#!/usr/bin/env python3

import sys
import html
import logging
import locale
from datetime import datetime, timedelta, timezone, date
from dateutil.rrule import rruleset, rrulestr

import icalendar


def _to_aware(dt):
    """Normalize a date or datetime to a timezone-aware UTC datetime."""
    if isinstance(dt, date) and not isinstance(dt, datetime):
        return datetime(dt.year, dt.month, dt.day, tzinfo=timezone.utc)
    if dt.tzinfo is None:
        return dt.replace(tzinfo=timezone.utc)
    return dt.astimezone(timezone.utc)


def vevent_to_event(event, rrstart=None):
    if rrstart is None:
        begin = _to_aware(event["DTSTART"].dt)
    else:
        begin = _to_aware(rrstart)

    return {
        "name": str(event.get("SUMMARY", "")),
        "url": str(event.get("URL", "")),
        "begin": begin
    }


def parse_single_event(event, start, end):
    logging.info(f"Processing single event {event.get('SUMMARY', '')}")
    dtstart = _to_aware(event["DTSTART"].dt)
    if dtstart >= start and dtstart < end:
        return vevent_to_event(event)


def parse_recurring_event(event, start, end):
    logging.info(f"Processing recurring event {event.get('SUMMARY', '')}")
    dtstart = _to_aware(event["DTSTART"].dt)
    rs = rruleset()
    rs.rrule(rrulestr(event["RRULE"].to_ical().decode("utf-8"), dtstart=dtstart))
    if "EXDATE" in event.keys():
        exdates = event["EXDATE"]
        if not isinstance(exdates, list):
            exdates = [exdates]
        for exdate_list in exdates:
            for dt in exdate_list.dts:
                rs.exdate(_to_aware(dt.dt))

    events = []
    for dt in rs.between(start, end, inc=True):
        events.append(vevent_to_event(event, dt))

    return events


def find_events(icsfilestr, start, end, num):
    with open(icsfilestr, "r") as icsfile:
        cal = icalendar.Calendar.from_ical(icsfile.read())

    events = []
    for event in cal.subcomponents:
        if event.name == "VEVENT":
            if "RRULE" in event.keys():
                events.extend(parse_recurring_event(event, start, end))
            else:
                ev = parse_single_event(event, start, end)
                if ev is not None:
                    events.append(ev)

    events = sorted(events, key=lambda k: k["begin"])
    events = events[0:num]

    return events


def format_events(events):
    print("<table class=\"table table-condensed\">")
    for event in events:
        name = html.escape(event['name'])
        url = html.escape(event['url'])
        print(
            "<tr>"
            f"<td>{event['begin'].strftime('%A, %d.%m um %H:%M Uhr')}</td>"
            f"<td><a href=\"{url}\">{name}</a></td>"
            "</tr>"
        )
    print("</table><!--/.table .table-condensed-->")


if __name__ == "__main__":
    if len(sys.argv) < 4:
        print(f"Usage: {sys.argv[0]} calendar max_days max_items")
        sys.exit(1)

    locale.setlocale(locale.LC_TIME, "de_DE.UTF-8")
    calendar = sys.argv[1]
    max_days = int(sys.argv[2])
    max_items = int(sys.argv[3])

    now = datetime.now(timezone.utc)
    events = find_events(calendar, now, now + timedelta(days=max_days), max_items)
    format_events(events)