VED-350: generic validation for require system when code is present

Author: Akol125

backend/src/models/fhir_immunization_pre_validators.py

@@ -799,9 +799,6 @@ def pre_validate_route_coding_display(self, values: dict) -> dict:
         except (KeyError, IndexError):
             pass
 
-    # TODO: need to validate that doseQuantity.system is "http://unitsofmeasure.org"?
-    # Check with Martin
-
     def pre_validate_dose_quantity_value(self, values: dict) -> dict:
         """
         Pre-validate that, if doseQuantity.value (legacy CSV field name: DOSE_AMOUNT) exists,
@@ -817,7 +814,28 @@ def pre_validate_dose_quantity_value(self, values: dict) -> dict:
             PreValidation.for_integer_or_decimal(field_value, "doseQuantity.value")
         except KeyError:
             pass
+    
+    def pre_validate_dose_quantity_system_and_code(self, values: dict) -> dict:
+        """
+        Pre-validate doseQuantity.code and doseQuantity.system:
+        1. If code exists, it must be a non-empty string (legacy CSV: DOSE_UNIT_CODE).
+        2. If system exists, it must be a non-empty string.
+        3. If code exists, system MUST also exist (FHIR SimpleQuantity rule).
+        """
+        field_value = values.get("doseQuantity", {})
+        code = field_value.get("code")
+        system = field_value.get("system")
 
+        if code is not None:
+            PreValidation.for_string(code, "doseQuantity.code")
+
+        if system is not None:
+            PreValidation.for_string(system, "doseQuantity.system")
+
+        PreValidation.require_system_when_code_present(
+        code, system, "doseQuantity.code", "doseQuantity.system"
+        )
+    
     def pre_validate_dose_quantity_code(self, values: dict) -> dict:
         """
         Pre-validate that, if doseQuantity.code (legacy CSV field name: DOSE_UNIT_CODE) exists,

backend/src/models/utils/pre_validator_utils.py

@@ -194,6 +194,17 @@ def for_integer_or_decimal(field_value: Union[int, Decimal], field_location: str
             or type(field_value) is Decimal  # pylint: disable=unidiomatic-typecheck
         ):
             raise TypeError(f"{field_location} must be a number")
+    
+    @staticmethod
+    def require_system_when_code_present(
+        code_value:str, 
+        system_value:str
+        ):
+        """
+        If code is present (non-empty), system must also be present (non-empty).
+        """
+        if code_value is not None and system_value is None:
+            raise ValueError(f"If {code_location} is present, {system_location} must also be present")
 
     @staticmethod
     def for_unique_list(