add transact method

spec/agent_spec.cr

@@ -63,4 +63,14 @@ describe "Mechanize Agent test" do
     File.exists?("mechanizecr_example.html").should eq true
     File.delete("mechanizecr_example.html")
   end
+
+  it "doesn't add page to history within transact block" do
+    agent = Mechanize.new
+    agent.get("http://example.com/")
+    agent.history.size.should eq 1
+    agent.transact do
+      agent.get("http://example.com/")
+    end
+    agent.history.size.should eq 1
+  end
 end

src/mechanize.cr

@@ -138,4 +138,16 @@ class Mechanize
     end
     page
   end
+
+  # Runs given block, then resets the page history as it was before.
+  def transact
+    # save the previous history status.
+    history_backup = MechanizeCr::History.new(@agent.history.max_size, @agent.history.array.dup)
+    begin
+      yield self
+    ensure
+      # restore the previous history.
+      @agent.history = history_backup
+    end
+  end
 end

src/mechanize/history.cr

@@ -4,11 +4,11 @@ class MechanizeCr::History
   property max_size : Int32
   property array : Array(MechanizeCr::Page)
 
-  forward_missing_to @array
+  delegate :size, :empty?, :last, to: array
 
-  def initialize(max_size = 100)
+  def initialize(max_size = 100, array = Array(MechanizeCr::Page).new)
     @max_size = max_size
-    @array = Array(MechanizeCr::Page).new
+    @array = array
   end
 
   def push(page, uri = nil)