further cleaned up code based on feedback

pr_agent/git_providers/bitbucket_server_provider.py

@@ -156,33 +156,33 @@ def get_diff_files(self) -> list[FilePatchInfo]:
         if self.diff_files:
             return self.diff_files
 
-        source_commits_list = list(self.bitbucket_client.get_pull_requests_commits(
-            self.workspace_slug,
-            self.repo_slug,
-            self.pr_num
-        ))
-
-        # defaults to basic diff functionality with a guaranteed common ancestor
-        base_sha, head_sha = source_commits_list[-1]['parents'][0]['id'], source_commits_list[0]['id']
-
-        # if Bitbucket api version is greater than or equal to 7.0 then use 2-way diff functionality for the base_sha
-        if self.bitbucket_api_version is not None and self.bitbucket_api_version >= LooseVersion("7.0"):
-            # Bitbucket endpoint for getting merge-base is available as of 8.16
-            if self.bitbucket_api_version >= LooseVersion("8.16"):
-                try:
-                    base_sha = self.bitbucket_client.get(self._get_best_common_ancestor())['id']
-                except Exception as e:
-                    get_logger().error(f"Failed to get the best common ancestor for PR: {self.pr_url}, \nerror: {e}")
-                    raise e
-            # for versions 7.0-8.15 try to calculate the merge-base on our own
-            else:
+        head_sha = self.pr.fromRef['latestCommit']
+
+        # if Bitbucket api version is >= 8.16 then use the merge-base api for 2-way diff calculation
+        if self.bitbucket_api_version is not None and self.bitbucket_api_version >= LooseVersion("8.16"):
+            try:
+                base_sha = self.bitbucket_client.get(self._get_merge_base())['id']
+            except Exception as e:
+                get_logger().error(f"Failed to get the best common ancestor for PR: {self.pr_url}, \nerror: {e}")
+                raise e
+        else:
+            source_commits_list = list(self.bitbucket_client.get_pull_requests_commits(
+                self.workspace_slug,
+                self.repo_slug,
+                self.pr_num
+            ))
+            # if Bitbucket api version is None or < 7.0 then do a simple diff with a guaranteed common ancestor
+            base_sha = source_commits_list[-1]['parents'][0]['id']
+            # if Bitbucket api version is 7.0-8.15 then use 2-way diff functionality for the base_sha
+            if self.bitbucket_api_version is not None and self.bitbucket_api_version >= LooseVersion("7.0"):
                 try:
                     destination_commits = list(
                         self.bitbucket_client.get_commits(self.workspace_slug, self.repo_slug, base_sha,
                                                           self.pr.toRef['latestCommit']))
                     base_sha = self.get_best_common_ancestor(source_commits_list, destination_commits, base_sha)
                 except Exception as e:
-                    get_logger().error(f"Failed to get the commit list for calculating best common ancestor for PR: {self.pr_url}, \nerror: {e}")
+                    get_logger().error(
+                        f"Failed to get the commit list for calculating best common ancestor for PR: {self.pr_url}, \nerror: {e}")
                     raise e
 
         diff_files = []
@@ -452,5 +452,5 @@ def get_pr_labels(self, update=False):
     def _get_pr_comments_path(self):
         return f"rest/api/latest/projects/{self.workspace_slug}/repos/{self.repo_slug}/pull-requests/{self.pr_num}/comments"
 
-    def _get_best_common_ancestor(self):
+    def _get_merge_base(self):
         return f"rest/api/latest/projects/{self.workspace_slug}/repos/{self.repo_slug}/pull-requests/{self.pr_num}/merge-base"