Add base page service

Add an abstract page service and a corresponding page_layout. The service is used to make the initialization of page services easier and less error prone.

Author: kulturbande

app/services/alchemy/base_page_service.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Alchemy
+  class BasePageService
+    attr_reader :page, :params, :preview_mode
+
+    def initialize(page, params: ActionController::Parameters.new, preview_mode: false)
+      @page = page
+      @params = params
+      @preview_mode = preview_mode
+    end
+
+    # entrypoint method of the page service
+    # It can initialize and load necessary data or raise an Alchemy::PageNotFound error
+    def call
+      raise NotImplementedError
+    end
+  end
+end

spec/dummy/app/services/dummy_page_service.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class DummyPageService < Alchemy::BasePageService
+  def call
+  end
+end

spec/dummy/config/alchemy/page_layouts.yml

@@ -59,5 +59,9 @@
     - menu
   layoutpage: true
 
+- name: with_service
+  service: DummyPageService
+  elements: [article]
+
 - name: <%= 'erb_' + 'layout' %>
   unique: true

spec/libraries/alchemy/tasks/usage_spec.rb

@@ -61,7 +61,8 @@
         {"page_layout" => "footer", "count" => 0},
         {"page_layout" => "news", "count" => 0},
         {"page_layout" => "readonly", "count" => 0},
-        {"page_layout" => "search", "count" => 0}
+        {"page_layout" => "search", "count" => 0},
+        {"page_layout" => "with_service", "count" => 0}
       ]
     end
   end

spec/models/alchemy/site_spec.rb

@@ -170,7 +170,7 @@ module Alchemy
 
         it "returns all non 'layoutpage' page layout names" do
           allow(Site).to receive(:definitions).and_return([])
-          expect(site.page_layout_names).to eq(%w[index readonly standard everything news search contact erb_layout])
+          expect(site.page_layout_names).to eq(%w[index readonly standard everything news search contact with_service erb_layout])
         end
 
         context "when layoutpages are requested" do
@@ -211,7 +211,8 @@ module Alchemy
             "contact",
             "footer",
             "erb_layout",
-            "search"
+            "search",
+            "with_service"
           ])
         end
       end