"""
Names crossing between a group and this machine, in both directions.

**Uploading**, the node decides: `SAFE_UPLOAD_NAME` and the Explorer-active types
in `meshbay_node/roots.py`. This is a copy of that rule, checked before anything
is sent so a folder holding one refused name is refused whole instead of
arriving with holes in it — as the Files tab does with its own copy.
`test_names.py` holds this copy to the node's answers.

**Downloading**, a name from the index is someone else's text. It is made
writable on this platform (`meshbay_common.paths.sanitize_for_download`, the
same rule the browser applies), and the resolved path must stay under the
destination: checked after resolution, never by comparing strings.
"""

import re
from pathlib import Path

from meshbay_common.paths import fold, sanitize_for_download

UPLOAD_NAME = re.compile(
    r"^[^\W_]"
    r"[\w .\-()\[\]'’,&+#@]{0,127}"
    r"(?<![ .])$",
    re.UNICODE)

SHELL_ACTIVE_NAMES = frozenset({"desktop.ini"})
SHELL_ACTIVE_SUFFIXES = (".lnk", ".url", ".scf", ".library-ms", ".searchconnector-ms")


def upload_name_problem(name: str, *, is_dir: bool = False) -> str | None:
    if not UPLOAD_NAME.match(name):
        return ("starts with something other than a letter or digit, ends with a space "
                "or a dot, holds a character the node does not accept, or is longer "
                "than 128 characters")
    lower = name.lower()
    if not is_dir and (lower in SHELL_ACTIVE_NAMES or lower.endswith(SHELL_ACTIVE_SUFFIXES)):
        return "a file type Windows Explorer acts on by itself; no node accepts it"
    return None


def same_name(a: str, b: str) -> bool:
    """As the node and the Files tab compare names in a folder: without case."""
    return fold(a) == fold(b)


class UnsafeName(Exception):
    pass


def local_path(dest: Path, parts: list[str]) -> tuple[Path, bool]:
    """
    Where a remote file or folder lands under `dest`, and whether a name had to
    be changed to be written here.
    """
    renamed = False
    out = dest
    for part in parts:
        safe = sanitize_for_download(part)
        if safe in (".", ".."):
            safe = "unnamed"
        renamed |= safe != part
        out = out / safe
    base = dest.resolve()
    try:
        out.resolve().relative_to(base)
    except ValueError:
        raise UnsafeName(f"{'/'.join(parts)!r} would land outside {dest}") from None
    return out, renamed