relative_date.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""various date/time utilities

<datetime.datetime> parsing behavior

  [year(-|/|.)month(-|/|.)day(_whitespace_)][[[hour]:minute]:second]

<datetime.timedelta> parsing behavior

  [days(_whitespace_)][[[hours]:minutes]:seconds]
"""

import re

from collections import defaultdict
from datetime import datetime, timedelta


DATETIME_FMT = re.compile(
        r"^((?P<year>\d+)[\-\./]"
        "(?P<month>\d+)[\-./]"
        "(?P<day>\d+)\s+)?"
        "(((?P<hour>\d+)"
        "(:(?P<minute>\d+))?)?"
        "(:(?P<second>\d+))?)?$"
        )

TIMEDELTA_FMT = re.compile(
        r"^((?P<days>\d+)\s+)?"
        "(((?P<hours>\d+)"
        "(:(?P<minutes>\d+))?)?"
        "(:(?P<seconds>\d+))?)?$"
        )

REPLACE_FMT = DATETIME_FMT


def _time_parser(timestamp, pattern):
    """Parses a string to date/time components with a regular expression"""

    parts = pattern.match(timestamp)
    if parts:
        time_components = defaultdict(int)
        for (name, value) in parts.groupdict().items():
            if value:
                time_components[name] = int(value)

        return time_components
    else:
        raise NotImplementedError("A date of unknown format provided: "
                                  "'{0}'".format(timestamp))


def strpdatetime(timestamp):
    """Parse datetime from string"""

    return datetime(**_time_parser(timestamp, DATETIME_FMT))


def strptimedelta(timestamp):
    """Parse timedelta from string"""

    return timedelta(**_time_parser(timestamp, TIMEDELTA_FMT))


def at(time, timestamp):
    """Set time and/or date from a parsed timestamp"""

    time_components = _time_parser(timestamp, REPLACE_FMT)
    return time.replace(**time_components, microsecond=0)


def days_from_now(days):
    """Set time and/or date from a parsed timestamp"""

    return datetime.now() + timedelta(days=days)


def months_from_now(months):
    """Gets a date N months from now"""

    now = datetime.now()
    y, m = divmod(now.month + months, 12)
    y += now.year
    if m == 0:
        m = 12
        y -= 1

    return now.replace(year=y, month=m)


def years_from_now(years):
    """Gets a date N years from now"""

    now = datetime.now()
    return now.replace(year=now.year+years)


def today_at(timestamp):
    """Sets the time from a string for today's date"""

    return at(datetime.now(), timestamp)


def tomorrow_at(timestamp):
    """Sets the time from a string for a date that's a day from now"""

    return at(days_from_now(1), timestamp)


def yesterday_at(timestamp):
    """Sets the time from a string for a date that's a day before now"""

    return at(days_from_now(-1), timestamp)


def next_week_at(timestamp):
    """Sets the time from a string for a date that's a week from now"""

    return at(days_from_now(7), timestamp)


def previous_week_at(timestamp):
    """Sets the time from a string for a date that's a week before now"""

    return at(days_from_now(-7), timestamp)


def next_month_at(timestamp):
    """Sets the time from a string for a date that's a month from now"""

    return at(months_from_now(1), timestamp)


def previous_month_at(timestamp):
    """Sets the time from a string for a date that's a month before now"""

    return at(months_from_now(-1), timestamp)


def next_year_at(timestamp):
    """Sets the time from a string for a date that's a year from now

    Leap years work too
    """

    return at(years_from_now(1), timestamp)


def previous_year_at(timestamp):
    """Sets the time from a string for a date that's a year before now

    Leap years work too
    """

    return at(years_from_now(-1), timestamp)


if __name__ == "__main__":
    from sys import argv, exit

    try:
        print("Previous year at:", previous_year_at(argv[1]))
        print("Previous month at:", previous_month_at(argv[1]))
        print("Previous week at:", previous_week_at(argv[1]))
        print("Yesterday at:", yesterday_at(argv[1]))
        print("Today at:", today_at(argv[1]))
        print("Tomorrow at:", tomorrow_at(argv[1]))
        print("Next week at:", next_week_at(argv[1]))
        print("Next month at:", next_month_at(argv[1]))
        print("Next year at:", next_year_at(argv[1]))
    except Exception as e:
        raise e

    exit(0)