from __future__ import annotations

import os
from contextlib import suppress
from pathlib import Path
from xml.etree import ElementTree

from repub.config import feed_output_path, staged_feed_output_path


def publish_staged_feed(*, out_dir: Path, feed_slug: str) -> Path:
    staged_path = staged_feed_output_path(out_dir=out_dir, feed_slug=feed_slug)
    public_path = feed_output_path(out_dir=out_dir, feed_slug=feed_slug)

    public_path.parent.mkdir(parents=True, exist_ok=True)
    _validate_staged_feed(staged_path)
    _fsync_file(staged_path)
    os.replace(staged_path, public_path)
    _fsync_directory(public_path.parent)
    return public_path


def _fsync_file(path: Path) -> None:
    with path.open("rb") as handle:
        os.fsync(handle.fileno())


def _validate_staged_feed(path: Path) -> None:
    try:
        root = ElementTree.parse(path).getroot()
    except ElementTree.ParseError as error:
        raise ValueError(f"Staged feed is not well-formed XML: {path}") from error

    if root.tag != "rss":
        raise ValueError(f"Staged feed is not an RSS document: {path}")
    if root.find("channel") is None:
        raise ValueError(f"Staged feed is missing an RSS channel: {path}")


def _fsync_directory(path: Path) -> None:
    flags = os.O_RDONLY | getattr(os, "O_DIRECTORY", 0)
    with suppress(OSError):
        fd = os.open(path, flags)
        try:
            os.fsync(fd)
        finally:
            os.close(fd)