#!/bin/bash
#
# ppa: brightbox/ruby-ng/ubuntu
#

BINS="gem irb rake ruby ri rdoc erb"
VERS="1.9 1.9.1 2.0 2.1 2.2 2.3"

function display_alternatives() {
  update-alternatives --display ${1:?"bin name"}
}

function install_alternative() {
  update-alternatives --install /usr/bin/${1:?"bin name"} ${1:?"bin name"} /usr/bin/${1:?"bin name"}${2:?"version"} ${3:-"1"}
}

function list_alternatives() {
  update-alternatives --list $1
}

function list_available() {
  for ver in ${1:-$VERS}; do
    for bin in $BINS; do
      which $bin$ver 2>/dev/null
    done
  done
}

function set_alternative() {
  update-alternatives --verbose --set ${1:?"bin name"} /usr/bin/${1:?"bin name"}${2:?"version"}
}

case $1 in
  clear)
    for ver in $VERS; do
      echo "removing $ver"

      for bin in $(list_available $ver); do
        update-alternatives --remove $(basename ${bin/$ver/}) $bin
      done
    done
  ;;

  set)
    for bin in $BINS; do
      set_alternative $bin ${2:?"version missing"}
    done
  ;;

  install)
    for ver in $VERS; do
      echo "configuring $ver"

      for bin in $(list_available $ver); do
        install_alternative $(basename ${bin/$ver/}) $ver
      done
    done
  ;;

  check)
    echo -e "current:"
    for bin in $BINS; do display_alternatives $bin | sed 's/^/\t/g'; done
  ;;

  list)
    echo -e "available:"
    list_available $2 | sed 's/^/\t/g'

    echo -e "\ninstalled:"
    for bin in $BINS; do list_alternatives $bin | sed 's/^/\t/g'; done
  ;;

  *)
    echo "$0 (check|install|list) [version]"
  ;;
esac