procurement-ingest/lambdas/api/serialization.py

"""JSON response helpers for the procurement API.

DynamoDB items come back through boto3 with numeric attributes as
``decimal.Decimal`` (e.g. purchase-orders ``total_amount``/``line_items``
prices), which ``json.dumps`` rejects. The encoder below renders integral
Decimals as JSON integers (exact) and non-integral Decimals as floats. For the
values this API serves -- currency amounts at PO magnitudes, well under ~15
significant digits -- the shortest-float repr round-trips the original digits
exactly. A Decimal carrying more precision than a float can hold (DynamoDB
Number supports 38 digits) would be truncated silently; the pipeline never
writes such values, but if that ever changes, switch non-integral Decimals to
``str(o)`` and update the OpenAPI number types.
"""

import decimal
import json


class _DecimalSafeEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, decimal.Decimal):
            if o == o.to_integral_value():
                return int(o)
            return float(o)
        if isinstance(o, set):
            return sorted(o)
        return super().default(o)


def dumps(payload) -> str:
    return json.dumps(payload, cls=_DecimalSafeEncoder)


def json_response(status_code: int, payload) -> dict:
    return {
        "statusCode": status_code,
        "headers": {"Content-Type": "application/json"},
        "body": dumps(payload),
    }


def error_response(status_code: int, message: str) -> dict:
    return json_response(status_code, {"error": message})