#!/usr/bin/env bash


_help() {
  SELF=$( basename "$0" )
  echo "Read arrows keys up/down

  Usage: $SELF [-c Char]
    -c Char   Print Char character at the start of line

  Returns
    100 - number of rows above start point
    0 if ctrl-c or ESC pressed

"
  exit
}

CHAR=""
for (( i=1; i<=$#; i++ )); do
  value=${!i}
  j=$(( i + 1 ))
  [[ "$value" = "-h" ]] && _help
  [[ "$value" = "--help" ]] && _help
  [[ "$value" = "-c" ]] && { CHAR="${!j}"; ((i++)); continue; }
done
printf -v EMPTYCHAR "%-${#CHAR}s" " "


ESC=$( printf "\033")
cursor_blink_on()  { printf "$ESC[?25h"; }
cursor_blink_off() { printf "$ESC[?25l"; }
cursor_to()        { printf "$ESC[$1;${2:-1}H"; }
get_cursor_row()   { IFS=';' read -sdR -p $'\E[6n' ROW COL; echo ${ROW#*[}; }
get_screen_rows()   { tput lines; }
key_input()        { read -s -n1 key1 2>/dev/null >&2
                     read -s -n2 -t 0.1 key2 2>/dev/null >&2
                     if [[ $key1 = ""     ]]; then echo enter; return; fi
                     if [[ $key1$key2 = $ESC[A ]]; then echo up; return; fi
                     if [[ $key1$key2 = $ESC[B ]]; then echo down; return; fi
                     if [[ -z "$key2" ]]; then
                       if [[ $key1 = $'\e'  ]]; then echo esc; return;   fi
                     fi
                }
reset_display()  {
    cursor_blink_on; stty echo;
}
print_char()     { printf -- "$CHAR\r"; }
print_empty()     { if [[ -n "$CHAR" ]]; then printf "$EMPTYCHAR\r"; fi; }

startrow=`get_cursor_row`
trap "cursor_blink_on; stty echo; cursor_to $startrow; exit 1" 2
#trap "cursor_blink_on; stty echo; printf '\n'; exit 1" 2
if [[ -n "$CHAR" ]]; then
    cursor_blink_off
fi
selected=0
while true; do
    cursor_to $(( $startrow - $selected))
    print_char
    # user key control
    case `key_input` in
        enter) break;;
        esc)   reset_display; exit 1;;
        up)
            cursor_to $(( $startrow - $selected))
            print_empty
            ((selected++));
            # limit going top
        ;;
        down)
            cursor_to $(( $startrow - $selected))
            print_empty
            ((selected--));
            # limit going down
        ;;
    esac
    lastrow=`get_cursor_row`
    if [ $(( $startrow - $selected )) -lt 1 ]; then
      ((selected--))
    fi
    if [ $(( startrow - $selected )) -gt `get_screen_rows` ]; then
      ((selected++))
    fi
done

cursor_blink_on
cursor_to $startrow

exit $(( 100 - $selected ))