Mini Shell

"""Provides the :class:`Arrow <arrow.formatter.DateTimeFormatter>` class, an improved formatter for datetimes."""

import re
import sys
from datetime import datetime, timedelta
from typing import Optional, Pattern, cast

from dateutil import tz as dateutil_tz

from arrow import locales
from arrow.constants import DEFAULT_LOCALE

if sys.version_info < (3, 8):  # pragma: no cover
    from typing_extensions import Final
else:
    from typing import Final  # pragma: no cover


FORMAT_ATOM: Final[str] = "YYYY-MM-DD HH:mm:ssZZ"
FORMAT_COOKIE: Final[str] = "dddd, DD-MMM-YYYY HH:mm:ss ZZZ"
FORMAT_RFC822: Final[str] = "ddd, DD MMM YY HH:mm:ss Z"
FORMAT_RFC850: Final[str] = "dddd, DD-MMM-YY HH:mm:ss ZZZ"
FORMAT_RFC1036: Final[str] = "ddd, DD MMM YY HH:mm:ss Z"
FORMAT_RFC1123: Final[str] = "ddd, DD MMM YYYY HH:mm:ss Z"
FORMAT_RFC2822: Final[str] = "ddd, DD MMM YYYY HH:mm:ss Z"
FORMAT_RFC3339: Final[str] = "YYYY-MM-DD HH:mm:ssZZ"
FORMAT_RSS: Final[str] = "ddd, DD MMM YYYY HH:mm:ss Z"
FORMAT_W3C: Final[str] = "YYYY-MM-DD HH:mm:ssZZ"


class DateTimeFormatter:

    # This pattern matches characters enclosed in square brackets are matched as
    # an atomic group. For more info on atomic groups and how to they are
    # emulated in Python's re library, see https://stackoverflow.com/a/13577411/2701578

    _FORMAT_RE: Final[Pattern[str]] = re.compile(
        r"(\[(?:(?=(?P<literal>[^]]))(?P=literal))*\]|YYY?Y?|MM?M?M?|Do|DD?D?D?|d?dd?d?|HH?|hh?|mm?|ss?|SS?S?S?S?S?|ZZ?Z?|a|A|X|x|W)"
    )

    locale: locales.Locale

    def __init__(self, locale: str = DEFAULT_LOCALE) -> None:

        self.locale = locales.get_locale(locale)

    def format(cls, dt: datetime, fmt: str) -> str:

        # FIXME: _format_token() is nullable
        return cls._FORMAT_RE.sub(
            lambda m: cast(str, cls._format_token(dt, m.group(0))), fmt
        )

    def _format_token(self, dt: datetime, token: Optional[str]) -> Optional[str]:

        if token and token.startswith("[") and token.endswith("]"):
            return token[1:-1]

        if token == "YYYY":
            return self.locale.year_full(dt.year)
        if token == "YY":
            return self.locale.year_abbreviation(dt.year)

        if token == "MMMM":
            return self.locale.month_name(dt.month)
        if token == "MMM":
            return self.locale.month_abbreviation(dt.month)
        if token == "MM":
            return f"{dt.month:02d}"
        if token == "M":
            return f"{dt.month}"

        if token == "DDDD":
            return f"{dt.timetuple().tm_yday:03d}"
        if token == "DDD":
            return f"{dt.timetuple().tm_yday}"
        if token == "DD":
            return f"{dt.day:02d}"
        if token == "D":
            return f"{dt.day}"

        if token == "Do":
            return self.locale.ordinal_number(dt.day)

        if token == "dddd":
            return self.locale.day_name(dt.isoweekday())
        if token == "ddd":
            return self.locale.day_abbreviation(dt.isoweekday())
        if token == "d":
            return f"{dt.isoweekday()}"

        if token == "HH":
            return f"{dt.hour:02d}"
        if token == "H":
            return f"{dt.hour}"
        if token == "hh":
            return f"{dt.hour if 0 < dt.hour < 13 else abs(dt.hour - 12):02d}"
        if token == "h":
            return f"{dt.hour if 0 < dt.hour < 13 else abs(dt.hour - 12)}"

        if token == "mm":
            return f"{dt.minute:02d}"
        if token == "m":
            return f"{dt.minute}"

        if token == "ss":
            return f"{dt.second:02d}"
        if token == "s":
            return f"{dt.second}"

        if token == "SSSSSS":
            return f"{dt.microsecond:06d}"
        if token == "SSSSS":
            return f"{dt.microsecond // 10:05d}"
        if token == "SSSS":
            return f"{dt.microsecond // 100:04d}"
        if token == "SSS":
            return f"{dt.microsecond // 1000:03d}"
        if token == "SS":
            return f"{dt.microsecond // 10000:02d}"
        if token == "S":
            return f"{dt.microsecond // 100000}"

        if token == "X":
            return f"{dt.timestamp()}"

        if token == "x":
            return f"{dt.timestamp() * 1_000_000:.0f}"

        if token == "ZZZ":
            return dt.tzname()

        if token in ["ZZ", "Z"]:
            separator = ":" if token == "ZZ" else ""
            tz = dateutil_tz.tzutc() if dt.tzinfo is None else dt.tzinfo
            # `dt` must be aware object. Otherwise, this line will raise AttributeError
            # https://github.com/arrow-py/arrow/pull/883#discussion_r529866834
            # datetime awareness: https://docs.python.org/3/library/datetime.html#aware-and-naive-objects
            total_minutes = int(cast(timedelta, tz.utcoffset(dt)).total_seconds() / 60)

            sign = "+" if total_minutes >= 0 else "-"
            total_minutes = abs(total_minutes)
            hour, minute = divmod(total_minutes, 60)

            return f"{sign}{hour:02d}{separator}{minute:02d}"

        if token in ("a", "A"):
            return self.locale.meridian(dt.hour, token)

        if token == "W":
            year, week, day = dt.isocalendar()
            return f"{year}-W{week:02d}-{day}"