BTHLABS-61: Service layer refactoring

A journey to fix `ValidationError` in Pocket imports turned service
layer refactoring :D

services/packages/soa/hotpocket_soa/exceptions/backend.py

@@ -0,0 +1,89 @@
+# -*- coding: utf-8 -*-
+from __future__ import annotations
+
+import typing
+
+from hotpocket_soa.constants import BackendServiceErrorCode
+
+if typing.TYPE_CHECKING:
+    from django.core.exceptions import ValidationError
+
+
+VALIDATION_CODE_INVALID = 'invalid'
+
+
+def get_validation_error_data(validation_error: typing.Any) -> typing.Any:  # Heh
+    if hasattr(validation_error, 'error_dict') is True:
+        return {
+            field: [
+                get_validation_error_data(inner_error)
+                for inner_error
+                in inner_errors
+            ]
+            for field, inner_errors in validation_error.error_dict.items()
+        }
+    elif hasattr(validation_error, 'error_list') is True and len(validation_error.error_list) > 1:
+        return [
+            get_validation_error_data(inner_error)
+            for inner_error
+            in validation_error.error_list
+        ]
+    elif hasattr(validation_error, 'code') is True:
+        return validation_error.code
+    elif isinstance(validation_error, (tuple, list)) is True:
+        return [
+            get_validation_error_data(inner_error)
+            for inner_error
+            in validation_error
+        ]
+    elif isinstance(validation_error, dict) is True:
+        return {
+            field: [
+                get_validation_error_data(inner_error)
+                for inner_error
+                in inner_errors
+            ]
+            for field, inner_errors in validation_error.items()
+        }
+    else:
+        return VALIDATION_CODE_INVALID
+
+
+class BackendServiceError(Exception):
+    CODE = BackendServiceErrorCode.INTERNAL
+
+    def __init__(self, message: str, *args):
+        super().__init__(message, *args)
+        self.message = message
+
+        self.data: typing.Any = None
+        if len(args) > 0:
+            self.data = args[0]
+
+
+class InternalError(BackendServiceError):
+    pass
+
+
+class NotFound(BackendServiceError):
+    CODE = BackendServiceErrorCode.NOT_FOUND
+
+
+class AccessDenied(BackendServiceError):
+    CODE = BackendServiceErrorCode.ACCESS_DENIED
+
+
+class Invalid(BackendServiceError):
+    CODE = BackendServiceErrorCode.INVALID
+
+    @classmethod
+    def from_django_validation_error(cls: type[typing.Self],
+                                     exception: ValidationError,
+                                     message: str | None = None,
+                                     ) -> typing.Self:
+        data = get_validation_error_data(exception)
+
+        result = cls(message or 'Invalid', data)
+        result.__cause__ = exception
+
+        return result