from typing import Dict, List, Iterable

import sys
import urllib.request
from datetime import datetime, date, timedelta
from threading import Timer

from dateutil import rrule
from icalendar import cal
from isodate import Duration

from icalendar_timeseries_server import __version__
from icalendar_timeseries_server.config import get_config, CalendarConfig
from icalendar_timeseries_server.event import Event


_SCRAPE_CACHE: Dict[str, List[Event]] = dict()

__py_version: str = f'{sys.version_info.major}.{sys.version_info.minor}.{sys.version_info.micro}'
USER_AGENT: str = f'icalendar-timeseries-server/{__version__} (Python/{__py_version})'


def _parse_recurring(event: cal.Event, start: datetime, end: datetime, duration: timedelta) -> List[datetime]:
    occurences: List[datetime] = []

    evstart = event.get('dtstart').dt
    # First occurence lies in the future; no need to process further
    if evstart >= end:
        return occurences

    # Extract recurrence rules from ical
    ical_lines = event.to_ical().decode('utf-8').split('\r\n')
    recurrence = '\n'.join(
        [x for x in ical_lines
         if x.startswith('RRULE') or x.startswith('RDATE') or x.startswith('EXRULE') or x.startswith('EXDATE')])
    # Create a generator that yields a timestamp for each recurrence
    generator = rrule.rrulestr(recurrence, dtstart=evstart)

    # Generate an event entry for each occurence of the event
    for dt in generator:
        # Skip past occurences and break once the the event lies too far in the future
        if dt + duration < start:
            continue
        if dt > end:
            break
        # Create an event entry
        occurences.append(dt)
    return occurences


def _scrape_calendar(name: str, config: CalendarConfig, start: datetime, end: datetime):
    global _SCRAPE_CACHE
    events = []

    opener: urllib.request.OpenerDirector = config.get_url_opener()
    with opener.open(config.url) as response:
        data = response.read().decode('utf-8')
    calendar = cal.Calendar.from_ical(data)

    for element in calendar.walk():
        if element.name == "VEVENT":
            dtstart = element.get('dtstart').dt
            if isinstance(dtstart, date):
                dtstart = datetime(dtstart.year, dtstart.month, dtstart.day, tzinfo=start.tzinfo)
            # Process either end timestamp or duration, if present
            if 'dtend' in element:
                evend = element.get('dtend').dt
                if isinstance(evend, date):
                    evend = datetime(evend.year, evend.month, evend.day, tzinfo=start.tzinfo)
                duration = evend - dtstart
            elif 'duration' in element:
                duration = element.get('duration').dt
            else:
                duration = timedelta(0)
            if element.get('rrule') is not None or element.get('rdate') is not None:
                occurences: Iterable[datetime] = _parse_recurring(element, start, end, duration)
            else:
                occurences = [dtstart]
            for occurence in occurences:
                if start <= occurence < end:
                    events.append(Event(name, element, occurence, occurence + duration))
    _SCRAPE_CACHE[name] = events


def scrape_calendar(name: str, config: CalendarConfig):
    # Get current time in configured timezone
    tz = get_config().tz
    now: datetime = datetime.now(tz)
    # Reschedule calendar scraping
    cron = Timer(config.interval.totimedelta(start=now).total_seconds(),
                 lambda: scrape_calendar(name, config))
    cron.start()
    # Compute interval for which to return events
    start_delta: Duration = get_config().start_delta
    end_delta: Duration = get_config().end_delta
    start: datetime = now + start_delta
    end: datetime = now + end_delta
    # Scrape and parse the calendar
    _scrape_calendar(name, config, start, end)


def start_scrape_calendar(name: str, config: CalendarConfig):
    # Get current time in configured timezone
    tz = get_config().tz
    now: datetime = datetime.now(tz)
    # Schedule first calendar scraping
    cron = Timer(0, lambda: scrape_calendar(name, config))
    cron.start()


def get_calendar(name: str):
    global _SCRAPE_CACHE
    return _SCRAPE_CACHE.get(name, [])