controlling media in macosx terminal

gistfile1.md

$ media [TAB] [TAB]
pause   play    skip    volume

$ media play [TAB] [TAB]
itunes spotify

$ media pause [TAB] [TAB]
itunes spotify

$ media skip [TAB] [TAB]
itunes spotify

$ media volume [RETURN]
output volume:20, input volume:100, alert volume:100, output muted:false

$ media volume [TAB] [TAB]
down up

$ media volume up 10 [RETURN]
output volume:30, input volume:100, alert volume:100, output muted:false

$ media volume down 10 [RETURN]
output volume:20, input volume:100, alert volume:100, output muted:false

media

#!/usr/bin/env bash

current_volume()
{
  VOL=$(osascript -e "get volume settings" | awk  '/output volume/ { print substr($2, 8, index($2, ",") - index($2, ":") - 1); }')
}

volume()
{
  case "$LEVEL" in
    up)
      current_volume
      if [ $INC ]; then
        VOL=$VOL+$INC
      else
        VOL=$VOL+1
      fi
      ;;
    down)
      current_volume
      if [ $INC ]; then
        VOL=$VOL-$INC
      else
        VOL=$VOL-1
      fi
      ;;
  esac

  if [ $VOL ]; then
    osascript -e "set volume output volume ${VOL}"
  fi
  osascript -e "get volume settings"
}

case "$1" in
  v|vol|volume)
    LEVEL=$2
    INC=$3
    volume
    ;;
  play|start)
    SOURCE=$2
    if [ $SOURCE ]; then
      osascript -e "tell application \"${SOURCE}\" to play"
    fi
    ;;
  skip)
    SOURCE=$2
    if [ $SOURCE ]; then
      osascript -e "tell application \"${SOURCE}\" to play next track"
    fi
    ;;
  pause|stop)
    SOURCE=$2
    if [ $SOURCE ]; then
      osascript -e "tell application \"${SOURCE}\" to pause"
    fi
    ;;
  *)
    echo "Usage: media ACTION [OPTION [VALUE]]"
    ;;
esac

media_completion

_media()
{
  cur=${COMP_WORDS[COMP_CWORD]}
  prev=${COMP_WORDS[COMP_CWORD-1]}
  case "${prev}" in
    play|pause|skip)
      COMPREPLY=( $(compgen -W "spotify itunes" -- $cur) )
      ;;
    volume)
      COMPREPLY=( $(compgen -W "up down" -- $cur) )
      ;;
    up|down)
      ;;
    *)
      COMPREPLY=( $(compgen -W "pause play skip volume" -- $cur) )
      ;;
  esac
}

complete -F _media media