[bibtex] Add priority filtering to bib-due

Can filter by priority using `-p` option, script will then go down the
list and display only paper of this priority or higher.

For example priority 3 will display 3,2,1 but not those without;
priority 1 will only display 1

bibtex/.local/bin/bib-due

@@ -72,7 +72,24 @@ filter_until() {
     lastprinted="$((lastline - 1))"
     entries=$(echo "$entries" | sed -n "1,${lastprinted}p;${lastline}q")
   fi
+}
 
+filter_priority() {
+  priority="$1"
+  # filter for dates, with line numbers
+  # filtered=$(echo "$entries" | grep -noE '[[:digit:]]{4}-[[:digit:]]{2}-[[:digit:]]{2}')
+  filtered=""
+  while [ "$priority" -gt 0 ]; do
+    current=$(echo "$entries" | grep -E "\($priority\)")
+
+    # append found to filtered entries
+    filtered=$(printf "%s\n%s" "$filtered" "$current")
+
+    # go to next 'higher' priority
+    priority="$((priority - 1))"
+  done
+  # sort them chronologically again, remove empty lines
+  entries="$(echo "$filtered" | sed -e '/^$/d' | sort)"
 }
 
 main() {
@@ -91,11 +108,14 @@ main() {
   if [ -n "$until" ]; then
     filter_until
   fi
+  if [ -n "$priority" ]; then
+    filter_priority "$priority"
+  fi
 
   echo "$entries"
 }
 
-while getopts "h?i:u:r:l:" opt; do
+while getopts "h?i:u:r:l:p:" opt; do
   case "$opt" in
   h | \?)
     show_help
@@ -115,6 +135,9 @@ while getopts "h?i:u:r:l:" opt; do
   u)
     until="$(date -d "$OPTARG" +%s)"
     ;;
+  p)
+    priority="$OPTARG"
+    ;;
   esac
 done
 shift $((OPTIND - 1))