Added start and end dates to parser output

rules-engine/src/rules_engine/pydantic_models.py

@@ -5,9 +5,10 @@
 from dataclasses import dataclass
 from datetime import date
 from enum import Enum
+from functools import cached_property
 from typing import Annotated, Any, Optional, Sequence
 
-from pydantic import BaseModel, BeforeValidator, ConfigDict, Field
+from pydantic import BaseModel, BeforeValidator, ConfigDict, Field, computed_field
 
 
 class AnalysisType(Enum):
@@ -106,6 +107,38 @@ class NaturalGasBillingInput(BaseModel):
 
     records: Sequence[NaturalGasBillingRecordInput]
 
+    # Suppress mypy error when computed_field is used with cached_property; see https://github.com/python/mypy/issues/1362
+    @computed_field  # type: ignore[misc]
+    @cached_property
+    def overall_start_date(self) -> date:
+        if len(self.records) == 0:
+            raise ValueError(
+                "Natural gas billing records cannot be empty."
+                + "Could not calculate overall start date from empty natural gas billing records."
+                + "Try again with non-empty natural gas billing records."
+            )
+
+        min_date = date.max
+        for record in self.records:
+            min_date = min(min_date, record.period_start_date)
+        return min_date
+
+    # Suppress mypy error when computed_field is used with cached_property; see https://github.com/python/mypy/issues/1362
+    @computed_field  # type: ignore[misc]
+    @cached_property
+    def overall_end_date(self) -> date:
+        if len(self.records) == 0:
+            raise ValueError(
+                "Natural gas billing records cannot be empty."
+                + "Could not calculate overall start date from empty natural gas billing records."
+                + "Try again with non-empty natural gas billing records."
+            )
+
+        max_date = date.min
+        for record in self.records:
+            max_date = max(max_date, record.period_end_date)
+        return max_date
+
 
 class NormalizedBillingPeriodRecordBase(BaseModel):
     """

rules-engine/tests/test_rules_engine/test_pydantic_models.py

@@ -0,0 +1,53 @@
+from datetime import date
+
+import pytest
+
+from rules_engine.pydantic_models import (
+    NaturalGasBillingInput,
+    NaturalGasBillingRecordInput,
+)
+
+_EXAMPLE_VALID_RECORDS = NaturalGasBillingInput(
+    records=[
+        NaturalGasBillingRecordInput(
+            period_start_date=date(2020, 1, 1),
+            period_end_date=date(2020, 1, 31),
+            usage_therms=10,
+            inclusion_override=None,
+        ),
+        NaturalGasBillingRecordInput(
+            period_start_date=date(2020, 2, 1),
+            period_end_date=date(2020, 2, 28),
+            usage_therms=10,
+            inclusion_override=None,
+        ),
+    ]
+)
+
+_EXAMPLE_INVALID_RECORDS = NaturalGasBillingInput(
+    records=[]  # create billing input with no records
+)
+
+
+def test_natural_gas_billing_input_overall_start_date():
+    expected_overall_start_date = date(2020, 1, 1)
+    actual_overall_start_date = _EXAMPLE_VALID_RECORDS.overall_start_date
+
+    assert expected_overall_start_date == actual_overall_start_date
+
+
+def test_natural_gas_billing_input_overall_end_date():
+    expected_overall_end_date = date(2020, 2, 28)
+    actual_overall_end_date = _EXAMPLE_VALID_RECORDS.overall_end_date
+
+    assert expected_overall_end_date == actual_overall_end_date
+
+
+def test_natural_gas_billing_input_overall_start_date_invalid():
+    with pytest.raises(ValueError):
+        _EXAMPLE_INVALID_RECORDS.overall_start_date
+
+
+def test_natural_gas_billing_input_overall_end_date_invalid():
+    with pytest.raises(ValueError):
+        _EXAMPLE_INVALID_RECORDS.overall_end_date