"""Date utils."""

import datetime
from datetime import timedelta


def get(string, date_format='%Y-%m-%d'):
    """Create a date from a string.

    Datetime offers strptime which takes a string and a format. In most cases,
    we use the format Year-Month-Day as a value, so this method creates a handy
    shortcut for this method.

    Example::

        from utils import date

        current_date = date.get('2014-10-10')

    Args:
        string (str): the date as a string.
        date_format (str): the date format.

    Returns:
        datetime.datetime: date object that represents the string.
    """
    return datetime.datetime.strptime(string, date_format)


def month_difference(start_date, end_date):
    """Return the number of months between two dates.

    Args:
        start_date (datetime): the datetime object that contains the date
            informations.
        end_date (datetime): similar to start_date.
    Returns:
        int: Number of months between two dates.
    """
    return (
        (end_date.year - start_date.year) * 12 - start_date.month + end_date.month
    ) + 1  # +1 to include the last month


def month_chunk(start_date, end_date, size=1):
    """Split a date range into tuples of x month(s).

    The goal of this method is to create chunk of date ranges that cover a
    period of time (defined by start date, end date). The size param defines
    the maximum number of months each date range should cover.

    Example::

        for start_date, end_date in month_range('10/10/2014', '12/25/2014'):
            print(start_date, end_date)
            # prints:
            # (10/10/2014, 10/31/2014)
            # (11/1/2014, 12/1/2014)
            # (12/1/2014, 12/25/2014)

        # Using a size of 3
        for start_date, end_date in month_range(
                '8/29/2014', '12/25/2014', size=3):
            print(start_date, end_date)
            # prints:
            # (8/29/2014, 10/31/2014) - 3 months (august, sept, oct)
            # (11/1/2014, 12/25/2014) - 2 remaining months (nov, dec)

    Args:
        start_date (datetime): the start date.
        end_date (datetime): the end date
        size (int): how many months should be in each chunk.

    Yield:
        tuple: first part contains the start date, second part contains
            the end date.
    """
    date_range = dict(start_date=start_date)
    generator = generator_month_between_dates(start_date, end_date)

    # The first date returned by the generator is start_date, which is not
    # needed.
    generator.__next__()
    for i, current in enumerate(generator):
        date_range.update(end_date=current - timedelta(days=1))

        if (i % size) + 1 == size:
            yield date_range.get('start_date'), date_range.get('end_date')
            date_range = dict(start_date=current)

    if date_range:
        yield date_range['start_date'], end_date


def generator_month_between_dates(start_date, end_date):
    """Generator that returns each month between two dates.

    This generator comes handy for any operations that requires the list of two
    months between two dates.

    Args:
        start_date (datetime): the start date.
        end_date (datetime): the end date (included.)
    Yields:
        datetime: The current date + 1 month.
    """
    current_year = start_date.year
    current_month = start_date.month
    current_date = start_date

    while current_date <= end_date:
        yield current_date

        current_month = current_month + 1
        if current_month > 12:
            current_month = 1
            current_year = current_year + 1

        current_date = datetime.datetime(current_year, current_month, 1)