"""Vault file IO shared by the markdown frontend and its mirror."""

from __future__ import annotations

import contextlib
import os
import tempfile
from typing import TYPE_CHECKING, Any

import aiofile
import frontmatter

if TYPE_CHECKING:
    from pathlib import Path

__all__ = ["read_or_empty", "reattach_frontmatter", "write_atomic"]


async def read_or_empty(path: Path) -> str:
    if not path.exists():  # noqa: ASYNC240
        return ""
    async with aiofile.async_open(path, "r", encoding="utf-8") as f:
        return await f.read()


async def write_atomic(path: Path, content: str) -> None:
    """Write via tmp + ``os.replace`` in the same directory: no torn reads."""
    path.parent.mkdir(parents=True, exist_ok=True)
    fd, tmp_path = tempfile.mkstemp(
        prefix=f".{path.name}.", suffix=".tmp", dir=str(path.parent)
    )
    try:
        async with aiofile.async_open(tmp_path, "w", encoding="utf-8") as f:
            await f.write(content)
        os.close(fd)
        os.replace(tmp_path, path)  # noqa: PTH105
    except BaseException:
        with contextlib.suppress(OSError):
            os.close(fd)
        with contextlib.suppress(OSError):
            os.unlink(tmp_path)  # noqa: PTH108
        raise


def reattach_frontmatter(metadata: dict[str, Any], body: str) -> str:
    """Re-emit a ``.md`` with YAML frontmatter; no block at all for empty metadata."""
    if not metadata:
        return body if body.endswith("\n") else body + "\n"
    post = frontmatter.Post(content=body, **metadata)
    return frontmatter.dumps(post) + "\n"