Support VTIMEZONE objects for daylight savings
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Reported by: [bburg](https://www.drupal.org/user/1867900)
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<p>The iCalendar spec provides the ability to define multiple timezones in a feed <a href="https://icalendar.org/iCalendar-RFC-5545/3-6-5-time-zone-component.html">https://icalendar.org/iCalendar-RFC-5545/3-6-5-time-zone-component.html</a>. This is important if you are using recurring events that span across daylight savings. <a href="https://stackoverflow.com/a/42941087/7948774">Here is a good write up on the importance of VTIMEZONE objects in iCalendars</a>. Also, recent observations seem to indicate that ical events imported into Outlook desktop client calendars, without VTIMEZONE objects, may not respect daylight savings time shifts, and end up displaying the incorrect time for events.</p>
<p>Below is an example of a timezone definition added to a eluceo/ical calendar object, It's basically adapted from the <a href="https://hotexamples.com/examples/-/Eluceo%255CiCal%255CComponent%255CCalendar/setTimezone/php-eluceo%255cical%255ccomponent%255ccalendar-settimezone-method-examples.html#0x29ada354f4def1ba8874bff912eeea4b984f241eccf12b689db3466d1643c8bf-24,,54,">documentaation</a> to use the current America/New_York timezone. It's rather verbose, and a version of this would be needed for every daylight savings/timezone in use. </p>
<div class="codeblock">
<pre><span style="color: #000000"><span style="color: #0000BB"><?php<br> $tz </span><span style="color: #007700">= </span><span style="color: #DD0000">'America/New_York'</span><span style="color: #007700">;<br> </span><span style="color: #0000BB">$dtz </span><span style="color: #007700">= new \</span><span style="color: #0000BB">DateTimeZone</span><span style="color: #007700">(</span><span style="color: #0000BB">$tz</span><span style="color: #007700">);<br><br> </span><span style="color: #FF8000">// 2. Create timezone rule object for Daylight Standard Time<br> </span><span style="color: #0000BB">$vTimezoneRuleStd </span><span style="color: #007700">= new \</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Component</span><span style="color: #007700">\</span><span style="color: #0000BB">TimezoneRule</span><span style="color: #007700">(\</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Component</span><span style="color: #007700">\</span><span style="color: #0000BB">TimezoneRule</span><span style="color: #007700">::</span><span style="color: #0000BB">TYPE_STANDARD</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleStd</span><span style="color: #007700">-></span><span style="color: #0000BB">setTzName</span><span style="color: #007700">(</span><span style="color: #DD0000">'EST'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleStd</span><span style="color: #007700">-></span><span style="color: #0000BB">setDtStart</span><span style="color: #007700">(new \</span><span style="color: #0000BB">DateTime</span><span style="color: #007700">(</span><span style="color: #DD0000">'2007-11-04 02:00:00'</span><span style="color: #007700">, </span><span style="color: #0000BB">$dtz</span><span style="color: #007700">));<br> </span><span style="color: #0000BB">$vTimezoneRuleStd</span><span style="color: #007700">-></span><span style="color: #0000BB">setTzOffsetFrom</span><span style="color: #007700">(</span><span style="color: #DD0000">'-0400'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleStd</span><span style="color: #007700">-></span><span style="color: #0000BB">setTzOffsetTo</span><span style="color: #007700">(</span><span style="color: #DD0000">'-0500'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$stdRecurrenceRule </span><span style="color: #007700">= new \</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Property</span><span style="color: #007700">\</span><span style="color: #0000BB">Event</span><span style="color: #007700">\</span><span style="color: #0000BB">RecurrenceRule</span><span style="color: #007700">();<br> </span><span style="color: #0000BB">$stdRecurrenceRule</span><span style="color: #007700">-></span><span style="color: #0000BB">setFreq</span><span style="color: #007700">(\</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Property</span><span style="color: #007700">\</span><span style="color: #0000BB">Event</span><span style="color: #007700">\</span><span style="color: #0000BB">RecurrenceRule</span><span style="color: #007700">::</span><span style="color: #0000BB">FREQ_YEARLY</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$stdRecurrenceRule</span><span style="color: #007700">-></span><span style="color: #0000BB">setByMonth</span><span style="color: #007700">(</span><span style="color: #0000BB">11</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$stdRecurrenceRule</span><span style="color: #007700">-></span><span style="color: #0000BB">setByDay</span><span style="color: #007700">(</span><span style="color: #DD0000">'1SU'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleStd</span><span style="color: #007700">-></span><span style="color: #0000BB">setRecurrenceRule</span><span style="color: #007700">(</span><span style="color: #0000BB">$stdRecurrenceRule</span><span style="color: #007700">);<br><br> </span><span style="color: #FF8000">// 3. Create timezone rule object for Daylight Time<br> </span><span style="color: #0000BB">$vTimezoneRuleDst </span><span style="color: #007700">= new \</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Component</span><span style="color: #007700">\</span><span style="color: #0000BB">TimezoneRule</span><span style="color: #007700">(\</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Component</span><span style="color: #007700">\</span><span style="color: #0000BB">TimezoneRule</span><span style="color: #007700">::</span><span style="color: #0000BB">TYPE_DAYLIGHT</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleDst</span><span style="color: #007700">-></span><span style="color: #0000BB">setTzName</span><span style="color: #007700">(</span><span style="color: #DD0000">'EDT'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleDst</span><span style="color: #007700">-></span><span style="color: #0000BB">setDtStart</span><span style="color: #007700">(new \</span><span style="color: #0000BB">DateTime</span><span style="color: #007700">(</span><span style="color: #DD0000">'2007-03-11 02:00:00'</span><span style="color: #007700">, </span><span style="color: #0000BB">$dtz</span><span style="color: #007700">));<br> </span><span style="color: #0000BB">$vTimezoneRuleDst</span><span style="color: #007700">-></span><span style="color: #0000BB">setTzOffsetFrom</span><span style="color: #007700">(</span><span style="color: #DD0000">'-0500'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleDst</span><span style="color: #007700">-></span><span style="color: #0000BB">setTzOffsetTo</span><span style="color: #007700">(</span><span style="color: #DD0000">'-0400'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$dstRecurrenceRule </span><span style="color: #007700">= new \</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Property</span><span style="color: #007700">\</span><span style="color: #0000BB">Event</span><span style="color: #007700">\</span><span style="color: #0000BB">RecurrenceRule</span><span style="color: #007700">();<br> </span><span style="color: #0000BB">$dstRecurrenceRule</span><span style="color: #007700">-></span><span style="color: #0000BB">setFreq</span><span style="color: #007700">(\</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Property</span><span style="color: #007700">\</span><span style="color: #0000BB">Event</span><span style="color: #007700">\</span><span style="color: #0000BB">RecurrenceRule</span><span style="color: #007700">::</span><span style="color: #0000BB">FREQ_YEARLY</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$dstRecurrenceRule</span><span style="color: #007700">-></span><span style="color: #0000BB">setByMonth</span><span style="color: #007700">(</span><span style="color: #0000BB">3</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$dstRecurrenceRule</span><span style="color: #007700">-></span><span style="color: #0000BB">setByDay</span><span style="color: #007700">(</span><span style="color: #DD0000">'2SU'</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezoneRuleDst</span><span style="color: #007700">-></span><span style="color: #0000BB">setRecurrenceRule</span><span style="color: #007700">(</span><span style="color: #0000BB">$dstRecurrenceRule</span><span style="color: #007700">);<br> </span><span style="color: #FF8000">// 4. Create timezone definition and add rules<br> </span><span style="color: #0000BB">$vTimezone </span><span style="color: #007700">= new \</span><span style="color: #0000BB">Eluceo</span><span style="color: #007700">\</span><span style="color: #0000BB">iCal</span><span style="color: #007700">\</span><span style="color: #0000BB">Component</span><span style="color: #007700">\</span><span style="color: #0000BB">Timezone</span><span style="color: #007700">(</span><span style="color: #0000BB">$tz</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezone</span><span style="color: #007700">-></span><span style="color: #0000BB">addComponent</span><span style="color: #007700">(</span><span style="color: #0000BB">$vTimezoneRuleStd</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$vTimezone</span><span style="color: #007700">-></span><span style="color: #0000BB">addComponent</span><span style="color: #007700">(</span><span style="color: #0000BB">$vTimezoneRuleDst</span><span style="color: #007700">);<br> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">calendar</span><span style="color: #007700">-></span><span style="color: #0000BB">setTimezone</span><span style="color: #007700">(</span><span style="color: #0000BB">$vTimezone</span><span style="color: #007700">);<br></span><span style="color: #0000BB">?></span></span></pre></div>
<p>Challenge for this module is finding a way to generate these entries in way that works for any provided time. We can't simply hard-code these values like the example does. </p>
<p>Using all times in UTC can sort of get around this problem. However, that seems to through off the logic for "All day" events. Making events appear to start at discrete times rather than using the "All day" feature, showing the event as a band across the top, provided by most calendar apps.</p>
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