try/check ID functions

src/lib.rs

@@ -145,6 +145,23 @@ fn segments_from_string(string: String) -> Vec<String> {
     output
 }
 
+/// tries to use an existing ID - if it is already in use, generate a new one
+/// then return the ID (either original or new)
+/// todo refactor (unnecessary clones etc.)
+fn try_id(ids: Vec<String>, id: String) -> String {
+    let id = id.clone();
+    let ids = ids.clone();
+    if is_id_available(&ids, &id) {
+        id
+    } else {
+        new_unique_id(ids)
+    }
+}
+
+fn is_id_available(ids: &Vec<String>, id: &String) -> bool {
+    ! ids.contains(id)
+}
+
 /// e.g. pass all tile IDs into this to get a new non-conflicting tile ID
 #[inline]
 fn new_unique_id(mut ids: Vec<String>) -> String {
@@ -188,7 +205,7 @@ impl Unquote for String {
 
 #[cfg(test)]
 mod test {
-    use crate::{from_base36, ToBase36, optional_data_line, mock, segments_from_string, Quote, Unquote, new_unique_id};
+    use crate::{from_base36, ToBase36, optional_data_line, mock, segments_from_string, Quote, Unquote, new_unique_id, try_id};
 
     #[test]
     fn test_from_base36() {
@@ -238,6 +255,20 @@ mod test {
         assert_eq!(output, expected);
     }
 
+    #[test]
+    fn test_try_id() {
+        // does a conflict generate a new ID?
+        assert_eq!(
+            try_id(vec!["0".to_string(), "1".to_string()], "1".to_string()),
+            "2".to_string()
+        );
+        // with no conflict, does the ID remain the same?
+        assert_eq!(
+            try_id(vec!["0".to_string(), "1".to_string()], "3".to_string()),
+            "3".to_string()
+        );
+    }
+
     #[test]
     fn test_new_unique_id() {
         // start