Added a proper validation function to check price_level_schedule and absolute_price_schedule (#31)

According the iso15118-20 schema file the charger can either send no price information, absolute or price_level.

Signed-off-by: Sebastian Lukas <sebastian.lukas@pionix.de>

Author: SebaLukas

iso15118/shared/messages/iso15118_20/common_messages.py

@@ -44,7 +44,10 @@
     V2GRequest,
     V2GResponse,
 )
-from iso15118.shared.validators import one_field_must_be_set
+from iso15118.shared.validators import (
+    one_field_must_be_set,
+    one_field_must_be_set_or_none,
+)
 
 
 class ECDHCurve(str, Enum):
@@ -713,24 +716,22 @@ class ChargingSchedule(BaseModel):
     @root_validator(pre=True)
     def either_price_levels_or_absolute_prices(cls, values):
         """
-        Either price_level_schedule or absolute_price_schedule must be set,
+        Either price_level_schedule, absolute_price_schedule or none must be set,
         depending on whether abstract price levels or absolute prices are used
         to indicate costs for the charging session.
-
         Pydantic validators are "class methods",
         see https://pydantic-docs.helpmanual.io/usage/validators/
         """
         # pylint: disable=no-self-argument
         # pylint: disable=no-self-use
-        if one_field_must_be_set(
+        if one_field_must_be_set_or_none(
             [
                 "price_level_schedule",
                 "PriceLevelSchedule",
                 "absolute_price_schedule",
                 "AbsolutePriceSchedule",
             ],
             values,
-            True,
         ):
             return values
 
@@ -750,24 +751,22 @@ class DischargingSchedule(BaseModel):
     @root_validator(pre=True)
     def either_price_levels_or_absolute_prices(cls, values):
         """
-        Either price_level_schedule or absolute_price_schedule must be set,
-        depending on abstract price levels or absolute prices are used to
-        indicate costs for the charging session.
-
+        Either price_level_schedule, absolute_price_schedule or none must be set,
+        depending on whether abstract price levels or absolute prices are used
+        to indicate costs for the charging session.
         Pydantic validators are "class methods",
         see https://pydantic-docs.helpmanual.io/usage/validators/
         """
         # pylint: disable=no-self-argument
         # pylint: disable=no-self-use
-        if one_field_must_be_set(
+        if one_field_must_be_set_or_none(
             [
                 "price_level_schedule",
                 "PriceLevelSchedule",
                 "absolute_price_schedule",
                 "AbsolutePriceSchedule",
             ],
             values,
-            True,
         ):
             return values
 

iso15118/shared/validators.py

@@ -78,3 +78,31 @@ def one_field_must_be_set(
         )
 
     return True
+
+
+def one_field_must_be_set_or_none(field_options: List[str], values: dict) -> bool:
+    """
+    In several messages, there is the option to choose one of two or more
+    possible fields, where all fields are defined as optional in the
+    corresponding model but exactly one or none of them needs to be set.
+
+    Args:
+        field_options: List of optional field names and aliases of a model.
+                       For each field, we need both the field name and the alias
+                       because when instantiating a pydantic model, we use the
+                       pythonic field names, but when de-serialising the model
+                       through JSON via the EXI codec, we use the aliases.
+        values: The dict with the model's fields
+    """
+    field_values = [values.get(f"{field_name}") for field_name in field_options]
+    set_fields = [x for x in field_values if x is not None]
+
+    if len(set_fields) > 1:
+        raise ValueError(
+            f"Exactly one field must be set but {len(set_fields)} "
+            "are set instead. "
+            f"\nSet fields: {set_fields}"
+            f"\nField options: {field_options}"
+        )
+
+    return True