#! /bin/sh

prog=`basename $0`

x=`echo 'x\c'`
if [ "$x" = x ] ; then X1= ; X2='\c' ; else X1='-n' ; X2= ; fi


usage() {
cat<<END
Usage: $prog  link-rootdir real-rootdir subdir...

Purpose:
	Create a "shadow" tree of symlinks pointing at real files:

	For each non-directory file  real-rootdir/subdir/XXX, we create
	a symbolic link named link-rootdir/subdir/XXX.
	For each directory file  real-rootdir/subdir/DDD, we create
	a directory link-rootdir/subdir/DDD, and recursively invoke
	$prog  on those files.

Example:
	If you have
		/opt/xyz/bin/prog1
		/opt/xyz/bin/prog2
		/opt/xyz/man/man1/prog1.1
		/opt/xyz/man/man1/prog2.1
		/opt/xyz/man/man4/prog1.4

	Then the command

		$prog /opt /opt/xyz   bin man

	will create links in /opt/bin and /opt/man that shadow the
	actual files in /opt/xyz/bin and /opt/xyz/man.

USE WITH CAUTION -- you can create lots of unwanted files!
END
}

case $# in [012] ) usage ; exit 1 ;; esac
case "$1" in -h ) usage ; exit 1 ;; esac

linkrootdir="$1"
realrootdir="$2"
shift 2

case $linkrootdir in /* ) link_isabs=y ;; * ) link_isabs=n ;; esac
case $realrootdir in /* ) real_isabs=y ;; * ) real_isabs=n ;; esac
case $link_isabs$real_isabs in
yy ) ;;
* ) echo "The link-rootdir and real-rootdir must be absolute paths."
    echo "This is to minimize accidents."
    echo "No links made."
    exit 0
    ;;
esac

test -d $realrootdir || { echo "$realrootdir isn't a directory!" ;
				echo "No links made." ; exit 1 ; }
test -d $linkrootdir || { echo "$linkrootdir isn't a directory!" ; 
				echo "No links made." ; exit 1 ; }

echo "$prog will create the following links:"
ok=1
for subdir in "$@" ; do
    todir=$realrootdir/$subdir 
    if [ ! -d $todir ] ; then
	echo "    Error: $todir isn't a directory!"
	ok=0
    else
	echo "    From: $linkrootdir/$subdir/XXX	   to: $realrootdir/$subdir/XXX"
    fi
done
test $ok = 1 || { echo "No links made." ; exit 1 ; }

ans=""
while
    case "$ans" in [yYnN] | [Yy][Ee][Ss] | [Nn][Oo] ) ok=1 ;; * ) ok=0 ;; esac
    test $ok = 0
do
    echo $X1 "Is this correct? (y/n) $X2"
    read ans
done

case $ans in
[yY]* ) ;;
* ) echo "No links made." ; exit 0 ;;
esac

# DRY RUN: check for existing files.
# a) Check for things that should be subdirectories, but are files.
tmpfile=/tmp/mklinks.$$
ls $tmpfile >/dev/null 2>&1
test $? || {
    echo "Temp file $tmpfile already exists!"
    ls -l $tmpfile
    echo "No links made."
    exit
}
trap "/bin/rm -f $tmpfile" 0

cd $realrootdir
is_ok=1
exec 3>$tmpfile
for subdir in `find "$@" -type d -print` ; do
    path="$linkrootdir/$subdir"
    test -f "$path" && {
	echo "$path" >&3
	echo "$path exists, and is supposed to be a directory, but it's not."
    }
done

# b) Check for links that already exist.
cd $realrootdir
find "$@" ! -type d -print | while read file ; do
    from="$linkrootdir/$file"
    test -f "$from" && {
	echo "$from" >&3
	echo "$from exists, but is supposed to be a new symlink."
    }
done
exec 3>&-
case `wc -l $tmpfile | awk '{print $1}'` in
0 ) action=none
    ;;
* )	ans=""
	while
	    case "$ans" in
		[qQ]* ) echo "No links made." ; exit 0 ;;
		[dD]* ) action=delete ; ok=1;;
		[rR]* ) action=rename ; ok=1;;
		* ) ok=0 ;;
	    esac
	    test $ok = 0
	do
	    echo $X1 "(q)uit, (d)elete the above, (r)ename them to *.bak: $X2"
	    read ans
	done
    ;;
esac

# Create missing subdirectories
cd $realrootdir
for subdir in `find "$@" -type d -print` ; do
    path="$linkrootdir/$subdir"
    test -f "$path" && {
	case $action in
	delete ) echo "Deleting old $path" ; rm -f "$path" ;;
	rename ) echo "Renaming old $path to $path.bak" ;
			mv "$path" "$path.bak" ;;
	esac
    }
    test -d "$path" || { echo "Creating $path" ; echo mkdir "$path" ; }
done

# Create links
cd $realrootdir
find "$@" ! -type d -print | while read file ; do
    linkfrom="$linkrootdir/$file"
    test -f "$linkfrom" && {
	case $action in
	delete ) echo "Deleting old $linkfrom" ; rm -f "$linkfrom" ;;
	rename ) echo "Renaming old $linkfrom to $linkfrom.bak" ;
			mv "$linkfrom" "$linkfrom.bak" ;;
	esac
    }
    echo ln -s "$realrootdir/$file" "$linkfrom"
	 ln -s "$realrootdir/$file" "$linkfrom"
done