#!/bin/sh
# script to output the APRX log data (APRS data received via RF/inet) to the display.
# the process in this script runing in a loop:
# 1) check if APRX runs still by checking existence of APRX_PID file.
# 2) check if there is a difference between APRXRF_LOG / APRX_LOG and PRXRF_LOG_TMP / APRX_LOG_TMP.
# 3a) if there is a difference send result to display.
# 3b) make a copy of log file APRXRF_LOG / APRX_LOG and APRXRF_LOG_TMP / APRX_LOG_TMP.
# 4) if there is no difference do nothing.
# 5) continue with step 1).

local NAME
local DISPLAY
local SOURCE
local APRX_LOG
local APRXRF_LOG
local APRX_LOG_TMP
local APRXRF_LOG_TMP

# variable definitions

NAME="aprs_log_loop"
DISPLAY="/dev/Display"
APRX_LOG="/var/log/aprx/aprx.log"
APRXRF_LOG="/var/log/aprx/aprx-rf.log"
APRX_LOG_TMP="/tmp/.aprx.log"
APRXRF_LOG_TMP="/tmp/.aprx-rf.log"
APRX_PID="/var/run/aprx.pid"
THIS_SCRIPT_PID="/var/run/display_aprx_log_loop.pid"

# generate the log files if they do not exist yet.

touch $APRX_LOG_TMP
touch $APRXRF_LOG_TMP
touch $APRX_LOG
touch $APRXRF_LOG

# check if this script is not yet running by checking existence of THIS_SCRIPT_PID
if [ ! -f $THIS_SCRIPT_PID ]; then
	# create the THIS_SCRIPT_PID file to indicate the running process
	touch $THIS_SCRIPT_PID
	# send message to display that the log output is started
	echo "APRX log start:" > $DISPLAY
	# write to system log that the log output is started
	logger -t "$NAME" "APRX log display start"
	# run this loop as long as the APRX program is running
	while [ -f $APRX_PID ]; do
		# check if there is a difference between APRXRF_LOG and APRXRF_LOG_TMP
		if [[ "$(diff -q $APRXRF_LOG $APRXRF_LOG_TMP)" == "Files $APRXRF_LOG and $APRXRF_LOG_TMP differ" ]]; then
			# difference found; send out difference to Display 
			diff $APRXRF_LOG $APRXRF_LOG_TMP | awk '/^-/ && !/^---/ { $1=""; print }' > $DISPLAY
			# copy APRXRF_LOG into APRXRF_LOG_TMP to avoid difference in next loop and dublicate output.
			cp -f $APRXRF_LOG $APRXRF_LOG_TMP
		fi
		# check if there is a difference between APRX_LOG and APRX_LOG_TMP
		if [[ "$(diff -q $APRX_LOG $APRX_LOG_TMP)" == "Files $APRX_LOG and $APRX_LOG_TMP differ" ]]; then
			# difference found; send out difference to Display 
			diff $APRX_LOG $APRX_LOG_TMP | awk '/^-/ && !/^---/ { $1=""; print }' > $DISPLAY
			# copy APRX_LOG into APRX_LOG_TMP to avoid difference in next loop and dublicate output.
			cp -f $APRX_LOG $APRX_LOG_TMP
		fi
	done
	# loop exit due to APRX not running anymore.
	echo "APRX stopped" > $DISPLAY
	# remove THIS_SCRIPT_PID to indicate that script has stopped working.
	rm -f $THIS_SCRIPT_PID
	# send message to display that output has stopped.
	echo "APRX log-display stopped" > $DISPLAY
	# write system log entry that output has stopped.
	logger -t "$NAME" "APRX log-display stopped"
	# exit the script
else
	# send message to display that log output is already running.
	echo "APRX log-display already running" > $DISPLAY
	# write system log entry that log output is already running.
	logger -t "$NAME" "APRX log-display already running"
fi
# exit the script

#diff -q $APRXRF_LOG $APRXRF_LOG_TMP <- delivers if there is a difference yes/no.
#diff $APRXRF_LOG $APRXRF_LOG_TMP    <- delivers the difference between the two files.
#awk '/^-/ && !/^---/ { $1=""; print }' <- removes the trailing "-" characters from the difference output.