added simple add-on dependency solver

to solve the registration order according to the dependencies

src/lib/registration/addon.rb

@@ -2,7 +2,7 @@
 # To change this template file, choose Tools | Templates
 # and open the template in the editor.
 
-require 'set'
+require 'tsort'
 
 module Registration
   class Addon
@@ -35,4 +35,29 @@ def required_addons
     end
   end
 
+  # @see TSort example http://ruby-doc.org/stdlib-2.1.0/libdoc/tsort/rdoc/TSort.html#module-TSort-label-A+Simple+Example
+  class AddonSorter < Hash
+    include TSort
+
+    alias tsort_each_node each_key
+
+    def tsort_each_child(node, &block)
+      fetch(node).each(&block)
+    end
+
+    def self.registration_order(addons)
+      solver = AddonSorter.new
+
+      # solve the name dependencies
+      addons.each do |a|
+        solver[a.name] = a.depends_on.map(&:name)
+      end
+
+      solved = solver.tsort
+
+      # convert names back to addons
+      solved.map{|name| addons.find{|a| a.name == name}}
+    end
+  end
+
 end

test/addon_spec.rb

@@ -64,3 +64,37 @@
   end
 
 end
+
+describe Registration::AddonSorter do
+  describe ".registration_order" do
+    it "returns registration order according to the dependencies" do
+      addon1 = Registration::Addon.new("SUSE_ADDON1", "12", "x86_64")
+      addon2 = Registration::Addon.new("SUSE_ADDON2", "12", "x86_64")
+      addon3 = Registration::Addon.new("SUSE_ADDON3", "12", "x86_64", depends_on: [addon1, addon2])
+      addon4 = Registration::Addon.new("SUSE_ADDON4", "12", "x86_64")
+      addon5 = Registration::Addon.new("SUSE_ADDON5", "12", "x86_64")
+      addon6 = Registration::Addon.new("SUSE_ADDON6", "12", "x86_64", depends_on: [addon4, addon5])
+      addon7 = Registration::Addon.new("SUSE_ADDON7", "12", "x86_64", depends_on: [addon3, addon6])
+
+      # deliberately use an order which does not follow dependencies to make sure it is changed
+      addons = [addon7, addon2, addon3, addon5, addon4, addon6, addon1]
+
+      solved = Registration::AddonSorter.registration_order(addons)
+
+      # check the order, iterate over the list and check for missing dependencies
+      registered = []
+      solved.each do |a|
+        # check that all dependendent add-ons are already registered
+        expect(a.depends_on - registered).to be_empty
+        registered << a
+      end
+    end
+
+    it "raises KeyError exception when there is an unresolved dependency" do
+      addon1 = Registration::Addon.new("SUSE_ADDON1", "12", "x86_64")
+      addon2 = Registration::Addon.new("SUSE_ADDON3", "12", "x86_64", depends_on: [addon1])
+
+      expect{Registration::AddonSorter.registration_order([addon2])}.to raise_error(KeyError)
+    end
+  end
+end