====== Creating a simple BPQ Application ======
This tutorial shows you how to set up a simple python script [[https://www.cantab.net/users/john.wiseman/Documents/LinBPQ%20Applications%20Interface.html|connected to linbpq as a telnet application]].

In order to do this we'll do the following:
  - Create a location for the script, data, and a python ''venv''
  - Write the script
  - Add the application to ''BPQ32.cfg''
  - Setup a ''systemd'' service to keep it running.

===== Setup =====
To organize this project, I created a python virtual environment called ''bpq-apps'' in my ''.local'' directory, and installed the ''telnetlib3'' module that it depends on.  Within the ''bpq-apps'' virtual environment directory, I also created a folder called scripts and a folder called data.  I'm going to install various small BPQ applications here.

I'm using the python virtual environment framework to help manage the various dependencies I might want to use for these scripts.

<code>
$ cd ~/.local
$ python -m venv bpq-apps
$ cd ./bpq-apps
$ mkdir scripts data
$ source ./bin/activate
(bpq-apps)$ pip install telnetlib3
</code>

===== Writing the program =====
I chose to write this in Python to be a //little// more clear than the Perl application provided in the link above.

The BPQ Application, called ''ROLL'' uses a file called ''messages.json'' to provide it a welcome message and the blocks of text.  The script itself was placed under the ''scripts'' directory created above, saved as ''rick.py''

==== Program Code ====
This program was adapted from the [[https://pypi.org/project/telnetlib3/|example for the ''telnetlib3'' Python module]]

<code>
import asyncio, telnetlib3, json, sys
from optparse import OptionParser

parser = OptionParser()
parser.add_option("-f", "--file", dest="filename", help="which json file with message and welcome", metavar="FILE")
parser.add_option("-p", "--port", dest="port", help="on which port?", metavar="PORT")
(options, args) = parser.parse_args()

messages = json.load(open(options.filename,'r'))

def print_log(*a):
    print(*a, file=sys.stderr)


async def shell(reader, writer):
    incall = await reader.readline()
    print_log("%s connected" % incall)
    writer.write("\r\nWelcome %s" % incall)
    writer.write("\r\n%s" % messages["welcome"])
    textblocks = messages["text"].copy()
    leave = False #inp[0].upper() in ["Q", "B"]
    rolled = False
    inp = await reader.read(1)
    while inp and not leave and len(textblocks) > 0:
        # print("writing next block")
        writer.write(textblocks.pop(0))
        await writer.drain()
        inp = await reader.readline()
        if not rolled: 
            # notify that rolling has happened
            print_log("%s rickrolled" % incall)
            rolled = True
        leave = inp[0].upper() in ["Q", "B"] and rolled
    writer.close()

loop = asyncio.get_event_loop()
coro = telnetlib3.create_server(port=options.port, shell=shell)
server = loop.run_until_complete(coro)
loop.run_until_complete(server.wait_closed())

</code>

==== ''messages.json'' file ====
<code>
{
	"welcome": "We're no strangers to love\r\nYou know the rules and so do I (Do I)\r\nA full commitment's what I'm thinking of\r\nYou wouldn't get this from any other guy\r\nI just wanna tell you how I'm feeling\r\nGotta make you understand\r\n",
	"text": ["Never gonna give you up\r\nNever gonna let you down\r\nNever gonna run around and desert you\r\nNever gonna make you cry\r\nNever gonna say goodbye\r\nNever gonna tell a lie and hurt you\r\n",
		 "\r\nWe've known each other for so long\r\nYour heart's been aching, but you're too shy to say it (To say it)\r\nInside, we both know what's been going on (Going on)\r\nWe know the game, and we're gonna play it\r\n\r\nAnd if you ask me how I'm feeling\r\nDon't tell me you're too blind to see\r\n",
		 "\r\nNever gonna give you up\r\nNever gonna let you down\r\nNever gonna run around and desert you\r\nNever gonna make you cry\r\nNever gonna say goodbye\r\nNever gonna tell a lie and hurt you\r\n",
		 "\r\nNever gonna give you up\r\nNever gonna let you down\r\nNever gonna run around and desert you\r\nNever gonna make you cry\r\nNever gonna say goodbye\r\nNever gonna tell a lie and hurt you\r\n",
		 "\r\nOoh (Give you up)\r\nOoh-ooh (Give you up)\r\nOoh-ooh\r\nNever gonna give, never gonna give (Give you up)\r\nOoh-ooh\r\nNever gonna give, never gonna give (Give you up)\r\n\r\nWe've known each other for so long\r\nYour heart's been aching, but you're too shy to say it (To say it)\r\n",
		 "\r\nInside, we both know what's been going on (Going on)\r\nWe know the game, and we're gonna play it\r\n\r\nI just wanna tell you how I'm feeling\r\nGotta make you understand\r\n",
		 "\r\nNever gonna give you up\r\nNever gonna let you down\r\nNever gonna run around and desert you\r\nNever gonna make you cry\r\nNever gonna say goodbye\r\nNever gonna tell a lie and hurt you\r\n",
		 "\r\nNever gonna give you up\r\nNever gonna let you down\r\nNever gonna run around and desert you\r\nNever gonna make you cry\r\nNever gonna say goodbye\r\nNever gonna tell a lie and hurt you\r\n",
		 "\r\nNever gonna give you up\r\nNever gonna let you down\r\nNever gonna run around and desert you\r\nNever gonna make you cry\r\nNever gonna say goodbye\r\nNever gonna tell a lie and hurt you\r\n"
	]
}

</code>

===== BPQ configuration =====
In my ''bpq32.cfg'' file, I added the port number to the telnet port, where the fourth entry, ''10001'' is the port for my new application:
<code>
CMDPORT=8005 63001 10001
</code>
and in the application list, I added a new entry, where ''HOST 2'' is due to being the 0th-indexed 3rd entry above.
<code>
APPLICATION 3,ROLL,C 1 HOST 2 S
</code>

===== Configuring this as a service =====
Next we'll configure a ''systemd'' service to make sure this script is always running and ready to accept connections.

Put this file in ''/etc/systemd/system/rick.service'':

<code>
# service for RRoAX25 server
# replace USER with the username under which you created the bpq-apps venv

[Unit]
Description="RRoAX25 service"
After=network.target
# this might be backwards, but I do need linbpq for this to work.
Requires=linbpq.service

[Service]
Type=simple
User=evan
Group=evan
WorkingDirectory=/home/USER/.local/bpq-apps/
ExecStart=/home/USER/.local/bpq-apps/bin/python /home/USER/.local/bpq-apps/scripts/rick.py -p 10001 -f /home/USER/.local/bpq-apps/data/messages.json
Restart=always
RestartSec=3

[Install]
WantedBy=default.target
</code>

Activate it by running:
<code>
sudo systemctl enable rick.service
sudo systemctl start rick.service
</code>

Then check the status to confirm it is working:

<code>
systemctl status rick.service
</code>

If you need to edit the service file, reload it with:
<code>
systemctl daemon-reload
</code>

Finally, to see who has used it:
<code>
journalctl -u rick.service -f
</code>