import calendar
from datetime import date, datetime
import json


def _calculate_release_weeks():
    """Prepare data for dim_release_week."""
    c = calendar.Calendar(firstweekday=calendar.FRIDAY)
    data = []
    for year in range(1900, 2050):
        week_number = 1
        for month in range(1, 13):
            weeks = c.monthdatescalendar(year, month)
            for week in weeks:
                if week[-1] <= date(
                        year, month, calendar.monthrange(year, month)[1]):
                    data.append({
                        'year': year,
                        'week_number': week_number,
                        'first_day': datetime.strftime(week[0], '%Y-%m-%d'),
                        'last_day': datetime.strftime(week[-1], '%Y-%m-%d')
                    })
                    week_number += 1
    res = json.dumps(data)
    with open('dates.json', 'wt') as f:
        f.write(res)