"""Util functions and helpers related to dates and timestamps calculations."""

import datetime


def get_prior_date_intervals(date, count=2, length=7):
    """Get n intervals of length m ending at given date.

    Starts with an interval with oldest dates, ends with an interval with
    the latest dates.

    Args:
        date (datetime.date): End date
        count (int): Number of intervals to get.
        length (int): Number of days in interval.

    Returns:
        list: A list of dicts:
            (dict): Dictionary representing an interval with keys
            start_date (datetime.date): Start date
            end_date (datetime.date): End date

    """
    intervals = []
    for interval_number in range(1, count + 1):
        interval = {
            "start_date": date
            - datetime.timedelta(days=(length * interval_number) - 1),
            "end_date": date - datetime.timedelta(days=length * (interval_number - 1)),
        }
        intervals.append(interval)
    return intervals[::-1]


def get_time_period(start_date=None, end_date=None, max_available_date=None):
    """Determine time_period based on max_date or start and end_date.

    Args:
        start_date (datetime.date): Start date
        end_date (datetime.date): End date
        max_available_date (datetime.date): Max available date

    Returns:
        Time period

    """
    if not (start_date and end_date):
        time_period, *_ = get_prior_date_intervals(
            max_available_date, count=1, length=28
        )
    else:
        time_period, *_ = get_prior_date_intervals(
            end_date, count=1, length=(end_date - start_date).days + 1
        )

    return time_period