♻️ refactor(rule_processor): add TRASH_LABEL, correct Gmail scopes, early returns, and improve idioms

src/rule_processor.rs

@@ -47,6 +47,17 @@ use google_gmail1::api::{BatchDeleteMessagesRequest, BatchModifyMessagesRequest}
 
 use crate::{EolAction, Error, GmailClient, Result, message_list::MessageList, rules::EolRule};
 
+/// Gmail label name for the trash folder.
+///
+/// This constant ensures consistent usage of the TRASH label throughout the module.
+const TRASH_LABEL: &str = "TRASH";
+
+/// Gmail API scope for modifying messages (recommended scope for most operations).
+///
+/// This scope allows adding/removing labels, moving messages to trash, and other
+/// modification operations. Preferred over broader scopes for security.
+const GMAIL_MODIFY_SCOPE: &str = "https://www.googleapis.com/auth/gmail.modify";
+
 /// Trait for processing Gmail messages according to configured end-of-life rules.
 ///
 /// This trait defines the interface for finding, filtering, and acting upon Gmail messages
@@ -221,7 +232,7 @@ impl RuleProcessor for GmailClient {
     /// The method respects the execute flag - when `false`, it runs in dry-run mode
     /// and only logs what would be done without making any changes.
     async fn find_rule_and_messages_for_label(&mut self, label: &str) -> Result<()> {
-        self.add_labels(&[label.to_string()])?;
+        self.add_labels(&[label.to_owned()])?;
 
         if self.label_ids().is_empty() {
             return Err(Error::LabelNotFoundInMailbox(label.to_string()));
@@ -240,10 +251,10 @@ impl RuleProcessor for GmailClient {
         log::info!("Ready to run");
         self.prepare(0).await?;
         if self.execute {
-            log::info!("***executing final delete messages***");
+            log::info!("Execute mode: applying rule action to messages");
             self.batch_trash().await
         } else {
-            log::warn!("Execution stopped for dry run");
+            log::info!("Dry-run mode: no changes made to messages");
             Ok(())
         }
     }
@@ -271,12 +282,19 @@ impl RuleProcessor for GmailClient {
     ///
     /// # API Scope Requirements
     ///
-    /// Uses `https://mail.google.com/` scope for maximum API access. Consider
-    /// using the more restrictive `https://www.googleapis.com/auth/gmail.modify`
-    /// scope if your application security policy allows it.
+    /// Uses `https://www.googleapis.com/auth/gmail.modify` scope for secure,
+    /// minimal privilege access. This scope provides sufficient permissions
+    /// for message deletion while following security best practices.
     async fn batch_delete(&self) -> Result<()> {
-        let ids = Some(self.message_ids());
+        let message_ids = self.message_ids();
 
+        // Early return if no messages to delete, avoiding unnecessary API calls
+        if message_ids.is_empty() {
+            log::info!("No messages to delete - skipping batch delete operation");
+            return Ok(());
+        }
+
+        let ids = Some(message_ids);
         let batch_request = BatchDeleteMessagesRequest { ids };
 
         log::trace!("{batch_request:#?}");
@@ -285,13 +303,13 @@ impl RuleProcessor for GmailClient {
             .hub()
             .users()
             .messages_batch_delete(batch_request, "me")
-            .add_scope("https://mail.google.com/")
+            .add_scope(GMAIL_MODIFY_SCOPE)
             .doit()
             .await
             .map_err(Box::new)?;
 
         for m in self.messages() {
-            log::info!("Message with subject `{}` deleted.", m.subject());
+            log::info!("Message with subject `{}` permanently deleted", m.subject());
         }
 
         Ok(())
@@ -308,11 +326,19 @@ impl RuleProcessor for GmailClient {
     ///
     /// # API Scope Requirements
     ///
-    /// Currently uses `https://www.google.com/` scope. Should be updated to use
-    /// `https://www.googleapis.com/auth/gmail.modify` for better security.
+    /// Uses `https://www.googleapis.com/auth/gmail.modify` scope for secure,
+    /// minimal privilege access to Gmail message modification operations.
     async fn batch_trash(&self) -> Result<()> {
-        let add_label_ids = Some(Vec::from(["TRASH".to_string()]));
-        let ids = Some(self.message_ids());
+        let message_ids = self.message_ids();
+
+        // Early return if no messages to trash, avoiding unnecessary API calls
+        if message_ids.is_empty() {
+            log::info!("No messages to trash - skipping batch trash operation");
+            return Ok(());
+        }
+
+        let add_label_ids = Some(vec![TRASH_LABEL.to_string()]);
+        let ids = Some(message_ids);
         let remove_label_ids = Some(self.label_ids());
 
         let batch_request = BatchModifyMessagesRequest {
@@ -327,13 +353,13 @@ impl RuleProcessor for GmailClient {
             .hub()
             .users()
             .messages_batch_modify(batch_request, "me")
-            .add_scope("https://www.google.com/")
+            .add_scope(GMAIL_MODIFY_SCOPE)
             .doit()
             .await
             .map_err(Box::new)?;
 
         for m in self.messages() {
-            log::info!("Message with subject `{}` moved to trash.", m.subject());
+            log::info!("Message with subject `{}` moved to trash", m.subject());
         }
 
         Ok(())