#!/usr/bin/env python3

import calendar
import datetime


class IsoWeek(datetime.date):
    """Datetime representing the Monday of an ISO-8601 week.
    """
    pass


class TeachingWeek(datetime.date):
    """Datetime representing the Monday of a teaching week.
    """
    pass


class BreakWeek(datetime.date):
    """Datetime representing the Monday of a break (e.g., mid-semester) week.
    """
    pass


class TeachingCalendar():
    """This class generates teaching-related dates for a specific paper
    offered in a specific teaching period of a specific year. If you
    don't provide teaching period details, it generates dates for the
    current ISO-8601 year.
    """
    weeks = []
    lecture_offsets = []
    skipped_lectures = []
    mondays = []
    period = "iso"
    year = datetime.date.today().year

    def __init__(self, year, period, paper, period_config=None,
        paper_config=None, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.year = year
        self.period = period
        self.paper = paper
        
        # This is likely to end up with one week too many at the end,
        # but that doesn't matter as there will never be any teaching
        # during the last week of December!
        cal = calendar.Calendar().yeardatescalendar(self.year, width=12)

        self.mondays = [week[0] for month in cal[0] for week in month]
        self.mondays = list(dict.fromkeys(self.mondays))
        if period_config:
            self.update_weeks(period_config["weeks"])
        else:
            last_week = datetime.date(self.year, 12, 28).isocalendar()[1]
            self.update_weeks([{"iso": [1, last_week]}])
        if paper_config:
            self.update_lectures(paper_config["lectures"])

    def week(self, week_type, start, end=None):
        end = start if end is None else end
        return [
            week_type(self.mondays[w].year, self.mondays[w].month,
                self.mondays[w].day)
            for w in range(start - 1, end)]

    def teaching_date(self, period, week, offset=0):
        pass

    def update_weeks(self, week_list):
        for w in week_list:
            for t, r in w.items():
                if t == "teach":
                    self.weeks += self.week(TeachingWeek, r[0], r[1])
                elif t == "break":
                    self.weeks += self.week(BreakWeek, r[0], r[1])
                elif t == "iso":
                    self.weeks += self.week(IsoWeek, r[0], r[1])
                else:
                    print("WARNING: ignored unknown week type {t}.".format(t=t))
    
    def update_lectures(self, lecture_list):
        for l in lecture_list:
            for t, v in l.items():
                if t == "offsets":
                    self.lecture_offsets = v
                elif t == "skip":
                    self.skipped_lectures = v
                else:
                    print("WARNING: ignored unknown lecture key {t}.".format(t=t))

    def calendar(self):
        period = {}
        week_num = break_num = 0
        for w in self.weeks:
            if isinstance(w, (TeachingWeek, IsoWeek)):
                # Increment first so that break weeks have the
                # same week number as the preceding teaching week.
                # This ensures the keys are always chronologically
                # sorted. Reset the break number for each new
                # teaching week.
                week_num += 1
                break_num = 0
                period[week_num] = w
            elif isinstance(w, BreakWeek):
                # Allow for up to 99 consecutive break weeks,
                # which should be sufficient :). Should probably
                # throw an exception if we exceed that.
                break_num += 0.01
                period[week_num + break_num] = w
        return period
    
    def lecture_dates(self):
        dates = {}
        lecture_num = 1
        teaching_weeks = [t for t in self.weeks if isinstance(t, TeachingWeek)]
        for week_index, monday in enumerate(teaching_weeks):
            for offset_index, offset in enumerate(self.lecture_offsets):
                lec = week_index * 2 + offset_index + 1
                if lec in self.skipped_lectures:
                    continue
                dates[lecture_num] = monday + datetime.timedelta(offset)
                lecture_num += 1
        return dates