1 files changed, 52 insertions, 0 deletions
diff --git a/lib/puppet/util/state_machine.rb b/lib/puppet/util/state_machine.rb
new file mode 100644
index 000000000..9329df3ce
--- /dev/null
+++ b/lib/puppet/util/state_machine.rb
@@ -0,0 +1,52 @@
+require 'puppet/util'
+
+# A simple class for defining simple state machines.  You define
+# the state transitions, which translate to the states a given property
+# can be in and the methods used to transition between those states.
+#
+# == Example
+#
+# newproperty(:ensure) do
+#
+#   :absent => :present (:create)
+#
+#   statemachine.new(:create => {:absent => :present}, :destroy => {:present => :absent})
+#
+#       mach.transition(:absent => :present).with :create
+#       mach.transition(:present => :absent).with :destroy
+#
+#       mach.transition :create => {:absent => :present}, :destroy => {:present => :absent}
+
+require 'puppet/simple_graph'
+require 'puppet/relationship'
+
+class Puppet::Util::StateMachine
+    class Transition < Puppet::Relationship
+    end
+
+    def initialize(&block)
+        @graph = Puppet::SimpleGraph.new
+        @docs = {}
+
+        instance_eval(&block) if block
+    end
+
+    # Define a state, with docs.
+    def state(name, docs)
+        @docs[name] = docs
+        @graph.add_vertex(name)
+    end
+
+    # Check whether a state is defined.
+    def state?(name)
+        @graph.vertex?(name)
+    end
+
+    def transition(from, to)
+        raise ArgumentError, "Unknown starting state %s" % from unless state?(from)
+        raise ArgumentError, "Unknown ending state %s" % to unless state?(to)
+        raise ArgumentError, "Transition %s => %s already exists" % [from, to] if @graph.edge?(from, to)
+        transition = Transition.new(from, to)
+        @graph.add_edge(transition)
+    end
+end