\section{Introduction}

The Asterisk Calendaring API aims to be a generic interface for integrating
Asterisk with various calendaring technologies. The goal is to be able to
support reading and writing of calendar events as well as allowing notification
of pending events through the Asterisk dialplan.

There are three calendaring modules that ship with Asterisk that provide support
for iCalendar, CalDAV, and Microsoft Exchange Server calendars. All three
modules support event notification. Both CalDAV and Exchange support reading
and writing calendars, while iCalendar is a read-only format.

\section{Configuring Asterisk Calendaring}

All asterisk calendaring modules are configured through calender.conf. Each
calendar module can define its own set of required parameters in addition to the
parameters available to all calendar types. An effort has been made to keep all
options the same in all calendaring modules, but some options will diverge over
time as features are added to each module.

An example calendar.conf might look like:
\begin{astlisting}
\begin{verbatim}
[calendar_joe]
type = ical
url = https://example.com/home/jdoe/Calendar
user = jdoe
secret = mysecret
refresh = 15
timeframe = 600
autoreminder = 10
channel = SIP/joe
context = calendar_event_notify
extension = s
waittime = 30
\end{verbatim}
\end{astlisting}

\subsection{Module-independent settings}

The settings related to calendar event notification are handled by the core
calendaring API. These settings are:
\begin{description}
\item[autoreminder] This allows the overriding of any alarms that may or may not
be set for a calendar event. It is specified in minutes.
\item[refresh] How often to refresh the calendar data; specified in minutes.
\item[timeframe] How far into the future each calendar refresh should look. This
is the amount of data that will be visible to queries from the dialplan. This
setting should always be greater than or equal to the refresh setting or events
may be missed. It is specified in minutes.
\item[channel] The channel that should be used for making the notification
attempt.
\item[waittime] How long to wait, in seconds, for the channel to answer a notification
attempt.
\end{description}

There are two ways to specify how to handle a notification. One option is
providing a context and extension, while the other is providing an application
and the arguments to that application. One (and only one) of these options
should be provided.

\begin{description}
\item[context] The context of the extension to connect to the notification
channel
\item[extension] The extension to connect to the notification. Note that the
priority will always be 1.
\end{description}

or

\begin{description}
\item[app] The dialplan application to execute upon the answer of a notification
\item[appdata] The data to pass to the notification dialplan application
\end{description}

\subsection{Module-dependent settings}

Connection-related options are specific to each module. Currently, all modules
take a url, user, and secret for configuration and no other module-specific
settings have been implemented. At this time, no support for HTTP redirects has
been implemented, so it is important to specify the correct URL--paying attention
to any trailing slashes that may be necessary.

\section{Dialplan functions}
\subsection{Read functions}

The simplest dialplan query is the CALENDAR\_BUSY query. It takes a single
option, the name of the calendar defined, and returns "1" for busy (including
tentatively busy) and "0" for not busy.

For more information about a calendar event, a combination of CALENDAR\_QUERY
and CALENDAR\_QUERY\_RESULT is used.  CALENDAR\_QUERY takes the calendar name
and optionally a start and end time in "unix time" (seconds from unix epoch). It
returns an id that can be passed to CALENDAR\_QUERY\_RESULT along with a field
name to return the data in that field. If multiple events are returned in the
query, the number of the event in the list can be specified as well. The available
fields to return are:
\begin{description}
\item[summary] A short summary of the event
\item[description] The full description of the event
\item[organizer] Who organized the event
\item[location] Where the event is located
\item[calendar] The name of the calendar from calendar.conf
\item[uid] The unique identifier associated with the event
\item[start] The start of the event in seconds since Unix epoch
\item[end] The end of the event in seconds since Unix epoch
\item[busystate] The busy state 0=Free, 1=Tentative, 2=Busy
\item[attendees] A comma separated list of attendees as stored in the event and
may include prefixes such as "mailto:".
\end{description}

When an event notification is sent to the dial plan, the CALENDAR\_EVENT
function may be used to return the information about the event that is causing
the notification. The fields that can be returned are the same as those from
CALENDAR\_QUERY\_RESULT.
\subsection{Write functions}

To write an event to a calendar, the CALENDAR\_WRITE function is used. This
function takes a calendar name and also uses the same fields as
CALENDAR\_QUERY\_RESULT. As a write function, it takes a set of comma-separated
values that are in the same order as the specified fields. For example:
\begin{astlisting}
\begin{verbatim}
CALENDAR_WRITE(mycalendar,summary,organizer,start,end,busystate)=
  "My event","mailto:jdoe@example.com",228383580,228383640,1)
\end{verbatim}
\end{astlisting}

\section{Dialplan Examples}
\subsection{Office hours}
A common business PBX scenario is would be executing dialplan logic based on
when the business is open and the phones staffed. If the business is closed for
holidays, it is sometimes desirable to play a message to the caller stating why
the business is closed.

The standard way to do this in asterisk has been doing a series of GotoIfTime
statements or time-based include statements. Either way can be tedious and
requires someone with access to edit asterisk config files.

With calendaring, the adminstrator only needs to set up a calendar that contains
the various holidays or even recurring events specifying the office hours. A
custom greeting filename could even be contained in the description field for
playback. For example:
\begin{astlisting}
\begin{verbatim}
[incoming]
exten => 5555551212,1,Answer
exten => 5555551212,n,GotoIf(${CALENDAR_BUSY(officehours)}?closed:attendant,s,1)
exten => 5555551212,n(closed),Set(id=${CALENDAR_QUERY(office,${EPOCH},${EPOCH})})
exten => 5555551212,n,Set(soundfile=${CALENDAR_QUERY_RESULT(${id},description)})
exten => 5555551212,n,Playback($[${ISNULL(soundfile)} ? generic-closed :: ${soundfile}])
exten => 5555551212,n,Hangup
\end{verbatim}
\end{astlisting}

\subsection{Meeting reminders}
One useful application of Asterisk Calendaring is the ability to execute
dialplan logic based on an event notification. Most calendaring technologies
allow a user to set an alarm for an event. If these alarms are set on a calendar
that Asterisk is monitoring and the calendar is set up for event notification
via calendar.conf, then Asterisk will execute notify the specified channel at
the time of the alarm. If an overrided notification time is set with the
autoreminder setting, then the notification would happen at that time instead.

The following example demonstrates the set up for a simple event notification
that plays back a generic message followed by the time of the upcoming meeting.
calendar.conf.
\begin{astlisting}
\begin{verbatim}
[calendar_joe]
type = ical
url = https://example.com/home/jdoe/Calendar
user = jdoe
secret = mysecret
refresh = 15
timeframe = 600
autoreminder = 10
channel = SIP/joe
context = calendar_event_notify
extension = s
waittime = 30
\end{verbatim}
\end{astlisting}

\begin{astlisting}
\begin{verbatim}
[calendar_event_notify]
exten => s,1,Answer
exten => s,n,Playback(you-have-a-meeting-at)
exten => s,n,SayUnixTime(${CALENDAR_EVENT(start)})
exten => s,n,Hangup
\end{verbatim}
\end{astlisting}

\subsection{Writing an event}
Both CalDAV and Exchange calendar servers support creating new events. The
following example demonstrates writing a log of a call to a calendar.
\begin{astlisting}
\begin{verbatim}
[incoming]
exten => 6000,1,Set(start=${EPOCH})
exten => 6000,n,Dial(SIP/joe)
exten => h,1,Set(end=${EPOCH})
exten => h,n,Set(CALENDAR_WRITE(calendar_joe,summary,start,end)=Call from ${CALLERID(all)},${start},${end})
\end{verbatim}
\end{astlisting}