This program is a simple alarm system for the raspberry pi, one GPIO
input sensor (e.g. an infrared sensor), an optional GPIO output device
(e.g. a relay based light bulb), also optional, a process to start
(e.g. mjpeg-streamer that streams mjpeg from a USB camera, using a
http server, included a demo script), and finally optional is to switch
a Philips hue light.

It mainly serves as an example of how to create an event based C program.

Build it by typing `make`. It's usage is

usage: ./alarm -i input-pin [-alarm 0|1][-o output-pin] [-c camera-app] [-r host:port] [-min ms] [-extra ms] [-max ms] [-hue hue-hub-ip:username:light[:extra]]

where the -i stands for an input GPIO pin, -o for an output pin. These
pin numbers are the BCM GPIO number (4, 17, 18, 22, 23, 24, 25).
The -alarm is default 1, but if the sensor is 1 when no alarm, use this
option '-alarm 0'.
A process can be started when passing '-c path-to-program'.
A tcp4 connection can be attempted during an alarm period using '-r' switch.
And finally three timers determine how long the alarm should be up at
minimum, maximum and -extra stands for the time the alarm stays off after
being on.

When the alarm sensor goes to alarm value, the output pin is set to 1 and
the program is started. When after the timeouts the alarm goes off, the
program is interupted. It should therefore handle SIGINT (Ctrl+C) and
terminate gracefully.

Also when -hue is given for Philips Hue systems, the give light is turned on.
These lights can be indepent timed when adding the extra parameter. But
note, the lights are then switched on *only* depending on the sun. You
must changed the latitude/longitude values in utils.c to match your location.
When 'hue-hub-ip' is equal to the string 'ssdp', then alarm will listen to
Simple Service Discovery Protocol messages to figure out the ip of the hue
bridge. May take a while before the IP is found.

To setup the GPIO's run the following as root (e.g. add it to rc.local),
the alarm program can run as normal user.
Example, using pin 18 as input, 23 as output for user 'pi'

echo 18 > /sys/class/gpio/export
echo 23 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio23/direction
echo both > /sys/class/gpio/gpio18/edge
chown pi /sys/class/gpio/gpio23/value

For the tcp4 case, a monitor utitlity is build too

monitor [-p listen-port] [-s program-to-run] [-r remote-http-port] [-o output-dir]

which is made for the mjpeg-streamer case. Run it on the host with IP is above
host and use port as '-p' parameter.
When a connections is made, it tries to connect to the mjpeg-streamer http
port, '-r' switch, and dumps the fetched jpegs in output-dir, '-o' parameter
(which defaults to '.')

Have fun!