1 files changed, 47 insertions, 0 deletions
diff --git a/actionpack/lib/action_dispatch/journey/gtg/simulator.rb b/actionpack/lib/action_dispatch/journey/gtg/simulator.rb
new file mode 100644
index 0000000000..94b0a24344
--- /dev/null
+++ b/actionpack/lib/action_dispatch/journey/gtg/simulator.rb
@@ -0,0 +1,47 @@
+require 'strscan'
+
+module ActionDispatch
+  module Journey # :nodoc:
+    module GTG # :nodoc:
+      class MatchData # :nodoc:
+        attr_reader :memos
+
+        def initialize(memos)
+          @memos = memos
+        end
+      end
+
+      class Simulator # :nodoc:
+        attr_reader :tt
+
+        def initialize(transition_table)
+          @tt = transition_table
+        end
+
+        def simulate(string)
+          ms = memos(string) { return }
+          MatchData.new(ms)
+        end
+
+        alias :=~    :simulate
+        alias :match :simulate
+
+        def memos(string)
+          input = StringScanner.new(string)
+          state = [0]
+          while sym = input.scan(%r([/.?]|[^/.?]+))
+            state = tt.move(state, sym)
+          end
+
+          acceptance_states = state.find_all { |s|
+            tt.accepting? s
+          }
+
+          return yield if acceptance_states.empty?
+
+          acceptance_states.flat_map { |x| tt.memo(x) }.compact
+        end
+      end
+    end
+  end
+end