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+# Copyright 1999-2003 Gentoo Technologies, Inc.
+# Distributed under the terms of the GNU General Public License v2
+# $Header: /var/cvsroot/gentoo-x86/eclass/alternatives.eclass,v 1.1 2003/10/07 17:21:40 liquidx Exp $
+
+# Author :     Alastair Tse <liquidx@gentoo.org> (03 Oct 2003)
+# Short Desc:  Creates symlink to the latest version of multiple slotted
+#              packages.
+#
+# Long Desc:
+#
+#  When a package is SLOT'ed, very often we need to have a symlink to the
+#  latest version. However, depending on the order the user has merged them,
+#  more often than not, the symlink maybe clobbered by the older versions.
+#
+#  This eclass provides a convenience function that needs to be given a 
+#  list of alternatives (descending order of recent-ness) and the symlink.
+#  It will choose the latest version if can find installed and create
+#  the desired symlink. 
+#
+#  There are two ways to use this eclass. First is by declaring two variables 
+#  $SOURCE and $ALTERNATIVES where $SOURCE is the symlink to be created and 
+#  $ALTERNATIVES is a list of alternatives. Second way is the use the function
+#  alternatives_makesym() like the example below.
+#
+# Example:
+#  
+#  pkg_postinst() {
+#      alternatives_makesym "/usr/bin/python" "/usr/bin/python2.3" "/usr/bin/python2.2"
+#  }
+#
+#  The above example will create a symlink at /usr/bin/python to either
+#  /usr/bin/python2.3 or /usr/bin/python2.2. It will choose python2.3 over
+#  python2.2 if both exist.
+#
+#  Alternatively, you can use this function:
+#
+#  pkg_postinst() {
+#     alternatives_auto_makesym "/usr/bin/python" "/usr/bin/python[0-9].[0-9]"
+#  }
+# 
+#  This will use bash pathname expansion to fill a list of alternatives it can
+#  link to. It is probably more robust against version upgrades. You should
+#  consider using this unless you are want to do something special.
+# 
+ECLASS="alternatives"
+INHERITED="$INHERITED $ECLASS"
+
+# automatic deduction based on a symlink and a regex mask
+alternatives_auto_makesym() {
+	local SOURCE REGEX ALT
+	local unsorted
+	SOURCE=$1
+	REGEX=$2
+
+	ALT="`ls -1 ${ROOT}${REGEX} | sort -r | xargs`"
+	if [ -n "${ALT}" ]; then
+		alternatives_makesym ${SOURCE} ${ALT}
+	else
+		eerror "regex ${REGEX} doesn't match any files."
+	fi		
+}
+
+alternatives_makesym() {
+	local ALTERNATIVES=""
+	local SOURCE=""
+	
+	# usage: alternatives_makesym <resulting symlink> [alternative targets..]
+	SOURCE=$1
+	shift
+	ALTERNATIVES=$@
+
+	# step through given alternatives from first to last
+	# and if one exists, link it and finish.
+	
+	for alt in ${ALTERNATIVES}; do
+		if [ -f "${ROOT}${alt}" ]; then
+			if [ -L "${ROOT}${SOURCE}" ]; then
+				rm -f ${ROOT}${SOURCE}
+			fi
+			einfo "Linking ${alt} to ${SOURCE}"
+			ln -s ${alt} ${ROOT}${SOURCE}
+			break
+		fi
+	done
+	
+	# report any errors
+	if [ ! -L ${ROOT}${SOURCE} ]; then
+		ewarn "Unable to establish ${SOURCE} symlink"
+	elif [ ! -f "`readlink ${ROOT}${SOURCE}`" -a ! -f "${ROOT}`readlink ${ROOT}${SOURE}`" ]; then
+		ewarn "${SOURCE} is a dead symlink."
+	fi		
+}		
+
+alternatives_pkg_postinst() {
+	if [ -n "${ALTERNATIVES}" -a -n "${SOURCE}" ]; then
+		alternatives_makesym ${SOURCE} ${ALTERNATIVES}
+	fi		
+}
+
+alternatives_pkg_postrm() {
+	if [ -n "${ALTERNATIVES}" -a -n "${SOURCE}" ]; then
+		alternatives_makesym ${SOURCE} ${ALTERNATIVES}
+	fi
+}
+
+EXPORT_FUNCTIONS pkg_postinst pkg_postrm
+