#!/usr/bin/env python3

"""Utilities related to dates and times and datetimes."""

import datetime
import enum
import logging
import re
from typing import Any, NewType, Tuple

import holidays  # type: ignore
import pytz

import constants

logger = logging.getLogger(__name__)


def replace_timezone(dt: datetime.datetime,
                     tz: datetime.tzinfo) -> datetime.datetime:
    """
    Replaces the timezone on a datetime object.

    >>> from pytz import UTC
    >>> d = now_pacific()
    >>> d.tzinfo.tzname(d)[0]     # Note: could be PST or PDT
    'P'
    >>> o = replace_timezone(d, UTC)
    >>> o.tzinfo.tzname(o)
    'UTC'

    """
    return dt.replace(tzinfo=None).astimezone(tz=tz)


def now() -> datetime.datetime:
    """
    What time is it?  Result returned in UTC
    """
    return datetime.datetime.now()


def now_pacific() -> datetime.datetime:
    """
    What time is it?  Result in US/Pacifit time (PST/PDT)
    """
    return replace_timezone(now(), pytz.timezone("US/Pacific"))


def date_to_datetime(date: datetime.date) -> datetime.datetime:
    """
    Given a date, return a datetime with hour/min/sec zero (midnight)

    >>> import datetime
    >>> date_to_datetime(datetime.date(2021, 12, 25))
    datetime.datetime(2021, 12, 25, 0, 0)

    """
    return datetime.datetime(
        date.year,
        date.month,
        date.day,
        0, 0, 0, 0
    )


def date_and_time_to_datetime(date: datetime.date,
                              time: datetime.time) -> datetime.datetime:
    """
    Given a date and time, merge them and return a datetime.

    >>> import datetime
    >>> d = datetime.date(2021, 12, 25)
    >>> t = datetime.time(12, 30, 0, 0)
    >>> date_and_time_to_datetime(d, t)
    datetime.datetime(2021, 12, 25, 12, 30)

    """
    return datetime.datetime(
        date.year,
        date.month,
        date.day,
        time.hour,
        time.minute,
        time.second,
        time.microsecond,
    )


def datetime_to_date_and_time(
        dt: datetime.datetime
) -> Tuple[datetime.date, datetime.time]:
    """Return the component date and time objects of a datetime.

    >>> import datetime
    >>> dt = datetime.datetime(2021, 12, 25, 12, 30)
    >>> (d, t) = datetime_to_date_and_time(dt)
    >>> d
    datetime.date(2021, 12, 25)
    >>> t
    datetime.time(12, 30)

    """
    return (dt.date(), dt.timetz())


def datetime_to_date(dt: datetime.datetime) -> datetime.date:
    """Return the date part of a datetime.

    >>> import datetime
    >>> dt = datetime.datetime(2021, 12, 25, 12, 30)
    >>> datetime_to_date(dt)
    datetime.date(2021, 12, 25)

    """
    return datetime_to_date_and_time(dt)[0]


def datetime_to_time(dt: datetime.datetime) -> datetime.time:
    """Return the time part of a datetime.

    >>> import datetime
    >>> dt = datetime.datetime(2021, 12, 25, 12, 30)
    >>> datetime_to_time(dt)
    datetime.time(12, 30)

    """
    return datetime_to_date_and_time(dt)[1]


class TimeUnit(enum.Enum):
    """An enum to represent units with which we can compute deltas."""
    MONDAYS = 0
    TUESDAYS = 1
    WEDNESDAYS = 2
    THURSDAYS = 3
    FRIDAYS = 4
    SATURDAYS = 5
    SUNDAYS = 6
    SECONDS = 7
    MINUTES = 8
    HOURS = 9
    DAYS = 10
    WORKDAYS = 11
    WEEKS = 12
    MONTHS = 13
    YEARS = 14

    @classmethod
    def is_valid(cls, value: Any):
        if type(value) is int:
            return value in cls._value2member_map_
        elif type(value) is TimeUnit:
            return value.value in cls._value2member_map_
        elif type(value) is str:
            return value in cls._member_names_
        else:
            print(type(value))
            return False


def n_timeunits_from_base(
    count: int,
    unit: TimeUnit,
    base: datetime.datetime
) -> datetime.datetime:
    """Return a datetime that is N units before/after a base datetime.
    e.g.  3 Wednesdays from base datetime, 2 weeks from base date, 10
    years before base datetime, 13 minutes after base datetime, etc...
    Note: to indicate before/after the base date, use a positive or
    negative count.

    >>> base = string_to_datetime("2021/09/10 11:24:51AM-0700")[0]

    The next (1) Monday from the base datetime:
    >>> n_timeunits_from_base(+1, TimeUnit.MONDAYS, base)
    datetime.datetime(2021, 9, 13, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    Ten (10) years after the base datetime:
    >>> n_timeunits_from_base(10, TimeUnit.YEARS, base)
    datetime.datetime(2031, 9, 10, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    Fifty (50) working days (M..F, not counting holidays) after base datetime:
    >>> n_timeunits_from_base(50, TimeUnit.WORKDAYS, base)
    datetime.datetime(2021, 11, 23, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    Fifty (50) days (including weekends and holidays) after base datetime:
    >>> n_timeunits_from_base(50, TimeUnit.DAYS, base)
    datetime.datetime(2021, 10, 30, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    Fifty (50) months before (note negative count) base datetime:
    >>> n_timeunits_from_base(-50, TimeUnit.MONTHS, base)
    datetime.datetime(2017, 7, 10, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    Fifty (50) hours after base datetime:
    >>> n_timeunits_from_base(50, TimeUnit.HOURS, base)
    datetime.datetime(2021, 9, 12, 13, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    Fifty (50) minutes before base datetime:
    >>> n_timeunits_from_base(-50, TimeUnit.MINUTES, base)
    datetime.datetime(2021, 9, 10, 10, 34, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    Fifty (50) seconds from base datetime:
    >>> n_timeunits_from_base(50, TimeUnit.SECONDS, base)
    datetime.datetime(2021, 9, 10, 11, 25, 41, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    """
    assert TimeUnit.is_valid(unit)
    if count == 0:
        return base

    # N days from base
    if unit == TimeUnit.DAYS:
        timedelta = datetime.timedelta(days=count)
        return base + timedelta

    # N hours from base
    elif unit == TimeUnit.HOURS:
        timedelta = datetime.timedelta(hours=count)
        return base + timedelta

    # N minutes from base
    elif unit == TimeUnit.MINUTES:
        timedelta = datetime.timedelta(minutes=count)
        return base + timedelta

    # N seconds from base
    elif unit == TimeUnit.SECONDS:
        timedelta = datetime.timedelta(seconds=count)
        return base + timedelta

    # N workdays from base
    elif unit == TimeUnit.WORKDAYS:
        if count < 0:
            count = abs(count)
            timedelta = datetime.timedelta(days=-1)
        else:
            timedelta = datetime.timedelta(days=1)
        skips = holidays.US(years=base.year).keys()
        while count > 0:
            old_year = base.year
            base += timedelta
            if base.year != old_year:
                skips = holidays.US(years=base.year).keys()
            if (
                    base.weekday() < 5 and
                    datetime.date(base.year,
                                  base.month,
                                  base.day) not in skips
            ):
                count -= 1
        return base

    # N weeks from base
    elif unit == TimeUnit.WEEKS:
        timedelta = datetime.timedelta(weeks=count)
        base = base + timedelta
        return base

    # N months from base
    elif unit == TimeUnit.MONTHS:
        month_term = count % 12
        year_term = count // 12
        new_month = base.month + month_term
        if new_month > 12:
            new_month %= 12
            year_term += 1
        new_year = base.year + year_term
        return datetime.datetime(
            new_year,
            new_month,
            base.day,
            base.hour,
            base.minute,
            base.second,
            base.microsecond,
            base.tzinfo,
        )

    # N years from base
    elif unit == TimeUnit.YEARS:
        new_year = base.year + count
        return datetime.datetime(
            new_year,
            base.month,
            base.day,
            base.hour,
            base.minute,
            base.second,
            base.microsecond,
            base.tzinfo,
        )

    if unit not in set([TimeUnit.MONDAYS,
                        TimeUnit.TUESDAYS,
                        TimeUnit.WEDNESDAYS,
                        TimeUnit.THURSDAYS,
                        TimeUnit.FRIDAYS,
                        TimeUnit.SATURDAYS,
                        TimeUnit.SUNDAYS]):
        raise ValueError(unit)

    # N weekdays from base (e.g. 4 wednesdays from today)
    direction = 1 if count > 0 else -1
    count = abs(count)
    timedelta = datetime.timedelta(days=direction)
    start = base
    while True:
        dow = base.weekday()
        if dow == unit.value and start != base:
            count -= 1
            if count == 0:
                return base
        base = base + timedelta


def get_format_string(
        *,
        date_time_separator=" ",
        include_timezone=True,
        include_dayname=False,
        use_month_abbrevs=False,
        include_seconds=True,
        include_fractional=False,
        twelve_hour=True,
) -> str:
    """
    Helper to return a format string without looking up the documentation
    for strftime.

    >>> get_format_string()
    '%Y/%m/%d %I:%M:%S%p%z'

    >>> get_format_string(date_time_separator='@')
    '%Y/%m/%d@%I:%M:%S%p%z'

    >>> get_format_string(include_dayname=True)
    '%a/%Y/%m/%d %I:%M:%S%p%z'

    >>> get_format_string(include_dayname=True, twelve_hour=False)
    '%a/%Y/%m/%d %H:%M:%S%z'

    """
    fstring = ""
    if include_dayname:
        fstring += "%a/"

    if use_month_abbrevs:
        fstring = f"{fstring}%Y/%b/%d{date_time_separator}"
    else:
        fstring = f"{fstring}%Y/%m/%d{date_time_separator}"
    if twelve_hour:
        fstring += "%I:%M"
        if include_seconds:
            fstring += ":%S"
        fstring += "%p"
    else:
        fstring += "%H:%M"
        if include_seconds:
            fstring += ":%S"
    if include_fractional:
        fstring += ".%f"
    if include_timezone:
        fstring += "%z"
    return fstring


def datetime_to_string(
    dt: datetime.datetime,
    *,
    date_time_separator=" ",
    include_timezone=True,
    include_dayname=False,
    use_month_abbrevs=False,
    include_seconds=True,
    include_fractional=False,
    twelve_hour=True,
) -> str:
    """
    A nice way to convert a datetime into a string; arguably better than
    just printing it and relying on it __repr__().

    >>> d = string_to_datetime(
    ...                        "2021/09/10 11:24:51AM-0700",
    ...                       )[0]
    >>> d
    datetime.datetime(2021, 9, 10, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))
    >>> datetime_to_string(d)
    '2021/09/10 11:24:51AM-0700'
    >>> datetime_to_string(d, include_dayname=True, include_seconds=False)
    'Fri/2021/09/10 11:24AM-0700'

    """
    fstring = get_format_string(
        date_time_separator=date_time_separator,
        include_timezone=include_timezone,
        include_dayname=include_dayname,
        include_seconds=include_seconds,
        include_fractional=include_fractional,
        twelve_hour=twelve_hour)
    return dt.strftime(fstring).strip()


def string_to_datetime(
        txt: str,
        *,
        date_time_separator=" ",
        include_timezone=True,
        include_dayname=False,
        use_month_abbrevs=False,
        include_seconds=True,
        include_fractional=False,
        twelve_hour=True,
) -> Tuple[datetime.datetime, str]:
    """A nice way to convert a string into a datetime.  Returns both the
    datetime and the format string used to parse it.  Also consider
    dateparse.dateparse_utils for a full parser alternative.

    >>> d = string_to_datetime(
    ...                        "2021/09/10 11:24:51AM-0700",
    ...                       )
    >>> d
    (datetime.datetime(2021, 9, 10, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200))), '%Y/%m/%d %I:%M:%S%p%z')

    """
    fstring = get_format_string(
        date_time_separator=date_time_separator,
        include_timezone=include_timezone,
        include_dayname=include_dayname,
        include_seconds=include_seconds,
        include_fractional=include_fractional,
        twelve_hour=twelve_hour)
    return (
        datetime.datetime.strptime(txt, fstring),
        fstring
    )


def timestamp() -> str:
    """Return a timestamp for right now in Pacific timezone."""
    ts = datetime.datetime.now(tz=pytz.timezone("US/Pacific"))
    return datetime_to_string(ts, include_timezone=True)


def time_to_string(
    dt: datetime.datetime,
    *,
    include_seconds=True,
    include_fractional=False,
    include_timezone=False,
    twelve_hour=True,
) -> str:
    """A nice way to convert a datetime into a time (only) string.
    This ignores the date part of the datetime.

    >>> d = string_to_datetime(
    ...                        "2021/09/10 11:24:51AM-0700",
    ...                       )[0]
    >>> d
    datetime.datetime(2021, 9, 10, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))

    >>> time_to_string(d)
    '11:24:51AM'

    >>> time_to_string(d, include_seconds=False)
    '11:24AM'

    >>> time_to_string(d, include_seconds=False, include_timezone=True)
    '11:24AM-0700'

    """
    fstring = ""
    if twelve_hour:
        fstring += "%l:%M"
        if include_seconds:
            fstring += ":%S"
        fstring += "%p"
    else:
        fstring += "%H:%M"
        if include_seconds:
            fstring += ":%S"
    if include_fractional:
        fstring += ".%f"
    if include_timezone:
        fstring += "%z"
    return dt.strftime(fstring).strip()


def seconds_to_timedelta(seconds: int) -> datetime.timedelta:
    """Convert a delta in seconds into a timedelta."""
    return datetime.timedelta(seconds=seconds)


MinuteOfDay = NewType("MinuteOfDay", int)


def minute_number(hour: int, minute: int) -> MinuteOfDay:
    """
    Convert hour:minute into minute number from start of day.

    >>> minute_number(0, 0)
    0

    >>> minute_number(9, 15)
    555

    >>> minute_number(23, 59)
    1439

    """
    return MinuteOfDay(hour * 60 + minute)


def datetime_to_minute_number(dt: datetime.datetime) -> MinuteOfDay:
    """
    Convert a datetime into a minute number (of the day).  Note that
    this ignores the date part of the datetime and only uses the time
    part.

    >>> d = string_to_datetime(
    ...                        "2021/09/10 11:24:51AM-0700",
    ...                       )[0]

    >>> datetime_to_minute_number(d)
    684

    """
    return minute_number(dt.hour, dt.minute)


def time_to_minute_number(t: datetime.time) -> MinuteOfDay:
    """
    Convert a datetime.time into a minute number.

    >>> t = datetime.time(5, 15)
    >>> time_to_minute_number(t)
    315

    """
    return minute_number(t.hour, t.minute)


def minute_number_to_time_string(minute_num: MinuteOfDay) -> str:
    """
    Convert minute number from start of day into hour:minute am/pm
    string.

    >>> minute_number_to_time_string(315)
    ' 5:15a'

    >>> minute_number_to_time_string(684)
    '11:24a'

    """
    hour = minute_num // 60
    minute = minute_num % 60
    ampm = "a"
    if hour > 12:
        hour -= 12
        ampm = "p"
    if hour == 12:
        ampm = "p"
    if hour == 0:
        hour = 12
    return f"{hour:2}:{minute:02}{ampm}"


def parse_duration(duration: str) -> int:
    """
    Parse a duration in string form into a delta seconds.

    >>> parse_duration('15 days, 2 hours')
    1303200

    >>> parse_duration('15d 2h')
    1303200

    >>> parse_duration('100s')
    100

    >>> parse_duration('3min 2sec')
    182

    """
    if duration.isdigit():
        return int(duration)
    seconds = 0
    m = re.search(r'(\d+) *d[ays]*', duration)
    if m is not None:
        seconds += int(m.group(1)) * 60 * 60 * 24
    m = re.search(r'(\d+) *h[ours]*', duration)
    if m is not None:
        seconds += int(m.group(1)) * 60 * 60
    m = re.search(r'(\d+) *m[inutes]*', duration)
    if m is not None:
        seconds += int(m.group(1)) * 60
    m = re.search(r'(\d+) *s[econds]*', duration)
    if m is not None:
        seconds += int(m.group(1))
    return seconds


def describe_duration(seconds: int, *, include_seconds = False) -> str:
    """
    Describe a duration represented as a count of seconds nicely.

    >>> describe_duration(182)
    '3 minutes'

    >>> describe_duration(182, include_seconds=True)
    '3 minutes, and 2 seconds'

    >>> describe_duration(100, include_seconds=True)
    '1 minute, and 40 seconds'

    describe_duration(1303200)
    '15 days, 2 hours'

    """
    days = divmod(seconds, constants.SECONDS_PER_DAY)
    hours = divmod(days[1], constants.SECONDS_PER_HOUR)
    minutes = divmod(hours[1], constants.SECONDS_PER_MINUTE)

    descr = ""
    if days[0] > 1:
        descr = f"{int(days[0])} days, "
    elif days[0] == 1:
        descr = "1 day, "

    if hours[0] > 1:
        descr = descr + f"{int(hours[0])} hours, "
    elif hours[0] == 1:
        descr = descr + "1 hour, "

    if not include_seconds and len(descr) > 0:
        descr = descr + "and "

    if minutes[0] == 1:
        descr = descr + "1 minute"
    else:
        descr = descr + f"{int(minutes[0])} minutes"

    if include_seconds:
        descr = descr + ', '
        if len(descr) > 0:
            descr = descr + 'and '
        s = minutes[1]
        if s == 1:
            descr = descr + '1 second'
        else:
            descr = descr + f'{s} seconds'
    return descr


def describe_timedelta(delta: datetime.timedelta) -> str:
    """
    Describe a duration represented by a timedelta object.

    >>> d = datetime.timedelta(1, 600)
    >>> describe_timedelta(d)
    '1 day, and 10 minutes'

    """
    return describe_duration(delta.total_seconds())


def describe_duration_briefly(seconds: int, *, include_seconds=False) -> str:
    """
    Describe a duration briefly.

    >>> describe_duration_briefly(182)
    '3m'

    >>> describe_duration_briefly(182, include_seconds=True)
    '3m 2s'

    >>> describe_duration_briefly(100, include_seconds=True)
    '1m 40s'

    describe_duration_briefly(1303200)
    '15d 2h'

    """
    days = divmod(seconds, constants.SECONDS_PER_DAY)
    hours = divmod(days[1], constants.SECONDS_PER_HOUR)
    minutes = divmod(hours[1], constants.SECONDS_PER_MINUTE)

    descr = ''
    if days[0] > 0:
        descr = f'{int(days[0])}d '
    if hours[0] > 0:
        descr = descr + f'{int(hours[0])}h '
    if minutes[0] > 0 or (len(descr) == 0 and not include_seconds):
        descr = descr + f'{int(minutes[0])}m '
    if minutes[1] > 0 and include_seconds:
        descr = descr + f'{int(minutes[1])}s'
    return descr.strip()


def describe_timedelta_briefly(delta: datetime.timedelta) -> str:
    """
    Describe a duration represented by a timedelta object.

    >>> d = datetime.timedelta(1, 600)
    >>> describe_timedelta_briefly(d)
    '1d 10m'

    """
    return describe_duration_briefly(delta.total_seconds())


if __name__ == '__main__':
    import doctest
    doctest.testmod()