implement to_string method, prevent memory index overwrite on validation step

src/profile/identity/gemini/auth/error.rs

@@ -3,3 +3,12 @@ pub enum Error {
     Database(sqlite::Error),
     Memory(super::memory::Error),
 }
+
+impl Error {
+    pub fn to_string(&self) -> String {
+        match self {
+            Self::Database(reason) => format!("Database error: {}", reason.to_string()),
+            Self::Memory(reason) => format!("Memory error: {}", reason.to_string()),
+        }
+    }
+}

src/profile/identity/gemini/auth/memory.rs

@@ -23,12 +23,17 @@ impl Memory {
     /// Add new record with `url` as key and `profile_identity_gemini_id` as value
     /// * validate record with same key does not exist yet
     pub fn add(&self, url: String, profile_identity_gemini_id: i64) -> Result<(), Error> {
-        match self
-            .index
-            .borrow_mut()
-            .insert(url, profile_identity_gemini_id)
-        {
-            Some(key) => Err(Error::Overwrite(key)), // @TODO prevent?
+        // Borrow shared index access
+        let mut index = self.index.borrow_mut();
+
+        // Prevent existing key overwrite
+        if index.contains_key(&url) {
+            return Err(Error::Overwrite(url));
+        }
+
+        // Slot should be free, let check it twice
+        match index.insert(url, profile_identity_gemini_id) {
+            Some(_) => return Err(Error::Unexpected),
             None => Ok(()),
         }
     }

src/profile/identity/gemini/auth/memory/error.rs

@@ -1,5 +1,18 @@
 #[derive(Debug)]
 pub enum Error {
     Clear,
-    Overwrite(i64),
+    Overwrite(String),
+    Unexpected,
+}
+
+impl Error {
+    pub fn to_string(&self) -> String {
+        match self {
+            Self::Clear => format!("Could not cleanup memory index"),
+            Self::Overwrite(key) => {
+                format!("Overwrite attempt for existing record `{key}`")
+            }
+            Self::Unexpected => format!("Unexpected error"),
+        }
+    }
 }