Add mock file audit backend

audit_core/mock_file_backend.py

@@ -0,0 +1,65 @@
+"""Development-only file backend for Audit Core.
+
+This backend intentionally writes local JSONL files under /tmp by default. It
+is useful for wiring integrations before the durable Audit Core archive exists,
+but it is not production audit custody.
+"""
+
+from __future__ import annotations
+
+import json
+import os
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+
+from audit_core.interface import AuditEvent
+
+
+class MockFileAuditBackend:
+    """Append audit events to hourly JSONL files and clean up old files."""
+
+    def __init__(
+        self,
+        base_dir: str | Path | None = None,
+        retention_days: int | None = None,
+        now: datetime | None = None,
+    ) -> None:
+        self.base_dir = Path(base_dir or os.environ.get("AUDIT_CORE_MOCK_DIR", "/tmp/audit-core"))
+        self.retention_days = int(
+            retention_days
+            if retention_days is not None
+            else os.environ.get("AUDIT_CORE_MOCK_RETENTION_DAYS", "7")
+        )
+        self._now = now
+
+    def emit(self, event: AuditEvent) -> str:
+        self.base_dir.mkdir(parents=True, exist_ok=True)
+        self.cleanup_old_files()
+        path = self.current_path()
+        record = event.as_record()
+        with path.open("a", encoding="utf-8") as handle:
+            handle.write(json.dumps(record, sort_keys=True, separators=(",", ":")) + "\n")
+        return str(path)
+
+    def cleanup_old_files(self) -> list[str]:
+        if self.retention_days < 0 or not self.base_dir.exists():
+            return []
+
+        cutoff = self.now() - timedelta(days=self.retention_days)
+        removed: list[str] = []
+        for path in self.base_dir.glob("audit-*.jsonl"):
+            try:
+                modified = datetime.fromtimestamp(path.stat().st_mtime, tz=timezone.utc)
+            except FileNotFoundError:
+                continue
+            if modified < cutoff:
+                path.unlink(missing_ok=True)
+                removed.append(str(path))
+        return removed
+
+    def current_path(self) -> Path:
+        stamp = self.now().strftime("%Y%m%dT%H")
+        return self.base_dir / f"audit-{stamp}.jsonl"
+
+    def now(self) -> datetime:
+        return self._now or datetime.now(timezone.utc)