etesync-android/app/src/main/java/at/bitfire/davdroid/DateUtils.java

/*
 * Copyright © 2013 – 2015 Ricki Hirner (bitfire web engineering).
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the GNU Public License v3.0
 * which accompanies this distribution, and is available at
 * http://www.gnu.org/licenses/gpl.html
 */

package at.bitfire.davdroid;

import android.util.Log;

import net.fortuna.ical4j.model.Date;
import net.fortuna.ical4j.model.DateList;
import net.fortuna.ical4j.model.DateTime;
import net.fortuna.ical4j.model.TimeZone;
import net.fortuna.ical4j.model.TimeZoneRegistry;
import net.fortuna.ical4j.model.TimeZoneRegistryFactory;
import net.fortuna.ical4j.model.parameter.Value;
import net.fortuna.ical4j.model.property.DateListProperty;

import org.apache.commons.lang3.StringUtils;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.LinkedList;
import java.util.List;
import java.util.SimpleTimeZone;

public class DateUtils {
    private final static String TAG = "davdroid.DateUtils";

	public static final TimeZoneRegistry tzRegistry = TimeZoneRegistryFactory.getInstance().createRegistry();

	static {
		// disable automatic time-zone updates (causes unwanted network traffic)
		System.setProperty("net.fortuna.ical4j.timezone.update.enabled", "false");
	}


	// time zones

    public static String findAndroidTimezoneID(String tz) {
        String deviceTZ = null;
        String availableTZs[] = SimpleTimeZone.getAvailableIDs();

        // first, try to find an exact match (case insensitive)
        for (String availableTZ : availableTZs)
            if (availableTZ.equalsIgnoreCase(tz)) {
                deviceTZ = availableTZ;
                break;
            }

        // if that doesn't work, try to find something else that matches
        if (deviceTZ == null) {
            Log.w(TAG, "Coulnd't find time zone with matching identifiers, trying to guess");
            for (String availableTZ : availableTZs)
                if (StringUtils.indexOfIgnoreCase(tz, availableTZ) != -1) {
                    deviceTZ = availableTZ;
                    break;
                }
        }

        // if that doesn't work, use UTC as fallback
        if (deviceTZ == null) {
	        final String defaultTZ = TimeZone.getDefault().getID();
            Log.e(TAG, "Couldn't identify time zone, using system default (" + defaultTZ + ") as fallback");
            deviceTZ = defaultTZ;
        }

        return deviceTZ;
    }


	// recurrence sets

	/**
	 * Concatenates, if necessary, multiple RDATE/EXDATE lists and converts them to
	 * a formatted string which Android calendar provider can process.
	 * Android expects this format: "[TZID;]date1,date2,date3" where date is "yyyymmddThhmmss" (when
	 * TZID is given) or "yyyymmddThhmmssZ". We don't use the TZID format here because then we're limited
	 * to one time-zone, while an iCalendar may contain multiple EXDATE/RDATE lines with different time zones.
	 * @param dates		one more more lists of RDATE or EXDATE
	 * @param allDay    indicates whether the event is an all-day event or not
	 * @return			formatted string for Android calendar provider:
	 *                  - in case of all-day events, all dates/times are returned as yyyymmddT000000Z
	 *                  - in case of timed events, all dates/times are returned as UTC time: yyyymmddThhmmssZ
	 */
	public static String recurrenceSetsToAndroidString(List<? extends DateListProperty> dates, boolean allDay) throws ParseException {
		List<String> strDates = new LinkedList<>();

		/*        rdate/exdate: DATE                                DATE_TIME
		    all-day             store as ...T000000Z                cut off time and store as ...T000000Z
		    event with time     (ignored)                           store as ...ThhmmssZ
		*/
		final DateFormat dateFormatUtcMidnight = new SimpleDateFormat("yyyyMMdd'T'000000'Z'");

		for (DateListProperty dateListProp : dates) {
			final Value type = dateListProp.getDates().getType();

			if (Value.DATE_TIME.equals(type)) {         // DATE-TIME values will be stored in UTC format for Android
				if (allDay) {
					DateList dateList = dateListProp.getDates();
					for (Date date : dateList)
						strDates.add(dateFormatUtcMidnight.format(date));
				} else {
					dateListProp.setUtc(true);
					strDates.add(dateListProp.getValue());
				}

			} else if (Value.DATE.equals(type))       // DATE values have to be converted to DATE-TIME <date>T000000Z for Android
				for (Date date : dateListProp.getDates())
					strDates.add(dateFormatUtcMidnight.format(date));
		}
		return StringUtils.join(strDates, ",");
	}

	/**
	 * Takes a formatted string as provided by the Android calendar provider and returns a DateListProperty
	 * constructed from these values.
	 * @param dbStr     formatted string from Android calendar provider (RDATE/EXDATE field)
	 *                  expected format: "[TZID;]date1,date2,date3" where date is "yyyymmddThhmmss[Z]"
	 * @param type      subclass of DateListProperty, e.g. RDate or ExDate
	 * @param allDay    true: list will contain DATE values; false: list will contain DATE_TIME values
	 * @return          instance of "type" containing the parsed dates/times from the string
	 */
	public static DateListProperty androidStringToRecurrenceSet(String dbStr, Class<? extends DateListProperty> type, boolean allDay) throws ParseException {
		// 1. split string into time zone and actual dates
		TimeZone timeZone;
		String datesStr;
		final int limiter = dbStr.indexOf(';');
		if (limiter != -1) {    // TZID given
			timeZone = DateUtils.tzRegistry.getTimeZone(dbStr.substring(0, limiter));
			datesStr = dbStr.substring(limiter + 1);
		} else {
			timeZone = null;
			datesStr = dbStr;
		}

		// 2. process date string and generate list of DATEs or DATE-TIMEs
		DateList dateList;
		if (allDay) {
			dateList = new DateList(Value.DATE);
			for (String s: StringUtils.split(datesStr, ','))
				dateList.add(new Date(new DateTime(s)));
		} else {
			dateList = new DateList(datesStr, Value.DATE_TIME, timeZone);
			if (timeZone == null)
				dateList.setUtc(true);
		}

		// 3. generate requested DateListProperty (RDate/ExDate) from list of DATEs or DATE-TIMEs
		DateListProperty list;
		try {
			list = (DateListProperty)type.getDeclaredConstructor(new Class[] { DateList.class } ).newInstance(dateList);
			if (dateList.getTimeZone() != null)
				list.setTimeZone(dateList.getTimeZone());
		} catch (Exception e) {
			throw new ParseException("Couldn't create date/time list by reflection", -1);
		}

		return list;
	}

}