import logging
from datetime import date, datetime, timezone
from email.utils import parsedate_to_datetime

logger = logging.getLogger(__name__)

# Common absolute-date formats encountered in news markup when ISO parsing fails.
_FALLBACK_FORMATS = (
    "%Y-%m-%d %H:%M:%S",
    "%Y-%m-%d %H:%M",
    "%Y/%m/%d %H:%M:%S",
    "%B %d, %Y",
    "%b %d, %Y",
    "%B %d, %Y %I:%M %p",
    "%b %d, %Y %I:%M %p",
)


def parse_datetime(value):
    """Best-effort parse of a publish timestamp into a ``datetime``.

    Handles ISO 8601 (including trailing ``Z`` and offsets), RFC 2822/email
    dates, and a few common human formats. Returns ``None`` when the value
    cannot be parsed — relative strings like "3 hours ago" are intentionally
    skipped.
    """
    if not value or not isinstance(value, str):
        return None
    text = value.strip()
    if not text:
        return None

    try:
        return datetime.fromisoformat(text)
    except ValueError:
        pass

    try:
        return parsedate_to_datetime(text)
    except (TypeError, ValueError, OverflowError):
        pass

    for fmt in _FALLBACK_FORMATS:
        try:
            return datetime.strptime(text, fmt)
        except ValueError:
            pass

    logger.debug("Could not parse datetime from value %r", value)
    return None


def parse_date_arg(value):
    """Parse a ``YYYY-MM-DD`` CLI argument, raising a friendly error otherwise."""
    try:
        return date.fromisoformat(value)
    except ValueError:
        raise ValueError("Invalid date %r; expected YYYY-MM-DD" % value)


def date_part(dt):
    """Return ``dt`` as a ``date``, normalized to UTC when timezone-aware."""
    if dt.tzinfo is not None:
        return dt.astimezone(timezone.utc).date()
    return dt.date()


def filter_by_date_window(headlines, since=None, until=None):
    """Keep headlines whose publication date falls in ``[since, until]``.

    ``since``/``until`` are ``datetime.date`` (or ``None`` for an open bound).
    When either bound is set, headlines with no parsable publication date are
    dropped because their recency cannot be established; without any bound they
    are all kept. Returns ``(kept, dropped_undated)``.
    """
    kept = []
    dropped_undated = 0
    bounding = since is not None or until is not None

    for h in headlines:
        if h.published_at is None:
            if bounding:
                dropped_undated += 1
                continue
            kept.append(h)
            continue

        d = date_part(h.published_at)
        if since is not None and d < since:
            continue
        if until is not None and d > until:
            continue
        kept.append(h)

    return kept, dropped_undated