import ICAL from 'ical.js';

const calendars = {
  "5WrcagPPARQ3BD87": {
    name: "Club réseau",
    color: null
  },
  "TFEAKjAgNFQZpNjo": {
    name: "hackENS",
    color: null
  }
};

export const calendarTree = {
  "COF": [
    "Club réseau",
    "hackENS"
  ]
};

const calendarIds = Object.keys(calendars);

function mkCalendarUrl(id) {
  return `/cal/${id}/?export&accept=jcal`;
}

function fetchCalendar(id) {
  return fetch(mkCalendarUrl(id), { credentials: 'omit' }).then(resp => resp.json()).catch(err => console.error(err));
}

class Calendar {
  constructor (id, calendar) {
    const metadata = calendars[id];
    this.name = metadata.name;
    this.color = metadata.color || calendar[1][4][3];
    this.events = calendar[2].filter(item => item[0] === 'vevent').map(item => this._parse_vevent(item[1]));
  }

  _parse_vevent(vevent) {
    const event = {};
    vevent.forEach(elt => {
      event[elt[0]] = elt[3];
    });
    return event;
  }
}

function fcEventFromjCalEvent(cal) {
  return function (evt) {
    const start = new Date(evt.dtstart);
    const end = new Date(evt.dtend);
    const fcEvent = {
      title: `${cal.name}: ${evt.summary}`,
      start,
      end,
      color: cal.color,
      duration: end - start // in ms
    };

    if (evt.description) {
      fcEvent.description = evt.description;
    }

    if (evt.rrule) {
      const { freq, byday, interval } = evt.rrule;
      fcEvent.rrule = {
        freq,
        byweekday: byday,
        dtstart: evt.dtstart,
      };

      if (interval) {
        fcEvent.rrule.interval = interval;
      }
    }

    return fcEvent;
  }
}

function mkEventsFromCalendar(id) {
  return fetchCalendar(id).then(calendar => {
    if (calendar[0] !== 'vcalendar') return;
    const cal = new Calendar(id, calendar)
    return cal.events.map(fcEventFromjCalEvent(cal))
  });
}

export function mkEvent(title, start, duration, ...rest) {
  start = new Date(start)
  const end = new Date(start)
  end.setMinutes(start.getMinutes() + duration)
  return {
    title,
    start,
    end,
    ...rest
  }
}

// TODO: move to FullCalendar custom fetcher to control start&end.
export function refreshEvents(selectedCalendars) {
  return Promise.all(calendarIds.filter(id => selectedCalendars ? selectedCalendars.includes(id) : true).map(mkEventsFromCalendar))
}