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<?php
/**
* Timezone Component
* @package qCal
* @copyright Luke Visinoni (luke.visinoni@gmail.com)
* @author Luke Visinoni (luke.visinoni@gmail.com)
* @license GNU Lesser General Public License
*
* RFC 2445 Definition
*
* Component Name: VTIMEZONE
*
* Purpose: Provide a grouping of component properties that defines a
* time zone.
*
* Formal Definition: A "VTIMEZONE" calendar component is defined by the
* following notation:
*
* timezonec = "BEGIN" ":" "VTIMEZONE" CRLF
*
* 2*(
*
* ; 'tzid' is required, but MUST NOT occur more
* ; than once
*
* tzid /
*
* ; 'last-mod' and 'tzurl' are optional,
* but MUST NOT occur more than once
*
* last-mod / tzurl /
*
* ; one of 'standardc' or 'daylightc' MUST occur
* ..; and each MAY occur more than once.
*
* standardc / daylightc /
*
* ; the following is optional,
* ; and MAY occur more than once
*
* x-prop
*
* )
*
* "END" ":" "VTIMEZONE" CRLF
*
* standardc = "BEGIN" ":" "STANDARD" CRLF
*
* tzprop
*
* "END" ":" "STANDARD" CRLF
*
* daylightc = "BEGIN" ":" "DAYLIGHT" CRLF
*
* tzprop
*
* "END" ":" "DAYLIGHT" CRLF
*
* tzprop = 3*(
*
* ; the following are each REQUIRED,
* ; but MUST NOT occur more than once
*
* dtstart / tzoffsetto / tzoffsetfrom /
*
* ; the following are optional,
* ; and MAY occur more than once
*
* comment / rdate / rrule / tzname / x-prop
*
* )
*
* Description: A time zone is unambiguously defined by the set of time
* measurement rules determined by the governing body for a given
* geographic area. These rules describe at a minimum the base offset
* from UTC for the time zone, often referred to as the Standard Time
* offset. Many locations adjust their Standard Time forward or backward
* by one hour, in order to accommodate seasonal changes in number of
* daylight hours, often referred to as Daylight Saving Time. Some
* locations adjust their time by a fraction of an hour. Standard Time
* is also known as Winter Time. Daylight Saving Time is also known as
* Advanced Time, Summer Time, or Legal Time in certain countries. The
* following table shows the changes in time zone rules in effect for
* New York City starting from 1967. Each line represents a description
* or rule for a particular observance.
*
* Effective Observance Rule
*
* Date (Date/Time) Offset Abbreviation
*
* 1967-* last Sun in Oct, 02:00 -0500 EST
*
* 1967-1973 last Sun in Apr, 02:00 -0400 EDT
*
* 1974-1974 Jan 6, 02:00 -0400 EDT
*
* 1975-1975 Feb 23, 02:00 -0400 EDT
*
* 1976-1986 last Sun in Apr, 02:00 -0400 EDT
*
* 1987-* first Sun in Apr, 02:00 -0400 EDT
*
* Note: The specification of a global time zone registry is not
* addressed by this document and is left for future study.
* However, implementers may find the Olson time zone database [TZ]
* a useful reference. It is an informal, public-domain collection
* of time zone information, which is currently being maintained by
* volunteer Internet participants, and is used in several
* operating systems. This database contains current and historical
* time zone information for a wide variety of locations around the
* globe; it provides a time zone identifier for every unique time
* zone rule set in actual use since 1970, with historical data
* going back to the introduction of standard time.
*
* Interoperability between two calendaring and scheduling applications,
* especially for recurring events, to-dos or journal entries, is
* dependent on the ability to capture and convey date and time
* information in an unambiguous format. The specification of current
* time zone information is integral to this behavior.
*
* If present, the "VTIMEZONE" calendar component defines the set of
* Standard Time and Daylight Saving Time observances (or rules) for a
* particular time zone for a given interval of time. The "VTIMEZONE"
* calendar component cannot be nested within other calendar components.
* Multiple "VTIMEZONE" calendar components can exist in an iCalendar
* object. In this situation, each "VTIMEZONE" MUST represent a unique
* time zone definition. This is necessary for some classes of events,
* such as airline flights, that start in one time zone and end in
* another.
*
* The "VTIMEZONE" calendar component MUST be present if the iCalendar
* object contains an RRULE that generates dates on both sides of a time
* zone shift (e.g. both in Standard Time and Daylight Saving Time)
* unless the iCalendar object intends to convey a floating time (See
* the section "4.1.10.11 Time" for proper interpretation of floating
* time). It can be present if the iCalendar object does not contain
* such a RRULE. In addition, if a RRULE is present, there MUST be valid
* time zone information for all recurrence instances.
*
* The "VTIMEZONE" calendar component MUST include the "TZID" property
* and at least one definition of a standard or daylight component. The
* standard or daylight component MUST include the "DTSTART",
* "TZOFFSETFROM" and "TZOFFSETTO" properties.
*
* An individual "VTIMEZONE" calendar component MUST be specified for
* each unique "TZID" parameter value specified in the iCalendar object.
*
* Each "VTIMEZONE" calendar component consists of a collection of one
* or more sub-components that describe the rule for a particular
* observance (either a Standard Time or a Daylight Saving Time
* observance). The "STANDARD" sub-component consists of a collection of
* properties that describe Standard Time. The "DAYLIGHT" sub-component
* consists of a collection of properties that describe Daylight Saving
* Time. In general this collection of properties consists of:
*
* - the first onset date-time for the observance
*
* - the last onset date-time for the observance, if a last onset
* is known.
*
* - the offset to be applied for the observance
*
* - a rule that describes the day and time when the observance
* takes effect
*
* - an optional name for the observance
*
* For a given time zone, there may be multiple unique definitions of
* the observances over a period of time. Each observance is described
* using either a "STANDARD" or "DAYLIGHT" sub-component. The collection
* of these sub-components is used to describe the time zone for a given
* period of time. The offset to apply at any given time is found by
* locating the observance that has the last onset date and time before
* the time in question, and using the offset value from that
* observance.
*
* The top-level properties in a "VTIMEZONE" calendar component are:
*
* The mandatory "TZID" property is a text value that uniquely
* identifies the VTIMZONE calendar component within the scope of an
* iCalendar object.
*
* The optional "LAST-MODIFIED" property is a UTC value that specifies
* the date and time that this time zone definition was last updated.
*
* The optional "TZURL" property is url value that points to a published
* VTIMEZONE definition. TZURL SHOULD refer to a resource that is
* accessible by anyone who might need to interpret the object. This
* SHOULD NOT normally be a file: URL or other URL that is not widely-
* accessible.
*
* The collection of properties that are used to define the STANDARD and
* DAYLIGHT sub-components include:
*
* The mandatory "DTSTART" property gives the effective onset date and
* local time for the time zone sub-component definition. "DTSTART" in
* this usage MUST be specified as a local DATE-TIME value.
*
* The mandatory "TZOFFSETFROM" property gives the UTC offset which is
* in use when the onset of this time zone observance begins.
* "TZOFFSETFROM" is combined with "DTSTART" to define the effective
* onset for the time zone sub-component definition. For example, the
* following represents the time at which the observance of Standard
* Time took effect in Fall 1967 for New York City:
*
* DTSTART:19671029T020000
*
* TZOFFSETFROM:-0400
*
* The mandatory "TZOFFSETTO " property gives the UTC offset for the
* time zone sub-component (Standard Time or Daylight Saving Time) when
* this observance is in use.
*
* The optional "TZNAME" property is the customary name for the time
* zone. It may be specified multiple times, to allow for specifying
* multiple language variants of the time zone names. This could be used
* for displaying dates.
*
* If specified, the onset for the observance defined by the time zone
* sub-component is defined by either the "RRULE" or "RDATE" property.
* If neither is specified, only one sub-component can be specified in
* the "VTIMEZONE" calendar component and it is assumed that the single
* observance specified is always in effect.
*
* The "RRULE" property defines the recurrence rule for the onset of the
* observance defined by this time zone sub-component. Some specific
* requirements for the usage of RRULE for this purpose include:
*
* - If observance is known to have an effective end date, the
* "UNTIL" recurrence rule parameter MUST be used to specify the
* last valid onset of this observance (i.e., the UNTIL date-time
* will be equal to the last instance generated by the recurrence
* pattern). It MUST be specified in UTC time.
*
* - The "DTSTART" and the "TZOFFSETTO" properties MUST be used
* when generating the onset date-time values (instances) from the
* RRULE.
*
* Alternatively, the "RDATE" property can be used to define the onset
* of the observance by giving the individual onset date and times.
* "RDATE" in this usage MUST be specified as a local DATE-TIME value in
* UTC time.
*
* The optional "COMMENT" property is also allowed for descriptive
* explanatory text.
*
* Example: The following are examples of the "VTIMEZONE" calendar
* component:
*
* This is an example showing time zone information for the Eastern
* United States using "RDATE" property. Note that this is only suitable
* for a recurring event that starts on or later than April 6, 1997 at
* 03:00:00 EDT (i.e., the earliest effective transition date and time)
* and ends no later than April 7, 1998 02:00:00 EST (i.e., latest valid
* date and time for EST in this scenario). For example, this can be
* used for a recurring event that occurs every Friday, 8am-9:00 AM,
* starting June 1, 1997, ending December 31, 1997.
*
* BEGIN:VTIMEZONE
* TZID:US-Eastern
* LAST-MODIFIED:19870101T000000Z
* BEGIN:STANDARD
* DTSTART:19971026T020000
* RDATE:19971026T020000
* TZOFFSETFROM:-0400
* TZOFFSETTO:-0500
* TZNAME:EST
* END:STANDARD
* BEGIN:DAYLIGHT
* DTSTART:19971026T020000
* RDATE:19970406T020000
* TZOFFSETFROM:-0500
* TZOFFSETTO:-0400
* TZNAME:EDT
* END:DAYLIGHT
* END:VTIMEZONE
*
* This is a simple example showing the current time zone rules for the
* Eastern United States using a RRULE recurrence pattern. Note that
* there is no effective end date to either of the Standard Time or
* Daylight Time rules. This information would be valid for a recurring
* event starting today and continuing indefinitely.
*
* BEGIN:VTIMEZONE
* TZID:US-Eastern
* LAST-MODIFIED:19870101T000000Z
* TZURL:http://zones.stds_r_us.net/tz/US-Eastern
* BEGIN:STANDARD
* DTSTART:19671029T020000
* RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
* TZOFFSETFROM:-0400
* TZOFFSETTO:-0500
* TZNAME:EST
* END:STANDARD
* BEGIN:DAYLIGHT
* DTSTART:19870405T020000
* RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
* TZOFFSETFROM:-0500
* TZOFFSETTO:-0400
* TZNAME:EDT
* END:DAYLIGHT
* END:VTIMEZONE
*
* This is an example showing a fictitious set of rules for the Eastern
* United States, where the Daylight Time rule has an effective end date
* (i.e., after that date, Daylight Time is no longer observed).
*
* BEGIN:VTIMEZONE
* TZID:US--Fictitious-Eastern
* LAST-MODIFIED:19870101T000000Z
* BEGIN:STANDARD
* DTSTART:19671029T020000
* RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
* TZOFFSETFROM:-0400
* TZOFFSETTO:-0500
* TZNAME:EST
* END:STANDARD
* BEGIN:DAYLIGHT
* DTSTART:19870405T020000
* RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
* TZOFFSETFROM:-0500
* TZOFFSETTO:-0400
* TZNAME:EDT
* END:DAYLIGHT
* END:VTIMEZONE
*
* This is an example showing a fictitious set of rules for the Eastern
* United States, where the first Daylight Time rule has an effective
* end date. There is a second Daylight Time rule that picks up where
* the other left off.
*
* BEGIN:VTIMEZONE
* TZID:US--Fictitious-Eastern
* LAST-MODIFIED:19870101T000000Z
* BEGIN:STANDARD
* DTSTART:19671029T020000
* RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
* TZOFFSETFROM:-0400
* TZOFFSETTO:-0500
* TZNAME:EST
* END:STANDARD
* BEGIN:DAYLIGHT
* DTSTART:19870405T020000
* RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
* TZOFFSETFROM:-0500
* TZOFFSETTO:-0400
* TZNAME:EDT
* END:DAYLIGHT
* BEGIN:DAYLIGHT
* DTSTART:19990424T020000
* RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=4
* TZOFFSETFROM:-0500
* TZOFFSETTO:-0400
* TZNAME:EDT
* END:DAYLIGHT
* END:VTIMEZONE
*/
class qCal_Component_Vtimezone extends qCal_Component {
protected $name = "VTIMEZONE";
protected $allowedComponents = array('VCALENDAR');
protected $requiredProperties = array('TZID');
/**
* Make sure that all of the rules specified above are followed
*/
protected function doValidation() {
$children = $this->getChildren();
if (!array_key_exists('DAYLIGHT', $children) && !array_key_exists('STANDARD', $children)) {
throw new qCal_Exception_MissingComponent('Either a STANDARD or DAYLIGHT component is required within a VTIMEZONE component');
}
}
}