[Enhance] API for purchases, items, operations

- Add API endpoints for purchases, items, and operations
- Header checker? :)

latest version/api/api_code.py

@@ -18,6 +18,11 @@ CODE_MSG = {
     -104: 'Invalid sort order parameter',
     -105: 'Invalid URL parameter',
     -110: 'Invalid user_id',
+    -120: 'Invalid item type',
+    -121: 'No such item',
+    -122: 'Item already exists',
+    -123: 'Purchase already has this item',
+    -124: 'Purchase does not have this item',
     -200: 'No permission',  # 2xx用户相关错误
     -201: 'Wrong username or password',
     -202: 'User is banned',