dnl @synopsis adl_COMPUTE_RELATIVE_PATHS(PATH_LIST)
dnl
dnl PATH_LIST is a space-separated list of colon-separated
dnl triplets of the form 'FROM:TO:RESULT'.  This function
dnl iterates over these triplets and set $RESULT to the
dnl relative path from $FROM to $TO.  Note that $FROM
dnl and $TO needs to be absolute filenames for this macro
dnl to success.
dnl
dnl For instance,
dnl
dnl    first=/usr/local/bin
dnl    second=/usr/local/share
dnl    adl_COMPUTE_RELATIVE_PATHS([first:second:fs second:first:sf])
dnl    # $fs is set to ../share
dnl    # $sf is set to ../bin
dnl
dnl $FROM and $TO are both eval'ed recursively and normalized,
dnl this means that you can call this macro with autoconf's dirnames
dnl like `prefix' or `datadir'.  For example:
dnl
dnl    adl_COMPUTE_RELATIVE_PATHS([bindir:datadir:bin_to_data])
dnl
dnl adl_COMPUTE_RELATIVE_PATHS should also works with DOS filenames.
dnl
dnl You may want to use this macro in order to make your package
dnl relocatable.  Instead of hardcoding $datadir into your programs
dnl just encode $bin_to_data and try to determine $bindir at run-time.
dnl
dnl This macro requires adl_NORMALIZE_PATH.
dnl
dnl @author Alexandre Duret-Lutz <duret_g@epita.fr>
dnl @version $Id: $
AC_DEFUN([adl_COMPUTE_RELATIVE_PATHS],
[for _lcl_i in $1; do
  _lcl_from=\[$]`echo "[$]_lcl_i" | sed 's,:.*$,,'`
  _lcl_to=\[$]`echo "[$]_lcl_i" | sed 's,^[[^:]]*:,,' | sed 's,:[[^:]]*$,,'`
  _lcl_result_var=`echo "[$]_lcl_i" | sed 's,^.*:,,'`
  adl_RECURSIVE_EVAL([[$]_lcl_from], [_lcl_from])
  adl_RECURSIVE_EVAL([[$]_lcl_to], [_lcl_to])
  _lcl_notation="$_lcl_from$_lcl_to"
  adl_NORMALIZE_PATH([_lcl_from],['/'])
  adl_NORMALIZE_PATH([_lcl_to],['/'])
  adl_COMPUTE_RELATIVE_PATH([_lcl_from], [_lcl_to], [_lcl_result_tmp])
  adl_NORMALIZE_PATH([_lcl_result_tmp],["[$]_lcl_notation"])
  eval $_lcl_result_var='[$]_lcl_result_tmp'
done])

## Note:
## *****
## The following helper macros are too fragile to be used out
## of adl_COMPUTE_RELATIVE_PATHS (mainly because they assume that
## paths are normalized), that's why I'm keeping them in the same file.
## Still, some of them maybe worth to reuse.

dnl adl_COMPUTE_RELATIVE_PATH(FROM, TO, RESULT)
dnl ===========================================
dnl Compute the relative path to go from $FROM to $TO and set the value
dnl of $RESULT to that value.  This function work on raw filenames
dnl (for instance it will consider /usr//local and /usr/local as
dnl two distinct paths), you should really use adl_COMPUTE_REALTIVE_PATHS
dnl instead to have the paths sanitized automatically.
dnl
dnl For instance:
dnl    first_dir=/somewhere/on/my/disk/bin
dnl    second_dir=/somewhere/on/another/disk/share
dnl    adl_COMPUTE_RELATIVE_PATH(first_dir, second_dir, first_to_second)
dnl will set $first_to_second to '../../../another/disk/share'.
AC_DEFUN([adl_COMPUTE_RELATIVE_PATH],
[adl_COMPUTE_COMMON_PATH([$1], [$2], [_lcl_common_prefix])
adl_COMPUTE_BACK_PATH([$1], [_lcl_common_prefix], [_lcl_first_rel])
adl_COMPUTE_SUFFIX_PATH([$2], [_lcl_common_prefix], [_lcl_second_suffix])
$3="[$]_lcl_first_rel[$]_lcl_second_suffix"])

dnl adl_COMPUTE_COMMON_PATH(LEFT, RIGHT, RESULT)
dnl ============================================
dnl Compute the common path to $LEFT and $RIGHT and set the result to $RESULT.
dnl
dnl For instance:
dnl    first_path=/somewhere/on/my/disk/bin
dnl    second_path=/somewhere/on/another/disk/share
dnl    adl_COMPUTE_COMMON_PATH(first_path, second_path, common_path)
dnl will set $common_path to '/somewhere/on'.
AC_DEFUN([adl_COMPUTE_COMMON_PATH],
[$3=''
_lcl_second_prefix_match=''
while test "[$]_lcl_second_prefix_match" != 0; do
  _lcl_first_prefix=`expr "x[$]$1" : "x\([$]$3/*[[^/]]*\)"`
  _lcl_second_prefix_match=`expr "x[$]$2" : "x[$]_lcl_first_prefix"`
  if test "[$]_lcl_second_prefix_match" != 0; then
    if test "[$]_lcl_first_prefix" != "[$]$3"; then
      $3="[$]_lcl_first_prefix"
    else
      _lcl_second_prefix_match=0
    fi
  fi
done])

dnl adl_COMPUTE_SUFFIX_PATH(PATH, SUBPATH, RESULT)
dnl ==============================================
dnl Substrack $SUBPATH from $PATH, and set the resulting suffix
dnl (or the empty string if $SUBPATH is not a subpath of $PATH)
dnl to $RESULT.
dnl
dnl For instance:
dnl    first_path=/somewhere/on/my/disk/bin
dnl    second_path=/somewhere/on
dnl    adl_COMPUTE_SUFFIX_PATH(first_path, second_path, common_path)
dnl will set $common_path to '/my/disk/bin'.
AC_DEFUN([adl_COMPUTE_SUFFIX_PATH],
[$3=`expr "x[$]$1" : "x[$]$2/*\(.*\)"`])

dnl adl_COMPUTE_BACK_PATH(PATH, SUBPATH, RESULT)
dnl ============================================
dnl Compute the relative path to go from $PATH to $SUBPATH, knowing that
dnl $SUBPATH is a subpath of $PATH (any other words, only repeated '../'
dnl should be needed to move from $PATH to $SUBPATH) and set the value
dnl of $RESULT to that value.  If $SUBPATH is not a subpath of PATH,
dnl set $RESULT to the empty string.
dnl
dnl For instance:
dnl    first_path=/somewhere/on/my/disk/bin
dnl    second_path=/somewhere/on
dnl    adl_COMPUTE_BACK_PATH(first_path, second_path, back_path)
dnl will set $back_path to '../../../'.
AC_DEFUN([adl_COMPUTE_BACK_PATH],
[adl_COMPUTE_SUFFIX_PATH([$1], [$2], [_lcl_first_suffix])
$3=''
_lcl_tmp='xxx'
while test "[$]_lcl_tmp" != ''; do
  _lcl_tmp=`expr "x[$]_lcl_first_suffix" : "x[[^/]]*/*\(.*\)"`
  if test "[$]_lcl_first_suffix" != ''; then
     _lcl_first_suffix="[$]_lcl_tmp"
     $3="../[$]$3"
  fi
done])


dnl adl_RECURSIVE_EVAL(VALUE, RESULT)
dnl =================================
dnl Interpolate the VALUE in loop until it doesn't change,
dnl and set the result to $RESULT.
dnl WARNING: It's easy to get an infinite loop with some unsane input.
AC_DEFUN([adl_RECURSIVE_EVAL],
[_lcl_receval="$1"
$2=`(test "x$prefix" = xNONE && prefix="$ac_default_prefix"
     test "x$exec_prefix" = xNONE && exec_prefix="${prefix}"
     _lcl_receval_old=''
     while test "[$]_lcl_receval_old" != "[$]_lcl_receval"; do
       _lcl_receval_old="[$]_lcl_receval"
       eval _lcl_receval="\"[$]_lcl_receval\""
     done
     echo "[$]_lcl_receval")`])