#!/bin/sh -e
#
# 
# "makelinks base linkdir realdir" does a "relative ln", relatively to "base". "linkdir" and "realdir" are relative path to subdirectories under "base". Symlinks are created into linkdir for files in realdir. The symlinks do not contain "base".
# 
#

test "$#" -ge 3 || { echo "makelinks: too few arguments" 1>&2 ; exit 100 ; }

computerelative() {
  source="$1"
  target="$2"

  common="$source"
  result=""

  while test "${target#$common}" = "$target" ; do
    common="$(dirname $common)"
    if test -z "$result" ; then
      result=".."
    else
      result="../$result"
    fi
  done

  if test "$common" = "/" ; then
    result="$result/"
  fi

  forward="${target#$common}"

  if test -n "$result" -a -n "$forward" ; then
    result="$result$forward"
  elif test -n "$forward" ; then
    result="${forward:1}"
  fi

  echo "$result"
}

base=${1%%/}
linkdir=${2%%/}
realdir=${3%%/}

targetdir=$(computerelative "$base$linkdir" "$base$realdir")

for i in $(ls -1 "$base$realdir") ; do
  ln -sf "$targetdir/$i" "$base$linkdir/$i" || true
done