#!/bin/sh
#
# This script takes at minimum one argument: the time that the alarm should go off
# using the format hh:mm, it does only rudimentary checks that the format is 
# specified is correct. An optional second argument specifies what should be done 
# when the alarm goes off. If no second argument is supplied, a simple shell bell 
# is used.
#
# Be sure this bell works before you go to sleep!
#
# If the second argument is included and the alarm method is more than one command,
# it will need to be enclosed in quotes.

# First check that the required minimum arguments have been supplied, and that
# the time is of the format hh:mm. If not exit with the proper usage.

if [ $# -eq 0 ]
then
        echo "Usage: $0 hh:mm [alarm-method]"
        echo "eg. $0 13:30 \"mplayer /media/music/dr_octagon/01.mp3\" "
        exit 1
else
        alarm_time="$1"

        # Check that the format for the alarm time is correct, the first digit
        # should be a number between 0-2, followed by a colon, and ending with a 
        # number between zero and 60. NB: This check is not perfect.

        if [ ! `echo "$alarm_time" | sed -n '/[0-2][[:digit:]]:[0-60]/p'` ]
        then
                echo "Incorrect time specified, please use format hh:mm"
                exit 1
        fi

fi

# Set the number of seconds in a minute
seconds=1

# Test to see if a second argument is supplied, if it is not then set the
# bell to a shell bell. The -e argument to echo specifies that echo should
# enable interpretation of the backslash character, and \a is defined in
# the echo(1) man page as a bell.

if [ ! $2 ]
then
        bell="echo -e \a"
else

        bell=$2
fi

# The wait_between_checks function sleeps for the specified number of
# seconds and then calls the check_time function when it is done sleeping.
# This makes the script only check the time once a minute, instead of constantly.

wait_between_checks ()
{
        sleep $seconds
        check_time
}

# The check_time function looks at the current time (in hh:mm format) and
# compares it to the $alarm_time, if they match, then it calls the wakeup function
# otherwise it goes back to sleep by calling the wait_between_checks function 
again.

check_time ()
{
        current_time=`date +%H:%M`

        if [ "$current_time" = "$alarm_time" ]
        then
                wakeup
        else
                wait_between_checks
        fi

}

# The wakeup function simply rings the bell over and over until the script
# is interrupted.

wakeup ()
{
        echo -n "Wake up! Hit control-c to stop the madness"
        $bell
        sleep 1
        wakeup
}

# Finally the main body of the script simply starts things up by calling the
# wait_between_checks function

wait_between_checks