Class FingerprintCache

ci/fingerprint/core.py:54–299

Two-layer file change detection using modification time and content hashing. Provides efficient change detection by: 1. Fast modification time comparison (microsecond performance) 2. Accurate content verification via MD5 hashing when needed NOTE: This is the legacy implementat

class FingerprintCache:
    """
    Two-layer file change detection using modification time and content hashing.

    Provides efficient change detection by:
    1. Fast modification time comparison (microsecond performance)
    2. Accurate content verification via MD5 hashing when needed

    NOTE: This is the legacy implementation. For new code, prefer TwoLayerFingerprintCache
    which supports batch operations and the safe pre-computed fingerprint pattern.
    """

    def __init__(self, cache_file: Path, modtime_only: bool = False):
        """
        Initialize fingerprint cache.

        Args:
            cache_file: Path to JSON cache file
            modtime_only: When True, disable hashing and rely solely on modtime.
        """
        self.cache_file = cache_file
        self._modtime_only: bool = modtime_only
        self.cache = self._load_cache()

    def _load_cache(self) -> dict[str, CacheEntry]:
        """
        Load cache from JSON file, return empty dict if file doesn't exist.

        Uses try-except instead of exists() check to avoid TOCTOU race condition.
        This is the same pattern used in meson_runner.py for test_list_cache.

        Returns:
            Dictionary mapping file paths to cache entries
        """
        try:
            with open(self.cache_file, "r") as f:
                data = json.load(f)

            # Convert JSON dict to CacheEntry objects
            cache: dict[str, CacheEntry] = {}
            for file_path, entry_data in data.items():
                cache[file_path] = CacheEntry(
                    modification_time=entry_data["modification_time"],
                    md5_hash=entry_data["md5_hash"],
                )
            return cache
        except FileNotFoundError:
            # Cache file doesn't exist yet - start fresh
            return {}
        except (json.JSONDecodeError, KeyError, TypeError, IOError, OSError):
            # Cache corrupted or inaccessible - start fresh
            return {}

    def _save_cache(self) -> None:
        """Save current cache state to JSON file."""
        # Ensure cache directory exists
        self.cache_file.parent.mkdir(parents=True, exist_ok=True)