#! /bin/bash
#
# Symlink a existing file to a new location.  Rename and link to old versions with datestamps.
#
# usage: link2 [options] target [link]
#     -v | --vrebose	Echo command names
#     -d | --debug	Additional debugging output
#     -h | --help		This text
#     -n | --dry-run	Do not execute
#     -r | --remove 	Remove link/file if it exists
#
# Examples:
#
#  $ link2 -v /etc/passwd
#  ln -s /etc/passwd /home/george/bin/passwd
#
#  $ link2 -v /etc/issue passwd
#  mv passwd passwd.20150609:052604EDT
#  ln -s /etc/issue passwd
#
#  $ link2 -r -v /etc/issue passwd
#  link2: passwd already points to /etc/issue
#
#  $ link2 -r -v /etc/issue passwd
#  rm -f passwd
#  ln -s /etc/issue passwd
#
#  $ link2 -v /etc/passwd $HOME
#  ln -s /etc/passwd /home/george/passwd
#
#
# Author:
#   George Jones

set -e -u

PROG_NAME=$0
PROG_NAME=`basename $0`
SHORT_OPTS='vdhnrs:'
LONG_OPTS='verbose,debug,dry-run,help,remove,stack-size:'
OPTS=`getopt -o $SHORT_OPTS --long $LONG_OPTS -n 'parse-options' -- "$@"`

function usage() {
  cat <<END >&2
usage: $PROG_NAME [options] target [link]
    -v | --verbose	Echo command names
    -d | --debug	Additional debugging output
    -h | --help		This text
    -n | --dry-run	Do not execute
    -r | --remove 	Remove link/file if it exists
END
exit 1
}

if [ $? != 0 ] ; then echo "Failed parsing options." >&2 ; exit 1 ; fi

eval set -- "$OPTS"

# Default values

VERBOSE=false
HELP=false
DRY_RUN=false
STACK_SIZE=0
DEBUG=false
REMOVE=false

# Set user selected options

while true; do
  case "$1" in
    -v | --verbose ) VERBOSE=true; shift ;;
    -d | --debug ) DEBUG=true; shift ;;
    -h | --help )    HELP=true; shift ;;
    -n | --dry-run ) DRY_RUN=true; shift ;;
    -r | --remove ) REMOVE=true; shift ;;
    -s | --stack-size ) STACK_SIZE="$2"; shift; shift ;;
    -- ) shift; break ;;
    * ) break ;;
  esac
done

if $DEBUG; then
  VERBOSE=true
fi

if $DEBUG; then
    echo VERBOSE=$VERBOSE
    echo DEBUG=$DEBUG
    echo HELP=$HELP
    echo DRY_RUN=$DRY_RUN
    echo REMOVE=$REMOVE
    echo STACK_SIZE=$STACK_SIZE
fi

# validate arguments

if [[ "$STACK_SIZE" =~ '"^[0-9]+$' ]]; then
  echo "$PROG_NAME: stack_size must be an integer.  Got /$STACK_SIZE/" >&2
  usage
fi


# get file arguments

if [ "$#" -lt 1 ]; then
  echo $PROG_NAME: Missing target
  usage
fi

if $HELP; then
  usage
fi

file=$1
whereto=${2:-"${PWD}"}

# figure out the link target, make sure it exists

target="`readlink -f $file`"
if $DEBUG; then echo target $target; fi

if [ ! -e ${target} ]; then
  echo $0: ${target} does not exist >&2
  exit 1
fi

# figure out the link source, using basename of target

base=`basename $file`

if [ -d `readlink -f "${whereto}"` ]; then
    link="${whereto}""/""${base}"
else
    link=${whereto}
fi

# Remove link if it exists

if  $REMOVE && [ -h $link -o -f $link ]; then
    if $DRY_RUN || $VERBOSE; then
	echo rm -f $link
    fi

    if  ! $DRY_RUN; then
	rm -f $link
    fi
fi


# move any pre-existing file to a dated save version, unless it's the same

now=`date "+%Y%m%d:%H%M%S%Z"`

if [ -e ${link} ]; then

    # TODO abort here if target already points to target.

    expandedLink=`readlink -e ${link}`
    expandedTarget=`readlink -e ${target}`

    if [ ${expandedLink} == ${expandedTarget} ]; then
       echo $PROG_NAME: ${link} already points to ${target} >&2
       exit 0
    fi

    if $DRY_RUN || $VERBOSE; then
	echo mv ${link} "${link}.${now}"
    fi

    if  ! $DRY_RUN; then
	mv ${link} "${link}.${now}"
    fi
  
fi

# finally, make the link

if $DEBUG; then echo target $target  >&2; fi

if $DRY_RUN ||  $VERBOSE; then    
    echo ln  -s ${target} ${link}
fi

if ! $DRY_RUN; then
    ln  -s ${target} ${link}
fi