"""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