#!/bin/bash
# Fix file creation for U-Blox GPS.
# If GPS reaches expected
# fix level, file GSP_FIXFILE is created.
# This is to know when to set the system
# and hardware clock, and when 
# it is safe to start ntp.
# DEBUG=1 to set debug
NAME=gpsd_ubx_fixed
shopt -s expand_aliases
alias LG=logger\ -t\ ${NAME}
if [[ -r /etc/default/gpsd ]] ; then
  . /etc/default/gpsd
else
  echo "Must configure GPSD requirements"
  exit 1
fi
UBXNAVSOL='b56201063400'
UBXNAVSOLLEN=60

function rm_gps_file
{
  if [[ -n "${GPS_FIXFILE}" ]] && [[ -f ${GPS_FIXFILE} ]] ; then
    rm -f "${GPS_FIXFILE}"
  fi
}
function kill_it
{
    cmd=$1
    pid=$2
    sig=$3
    ((DEBUG)) && LG -p user.info "terminating $cmd(${pid}) with SIG${sig}"
    kill -SIG${sig} ${pid} >/dev/null 2>&1
    result=$?                                                                                                                                                                                      
    ((DEBUG)) && LG -p user.info "kill -SIG${sig} ${pid} result is $result"  
}        


# Most exits are errors, so remove the GPS fix file.
trap rm_gps_file EXIT

if ! [[ -x /usr/bin/gpsmon ]] ; then
  LG -p user.err "Please install gpsmon"
  exit 0
fi

# Terminate gpsmon after 10 seconds if it is our child
# gpsmon has issues with terminals and stalling on terminal
# read of the console.
(
  sleep 10
  # We use BASHPID because our parent, $$, may have already exited, and
  # then ps will not work.  BASHPID is the current subshell.
  ppid=$BASHPID
  pgid=$(ps --no-heading -o pgid -p $ppid)
  
  if ((${#pgid} == 0)) ; then
    LG -p user.err "Could not find a pgid for $ppid"
    ps -fjp $ppid | LG -p user.error
  fi

  gpsmonpid=$(pgrep -lg $pgid | egrep '[[:space:]]gpsmon$' | sed 's/[[:space:]].*//')
  ((DEBUG)) && LG -p user.info "$pgid is pgid $gpsmonpid is gpsmonpid"
  # Find the gpsmonpid that is our grandchild
  ((didkill=0))
  
  # for loop is in case gpsmonpid has children.
  for p in ${gpsmonpid} ; do
    if ((${#p})) ; then
        kill_it gpsmon $p TERM
        ((didkill=p))
        break
    fi
  done
  if ((didkill == 0)) ; then
    exit 0
  fi
  # Do a sigkill to be sure.
  sleep 2
  kill_it gpsmon $didkill KILL
) &

fix=""
status=""

# egrep in busybox has a horrible buffering issue.
# echo My shell pid is $$
# echo Place data fix, status
stuff="$(gpsmon -a 2>&1 | {
  OIFS=${IFS}
  IFS=$'\n'
  while read ln ; do
    if [[ $ln =~ ^[[:space:]]*\(${UBXNAVSOLLEN}\)[[:space:]]*${UBXNAVSOL}....................(..)(.) ]] ; then
      IFS=${OIFS} 
      fix="${BASH_REMATCH[1]}"
      if ((${#fix} == 0)) ; then
	fix="unknown"
      fi
      status=$(echo "${BASH_REMATCH[2]}")
      if ((${#status} == 0)) ; then
	status="unknown"
      fi
      break;
    fi
    oldln="${ln}"
  done
  if ((${#fix})) && ((${#status})) ; then
    echo "$fix,$status"
  else
    echo "${oldln}"
  fi
})"

if ((${#stuff} == 0)) ; then
  LG -p user.err "No data from GPS"
  exit 1
fi

if [[ -t 1 ]] ; then
  stty echo icanon 2>/dev/null
fi

OIFS=${IFS}
IFS=,
set $stuff
fix="$1"
status="$2"
IFS=${OIFS}

# fixOK is the least significant bit of a hex single digit
case $status in
  [13579bBdDfF])
    ((fixOK=1))
    ;;
  [02468aAcCeE])
    ((fixOK=0))
    ;;
  *)
    LG -p user.err "Is GPSD running?"
    LG -p user.err "FIX OK field should be single hex digit: gpsmon data: $stuff"
    exit 1
    break
    ;;
esac

# echo "status is $status.  fixOK is $fixOK"


if ((fixOK == 0)) ; then
  LG -p user.err "Problem with the GPS fix.  The fix is an even value, \"$status\", and should be an odd value.  fixOK=${fixOK}"
  exit 1
  # Retry later.  How?
fi

# echo "fix is $fix.   Is it in $GPSFIX?"
# Test the GPS fixOK
for x in $GPSFIX ; do
  # echo test $x with $fix
  if [[ $x == $fix ]] ; then
    LG -p user.info "GPS has fix $fix found in list GPSFIX: $GPSFIX"
    echo $x >"${GPS_FIXFILE}"
    GPS_FIXFILE=""
    exit 0
  fi
done

LG -p user.info "GPS fix is bad: $fix and should be one of: $GPSFIX"
# Start later
exit 1