"""Small filesystem helpers shared by core modules."""
from __future__ import annotations

import json
import os
import re
import tempfile
from pathlib import Path, PurePosixPath
from typing import Any


def atomic_write_bytes(path: Path, data: bytes, mode: int | None = None) -> None:
    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    fd, tmp = tempfile.mkstemp(dir=path.parent, prefix=f".{path.name}.", suffix=".tmp")
    try:
        with os.fdopen(fd, "wb") as fh:
            fh.write(data)
            fh.flush()
            os.fsync(fh.fileno())
        if mode is not None:
            os.chmod(tmp, mode)
        os.replace(tmp, path)
    except BaseException:
        try:
            os.unlink(tmp)
        except OSError:
            pass
        raise


def atomic_write_text(path: Path, text: str, mode: int | None = None) -> None:
    atomic_write_bytes(path, text.encode("utf-8"), mode)


def atomic_write_json(path: Path, obj: Any, mode: int | None = None) -> None:
    atomic_write_text(path, json.dumps(obj, indent=2, sort_keys=True) + "\n", mode)


def read_json(path: Path, default: Any) -> Any:
    try:
        with open(path, "r", encoding="utf-8") as fh:
            return json.load(fh)
    except (FileNotFoundError, json.JSONDecodeError):
        return default


def slugify(text: str, fallback: str = "mod") -> str:
    slug = re.sub(r"[^a-z0-9]+", "-", text.lower()).strip("-")
    return slug[:48] or fallback


def safe_relpath(rel: str) -> str | None:
    """Normalise an archive/dest path. Returns None if it is absolute or escapes."""
    rel = rel.replace("\\", "/")
    if not rel or "\0" in rel or rel.startswith("/") or re.match(r"^[A-Za-z]:", rel):
        return None
    parts = [p for p in PurePosixPath(rel).parts if p not in ("", ".")]
    if not parts or any(p == ".." for p in parts):
        return None
    return "/".join(parts)


def is_within(child: Path, parent: Path) -> bool:
    try:
        Path(os.path.realpath(child)).relative_to(os.path.realpath(parent))
        return True
    except ValueError:
        return False