#!/usr/bin/env bash
#
# Update /etc/default/postfwd (idempotent) and restart postfwd if needed.
#
#   For every variable below:
#     - already set to the wanted value  -> nothing to do
#     - set to a different value         -> comment out the current setting
#                                           and add the new one directly below
#     - not set at all                   -> append the new setting
#
#   Quotes around values are ignored when comparing (PORT="10040" == PORT=10040).
#
#   At the end:
#     - file changed   -> 'systemctl restart postfwd'
#                         (ARGS, INET and PORT are start parameters of the
#                         daemon - a reload does NOT apply them)
#     - file unchanged -> postfwd is left alone (no restart, no reload)
#

postfwd_default_file="/etc/default/postfwd"

# - Wanted settings: "VAR|VALUE" (VALUE written exactly as it should appear)
wanted_settings=(
   'STARTUP|1'
   'CONF|/etc/postfix/postfwd.cf'
   'INET|127.0.0.1'
   'PORT|10040'
   'ARGS|"--summary=600 --cache=0"'
)


# -------------
# --- Some functions
# -------------

log_file="$(mktemp)"

clean_up() {
   rm -f "$log_file"
   exit $1
}

echononl() {
   echo -e -n "$*"
}
echo_ok() {
   echo -e "\033[60G[ \033[32mok\033[m ]"
}
echo_skipped() {
   echo -e "\033[60G[ \033[33m\033[1mskipped\033[m ]"
}
echo_failed() {
   echo -e "\033[60G[ \033[1;31mfailed\033[m ]"
}
error() {
   echo ""
   echo -e "\t[ \033[31m\033[1mError\033[m ]: $*"
   echo ""
}
fatal() {
   error "$*"
   echo -e "\t\033[31m\033[1mScript will be interrupted\033[m"
   echo ""
   clean_up 1
}

# - set_postfwd_default <VAR> <VALUE>
# -
# - returns 0 if the file was changed, 1 if nothing changed, 2 on error
# -
set_postfwd_default() {
   local _var="$1"
   local _val="$2"
   local _tmp_file
   local _rval

   echononl "   ${_var}=${_val}"

   _tmp_file="$(mktemp)"
   awk -v var="$_var" -v val="$_val" '
      function unq(s) {
         gsub(/^[ \t\r]+|[ \t\r]+$/, "", s)
         if (s ~ /^".*"$/ || s ~ /^\047.*\047$/) s = substr(s, 2, length(s) - 2)
         return s
      }
      function is_set(s) { return s ~ ("^[ \t]*" var "=") }
      function is_wanted(s) {
         sub("^[ \t]*" var "=", "", s)
         return unq(s) == unq(val)
      }
      # - Read the whole file first: a line with the wanted value must stay
      # - untouched, no matter which other settings of VAR precede it.
      {
         line[NR] = $0
         if (is_set($0) && is_wanted($0)) found = 1
      }
      END {
         for (i = 1; i <= NR; i++) {
            if (! is_set(line[i])) { print line[i] ; continue }
            if (is_wanted(line[i])) { print line[i] ; continue }
            print "#" line[i]
            if (! found) { print var "=" val ; found = 1 }
         }
         if (! found) print var "=" val
      }
   ' "$postfwd_default_file" > "$_tmp_file" 2> "$log_file"

   if [[ $? -ne 0 ]] ; then
      echo_failed
      error "$(cat "$log_file")"
      _rval=2
   elif cmp -s "$_tmp_file" "$postfwd_default_file" ; then
      echo_skipped
      _rval=1
   else
      # - cat instead of mv/cp keeps owner and permissions of the original file
      if cat "$_tmp_file" > "$postfwd_default_file" 2> "$log_file" ; then
         echo_ok
         _rval=0
      else
         echo_failed
         error "$(cat "$log_file")"
         _rval=2
      fi
   fi

   rm -f "$_tmp_file"
   return $_rval
}


# -------------
# --- Main
# -------------

[[ "$(id -u)" -eq 0 ]] || fatal "This script must be run as root."

command -v postfwd > /dev/null 2>&1 || fatal "postfwd is not installed."

if [[ ! -f "$postfwd_default_file" ]] ; then
   touch "$postfwd_default_file" 2> "$log_file" || fatal "$(cat "$log_file")"
fi

echo ""
echo "Update ${postfwd_default_file}"
echo ""

file_changed=false
errors=false

for _setting in "${wanted_settings[@]}" ; do
   set_postfwd_default "${_setting%%|*}" "${_setting#*|}"
   case $? in
      0) file_changed=true ;;
      2) errors=true ;;
   esac
done

echo ""

if $errors ; then
   fatal "Errors while updating '${postfwd_default_file}' - postfwd NOT restarted."
fi

if ! $file_changed ; then
   echo "   Nothing changed - postfwd is left alone."
   echo ""
   clean_up 0
fi

echononl "   Restart postfwd (start parameters changed)"
if systemctl restart postfwd > "$log_file" 2>&1 ; then
   echo_ok
else
   echo_failed
   error "$(cat "$log_file")"
   clean_up 1
fi

echo ""
clean_up 0