"""
Functions to parse datetime objects.

We're using regular expressions rather than time.strptime because:
- They provide both validation and parsing.
- They're more flexible for datetimes.
- The date/datetime/time constructors produce friendlier error messages.

Stolen from https://raw.githubusercontent.com/django/django/master/django/utils/dateparse.py at
9718fa2e8abe430c3526a9278dd976443d4ae3c6

Changed to:
* use standard python datetime types not django.utils.timezone
* raise ValueError when regex doesn't match rather than returning None
* support parsing unix timestamps for dates and datetimes
"""
import re
from datetime import date, datetime, time, timedelta, timezone
from typing import Dict, Optional, Type, Union

from . import errors

date_expr = r'(?P<year>\d{4})-(?P<month>\d{1,2})-(?P<day>\d{1,2})'
time_expr = (
    r'(?P<hour>\d{1,2}):(?P<minute>\d{1,2})'
    r'(?::(?P<second>\d{1,2})(?:\.(?P<microsecond>\d{1,6})\d{0,6})?)?'
    r'(?P<tzinfo>Z|[+-]\d{2}(?::?\d{2})?)?$'
)

date_re = re.compile(f'{date_expr}$')
time_re = re.compile(time_expr)
datetime_re = re.compile(f'{date_expr}[T ]{time_expr}')

standard_duration_re = re.compile(
    r'^'
    r'(?:(?P<days>-?\d+) (days?, )?)?'
    r'((?:(?P<hours>-?\d+):)(?=\d+:\d+))?'
    r'(?:(?P<minutes>-?\d+):)?'
    r'(?P<seconds>-?\d+)'
    r'(?:\.(?P<microseconds>\d{1,6})\d{0,6})?'
    r'$'
)

# Support the sections of ISO 8601 date representation that are accepted by timedelta
iso8601_duration_re = re.compile(
    r'^(?P<sign>[-+]?)'
    r'P'
    r'(?:(?P<days>\d+(.\d+)?)D)?'
    r'(?:T'
    r'(?:(?P<hours>\d+(.\d+)?)H)?'
    r'(?:(?P<minutes>\d+(.\d+)?)M)?'
    r'(?:(?P<seconds>\d+(.\d+)?)S)?'
    r')?'
    r'$'
)

EPOCH = datetime(1970, 1, 1)
# if greater than this, the number is in ms, if less than or equal it's in seconds
# (in seconds this is 11th October 2603, in ms it's 20th August 1970)
MS_WATERSHED = int(2e10)
# slightly more than datetime.max in ns - (datetime.max - EPOCH).total_seconds() * 1e9
MAX_NUMBER = int(3e20)
StrBytesIntFloat = Union[str, bytes, int, float]


def get_numeric(value: StrBytesIntFloat, native_expected_type: str) -> Union[None, int, float]:
    if isinstance(value, (int, float)):
        return value
    try:
        return float(value)
    except ValueError:
        return None
    except TypeError:
        raise TypeError(f'invalid type; expected {native_expected_type}, string, bytes, int or float')


def from_unix_seconds(seconds: Union[int, float]) -> datetime:
    if seconds > MAX_NUMBER:
        return datetime.max
    elif seconds < -MAX_NUMBER:
        return datetime.min

    while abs(seconds) > MS_WATERSHED:
        seconds /= 1000
    dt = EPOCH + timedelta(seconds=seconds)
    return dt.replace(tzinfo=timezone.utc)


def _parse_timezone(value: Optional[str], error: Type[Exception]) -> Union[None, int, timezone]:
    if value == 'Z':
        return timezone.utc
    elif value is not None:
        offset_mins = int(value[-2:]) if len(value) > 3 else 0
        offset = 60 * int(value[1:3]) + offset_mins
        if value[0] == '-':
            offset = -offset
        try:
            return timezone(timedelta(minutes=offset))
        except ValueError:
            raise error()
    else:
        return None


def parse_date(value: Union[date, StrBytesIntFloat]) -> date:
    """
    Parse a date/int/float/string and return a datetime.date.

    Raise ValueError if the input is well formatted but not a valid date.
    Raise ValueError if the input isn't well formatted.
    """
    if isinstance(value, date):
        if isinstance(value, datetime):
            return value.date()
        else:
            return value

    number = get_numeric(value, 'date')
    if number is not None:
        return from_unix_seconds(number).date()

    if isinstance(value, bytes):
        value = value.decode()

    match = date_re.match(value)  # type: ignore
    if match is None:
        raise errors.DateError()

    kw = {k: int(v) for k, v in match.groupdict().items()}

    try:
        return date(**kw)
    except ValueError:
        raise errors.DateError()


def parse_time(value: Union[time, StrBytesIntFloat]) -> time:
    """
    Parse a time/string and return a datetime.time.

    Raise ValueError if the input is well formatted but not a valid time.
    Raise ValueError if the input isn't well formatted, in particular if it contains an offset.
    """
    if isinstance(value, time):
        return value

    number = get_numeric(value, 'time')
    if number is not None:
        if number >= 86400:
            # doesn't make sense since the time time loop back around to 0
            raise errors.TimeError()
        return (datetime.min + timedelta(seconds=number)).time()

    if isinstance(value, bytes):
        value = value.decode()

    match = time_re.match(value)  # type: ignore
    if match is None:
        raise errors.TimeError()

    kw = match.groupdict()
    if kw['microsecond']:
        kw['microsecond'] = kw['microsecond'].ljust(6, '0')

    tzinfo = _parse_timezone(kw.pop('tzinfo'), errors.TimeError)
    kw_: Dict[str, Union[None, int, timezone]] = {k: int(v) for k, v in kw.items() if v is not None}
    kw_['tzinfo'] = tzinfo

    try:
        return time(**kw_)  # type: ignore
    except ValueError:
        raise errors.TimeError()


def parse_datetime(value: Union[datetime, StrBytesIntFloat]) -> datetime:
    """
    Parse a datetime/int/float/string and return a datetime.datetime.

    This function supports time zone offsets. When the input contains one,
    the output uses a timezone with a fixed offset from UTC.

    Raise ValueError if the input is well formatted but not a valid datetime.
    Raise ValueError if the input isn't well formatted.
    """
    if isinstance(value, datetime):
        return value

    number = get_numeric(value, 'datetime')
    if number is not None:
        return from_unix_seconds(number)

    if isinstance(value, bytes):
        value = value.decode()

    match = datetime_re.match(value)  # type: ignore
    if match is None:
        raise errors.DateTimeError()

    kw = match.groupdict()
    if kw['microsecond']:
        kw['microsecond'] = kw['microsecond'].ljust(6, '0')

    tzinfo = _parse_timezone(kw.pop('tzinfo'), errors.DateTimeError)
    kw_: Dict[str, Union[None, int, timezone]] = {k: int(v) for k, v in kw.items() if v is not None}
    kw_['tzinfo'] = tzinfo

    try:
        return datetime(**kw_)  # type: ignore
    except ValueError:
        raise errors.DateTimeError()


def parse_duration(value: StrBytesIntFloat) -> timedelta:
    """
    Parse a duration int/float/string and return a datetime.timedelta.

    The preferred format for durations in Django is '%d %H:%M:%S.%f'.

    Also supports ISO 8601 representation.
    """
    if isinstance(value, timedelta):
        return value

    if isinstance(value, (int, float)):
        # below code requires a string
        value = str(value)
    elif isinstance(value, bytes):
        value = value.decode()

    try:
        match = standard_duration_re.match(value) or iso8601_duration_re.match(value)
    except TypeError:
        raise TypeError('invalid type; expected timedelta, string, bytes, int or float')

    if not match:
        raise errors.DurationError()

    kw = match.groupdict()
    sign = -1 if kw.pop('sign', '+') == '-' else 1
    if kw.get('microseconds'):
        kw['microseconds'] = kw['microseconds'].ljust(6, '0')

    if kw.get('seconds') and kw.get('microseconds') and kw['seconds'].startswith('-'):
        kw['microseconds'] = '-' + kw['microseconds']

    kw_ = {k: float(v) for k, v in kw.items() if v is not None}

    return sign * timedelta(**kw_)
