)

Co-authored-by: shayne-snap <shayne-snap@users.noreply.github.com>

Author: shayne-snap

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "waylog"
-version = "0.2.0"
+version = "0.2.1"
 edition = "2021"
 authors = ["WayLog Contributors"]
 description = "Automatically save chats from Claude, Codex, and Gemini CLI to local Markdown files."

Cargo.toml

@@ -55,10 +55,12 @@ pub(crate) fn extract_title(messages: &[ChatMessage]) -> String {
         .iter()
         .find(|m| matches!(m.role, MessageRole::User))
         .map(|m| {
-            // Take first line or first 60 characters
+            // Take first line or first 60 characters (char-boundary safe)
             let first_line = m.content.lines().next().unwrap_or("Untitled Session");
-            if first_line.len() > 60 {
-                format!("{}...", &first_line[..60])
+            let char_count = first_line.chars().count();
+            if char_count > 60 {
+                let truncated: String = first_line.chars().take(60).collect();
+                format!("{}...", truncated)
             } else {
                 first_line.to_string()
             }
@@ -70,3 +72,115 @@ pub(crate) fn extract_title(messages: &[ChatMessage]) -> String {
 pub(crate) fn format_datetime(dt: &DateTime<Utc>) -> String {
     dt.format("%Y-%m-%d %H:%M:%S UTC").to_string()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::providers::base::MessageMetadata;
+
+    fn create_test_message(content: &str, role: MessageRole) -> ChatMessage {
+        ChatMessage {
+            id: "test-id".to_string(),
+            role,
+            content: content.to_string(),
+            timestamp: Utc::now(),
+            metadata: MessageMetadata::default(),
+        }
+    }
+
+    #[test]
+    fn test_extract_title_short_english() {
+        let messages = vec![create_test_message("Hello world", MessageRole::User)];
+        let title = extract_title(&messages);
+        assert_eq!(title, "Hello world");
+    }
+
+    #[test]
+    fn test_extract_title_long_english() {
+        let long_text =
+            "This is a very long message that exceeds sixty characters and should be truncated";
+        let messages = vec![create_test_message(long_text, MessageRole::User)];
+        let title = extract_title(&messages);
+        assert!(title.ends_with("..."));
+        assert!(title.len() <= 63); // 60 chars + "..."
+    }
+
+    #[test]
+    fn test_extract_title_short_chinese() {
+        let messages = vec![create_test_message("你好世界", MessageRole::User)];
+        let title = extract_title(&messages);
+        assert_eq!(title, "你好世界");
+    }
+
+    #[test]
+    fn test_extract_title_long_chinese() {
+        let long_chinese =
+            "把 pg_stateful.yaml 改写为 docker compose 可以运行的yaml，输出到 docker-compose.yaml";
+        let messages = vec![create_test_message(long_chinese, MessageRole::User)];
+        // This should not panic
+        let title = extract_title(&messages);
+        assert!(title.ends_with("..."));
+    }
+
+    #[test]
+    fn test_extract_title_mixed_long() {
+        let mixed = "这是一个包含English和中文的very long message that should be truncated properly without panic";
+        let messages = vec![create_test_message(mixed, MessageRole::User)];
+        let title = extract_title(&messages);
+        assert!(title.ends_with("..."));
+    }
+
+    #[test]
+    fn test_extract_title_multiline() {
+        let multiline = "First line\nSecond line\nThird line";
+        let messages = vec![create_test_message(multiline, MessageRole::User)];
+        let title = extract_title(&messages);
+        assert_eq!(title, "First line");
+    }
+
+    #[test]
+    fn test_extract_title_empty_messages() {
+        let messages: Vec<ChatMessage> = vec![];
+        let title = extract_title(&messages);
+        assert_eq!(title, "Untitled Session");
+    }
+
+    #[test]
+    fn test_extract_title_no_user_messages() {
+        let messages = vec![
+            create_test_message("Assistant response", MessageRole::Assistant),
+            create_test_message("System message", MessageRole::System),
+        ];
+        let title = extract_title(&messages);
+        assert_eq!(title, "Untitled Session");
+    }
+
+    #[test]
+    fn test_extract_title_exactly_60_chars() {
+        let exactly_60 = "a".repeat(60);
+        let messages = vec![create_test_message(&exactly_60, MessageRole::User)];
+        let title = extract_title(&messages);
+        assert_eq!(title, exactly_60);
+        assert!(!title.ends_with("..."));
+    }
+
+    #[test]
+    fn test_extract_title_with_emoji() {
+        let with_emoji = "Hello 👋 this is a message with emoji 🎉 that might be long enough to truncate properly";
+        let messages = vec![create_test_message(with_emoji, MessageRole::User)];
+        let title = extract_title(&messages);
+        // Should not panic on emoji boundaries
+        assert!(title.len() > 0);
+    }
+
+    #[test]
+    fn test_extract_title_finds_first_user_message() {
+        let messages = vec![
+            create_test_message("System init", MessageRole::System),
+            create_test_message("First user message", MessageRole::User),
+            create_test_message("Second user message", MessageRole::User),
+        ];
+        let title = extract_title(&messages);
+        assert_eq!(title, "First user message");
+    }
+}