const clouds = {
  KLUB_RESEAU: 'klub-reseau',
  ELEVES_ENS: 'eleves-ens'
}

const calendars = {
  '5WrcagPPARQ3BD87': {
    cloud: clouds.KLUB_RESEAU,
    name: 'Club réseau',
    color: null
  },
  TFEAKjAgNFQZpNjo: {
    cloud: clouds.KLUB_RESEAU,
    name: 'hackENS',
    color: null
  },
  LLWm8qK9iC5YGrrR: {
    cloud: clouds.ELEVES_ENS,
    name: 'Délégation Générale',
    short_name: 'DG',
    color: null
  },
  w442JdS5AaQ6czrP: {
    cloud: clouds.ELEVES_ENS,
    name: "Écriv'ENS",
    color: null,
  }
}

const calendarsByName = Object.fromEntries(
  Object.entries(calendars).map(([id, {name}]) => ([name, id]))
);

export const calendarTree = {
  'Clubs COF': {
    'Club réseau': {},
    hackENS: {},
    "Écriv'ENS": {}
  },
  COF: {
    BDA: {
      Philharmonie: {}
    },
    AG: {}
  },
  BDS: {},
  'Délégation Générale': {}
}

const calendarIds = Object.keys(calendars)

function mkCalendarUrl(id, { cloud }, extra={}) {
  return `/cal/${cloud}/${id}/?` + new URLSearchParams({
    ...extra,
    export: true,
    expand: true,
    accept: 'jcal'
  });
}

function fetchCalendar(id, cal, extra={}) {
  return fetch(mkCalendarUrl(id, cal, extra), { 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.short_name = metadata.short_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.short_name ?? cal.name} : ${evt.summary}`,
      start: evt.dtstart,
      end: evt.dtend,
      color: cal.color,
      duration: end - start // in ms
    }

    fcEvent.calendar = cal.name
    fcEvent.short_name = evt.summary

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

    if (evt.location) {
      fcEvent.location = evt.location
    }

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

export function mkSource(name) {
  const calendarId = calendarsByName[name];
  if (!calendarId) return null;
  const calendar = calendars[calendarId];

  return {
    id: name,
    ...(calendar?.meta || {}),
    success: calendarData => {
      if (calendarData[0] !== 'vcalendar') return;
      const cal = new Calendar(calendarId, calendarData);
      return cal.events.map(fcEventFromjCalEvent(cal));
    },
    failure: error => {
      console.error(`Fatal error during event source fetching of '${name}': ${error}`);
    },
    events: (info, successCallback, failureCallback) => {
      const { start, end } = info;
      fetchCalendar(calendarId, calendar, {
        start: start.valueOf() / 1000,
        end: end.valueOf() / 1000
      })
      .then(successCallback, failureCallback);
    }
  }
}