feat: implement backend API clients for multi-marketplace integration and frontend service layer

backend/test_avito_api.py

@@ -0,0 +1,44 @@
+import os
+import sys
+from dotenv import load_dotenv
+
+# Add parent dir to path so we can import backend packages
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from backend.avito_api import AvitoAPI
+from backend.avito_api.exceptions import AvitoAPIError, AvitoAuthError
+
+def test_avito_api():
+    # Load environment variables
+    env_path = os.path.join(os.path.dirname(__file__), '.env')
+    load_dotenv(env_path)
+    
+    # Check if keys are loaded
+    client_id = os.getenv('AVITO_CLIENT_ID')
+    client_secret = os.getenv('AVITO_CLIENT_SECRET')
+    
+    if not client_id or not client_secret:
+        print("Error: AVITO_CLIENT_ID and AVITO_CLIENT_SECRET must be in backend/.env")
+        return
+        
+    print(f"Initializing AvitoAPI (Authenticating...)")
+
+    try:
+        api = AvitoAPI()
+        print("Success! Successfully authenticated and received access token.")
+        print(f"Token snippet: {api.client.access_token[:10]}...")
+        
+        # For full testing we would need user_id (Avito user id)
+        # print("\n--- Testing Messenger API ---")
+        # chats_response = api.messenger.get_chats(user_id="12345", limit=5)
+        # print("Success! Response keys:", chats_response.keys())
+            
+    except AvitoAuthError as e:
+        print(f"Authentication Failed: {e}")
+    except AvitoAPIError as e:
+        print(f"API Error: {e}")
+    except Exception as e:
+        print(f"Unexpected Error: {e}")
+
+if __name__ == '__main__':
+    test_avito_api()