Workspace Script: Invite to ICS events

ics sync and invite.gs

// === CONFIGURATION ===
const ICS_URL = 'YOUR ICS URL';
const CALENDAR_ID = 'HIDDEN CALENDAR ID @group.calendar.google.com';
const INVITE_CALENDAR_ID = 'VISIBLE CALENDAR DI @group.calendar.google.com';
const MAX_CHANGES_PER_RUN = 500;
const PROGRESS_KEY = 'ics_sync_progress';

// === TITLE ABBREVIATION MAP ===
const TITLE_ABBREVIATIONS = {
  // 'Original Text': 'Replacement',
  "Investment & Financial Management": "IFM",
  ": Introduction": "",
  "Introduction to ": "",
  "Technology and Innovation": "Technology & Innovation",
  "Logistics and Supply Chain": "Logistics & Supply Chain",
};

// === TITLE PROCESSING ===
function processEventTitle(rawSummary) {
  if (!rawSummary) return { title: '(No title)', extraDescription: '' };

  let title = rawSummary.replace(/\\/g, '');
  let extraDescription = '';

  const hasUE = title.includes('UE,');
  const hasSE = title.includes('SE,');

  // Move everything after the first '(' to the description, unless title contains "Prüfung"
  if (!title.includes('Prüfung')) {
    const bracketIndex = title.indexOf('(');
    if (bracketIndex !== -1) {
      extraDescription = title.substring(bracketIndex);
      title = title.substring(0, bracketIndex).trimEnd();
    }
  }

  if (title.endsWith(': Exercise')) {
    title = title.substring(0, title.length - ': Exercise'.length);
  }

  for (const [key, value] of Object.entries(TITLE_ABBREVIATIONS)) {
    title = title.split(key).join(value);
  }

  if (hasUE) title += ' [Exercise]';
  if (hasSE) title += ' [Seminar]';

  return { title: title.trim(), extraDescription: extraDescription };
}

// === MAIN SYNC FUNCTION ===
function syncICSToGoogleCalendar() {
  const scriptProperties = PropertiesService.getScriptProperties();
  const calendar = CalendarApp.getCalendarById(CALENDAR_ID);
  if (!calendar) {
    Logger.log('Calendar not found!');
    return;
  }

  Logger.log('--- Sync started ---');

  const icsData = fetchICSData(ICS_URL);
  if (!icsData) return;
  const allIcsEvents = parseICS(icsData);

  const now = new Date();
  const icsEvents = allIcsEvents.filter(e => {
    const eventEnd = e.end || new Date(e.start.getTime() + (e.isAllDay ? 24 * 60 * 60 * 1000 : 60 * 60 * 1000));
    return eventEnd >= now;
  });
  Logger.log(`Filtered to ${icsEvents.length} future events (skipped ${allIcsEvents.length - icsEvents.length} past events).`);

  let progress = JSON.parse(scriptProperties.getProperty(PROGRESS_KEY) || '{}');
  if (!progress || !progress.mode) progress = { mode: 'upsert', index: 0, eventUids: [] };

  const existingEvents = getExistingEvents(calendar);

  const icsEventMap = new Map();
  icsEvents.forEach(e => icsEventMap.set(e.uid, e));

  let changes = 0;

  // === UPSERT (CREATE/UPDATE) EVENTS ===
  if (progress.mode === 'upsert') {
    Logger.log('Upsert phase started (creating/updating events)');
    for (let i = progress.index; i < icsEvents.length; i++) {
      const icsEvent = icsEvents[i];
      progress.eventUids.push(icsEvent.uid);
      const existingEvent = existingEvents.get(icsEvent.uid);

      if (existingEvent) {
        if (hasEventChanged(existingEvent, icsEvent)) {
          updateEvent(existingEvent, icsEvent);
          const processed = processEventTitle(icsEvent.summary);
          Logger.log(`[UPDATED] UID: ${icsEvent.uid} | Title: ${processed.title || '(No title)'} | Location: ${icsEvent.location ? icsEvent.location.replace(/\\/g, '') : ''}`);
          changes++;
        } else {
          Logger.log(`[NO CHANGE] UID: ${icsEvent.uid} | Title: ${icsEvent.summary || '(No title)'}`)
        }
      } else {
        createEvent(calendar, icsEvent);
        const processed = processEventTitle(icsEvent.summary);
        Logger.log(`[CREATED] UID: ${icsEvent.uid} | Title: ${processed.title || '(No title)'} | Location: ${icsEvent.location ? icsEvent.location.replace(/\\/g, '') : ''}`);
        changes++;
      }

      if (changes >= MAX_CHANGES_PER_RUN) {
        progress.index = i + 1;
        scriptProperties.setProperty(PROGRESS_KEY, JSON.stringify(progress));
        Logger.log(`Upserted ${changes} events this run. Progress saved at index ${progress.index}.`);
        Logger.log('--- Sync paused due to quota limit ---');
        return;
      }
      Utilities.sleep(200);
    }
    progress.mode = 'delete';
    progress.index = 0;
    scriptProperties.setProperty(PROGRESS_KEY, JSON.stringify(progress));
    Logger.log('Upsert phase complete, moving to deletion phase.');
    Logger.log('--- Sync paused, will continue with deletions next run ---');
    return;
  }

  // === DELETE FUTURE EVENTS NOT IN ICS ===
  if (progress.mode === 'delete') {
    Logger.log('Delete phase started (removing future events not in ICS)');
    const eventUidsToKeep = new Set(progress.eventUids);
    const allUids = Array.from(existingEvents.keys());
    for (let i = progress.index; i < allUids.length; i++) {
      const uid = allUids[i];
      if (!eventUidsToKeep.has(uid)) {
        const event = existingEvents.get(uid);
        // Only delete future events, leave past events alone
        if (event.getEndTime() >= now) {
          Logger.log(`[REMOVED] UID: ${uid} | Title: ${event.getTitle()} | Location: ${event.getLocation()}`);
          event.deleteEvent();
          changes++;
        }
      }
      if (changes >= MAX_CHANGES_PER_RUN) {
        progress.index = i + 1;
        scriptProperties.setProperty(PROGRESS_KEY, JSON.stringify(progress));
        Logger.log(`Deleted ${changes} events this run. Progress saved at index ${progress.index}.`);
        Logger.log('--- Sync paused due to quota limit ---');
        return;
      }
      Utilities.sleep(400);
    }
    scriptProperties.deleteProperty(PROGRESS_KEY);
    Logger.log('Sync completed successfully!');
    Logger.log('--- Sync finished ---');
  }
}

// === CLEANUP DUPLICATE PAST EVENTS ===
function cleanupDuplicatePastEvents() {
  const calendar = CalendarApp.getCalendarById(CALENDAR_ID);
  if (!calendar) {
    Logger.log('Calendar not found!');
    return;
  }

  const now = new Date();
  // Look back up to 2 years for duplicates
  const pastDate = new Date(now.getTime() - (730 * 24 * 60 * 60 * 1000));
  const events = calendar.getEvents(pastDate, now);

  Logger.log(`Found ${events.length} past events to scan for duplicates.`);

  // Group events by UID
  const uidGroups = new Map();
  events.forEach(event => {
    const uid = event.getTag('ics_uid');
    if (uid) {
      if (!uidGroups.has(uid)) {
        uidGroups.set(uid, []);
      }
      uidGroups.get(uid).push(event);
    }
  });

  let deletedCount = 0;
  let duplicateGroups = 0;

  uidGroups.forEach((eventList, uid) => {
    if (eventList.length <= 1) return;
    duplicateGroups++;

    // Find event with an RSVP (any response other than INVITED / no response)
    let rsvpEvent = null;
    for (const event of eventList) {
      const guests = event.getGuestList();
      const hasResponse = guests.some(
        guest => guest.getGuestStatus() !== CalendarApp.GuestStatus.INVITED
      );
      if (hasResponse) {
        rsvpEvent = event;
        break;
      }
    }

    // Keep the RSVP'd event, or the first one if none were RSVP'd
    const keepEvent = rsvpEvent || eventList[0];
    const keepReason = rsvpEvent ? 'has RSVP' : 'first instance (no RSVPs found)';

    Logger.log(`[DUPLICATES] UID: ${uid} | Title: ${keepEvent.getTitle()} | ${eventList.length} copies | Keeping: ${keepReason}`);

    for (const event of eventList) {
      if (event.getId() !== keepEvent.getId()) {
        event.deleteEvent();
        deletedCount++;
        Utilities.sleep(50);
      }
    }
  });

  Logger.log(`Cleanup complete. Found ${duplicateGroups} duplicate groups, deleted ${deletedCount} events.`);
}

// === ICS FETCHING AND PARSING ===
function fetchICSData(url) {
  try {
    const response = UrlFetchApp.fetch(url, { muteHttpExceptions: true });
    const statusCode = response.getResponseCode();
    if (statusCode !== 200) {
      Logger.log(`Aborting sync: ICS server returned HTTP ${statusCode}.`);
      return null;
    }
    const text = response.getContentText();
    if (!text || !text.includes('BEGIN:VCALENDAR')) {
      Logger.log('Aborting sync: Response does not contain a valid ICS calendar.');
      return null;
    }
    Logger.log('ICS data fetched successfully.');
    return text;
  } catch (error) {
    Logger.log(`Aborting sync: Error fetching ICS data: ${error}`);
    return null;
  }
}


function parseICS(icsData) {
  const events = [];
  const lines = icsData.split(/\r?\n/);
  let currentEvent = null;
  for (let i = 0; i < lines.length; i++) {
    let line = lines[i].trim();
    while (i + 1 < lines.length && (lines[i + 1].startsWith(' ') || lines[i + 1].startsWith('\t'))) {
      i++;
      line += lines[i].substring(1);
    }
    if (line === 'BEGIN:VEVENT') {
      currentEvent = {};
    } else if (line === 'END:VEVENT' && currentEvent) {
      if (currentEvent.uid && currentEvent.start) {
        events.push(currentEvent);
      }
      currentEvent = null;
    } else if (currentEvent) {
      const colonIndex = line.indexOf(':');
      const semicolonIndex = line.indexOf(';');
      let key, value, params = {};
      if (semicolonIndex !== -1 && (colonIndex === -1 || semicolonIndex < colonIndex)) {
        key = line.substring(0, semicolonIndex);
        const paramString = line.substring(semicolonIndex + 1, colonIndex);
        value = line.substring(colonIndex + 1);
        paramString.split(';').forEach(param => {
          const [pKey, pValue] = param.split('=');
          if (pKey && pValue) params[pKey] = pValue;
        });
      } else if (colonIndex !== -1) {
        key = line.substring(0, colonIndex);
        value = line.substring(colonIndex + 1);
      } else {
        continue;
      }
      switch (key) {
        case 'UID':
          currentEvent.uid = value;
          break;
        case 'SUMMARY':
          currentEvent.summary = value;
          break;
        case 'DESCRIPTION':
          currentEvent.description = value.replace(/\\;/g, '\n').replace(/\\n/g, '\n').replace(/\\,/g, ',');
          break;
        case 'LOCATION':
          currentEvent.location = value ? value.replace(/\\/g, '') : '';
          break;
        case 'DTSTART':
          currentEvent.start = parseICSDate(value, params);
          currentEvent.isAllDay = !value.includes('T');
          break;
        case 'DTEND':
          currentEvent.end = parseICSDate(value, params);
          break;
        case 'LAST-MODIFIED':
        case 'DTSTAMP':
          if (!currentEvent.lastModified) {
            currentEvent.lastModified = parseICSDate(value, params);
          }
          break;
      }
    }
  }
  Logger.log(`Parsed ${events.length} events from ICS feed.`);
  return events;
}

function parseICSDate(dateString, params) {
  dateString = dateString.replace(/TZID=[^:]+:/, '');
  if (dateString.length === 8) {
    const year = parseInt(dateString.substring(0, 4));
    const month = parseInt(dateString.substring(4, 6)) - 1;
    const day = parseInt(dateString.substring(6, 8));
    return new Date(year, month, day);
  } else {
    const year = parseInt(dateString.substring(0, 4));
    const month = parseInt(dateString.substring(4, 6)) - 1;
    const day = parseInt(dateString.substring(6, 8));
    const hour = parseInt(dateString.substring(9, 11));
    const minute = parseInt(dateString.substring(11, 13));
    const second = parseInt(dateString.substring(13, 15));
    if (dateString.endsWith('Z')) {
      return new Date(Date.UTC(year, month, day, hour, minute, second));
    } else {
      return new Date(year, month, day, hour, minute, second);
    }
  }
}

// === EXISTING EVENTS MAP (UID -> Event) ===
function getExistingEvents(calendar) {
  const eventMap = new Map();
  const now = new Date();
  const futureDate = new Date(now.getTime() + (365 * 24 * 60 * 60 * 1000));
  // Small buffer into the past to catch currently-running events
  const pastDate = new Date(now.getTime() - (24 * 60 * 60 * 1000));
  const events = calendar.getEvents(pastDate, futureDate);
  events.forEach(event => {
    const uid = event.getTag('ics_uid');
    if (uid) eventMap.set(uid, event);
  });
  Logger.log(`Loaded ${eventMap.size} existing events from calendar.`);
  return eventMap;
}

// === DESCRIPTION BUILDER WITH NAVIGATUM LINK ===
function buildDescription(icsEvent) {
  const { extraDescription } = processEventTitle(icsEvent.summary);
  let desc = '';
  let roomCode = null;
  if (icsEvent.location) {
    const match = icsEvent.location.match(/\(([^\]]+)\)\s*$/);
    if (match) {
      roomCode = match[1].trim();
    }
  }
  if (roomCode) {
    desc += 'NavigaTUM: https://nav.tum.de/en/room/' + encodeURIComponent(roomCode) + '\n\n';
  }
  if (extraDescription) {
    desc += extraDescription + '\n\n';
  }
  desc += icsEvent.description || '';
  return desc;
}

// === EVENT CREATION/UPDATE LOGIC ===
function createEvent(calendar, icsEvent) {
  let event;
  const { title } = processEventTitle(icsEvent.summary);
  const description = buildDescription(icsEvent);
  if (icsEvent.isAllDay) {
    const endDate = icsEvent.end || new Date(icsEvent.start.getTime() + 24 * 60 * 60 * 1000);
    event = calendar.createAllDayEvent(
      title,
      icsEvent.start,
      endDate,
      {
        description: description,
        location: icsEvent.location ? icsEvent.location.replace(/\\/g, '') : '',
        guests: INVITE_CALENDAR_ID,
        sendInvites: true
      }
    );
  } else {
    const endDate = icsEvent.end || new Date(icsEvent.start.getTime() + 60 * 60 * 1000);
    event = calendar.createEvent(
      title,
      icsEvent.start,
      endDate,
      {
        description: description,
        location: icsEvent.location ? icsEvent.location.replace(/\\/g, '') : '',
        guests: INVITE_CALENDAR_ID,
        sendInvites: true
      }
    );
  }
  event.setTag('ics_uid', icsEvent.uid);
  return event;
}

function updateEvent(event, icsEvent) {
  const { title } = processEventTitle(icsEvent.summary);
  const description = buildDescription(icsEvent);
  event.setTitle(title);
  event.setDescription(description);
  event.setLocation(icsEvent.location ? icsEvent.location.replace(/\\/g, '') : '');
  const endDate = icsEvent.end || new Date(icsEvent.start.getTime() + 60 * 60 * 1000);
  if (icsEvent.isAllDay) {
    event.setAllDayDate(icsEvent.start);
  } else {
    event.setTime(icsEvent.start, endDate);
  }
  const guests = event.getGuestList().map(g => g.getEmail());
  if (!guests.includes(INVITE_CALENDAR_ID)) {
    event.addGuest(INVITE_CALENDAR_ID);
  }
}

function hasEventChanged(event, icsEvent) {
  const { title } = processEventTitle(icsEvent.summary);
  const description = event.getDescription();
  const location = event.getLocation();
  const startTime = event.getStartTime().getTime();
  const icsEndDate = icsEvent.end || new Date(icsEvent.start.getTime() + 60 * 60 * 1000);
  const endTime = event.getEndTime().getTime();
  const newDescription = buildDescription(icsEvent);
  return title !== event.getTitle() ||
         description !== newDescription ||
         location !== (icsEvent.location ? icsEvent.location.replace(/\\/g, '') : '') ||
         startTime !== icsEvent.start.getTime() ||
         endTime !== icsEndDate.getTime();
}

// === OPTIONAL: TRIGGER SETUP ===
function setupTrigger() {
  const triggers = ScriptApp.getProjectTriggers();
  triggers.forEach(trigger => {
    if (trigger.getHandlerFunction() === 'syncICSToGoogleCalendar') {
      ScriptApp.deleteTrigger(trigger);
    }
  });
  ScriptApp.newTrigger('syncICSToGoogleCalendar')
    .timeBased()
    .everyHours(1)
    .create();
  Logger.log('Trigger set up to run every hour');
}