#!/usr/bin/env bash

# Renders a text based list of options that can be selected by the
# user using up, down and enter keys and returns the chosen option.
#
#   Arguments   : list of options, maximum of 256
#                 "opt1" "opt2" ...
#   Return value: selected index (0 for opt1, 1 for opt2 ...)


function select_option {
    local nformat
    local optcount=$#
    printf -v nformat "%%%dd. " ${#optcount}
    local max_opt=0
    for opt; do
      if [[ "${#opt}" -gt $max_opt ]]; then
        max_opt=${#opt}
      fi
    done

    # little helpers for terminal print control and key input
    ESC=$( printf "\033")
    cursor_blink_on()  { printf "$ESC[?25h"; }
    cursor_blink_off() { printf "$ESC[?25l"; }
    cursor_to()        { printf "$ESC[$1;${2:-1}H"; }
    if [[ $SELECT_MONOCHROME -eq 1 ]]; then
        print_option()     { printf "   $1 "; }
        print_selected()   { printf "  [$ESC[1m$1$ESC[0m] "; }
    else
        print_option()     { printf "  $ESC[33m $1 $ESC[0m "; }
        print_selected()   { printf "  [$ESC[37;1m$1$ESC[0m] "; }
    fi
    get_cursor_row()   { IFS=';' read -sdR -p $'\E[6n' ROW COL; echo ${ROW#*[}; }
    key_input()        { read -s -n1 key1 2>/dev/null >&2
                         read -s -n2 -t 0.1 key2 2>/dev/null >&2
                         if [[ "$key1" =~ ^[0-9]+$ ]]; then
                           echo $key1; return;
                         fi
                         if [[ $key1$key2 = $ESC[A ]]; then echo up; return; fi
                         if [[ $key1$key2 = $ESC[B ]]; then echo down; return; fi
                         if [[ $key1 = $'\e'  ]]; then echo esc; return;   fi
                         if [[ $key1 = ""     ]]; then echo enter; return; fi
                    }
    reset_display()  {
        cursor_blink_on; stty echo; printf '\n';
    }
    # initially print empty new lines (scroll down if at bottom of screen)
    for opt; do printf "\n"; done

    # determine current screen position for overwriting the options
    local lastrow=`get_cursor_row`
    local startrow=$(($lastrow - $#))

    # ensure cursor and input echoing back on upon a ctrl+c during read -s
    trap "cursor_blink_on; stty echo; printf '\n'; exit 1" 2
    cursor_blink_off

    local selected=0
    while true; do
        # print options by overwriting the last lines
        local idx=0
        local nidx

        for opt; do
            if [[ $SELECT_UNDERSCORES -eq 1 ]]; then
                opt=${opt//_/ }
            fi
            if [[ $SELECT_NUMBERS -eq 1 ]]; then
                printf -v nidx "$nformat" $(( idx + 1 ))
            fi
            printf -v padopt "%-${max_opt}s" "$opt"
            cursor_to $(($startrow + $idx))
            if [ $idx -eq $selected ]; then
                print_selected "$nidx$padopt"
            else
                print_option "$nidx$padopt"
            fi
            ((idx++))
        done

        # user key control
        local user_input=`key_input`
        case "$user_input" in
            enter) break;;
            esc)   reset_display; exit 1;;
            up)    ((selected--));
                   if [ $selected -lt 0 ]; then selected=$(($# - 1)); fi;;
            down)  ((selected++));
                   if [ $selected -ge $# ]; then selected=0; fi;;
            [0-9]) selected=$(( $user_input - 1 )) ;;
        esac
    done

    # cursor position back to normal
    cursor_to $lastrow
    reset_display
    if [[ -n "$SELECT_TOFILE" ]]; then
      local idx=0
      for opt; do
        if [ $idx -eq $selected ]; then
          echo "$opt" > "$SELECT_TOFILE"
        fi
        ((idx++))
      done
    fi
    return $(( 10 + $selected ))
}

[[ $_ == $0 ]] && {
_help() {
  SELF=$( basename "$0" )
  echo "Select Option

  Usage: $SELF [-n] [--nc] [-o File] [-_] list of options
    -n       Number list
    --nc     No colors
    -o File  Save the choice in a file
    -_       Print spaces instead of underscores

  Returns
    (10 + index) of selection (first option = 10)
    1 if ctrl-c or ESC pressed

  Example:
    $SELF -n one two three
    EC=\$?
    [[ \$EC -lt 10 ]] && { echo Exited..; } || { echo You selected \$(( \$EC - 9 )); }
"
  exit
}

SELECT_MONOCHROME=0
SELECT_NUMBERS=0
SELECT_UNDERSCORES=0
SELECT_TOFILE=""
for (( i=1; i<=$#; i++ )); do
  value=${!i}
  j=$(( i + 1 ))
  [[ "$value" = "-h" ]] && _help
  [[ "$value" = "--help" ]] && _help
  [[ "$value" = "--nc" ]] && { SELECT_MONOCHROME=1; continue; }
  [[ "$value" = "-n" ]] && { SELECT_NUMBERS=1; continue; }
  [[ "$value" = "-_" ]] && { SELECT_UNDERSCORES=1; continue; }
  [[ "$value" = "-o" ]] && { SELECT_TOFILE="${!j}"; ((i++)); continue; }
  opts+=( "$value" )
done

select_option "${opts[@]}"
exit $?
}