Persist and Use MRU Backend History

Author: tninja

ai-code-backends.el

@@ -423,6 +423,32 @@ configuration paths, upgrade commands, and skill-install commands."
                                                        (const :tag "Not supported" nil))))
   :group 'ai-code)
 
+(defvar ai-code-backends-history-file
+  (expand-file-name "ai-code-backends-history.el" user-emacs-directory)
+  "File path to store the MRU history of selected backends.")
+
+(defun ai-code--load-backends-history ()
+  "Load the MRU backend history from `ai-code-backends-history-file'."
+  (if (file-exists-p ai-code-backends-history-file)
+      (condition-case nil
+          (with-temp-buffer
+            (insert-file-contents ai-code-backends-history-file)
+            (let ((content (buffer-string)))
+              (unless (string-empty-p content)
+                (read content))))
+        (error nil))
+    nil))
+
+(defun ai-code--save-backend-history (backend)
+  "Save BACKEND to the MRU history list file."
+  (let* ((history (ai-code--load-backends-history))
+         (updated-history (cons backend (seq-remove (lambda (x) (eq x backend)) history))))
+    (condition-case nil
+        (with-temp-file ai-code-backends-history-file
+          (insert (let ((print-circle nil))
+                    (prin1-to-string updated-history))))
+      (error nil))))
+
 (defvar ai-code-selected-backend 'claude-code
   "Currently selected backend key from `ai-code-backends'.")
 
@@ -432,7 +458,8 @@ configuration paths, upgrade commands, and skill-install commands."
     (user-error "Unknown backend: %s" new-backend))
   (setq ai-code-selected-backend new-backend)
   (ai-code--apply-backend new-backend)
-  (ai-code--remember-current-backend-for-repo))
+  (ai-code--remember-current-backend-for-repo)
+  (ai-code--save-backend-history new-backend))
 
 (defun ai-code--backend-spec (key)
   "Return backend plist for KEY from `ai-code-backends'."
@@ -519,19 +546,22 @@ invoke `ai-code-cli-resume'; otherwise call `ai-code-cli-start'."
                               (cons (format "%s" label) key)))
                           ai-code-backends))
          (effective-backend (ai-code--effective-backend))
-         (current-label (car (seq-find (lambda (it)
-                                         (eq (cdr it) effective-backend))
-                                       choices)))
-         (ordered-choices (if current-label
-                              (let ((current (assoc current-label choices)))
-                                (cons current
-                                      (seq-remove (lambda (it)
-                                                    (equal (car it) current-label))
-                                                  choices)))
-                            choices))
+         (history (ai-code--load-backends-history))
+         (history-choices (seq-filter #'identity
+                                      (mapcar (lambda (key)
+                                                (seq-find (lambda (c) (eq (cdr c) key)) choices))
+                                              history)))
+         (other-choices (seq-remove (lambda (c) (member c history-choices)) choices))
+         (sorted-choices (append history-choices other-choices))
+         (current-choice (seq-find (lambda (it) (eq (cdr it) effective-backend)) sorted-choices))
+         (ordered-choices (if current-choice
+                              (cons current-choice
+                                    (seq-remove (lambda (it) (eq (cdr it) effective-backend))
+                                                sorted-choices))
+                            sorted-choices))
          (choice (completing-read "Select backend: "
                                   (mapcar #'car ordered-choices)
-                                  nil t nil nil current-label))
+                                  nil t nil nil (car current-choice)))
          (key (cdr (assoc choice ordered-choices))))
     (ai-code-set-backend key)
     (when (fboundp 'ai-code-onboarding-show-backend-switch-hint)

test/test_ai-code-backends.el

@@ -405,6 +405,49 @@
     (should spec)
     (should-not (plist-get (cdr spec) :install-skills))))
 
+(ert-deftest ai-code-test-select-backend-mru-ordering ()
+  "Test that backend selection ordering follows the MRU list loaded from the history file, and updates it upon selection."
+  (let* ((temp-file (make-temp-file "ai-code-backends-history-"))
+         (ai-code-backends-history-file temp-file)
+         (ai-code-backends '((backend-a :label "Backend A" :start ignore :switch ignore :send ignore)
+                              (backend-b :label "Backend B" :start ignore :switch ignore :send ignore)
+                              (backend-c :label "Backend C" :start ignore :switch ignore :send ignore)))
+         (ai-code-selected-backend 'backend-a)
+         (captured-candidates nil)
+         (selected-choice "Backend B"))
+    (unwind-protect
+        (progn
+          ;; Write initial history: backend-c was used recently, backend-b before that
+          (with-temp-file temp-file
+            (insert (prin1-to-string '(backend-c backend-b))))
+          
+          ;; Spy completing-read to capture the candidates offered to the user
+          (cl-letf (((symbol-function 'completing-read)
+                     (lambda (_prompt candidates &rest _args)
+                       (setq captured-candidates candidates)
+                       selected-choice))
+                    ((symbol-function 'ai-code-onboarding-show-backend-switch-hint) #'ignore)
+                    ((symbol-function 'message) #'ignore))
+            (ai-code-select-backend)
+            
+            ;; 1. The selected backend should be switched to backend-b
+            (should (eq ai-code-selected-backend 'backend-b))
+            
+            ;; 2. The candidates list passed to completing-read should have:
+            ;;   - First: Current effective backend (backend-a)
+            ;;   - Then: history items in order (backend-c, backend-b) excluding current
+            ;; So candidates should be '("Backend A" "Backend C" "Backend B")
+            (should (equal captured-candidates '("Backend A" "Backend C" "Backend B")))
+            
+            ;; 3. The history file should have been updated after selection:
+            ;; New selection B is now at the top, C is next
+            (let ((new-history (with-temp-buffer
+                                 (insert-file-contents temp-file)
+                                 (read (buffer-string)))))
+              (should (equal new-history '(backend-b backend-c))))))
+      (when (file-exists-p temp-file)
+        (delete-file temp-file)))))
+
 (provide 'test_ai-code-backends)
 
 ;;; test_ai-code-backends.el ends here