fix: align code with spec

crates/bds-core/src/util/slug.rs

@@ -1,4 +1,5 @@
 use deunicode::deunicode;
+use std::time::{SystemTime, UNIX_EPOCH};
 
 /// Generate a URL-safe slug from a title string.
 ///
@@ -25,6 +26,30 @@ pub fn slugify(input: &str) -> String {
     slug
 }
 
+/// Ensure a slug is unique within a project, using the spec's algorithm:
+/// tries base, then {slug}-2 .. {slug}-999, then {slug}-{timestamp}.
+///
+/// `exists` is a predicate that returns true if the candidate slug is already taken.
+pub fn ensure_unique<F>(base: &str, exists: F) -> String
+where
+    F: Fn(&str) -> bool,
+{
+    if !exists(base) {
+        return base.to_string();
+    }
+    for n in 2..=999 {
+        let candidate = format!("{base}-{n}");
+        if !exists(&candidate) {
+            return candidate;
+        }
+    }
+    let ts = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_secs();
+    format!("{base}-{ts}")
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -58,4 +83,40 @@ mod tests {
     fn consecutive_special_chars() {
         assert_eq!(slugify("a --- b"), "a-b");
     }
+
+    #[test]
+    fn ensure_unique_base_available() {
+        let slug = ensure_unique("hello", |_| false);
+        assert_eq!(slug, "hello");
+    }
+
+    #[test]
+    fn ensure_unique_base_taken() {
+        let slug = ensure_unique("hello", |s| s == "hello");
+        assert_eq!(slug, "hello-2");
+    }
+
+    #[test]
+    fn ensure_unique_sequential_taken() {
+        let slug = ensure_unique("hello", |s| s == "hello" || s == "hello-2" || s == "hello-3");
+        assert_eq!(slug, "hello-4");
+    }
+
+    #[test]
+    fn ensure_unique_all_999_taken() {
+        let slug = ensure_unique("x", |s| {
+            if s == "x" { return true; }
+            if let Some(suffix) = s.strip_prefix("x-") {
+                if let Ok(n) = suffix.parse::<u32>() {
+                    return n <= 999;
+                }
+            }
+            false
+        });
+        // Should fall back to timestamp-based slug
+        assert!(slug.starts_with("x-"));
+        let suffix = slug.strip_prefix("x-").unwrap();
+        let ts: u64 = suffix.parse().expect("should be a timestamp");
+        assert!(ts > 1_000_000_000);
+    }
 }