Refactor radar system

python_app/file_io.py

@@ -0,0 +1,47 @@
+"""Atomic writes for JSON settings shared by GUI and pipeline processes."""
+
+from __future__ import annotations
+
+import json
+import os
+from contextlib import suppress
+from pathlib import Path
+import tempfile
+
+
+def atomic_write_json(path: Path, payload: object, *, durable: bool = False) -> Path:
+    """Serialize strict JSON before opening any files, then atomically commit it."""
+    return atomic_write_text(path, json.dumps(payload, indent=2, allow_nan=False), durable=durable)
+
+
+def atomic_write_text(path: Path, text: str, *, durable: bool = False) -> Path:
+    """Replace a text file only after a complete write, cleaning up failed writes.
+
+    Each call owns its temporary file, so concurrent writers cannot truncate or
+    rename one another's work. Durable writes also sync the file and directory;
+    frequent live settings can omit those syncs to avoid unnecessary disk I/O.
+    """
+    path.parent.mkdir(parents=True, exist_ok=True)
+    temporary = None
+    try:
+        with tempfile.NamedTemporaryFile(
+            mode="w", encoding="utf-8", dir=path.parent,
+            prefix=f".{path.name}.", suffix=".tmp", delete=False,
+        ) as handle:
+            temporary = Path(handle.name)
+            handle.write(text)
+            if durable:
+                handle.flush()
+                os.fsync(handle.fileno())
+        os.replace(temporary, path)
+        if durable:
+            directory_fd = os.open(path.parent, os.O_RDONLY | os.O_DIRECTORY)
+            try:
+                os.fsync(directory_fd)
+            finally:
+                os.close(directory_fd)
+    finally:
+        if temporary is not None:
+            with suppress(OSError):
+                temporary.unlink(missing_ok=True)
+    return path