Voicemail Lesson 3

We now know how to play and record messages. Let's introduce a few more interesting techniques, including use of the file management system to check for the existence of specific files and use of application parameters to determine the voicemail box that the application is accessing.

Sample Files:
- Samples\voicemail_3.py
Specifying a Voicemail Box

This step makes use of the application_parameters argument that contains the user-defined string originating from the Inbound Service configuration. This string is expected to contain the name we have set up to be our voicemail box. We set up a format for all voicemail filenames that locates them in a voicemailbox subfolder on the cloud.

After answering the call the application identifies the level of access for the caller. It does this by comparing the caller Id with the voicemail box name, as determined from application_parameters.

If the caller Id and voicemail box name match then the caller is deemed to be the owner of the voicemail box and the application calls top_level_menu() that allows the caller to listen and delete all messages. In the main function, we can do this using the file_man.exists() function, with the filename as a parameter. This will test for the existence of the file on the Cloud. We keep incrementing a counter until the filename is not found.

If the caller Id and voicemail box name do not match, the caller is simply allowed to record a new message.

Using the channel

One of the first things we do is to call our get_caller function. This extacts information from the call_from property of the channel we've been given, which supplies a SIP address. Our telephony system which answers the client encapsulates the phone number information within a SIP format, which is then used by our Cloud. Our function extracts the phone number information from the SIP address.

The application parameters are given to us as a string, accessable by the application_parameters variable. In our example, we compare the parameter against the caller number, to identify if the caller is actually the owner of our voicemail service. If they are the caller, the application jumps to the top_level_menu subroutine, otherwise to record_new_message.

Dealing with DTMF

The top level menu subroutine uses a function called get_menu_select. We saw in the previous example how to access DTMF tones via the keypad. This routine will play some TTS to the user, and then wait for a valid response. Once the user has entered a valid response, the keypad press will be returned. We can then simply check the return code and act appropriately.

In play_all_messages(), we use a counter, checking if a filename derived from the counter exists, and if so, says some TTS and then the file itself. delete_all_messages() works in a similar manner, but rather than play each file, we delete the file using the file_man.delete_file call.

__uas_identify__ = "application"
__uas_version__ = "1.0b1"

from prosody.uas import Hangup, Error, ICanRun

"""

    An inbound application that answers the call and says
    "Welcome to the voicemail server for <name>". <name> is obtained from the
    application_parameters and must be registered on the inbound services
    page of the CWP.

    The application uses <name> to determine whether the caller owns the
    voicemail box. It does this by comparing <name> with the <call_from>
    property of the inbound call.

    If the caller owns the voicemail box, the top level options given are:

        1. Play all existing messages
        2. Delete all existing messages

    If the caller does not own the voicemail box, he can leave a new
    message. The name of the WAV file to save to will be
    "samples/voicemail3/<name>/msg<counter>.wav". The <counter> is a
    variable, initialised to 1, which increments each time a message is
    successfully saved.

    This application is part of the online Voice Mail tutorial.
"""

class VoiceMailBox:
    def __init__(self, box_name, channel, file_manager, logger):
        self._channel = channel
        self._file_manager = file_manager
        self._logger = logger
        self._file_format = "samples/voicemail3/" + box_name + "/msg{0}.wav"
        self._recorded_file_counter = 1
        self._set_message_counter()


    def _set_message_counter(self):
        # check the message box and set the counter
        while(self._file_manager.exists(self._file_format.format(self._recorded_file_counter))):
            self._logger.info("{0} exists".format(self._recorded_file_counter))
            self._recorded_file_counter += 1


    def say_tts(self, message, bargein=False, beep=False):
        cause = self._channel.FilePlayer.say(message, barge_in=bargein)
        if cause == self._channel.FilePlayer.Cause.BARGEIN:
            return
        if cause == self._channel.FilePlayer.Cause.NORMAL:
            if beep is True:
                cause = self._channel.DTMFPlayer.play("#");
                if cause != self._channel.DTMFPlayer.Cause.NORMAL:
                    raise Error("Play tone failed: caused is {0}".format(cause))
        else:
            raise Error("Say '{0}' failed: cause is {1}".format(message, cause))


    def play_file(self, filename):
        cause = self._channel.FilePlayer.play(filename)
        if cause != self._channel.FilePlayer.Cause.NORMAL:
            raise Error("Play '{0}' failed: cause is {1}".format(filename, cause))


    def record_new_message(self, replace=False):

        if replace is True and self._recorded_file_counter > 1:
            self._recorded_file_counter -= 1

        filename = self._file_format.format(self._recorded_file_counter)
        self._recorded_file_counter += 1

        self.say_tts("Please record a message after the tone. Press any digit to stop the recording.", beep=True)

        cause = self._channel.FileRecorder.record(filename, milliseconds_max_silence=3000,
                                                  seconds_timeout=60, barge_in=True)
        if cause != self._channel.FileRecorder.Cause.SILENCE and cause != self._channel.FileRecorder.Cause.BARGEIN:
            raise Error("Record message failed: cause is {0}".format(cause))
        # check whether the file has been saved correctly, does it exist?
        if not self._file_manager.exists(filename):
            self.say_tts("Your message could not be saved.")
        else:
            self.say_tts("The following message has been recorded")
            self.play_file(filename)


    def play_all_messages(self):
        counter = 1
        filename = self._file_format.format(counter)

        while self._file_manager.exists(filename):
            self.say_tts("Message {0}".format(counter))
            self.play_file(filename)
            counter += 1
            filename = self._file_format.format(counter)

        if counter == 1:
            self.say_tts("You have no messages to play.")
        else:
            self.say_tts("End of messages.")


    def delete_all_messages(self):
        counter = 1
        filename = self._file_format.format(counter)

        while self._file_manager.exists(filename):
            self._file_manager.delete_file(filename)
            counter += 1
            filename = self._file_format.format(counter)

        if counter == 1:
            self.say_tts("You have no messages to delete.")
        else:
            self.say_tts("All messages deleted.")

        self._recorded_file_counter = 1


def main(channel, application_instance_id, file_man, my_log, application_parameters):
    my_log.info ("Voicemail 3 started.")
    return_code = 0
    try:

        # The voicemail box name must have been configured at service registration
        if len(application_parameters) == 0:
            raise Error("Argument list is empty")

        mailbox = VoiceMailBox(application_parameters, channel, file_man, my_log)

        channel.ring(2)
        channel.answer()
        caller = get_caller(channel)

        my_log.info ("Call from {0} to {1}'s Voicemail answered".format(caller, application_parameters))

        mailbox.say_tts("Welcome to the voicemail server for {0}".format(" ".join(list(application_parameters))))

        if caller == application_parameters:
            top_level_menu(channel, mailbox)
        else:
            replace = False
            # wait on i_can_run to prevent an accidental infinite loop
            i_can_run = ICanRun(channel)
            while i_can_run:
                mailbox.record_new_message(replace)
                key_selected = get_menu_select(channel, mailbox,
                                               "Please press 1 to keep this message or 2 to record an alternative message",
                                               20, "12")

                if key_selected == '1':
                    mailbox.say_tts("Message saved.")
                    break
                replace = True

        mailbox.say_tts("Goodbye.")

        channel.hang_up();

    except Hangup as exc:
        my_log.info("Completed with Hangup: {0}".format(exc))
        return_code = -100

    except Error as exc:
        my_log.error("Completed with Error exception! {0}".format(exc))
        return_code = -101

    except Exception as exc:
        my_log.exception("Completed with exception! {0}".format(exc))
        return_code = -102

    finally:
        if channel.state() != channel.State.IDLE:
            channel.hang_up()
    my_log.info("Voicemail 3 example completed")
    return return_code



def get_caller(channel):
    caller = channel.Details.call_from
    # Extract the username from the SIP address
    if caller.startswith("sip:"):
        caller = caller[4:]
    return caller.split('@', 1)[0]


def top_level_menu(channel, mailbox):

    key_selected = get_menu_select(channel, mailbox,
                                  "Press 1 to listen to all messages. \
                                  Press 2 to delete all messages. \
                                  Press 3 to quit.",
                                  20, "123")
    if key_selected == '1':
        mailbox.play_all_messages()
    elif key_selected == '2':
        mailbox.delete_all_messages()


def get_menu_select(channel, mailbox, prompt, seconds_repeat_prompt, valid_keys):
    channel.DTMFDetector.clear_digits()

    # wait on i_can_run to prevent an accidental infinite loop
    i_can_run = ICanRun(channel)
    while i_can_run:
        mailbox.say_tts(prompt, bargein=True, beep=True)

        digits = channel.DTMFDetector.get_digits(end=valid_keys, seconds_predigits_timeout=seconds_repeat_prompt)
        cause = channel.DTMFDetector.cause()
        if cause == channel.DTMFDetector.Cause.END:
            return digits[-1]
        else:
            mailbox.say_tts("Invalid selection.")

Sample Files:
- Samples\C#\Voicemail3\Voicemail3.cs
Specifying a Voicemail Box

This step makes use of the applicationArguments argument that contains the user-defined string originating from the Inbound Service configuration. This string is expected to contain the name we have set up to be our voicemail box. We set up a format for all voicemail filenames that locates them in a voicemailbox subfolder on the cloud.

After answering the call the application identifies the level of access for the caller. It does this by comparing the caller Id with the voicemailBox name, as determined from applicationArguments. For SIP calls, the voicemailBox name is matched with the Username of the caller (the string before the '@' character) while for PSTN calls the caller Id is simply the calling number.

If the caller Id and voicemailBox name match then the caller is deemed to be the owner of the voicemail box and the application calls TopLevelMenu() that allows the caller to listen and delete all messages. Otherwise the caller is simply allowed to record a new message.

File checking

In the Run() method we check for the existence of a file using the FileManager.FileExists() method. We continually increment the recordedFileCounter variable until we identify a free filename - this is our next filename for recording.

Dealing with DTMF

For menu entry via the keypad, a new method has been created called GetMenuSelection(). This reads out a prompt, passed as a parameter, a predigit timeout value, and also any valid selections that the user is able to press. A string of the single digit reply is returned. In the TopLevelMenu() method, pressing a '1' will call the PlayAllMessages() method and pressing a '2' will call DeleteAllMessage().

Voicemail functionality

In PlayAllMessages(), a counter is incremented from 1, testing with a derived filename is the file exists, and if so, will play the file. This continues until there are no more messages. DeleteAllMessage() does a similar job, testing for the existence of a derived filename, but rather than play it, will delete the file with the FileManager.DeleteFile() method.

The RecordNewMessage() method behaves like the record method in the previous step, except that it now uses the GetMenuSelection method to determine user input.

using System;
using System.Threading;
using AMSClassLibrary;
using UASAppAPI;

// An inbound application that answers the call, says "Welcome to the
// voicemail server for <name>."
// <name> is obtained from the applicationArguments.
// It is compared with the <callFrom> property of the inbound call.
//
// If <callFrom> equals <name>
//     Say "Press 1 to hear all messages, press 2 to delete all messages".
//     1. Play all existing messages
//     2. Delete all existing messages
// else
//     Do recording as in voicemail 2.
//
// All options return to the above menu.
// The app only completes when the call is hung up.
// The name of the .wav file to save to will be "samples/voicemail3/name/msg<counter>.wav".
// The <counter> is a variable, initialised to 1, which increments each time a
// message is successfully saved.
//
// Requires:
// [applicationParameters = voicemail box name]
namespace Voicemail3
{
    public class Voicemail3 : UASInboundApplication
    {
        // Possible return codes
        enum ReturnCode
        {
            // Success Codes:
            Success = 0,
            // ... any positive integer
            RecordedAMessage = 1,
            CallHungUp = 2,

            // Fail Codes:
            // -1 to -99 reserved
            ExceptionThrown = -100,
            ArgumentEmpty = -101,
            RecordingFailedToStart = -102
        }

        // This is the entry point for the application
        public override int Run(UASCallChannel channel,
                                string applicationParameters)
        {
            this.Trace.TraceInfo("Started");
            ReturnCode reply = ReturnCode.Success;

            // The voicemail box name must have been configured at service registration
            voicemailBoxName = applicationParameters;
            if (voicemailBoxName.Length == 0)
            {
                return (int)ReturnCode.ArgumentEmpty;
            }

            recordFilenameFormat = "samples/voicemail3/" + voicemailBoxName + "/msg{0}.wav";

            // Obtain the next free counter
            recordedFileCounter = 1;
            while (this.FileManager.FileExists(String.Format(recordFilenameFormat, recordedFileCounter.ToString())))
            {
                recordedFileCounter++;
            }

            try
            {
                // Answer the call
                CallState state = channel.Answer();
                if (state == CallState.Answered)
                {
                    string caller = GetCaller(channel);
                    this.Trace.TraceInfo("Call from {0} to {1}'s Voicemail answered",
                                                caller, voicemailBoxName);

                    PlayWelcomeMessage(channel, voicemailBoxName);

                    if (caller == voicemailBoxName)
                    {
                        TopLevelMenu(channel);
                    }
                    else
                    {
                        RecordNewMessage(channel);
                        channel.FilePlayer.Say("Goodbye.");
                    }
                }
            }
            catch (Exception e)
            {
                this.Trace.TraceError("Exception thrown {0}", e.Message);
                reply = ReturnCode.ExceptionThrown;
            }
            finally
            {
                channel.HangUp();
            }

            this.Trace.TraceInfo("Completed");
            return (int)reply;
        }

        private ReturnCode PlayWelcomeMessage(UASCallChannel channel, string name)
        {
            channel.FilePlayer.Say("Welcome to the voicemail server for {0}", name);
            return ReturnCode.Success;
        }

        private string GetCaller(UASCallChannel channel)
        {
            // Extract the user part of a SIP address
            string caller = channel.CallDetails.CallFrom;
            if (caller.Contains("sip:"))
            {
                caller = caller.Substring(4);
                int pos = caller.IndexOf('@');
                if (pos >= 0)
                {
                    caller = caller.Remove(pos);
                }
            }
            return caller;
        }

        private ReturnCode TopLevelMenu(UASCallChannel channel)
        {
            ReturnCode reply = ReturnCode.Success;
            string prompt = "Press 1 to listen to all messages. " +
                            "Press 2 to delete all messages. " +
                            "Press hash to exit.";
            char keySelected;

            do
            {
                reply = GetMenuSelection(channel, prompt, 20, "12#", out keySelected);
                if (reply == ReturnCode.Success)
                {
                    switch (keySelected)
                    {
                        case '1':
                            reply = PlayAllMessages(channel);
                            break;
                        case '2':
                            reply = DeleteAllMessages(channel);
                            break;
                        case '#':
                            return reply;
                    }
                }
            } while (reply == ReturnCode.Success);

            return reply;
        }

        private ReturnCode RecordNewMessage(UASCallChannel channel)
        {
            ReturnCode reply = ReturnCode.Success;

            string filename = String.Format(recordFilenameFormat, recordedFileCounter.ToString());
            recordedFileCounter++;

            // Loop round until have recorded a message acceptable to the caller
            // or caller has hung up
            bool satisfiedWithMessage = false;
            do
            {
                // Prompt to leave a message
                channel.FilePlayer.Say("Please record a message after the tone. " +
                                       "Press any digit to stop the recording.");

                // Delay before starting the recording and playing the tone (for effect)
                Thread.Sleep(1000);

                // Clear any received digits
                channel.DtmfDetector.ClearDigits();

                // Start recording, enabling barge in
                this.Trace.TraceInfo("Recording message to file: [{0}]", filename);
                if (!channel.FileRecorder.Start(filename, true))
                {
                    this.Trace.TraceError("Recording failed to start cause = {0}",
                                          channel.FileRecorder.Cause);
                    reply = ReturnCode.RecordingFailedToStart;
                    break;
                }

                // Play a tone to signal that recording has started
                channel.DtmfPlayer.Play("0");

                // Wait for a period for recording to complete or
                // the call to have been hung up
                FileRecorderCause recCause = channel.FileRecorder.WaitUntilFinished(60);
                if (recCause == FileRecorderCause.HangUp)
                {
                    this.Trace.TraceInfo("Call has been hung up");
                    reply = ReturnCode.CallHungUp;
                    break;
                }
                if (recCause == FileRecorderCause.Timeout)
                {
                    this.Trace.TraceInfo("Recording has stopped after 60 seconds");
                    channel.FileRecorder.Stop();
                }

                // Replay the recorded message
                channel.FilePlayer.Say("The following message has been recorded");
                if (channel.FilePlayer.Play(filename, true) == FilePlayerCause.HangUp)
                {
                    this.Trace.TraceInfo("Call has been hung up");
                    reply = ReturnCode.CallHungUp;
                    break;
                }

                // Check if the user is satisfied with the recorded message
                string prompt = "Please press 1 to keep this message or 2 to record an " +
                                "alternative message";
                char keySelected;

                reply = GetMenuSelection(channel, prompt, 20, "12", out keySelected);
                if (reply == ReturnCode.Success)
                {
                    if (keySelected == '1')
                    {
                        satisfiedWithMessage = true;
                        channel.FilePlayer.Say("Message saved.");
                    }
                }
            } while (!satisfiedWithMessage && (reply == ReturnCode.Success));

            return reply;
        }

        private ReturnCode PlayAllMessages(UASCallChannel channel)
        {
            ReturnCode reply = ReturnCode.Success;
            int counter = 1;

            string filename = String.Format(recordFilenameFormat, counter.ToString());

            while (this.FileManager.FileExists(filename))
            {
                channel.FilePlayer.Say("Message " + counter.ToString());

                channel.FilePlayer.Play(filename);
                if (channel.FilePlayer.Cause == FilePlayerCause.HangUp)
                {
                    reply = ReturnCode.CallHungUp;
                    break;
                }

                counter++;
                filename = String.Format(recordFilenameFormat, counter.ToString());
            }

            if (reply == ReturnCode.Success)
            {
                channel.FilePlayer.Say("No more messages.");
            }

            return reply;
        }

        private ReturnCode DeleteAllMessages(UASCallChannel channel)
        {
            ReturnCode reply = ReturnCode.Success;
            int counter = 1;

            string filename = String.Format(recordFilenameFormat, counter.ToString());

            while (this.FileManager.FileExists(filename))
            {
                this.FileManager.DeleteFile(filename);

                counter++;
                filename = String.Format(recordFilenameFormat, counter.ToString());
            }

            if (reply == ReturnCode.Success)
            {
                channel.FilePlayer.Say("All messages deleted.");
            }

            return reply;
        }

        // Returns: Success if a valid key was selected, CallHungUp if call hung up.
        private ReturnCode GetMenuSelection(UASCallChannel channel, string prompt, int secondsRepeatPrompt, string validKeys, out char keySelected)
        {
            keySelected = '\0';

            // Prepare to receive digits
            channel.DtmfDetector.ClearDigits();

            do
            {
                FilePlayerCause cause = channel.FilePlayer.Say(prompt, true);
                if (cause == FilePlayerCause.HangUp)
                {
                    return ReturnCode.CallHungUp;
                }

                string digits;
                channel.DtmfDetector.GetDigits(1, out digits, secondsRepeatPrompt);
                if (channel.DtmfDetector.Cause == DtmfDetectorCause.Count)
                {
                    if (validKeys.Contains(digits))
                    {
                        this.Trace.TraceInfo("Got keypress {0}", digits[0]);
                        keySelected = digits[0];
                        return ReturnCode.Success;
                    }
                    else
                    {
                        channel.FilePlayer.Say("Selection not valid.");
                    }
                }
            } while (channel.DtmfDetector.Cause != DtmfDetectorCause.HangUp);

            // returning on hangup
            return ReturnCode.CallHungUp;
        }

        private string voicemailBoxName;
        private string recordFilenameFormat;
        private int recordedFileCounter;
    }
}

Sample Files:
- Samples\VB\Voicemail3\Voicemail3.vb
Specifying a Voicemail Box

This step makes use of the applicationArguments argument that contains the user-defined string originating from the Inbound Service configuration. This string is expected to contain the name we have set up to be our voicemail box. We set up a format for all voicemail filenames that locates them in a voicemailbox subfolder on the cloud.

After answering the call the application identifies the level of access for the caller. It does this by comparing the caller Id with the voicemailBox name, as determined from applicationArguments. For SIP calls, the voicemailBox name is matched with the Username of the caller (the string before the '@' character) while for PSTN calls the caller Id is simply the calling number.

If the caller Id and voicemailBox name match then the caller is deemed to be the owner of the voicemail box and the application calls TopLevelMenu() that allows the caller to listen and delete all messages. Otherwise the caller is simply allowed to record a new message.

File checking

In the Run() method we check for the existence of a file using the FileManager.FileExists() method. We continually increment the recordedFileCounter variable until we identify a free filename - this is our next filename for recording.

Dealing with DTMF

For menu entry via the keypad, a new method has been created called GetMenuSelection(). This reads out a prompt, passed as a parameter, a predigit timeout value, and also any valid selections that the user is able to press. A string of the single digit reply is returned. In the TopLevelMenu() method, pressing a '1' will call the PlayAllMessages() method and pressing a '2' will call DeleteAllMessage().

Voicemail functionality

In PlayAllMessages(), a counter is incremented from 1, testing with a derived filename is the file exists, and if so, will play the file. This continues until there are no more messages. DeleteAllMessage() does a similar job, testing for the existence of a derived filename, but rather than play it, will delete the file with the FileManager.DeleteFile() method.

The RecordNewMessage() method behaves like the record method in the previous step, except that it now uses the GetMenuSelection method to determine user input.

Imports AMSClassLibrary
Imports UASAppAPI

' An inbound application that answers the call, says "Welcome to the
' voicemail server for <name>."
' <name> is obtained from the applicationArguments.
' It is compared with the <callFrom> property of the inbound call.
'
' If <callFrom> equals <name>
'     Say "Press 1 to hear all messages, press 2 to delete all messages".
'     1. Play all existing messages
'     2. Delete all existing messages
' else
'     Do recording as in voicemail 2.
'
' All options return to the above menu.
' The app only completes when the call is hung up.
' The name of the .wav file to save to will be "samples/voicemail3/name/msg<counter>.wav".
' The <counter> is a variable, initialised to 1, which increments each time a
' message is successfully saved.
'
' Requires:
' [applicationParameters = voicemail box name]
Namespace Voicemail3

    ' The application class.
    ' This must have the same name as the assembly and must inherit from either
    ' UASInboundApplication or UASOutboundApplication.
    ' It must override the Run method.
    Public Class Voicemail3
        Inherits UASInboundApplication

        ' Possible return codes
        Enum ReturnCode
            ' Success Codes:
            Success = 0
            RecordedAMessage = 1
            CallHungUp = 2

            ' Fail Codes:
            ' -1 to -99 reserved
            ExceptionThrown = -100
            ArgumentEmpty = -101
            RecordingFailedToStart = -102
        End Enum

        ' This is the entry point for the application
        Overrides Function Run(ByVal channel As UASCallChannel, _
                               ByVal applicationParameters As String) _
                               As Integer

            Me.Trace.TraceInfo("Started")
            Dim reply As ReturnCode = ReturnCode.Success

            ' The voicemail box name must have been configured at service registration
            voicemailBoxName = applicationParameters
            If voicemailBoxName.Length = 0 Then
                Return ReturnCode.ArgumentEmpty
            End If

            recordFilenameFormat = "samples/voicemail3/" + voicemailBoxName + "/msg{0}.wav"

            ' Obtain the next free counter
            recordedFileCounter = 1
            While Me.FileManager.FileExists(String.Format(recordFilenameFormat, recordedFileCounter.ToString()))
                recordedFileCounter += 1
            End While

            Try
                ' Answer the call
                Dim state As CallState
                state = channel.Answer()
                If state = CallState.Answered Then
                    Dim caller = GetCaller(channel)
                    Me.Trace.TraceInfo("Call from {0} to {1}'s Voicemail answered", _
                                                caller, voicemailBoxName)

                    PlayWelcomeMessage(channel, voicemailBoxName)

                    If caller = voicemailBoxName Then
                        TopLevelMenu(channel)
                    Else
                        RecordNewMessage(channel)
                        channel.FilePlayer.Say("Goodbye.")
                    End If
                End If

            Catch ex As Exception
                Me.Trace.TraceError("Exception thrown {0}", ex.Message)
                reply = ReturnCode.ExceptionThrown
            Finally
                channel.HangUp()
            End Try

            Me.Trace.TraceInfo("Completed")
            Return reply

        End Function

        Private Function PlayWelcomeMessage(ByVal channel As UASCallChannel, ByVal name As String) As ReturnCode
            channel.FilePlayer.Say("Welcome to the voicemail server for {0}", name)
            Return ReturnCode.Success
        End Function

        Private Function GetCaller(ByVal channel As UASCallChannel) As String
            ' Extract the user part of a SIP address
            Dim caller = channel.CallDetails.CallFrom
            If caller.Contains("sip:") Then
                caller = caller.Substring(4)
                Dim pos = caller.IndexOf("@")
                If (pos >= 0) Then
                    caller = caller.Remove(pos)
                End If
            End If
            Return caller
        End Function

        Private Function TopLevelMenu(ByVal channel As UASCallChannel) As ReturnCode
            Dim reply = ReturnCode.Success
            Dim prompt = "Press 1 to listen to all messages. " + _
                         "Press 2 to delete all messages. " + _
                         "Press hash to exit."
            Dim keySelected As Char

            Do
                reply = GetMenuSelection(channel, prompt, 20, "12#", keySelected)
                If reply = ReturnCode.Success Then
                    Select Case keySelected
                        Case "1"
                            reply = PlayAllMessages(channel)
                        Case "2"
                            reply = DeleteAllMessages(channel)
                        Case "#"
                            Return reply
                    End Select
                End If
            Loop While reply = ReturnCode.Success

            Return reply
        End Function

        Private Function RecordNewMessage(ByVal channel As UASCallChannel) As ReturnCode
            Dim reply = ReturnCode.Success

            Dim filename = String.Format(recordFilenameFormat, recordedFileCounter.ToString())
            recordedFileCounter += 1

            ' Loop round until have recorded a message acceptable to the caller
            ' or caller has hung up
            Dim satisfiedWithMessage = False
            Do
                ' Prompt to leave a message
                channel.FilePlayer.Say("Please record a message after the tone. " + _
                                       "Press any digit to stop the recording.")

                ' Delay before starting the recording and playing the tone (for effect)
                Thread.Sleep(1000)

                ' Clear any received digits
                channel.DtmfDetector.ClearDigits()

                ' Start recording, enabling barge in
                Me.Trace.TraceInfo("Recording message to file: [{0}]", filename)
                If Not channel.FileRecorder.Start(filename, True) Then
                    Me.Trace.TraceError("Recording failed to start cause = {0}", _
                                          channel.FileRecorder.Cause)
                    reply = ReturnCode.RecordingFailedToStart
                    Exit Do
                End If

                ' Play a tone to signal that recording has started
                channel.DtmfPlayer.Play("0")

                ' Wait for a period for recording to complete or
                ' the call to have been hung up
                Dim recCause = channel.FileRecorder.WaitUntilFinished(60)
                If recCause = FileRecorderCause.HangUp Then
                    Me.Trace.TraceInfo("Call has been hung up")
                    reply = ReturnCode.CallHungUp
                    Exit Do
                End If
                If recCause = FileRecorderCause.Timeout Then
                    Me.Trace.TraceInfo("Recording has stopped after 60 seconds")
                    channel.FileRecorder.Stop()
                End If

                ' Replay the recorded message
                channel.FilePlayer.Say("The following message has been recorded")
                If channel.FilePlayer.Play(filename, True) = FilePlayerCause.HangUp Then
                    Me.Trace.TraceInfo("Call has been hung up")
                    reply = ReturnCode.CallHungUp
                    Exit Do
                End If

                ' Check if the user is satisfied with the recorded message
                Dim prompt = "Please press 1 to keep this message or 2 to record an " + _
                                "alternative message"
                Dim keySelected As Char

                reply = GetMenuSelection(channel, prompt, 20, "12", keySelected)
                If reply = ReturnCode.Success Then
                    If keySelected = "1" Then
                        satisfiedWithMessage = True
                        channel.FilePlayer.Say("Message saved.")
                    End If
                End If
            Loop While Not satisfiedWithMessage And (reply = ReturnCode.Success)

            Return reply
        End Function

        Private Function PlayAllMessages(ByVal channel As UASCallChannel) As ReturnCode
            Dim reply = ReturnCode.Success
            Dim counter = 1

            Dim filename = String.Format(recordFilenameFormat, counter.ToString())

            While Me.FileManager.FileExists(filename)
                channel.FilePlayer.Say("Message " + counter.ToString())

                channel.FilePlayer.Play(filename)
                If channel.FilePlayer.Cause = FilePlayerCause.HangUp Then
                    reply = ReturnCode.CallHungUp
                    Exit While
                End If

                counter += 1
                filename = String.Format(recordFilenameFormat, counter.ToString())
            End While

            If reply = ReturnCode.Success Then
                channel.FilePlayer.Say("No more messages.")
            End If

            Return reply
        End Function

        Private Function DeleteAllMessages(ByVal channel As UASCallChannel) As ReturnCode
            Dim reply = ReturnCode.Success
            Dim counter = 1

            Dim filename = String.Format(recordFilenameFormat, counter.ToString())

            While Me.FileManager.FileExists(filename)
                Me.FileManager.DeleteFile(filename)

                counter += 1
                filename = String.Format(recordFilenameFormat, counter.ToString())
            End While

            If reply = ReturnCode.Success Then
                channel.FilePlayer.Say("All messages deleted.")
            End If

            Return reply
        End Function

        ' Returns: Success if a valid key was selected, CallHungUp if call hung up.
        Private Function GetMenuSelection(ByVal channel As UASCallChannel, ByVal prompt As String, ByVal secondsRepeatPrompt As Integer, ByVal validKeys As String, ByRef keySelected As Char) As ReturnCode
            keySelected = "\0"

            ' Prepare to receive digits
            channel.DtmfDetector.ClearDigits()

            Do
                Dim cause = channel.FilePlayer.Say(prompt, True)
                If cause = FilePlayerCause.HangUp Then
                    Return ReturnCode.CallHungUp
                End If

                Dim digits As String = ""
                channel.DtmfDetector.GetDigits(1, digits, secondsRepeatPrompt)
                If channel.DtmfDetector.Cause = DtmfDetectorCause.Count Then
                    If (validKeys.Contains(digits)) Then
                        Me.Trace.TraceInfo("Got keypress {0}", digits(0))
                        keySelected = digits(0)
                        Return ReturnCode.Success
                    Else
                        channel.FilePlayer.Say("Invalid selection.")
                    End If
                End If
            Loop While channel.DtmfDetector.Cause <> DtmfDetectorCause.HangUp

            ' returning on hangup
            Return ReturnCode.CallHungUp
        End Function

        Private voicemailBoxName As String
        Private recordFilenameFormat As String
        Private recordedFileCounter As String

    End Class

End Namespace

Next time...

So, we have a simple bare-bone voicemail system up and running. We could personalise the voicemail box some more though. How about allowing the owner of the voicemail box to record their own introduction message and use the file as a welcome message? Additionally we could allow the owner to select messages to keep or delete. Read on to find out how...

Lesson 4