#
# DIRECTORY MANIPULATION FUNCTIONS pushd, popd, and dirs
#
# This example is from pages 270 - 273 in the "The New Korn Shell Command
# and Programming Language" by Morris I. Bolsky and David G. Korn (1995
# Prentice Hall).
#
# Usage:    dirs
#           pushd [directory]
#           pushd +n
#
# Uses global variables _push_max _push_top _push_stack
integer _push_max=100 _push_top=100

# Display directory stack -- $HOME displayed as ~
function dirs {
   typeset dir=${PWD#$HOME/}
   case $dir in
      $HOME)
         dir=\~ ;;
      /*)
         ;;
      *)
         dir=\~/$dir ;;
   esac
   print -r -- "$dir ${_push_stack[@]}"
}

# Change directory and put directory on front of stack
function pushd {
   typeset dir= type=0
   integer i

   case $1 in
      "")
         # pushd
         if ((_push_top >= _push_max)) ; then
            print -u2 pushd: No other directory.
            return 1
         fi

         type=1 dir=${_push_stack[_push_top]} ;;
      +[1-9]*([0-9]))
         # pushd +n
         integer i=_push_top$1-1

         if ((i >= _push_max)) ; then
            print -u2 pushd: Directory stack not that deep
            return 1
         fi

         type=2 dir=${_push_stack[i]} ;;
      *)
         if ((_push_top <= 0)) ; then
            print -u2 pushd: Directory stack overflow.
            return 1
         fi ;;
   esac

   case $dir in
      ~*)
         dir=$HOME${dir#~} ;;
   esac

   cd "${dir:~$1}" || return 1
   dir=${OLDPWD#$HOME/}
   case $dir in
      $HOME)
         dir=\~ ;;
      /*)
         ;;
      *)
         dir=\~/$dir ;;
   esac

   case $type in
      0)
         # pushd name
         _push_stack[_push_top=_push_top-1]=$dir ;;
      1)
         # pushd
         _push_stack[_push_top]=$dir ;;
      2)
         # pushd +n
         type=${1#+} i=_push_top-1
         set -- "${_push_stack[@]}" "$dir" "${_push_stack[@]}"
         shift $type

         for dir ; do
            (((i=i+1) < _push_max)) || break
            _push_stack[i]=$dir
         done ;;
   esac

   dirs
}

# Pops the top directory
function popd {
   typeset dir

   if ((_push_top >= _push_max)) ; then
      print -u2 popd: Nothing to pop.
      return 1
   fi

   case $1 in
      "")
         dir=${_push_stack[_push_top]}

         case $dir in
            ~*)
               dir=$HOME${dir#~} ;;
         esac

         cd "$dir" ;;
      +[1-9]*([0-9]))
         integer i=_push_top$1-1

         if ((i >= _push_max)) ; then
            print -u2 pushd: Directory stack not that deep
            return 1
         fi

         while ((i > _push_top)) ; do
            _push_stack[i]=${_push_stack[i-1]}
            (( i -= 1 ))
         done ;;
      *)
         print pushd: Bad directory.
         return 1 ;;
   esac

   unset _push_stack[_push_top]
   (( _push_top += 1))

   dirs
}