"""Safe ``tar.gz`` primitives shared by the profile and kanban transfer paths.

Both ``hermes profile export|import`` and ``hermes kanban export|import``
ship a directory to another machine and unpack whatever comes back. The
unpack side is the dangerous half: a hand-crafted archive can carry
``../`` members, absolute paths, symlinks, or device nodes, any of which
turn an import into an arbitrary-write primitive. These helpers are the
one place that logic lives so a second transfer surface can't ship a
second, subtly weaker extractor.

The writer is deliberately not :func:`shutil.make_archive`: that emits
PAX (Python's tarfile default since 3.8), whose fractional-mtime records
macOS Archive Utility rejects — double-clicking an exported profile threw
"Error 94 - Bad message." GNU format keeps long paths working (longlink
extensions) and stays integer-mtime, so Finder, bsdtar, and gnutar all
extract it.
"""

from __future__ import annotations

import os
import shutil
import tarfile
import tempfile
from pathlib import Path, PurePosixPath, PureWindowsPath


def normalize_archive_parts(member_name: str) -> list[str]:
    """Return safe path parts for an archive member, or raise.

    Rejects absolute paths (POSIX and Windows, including drive letters),
    empty names, and any ``..`` component. Backslashes are folded to
    ``/`` first so a Windows-authored archive can't smuggle a separator
    past the POSIX parse.
    """
    normalized_name = member_name.replace("\\", "/")
    posix_path = PurePosixPath(normalized_name)
    windows_path = PureWindowsPath(member_name)

    if (
        not normalized_name
        or posix_path.is_absolute()
        or windows_path.is_absolute()
        or windows_path.drive
    ):
        raise ValueError(f"Unsafe archive member path: {member_name}")

    parts = [part for part in posix_path.parts if part not in {"", "."}]
    if not parts or any(part == ".." for part in parts):
        raise ValueError(f"Unsafe archive member path: {member_name}")
    return parts


def make_targz(base: str, root_dir: str, base_dir: str) -> str:
    """Create ``<base>.tar.gz`` of ``root_dir/base_dir`` in GNU tar format.

    Writes to a sibling temp file and renames onto ``archive_path`` only
    after the archive is fully written. ``tarfile.open`` on a path truncates
    the destination the instant it opens, so writing there directly means a
    failure partway through ``tf.add`` (disk full, permission loss,
    interruption) destroys whatever was already at that path — including an
    existing export the caller chose to overwrite.
    """
    archive_path = f"{base}.tar.gz"
    dest_dir = os.path.dirname(archive_path) or "."
    fd, tmp_path = tempfile.mkstemp(
        dir=dest_dir, prefix=".archive_", suffix=".tar.gz.tmp"
    )
    try:
        with os.fdopen(fd, "wb") as f:
            with tarfile.open(fileobj=f, mode="w:gz", format=tarfile.GNU_FORMAT) as tf:
                tf.add(str(Path(root_dir) / base_dir), arcname=base_dir)
        os.replace(tmp_path, archive_path)
    except BaseException:
        try:
            os.unlink(tmp_path)
        except OSError:
            pass
        raise
    return archive_path


def safe_extract_targz(archive: Path, destination: Path) -> None:
    """Extract ``archive`` into ``destination`` without path escapes or links.

    Only directories and regular files are extracted; symlinks, hardlinks,
    and device nodes raise rather than being silently skipped, so a
    tampered archive fails the import instead of landing a partial tree.
    """
    with tarfile.open(archive, "r:gz") as tf:
        for member in tf.getmembers():
            parts = normalize_archive_parts(member.name)
            target = destination.joinpath(*parts)

            if member.isdir():
                target.mkdir(parents=True, exist_ok=True)
                continue

            if not member.isfile():
                raise ValueError(
                    f"Unsupported archive member type: {member.name}"
                )

            target.parent.mkdir(parents=True, exist_ok=True)
            extracted = tf.extractfile(member)
            if extracted is None:
                raise ValueError(f"Cannot read archive member: {member.name}")

            with extracted, open(target, "wb") as dst:
                shutil.copyfileobj(extracted, dst)

            try:
                os.chmod(target, member.mode & 0o777)
            except OSError:
                pass


def archive_root_dirs(archive: Path) -> set[str]:
    """Return the archive's top-level directory names.

    Transfer archives carry exactly one root directory, which names the
    thing being imported. Inspecting the archive before extraction lets
    the caller resolve the target name (and refuse a malformed archive)
    without first mutating a live tree.
    """
    with tarfile.open(archive, "r:gz") as tf:
        return {
            parts[0]
            for member in tf.getmembers()
            for parts in [normalize_archive_parts(member.name)]
            if len(parts) > 1 or member.isdir()
        }


def copy_regular_files(src: Path, dst: Path) -> int:
    """Copy the regular files under ``src`` into ``dst``, skipping symlinks.

    Used on the *export* side so a symlink planted in an attachments or
    logs tree can't pull an arbitrary file into the archive. Returns the
    number of files copied; a missing ``src`` copies nothing.
    """
    if not src.is_dir():
        return 0
    copied = 0
    for entry in sorted(src.rglob("*")):
        if entry.is_symlink() or not entry.is_file():
            continue
        target = dst / entry.relative_to(src)
        target.parent.mkdir(parents=True, exist_ok=True)
        shutil.copyfile(entry, target)
        copied += 1
    return copied