#!/usr/bin/env python3

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

import datetime
import enum
import logging
import re
from typing import 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:
    return dt.replace(tzinfo=None).astimezone(tz=tz)


def now() -> datetime.datetime:
    return datetime.datetime.now()


def now_pst() -> datetime.datetime:
    return replace_timezone(now(), pytz.timezone("US/Pacific"))


def date_to_datetime(date: datetime.date) -> datetime.datetime:
    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:
    return datetime.datetime(
        date.year,
        date.month,
        date.day,
        time.hour,
        time.minute,
        time.second,
        time.millisecond
    )


def datetime_to_date(date: datetime.datetime) -> datetime.date:
    return datetime.date(
        date.year,
        date.month,
        date.day
    )


# An enum to represent units with which we can compute deltas.
class TimeUnit(enum.Enum):
    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


def n_timeunits_from_base(
    count: int,
    unit: TimeUnit,
    base: datetime.datetime
) -> datetime.datetime:
    if count == 0:
        return base

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

    # 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,
        )

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

    if use_month_abbrevs:
        fstring = f"%Y/%b/%d{date_time_separator}"
    else:
        fstring = f"%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."""
    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.  Also consider
    dateparse.dateparse_utils for a full parser.
    """
    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 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."""
    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."""
    return MinuteOfDay(hour * 60 + minute)


def datetime_to_minute_number(dt: datetime.datetime) -> MinuteOfDay:
    """Convert a datetime into a minute number (of the day)"""
    return minute_number(dt.hour, dt.minute)


def minute_number_to_time_string(minute_num: MinuteOfDay) -> str:
    """Convert minute number from start of day into hour:minute am/pm
    string.
    """
    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."""
    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(age: int) -> str:
    """Describe a duration."""
    days = divmod(age, 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 len(descr) > 0:
        descr = descr + "and "
    if minutes[0] == 1:
        descr = descr + "1 minute"
    else:
        descr = descr + f"{int(minutes[0])} minutes"
    return descr


def describe_duration_briefly(age: int) -> str:
    """Describe a duration briefly."""
    days = divmod(age, 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:
        descr = descr + f"{int(minutes[0])}m"
    return descr.strip()