from operator import attrgetter

import arrow
from django.conf import settings
from ics import Calendar

EVENT_KEYS = ("begin", "end", "all_day", "name", "description", "location")


def parse_ical(source):
    """Parses iCalendar source and returns events as list of dicts."""
    cal = Calendar(source)
    events = []
    for event in sorted(cal.events, key=attrgetter("begin"), reverse=True):
        events.append({key: getattr(event, key) for key in EVENT_KEYS})
    return events


def split_events(events):
    """Splits events and returns list of past events and future events."""
    now = arrow.utcnow()
    past = [ev for ev in events if ev["end"] < now]
    future = [ev for ev in events if ev["end"] > now]
    return past, future


def set_event_duration(event):
    """Sets duration for event."""
    if event["all_day"]:
        event["duration"] = "celý den"
        return event

    delta = event["end"] - event["begin"]
    if delta.days < 1:
        begin = event["begin"].to(settings.TIME_ZONE).format("H:mm")
        end = event["end"].to(settings.TIME_ZONE).format("H:mm")
        event["duration"] = f"{begin} - {end}"
    else:
        begin = event["begin"].to(settings.TIME_ZONE).format("H:mm")
        end = event["end"].to(settings.TIME_ZONE).format("H:mm (D.M.)")
        event["duration"] = f"{begin} - {end}"
    return event


def process_ical(source):
    """Parses iCalendar source and returns events as list of dicts. Returns
    tuple of past and future events.
    """
    events = parse_ical(source)
    events = list(map(set_event_duration, events))
    return split_events(events)