# Copyright 2026 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
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# SPDX-License-Identifier: Apache-2.0
"""Deterministic hashing and cache key generation.
Provides a stable, collision-resistant cache key function that works
with Pydantic models, dicts, and plain strings. Used by the response
cache (``src/cache.py``) to identify identical flow inputs.
Design decisions:
- **SHA-256** for collision resistance (16-char hex prefix = 64 bits).
- **Pydantic's ``model_dump_json``** for stable serialization of models.
- **``json.dumps(sort_keys=True)``** for stable dict serialization.
- **Prefix with flow name** so keys from different flows never collide.
"""
from __future__ import annotations
import hashlib
import json
from typing import Any
from pydantic import BaseModel
def make_cache_key(namespace: str, input_data: BaseModel | dict[str, Any] | str) -> str:
"""Create a deterministic cache key from a namespace and input.
Args:
namespace: Logical namespace (e.g. flow name like
``"translate_text"``). Prefixed to the key so different
namespaces never collide.
input_data: The data to hash — a Pydantic model, dict, or
string. Pydantic models are serialized via
``model_dump_json(exclude_none=True)``; dicts via
``json.dumps(sort_keys=True)``; strings via ``str()``.
Returns:
A string of the form ``"namespace:hex_prefix"`` where
``hex_prefix`` is the first 16 hex characters of the
SHA-256 digest.
Examples::
>>> from pydantic import BaseModel
>>> class Input(BaseModel):
... text: str = 'hello'
>>> make_cache_key('translate', Input())
'translate:...'
>>> make_cache_key('translate', Input()) == make_cache_key('translate', Input())
True
>>> make_cache_key('a', Input()) != make_cache_key('b', Input())
True
"""
if isinstance(input_data, BaseModel):
serialized = input_data.model_dump_json(exclude_none=True)
elif isinstance(input_data, dict):
serialized = json.dumps(input_data, sort_keys=True, default=str)
else:
serialized = str(input_data)
input_hash = hashlib.sha256(serialized.encode()).hexdigest()[:16]
return f"{namespace}:{input_hash}"
