refactor: separate handler chain from dispatcher

Handler Chain is  of handlers that respond to call.
Invoking handle(*args) on the chain will call the handlers with the given args
until one of them returns a result that is truethy (i.e. not false or nil).

Extracted from the dispatcher so we can also handle exceptions there in the
future. (So that if one of the network connections to the request_handlers
fails we can continue while still tracking the failed exception.)

3 files changed, 73 insertions, 7 deletions

diff --git a/lib/nickserver/dispatcher.rb b/lib/nickserver/dispatcher.rb
index 7a584e5..9968e95 100644
--- a/lib/nickserver/dispatcher.rb
+++ b/lib/nickserver/dispatcher.rb
@@ -35,10 +35,7 @@ module Nickserver
     protected
 
     def handle(request)
-      handler_chain.each do |handler|
-        response = handler.call request
-        return response if response
-      end
+      handler_chain.handle request
     rescue RuntimeError => exc
       puts "Error: #{exc}"
       puts exc.backtrace
@@ -46,13 +43,11 @@ module Nickserver
     end
 
     def handler_chain
-      [
-        RequestHandlers::InvalidEmailHandler,
+      HandlerChain.new RequestHandlers::InvalidEmailHandler,
         RequestHandlers::LocalEmailHandler,
         RequestHandlers::HkpEmailHandler,
         RequestHandlers::FingerprintHandler,
         Proc.new { Nickserver::Response.new(404, "404 Not Found\n") }
-      ]
     end
 
     def send_response(response)
diff --git a/lib/nickserver/handler_chain.rb b/lib/nickserver/handler_chain.rb
new file mode 100644
index 0000000..a0eba4d
--- /dev/null
+++ b/lib/nickserver/handler_chain.rb
@@ -0,0 +1,26 @@
+#
+# Handler Chain
+#
+# A chain of handlers that respond to call. Invoking handle(*args) on the chain
+# will call the handlers with the given args until one of them returns a result
+# that is truethy (i.e. not false or nil).
+#
+# Extracted from the dispatcher so we can also handle exceptions here in the
+# future.
+#
+
+module Nickserver
+  class HandlerChain
+
+    def initialize(*handlers)
+      @handlers = handlers
+    end
+
+    def handle(*args)
+      result = nil
+      _handled_by = @handlers.find{|h| result = h.call(*args)}
+      result
+    end
+
+  end
+end
diff --git a/test/unit/handler_chain_test.rb b/test/unit/handler_chain_test.rb
new file mode 100644
index 0000000..067f11e
--- /dev/null
+++ b/test/unit/handler_chain_test.rb
@@ -0,0 +1,45 @@
+require 'test_helper'
+require 'nickserver/handler_chain'
+
+class HandlerChainTest < Minitest::Test
+
+  def test_initialization
+    assert chain
+  end
+
+  def test_noop
+    assert_nil chain.handle
+  end
+
+  def test_triggering_handlers
+    handler_mock.expect :call, nil, [:a, :b]
+    chain handler_mock
+    chain.handle :a, :b
+    handler_mock.verify
+  end
+
+  def test_returns_handler_result
+    chain  handler_with_nil, handler_with_result
+    assert_equal :result, chain.handle
+  end
+
+
+  protected
+
+  def chain(*handlers)
+    @chain ||= Nickserver::HandlerChain.new(*handlers)
+  end
+
+  def handler_mock
+    @handler ||= Minitest::Mock.new
+  end
+
+  def handler_with_nil
+    Proc.new {}
+  end
+
+  def handler_with_result
+    Proc.new { :result }
+  end
+
+end