require 'rpm'
require 'getopts'

group='System/Libraries'

if ((!getopts('g?h', 'help')) || $OPT_h || $OPT_help)
	puts "usage: #{$0} [-h] [-g [group]]
  	-h|--help	print this help message.
	-g [group]	restrict results to given group or #{group} if none"
	exit 1
end

if($OPT_g)
	restrict_group = true
	group = $OPT_g unless $OPT_g==true
	group = /#{Regexp.quote(group)}/i
end

db = RPM::DB.new
provides={}
notleaves={}
db.each{ |package|
	package.provides.each{|provide| 
	begin
		provides[provide.name].push package.name 
	rescue
		provides[provide.name]=[package.name]
	end
	}
	if ((!restrict_group) || (group =~ package[RPM::TAG_GROUP]))
		notleaves[package.name] = false
	end
}

db.each{ |package| package.requires.each{|req|
	if(provides[req.name]) 
		provides[req.name].each{|p| notleaves[p]=true if p!=package.name}
	end
	}
}

leaves=[];
db.each{|package| notleaves[package.name]==false and leaves << package.name}
puts leaves.sort.uniq.join("\n")