Make the preview url configurable

By default Alchemy uses its internal page preview renderer,
but you can configure it now to be any URL instead.

Basic Auth is supported as well.

Example config/alchemy/config.yml

    preview:
      host: https://www.my-static-site.com
      auth:
        username: <%= ENV["BASIC_AUTH_USERNAME"] %>
        password: <%= ENV["BASIC_AUTH_PASSWORD"] %>

This is great for static sites.

app/controllers/alchemy/admin/pages_controller.rb

@@ -85,6 +85,7 @@ def edit
         elsif page_needs_lock?
           @page.lock_to!(current_alchemy_user)
         end
+        @preview_url = Alchemy::Admin::PREVIEW_URL.url_for(@page)
         @layoutpage = @page.layoutpage?
       end
 

app/views/alchemy/admin/pages/edit.html.erb

@@ -190,7 +190,7 @@
       }
     });
 
-    Alchemy.PreviewWindow.init('<%= admin_page_path(@page) %>');
+    Alchemy.PreviewWindow.init('<%= @preview_url %>');
 
     $('#preview_size').bind('open.selectBoxIt', function (e) {
       $('#top_menu').css('z-index', 5000);

config/alchemy/config.yml

@@ -62,6 +62,19 @@ url_nesting: true
 # In Alchemy's Admin, change how many items you would get shown per page by Kaminari
 items_per_page: 15
 
+# === Preview window URL configuration
+#
+# By default Alchemy uses its internal page preview renderer,
+# but you can configure it to be any URL instead.
+#
+# Basic Auth is supported.
+#
+# preview:
+#   host: https://www.my-static-site.com
+#   auth:
+#     username: <%= ENV["BASIC_AUTH_USERNAME"] %>
+#     password: <%= ENV["BASIC_AUTH_PASSWORD"] %>
+
 # === Picture rendering settings
 #
 # Alchemy uses Dragonfly to render images. Use {size: "XXXxYYY", crop: BOOLEAN [true]} to resize images.

lib/alchemy/admin/preview_url.rb

@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+require "uri"
+
+module Alchemy
+  module Admin
+    # = Preview window URL configuration
+    #
+    # By default Alchemy uses its internal page preview renderer,
+    # but you can configure it to be any URL instead.
+    #
+    # Basic Auth is supported.
+    #
+    # == Example config/alchemy/config.yml
+    #
+    #     preview:
+    #       host: https://www.my-static-site.com
+    #       auth:
+    #         username: <%= ENV["BASIC_AUTH_USERNAME"] %>
+    #         password: <%= ENV["BASIC_AUTH_PASSWORD"] %>
+    #
+    class PreviewUrl
+      class MissingProtocolError < StandardError; end
+
+      def initialize(routes:)
+        @routes = routes.url_helpers
+        @preview_config = Alchemy::Config.get(:preview)
+      end
+
+      def url_for(page)
+        if preview_config
+          uri_class.build(
+            host: uri.host,
+            path: "/#{page.urlname}",
+            userinfo: userinfo,
+          ).to_s
+        else
+          routes.admin_page_path(page)
+        end
+      end
+
+      private
+
+      attr_reader :preview_config, :routes
+
+      def uri
+        URI(preview_config["host"])
+      end
+
+      def uri_class
+        if uri.class == URI::Generic
+          raise MissingProtocolError.new("Please provide the protocol with preview['host']")
+        else
+          uri.class
+        end
+      end
+
+      def userinfo
+        auth = preview_config["auth"]
+        auth ? "#{auth["username"]}:#{auth["password"]}" : nil
+      end
+    end
+  end
+end

lib/alchemy/engine.rb

@@ -9,6 +9,10 @@ class Engine < Rails::Engine
       Alchemy::LOOKUP_CONTEXT = ActionView::LookupContext.new(Rails.root.join("app", "views", "alchemy"))
     end
 
+    initializer "alchemy.admin.preview_url" do
+      Alchemy::Admin::PREVIEW_URL = Alchemy::Admin::PreviewUrl.new(routes: Alchemy::Engine.routes)
+    end
+
     initializer "alchemy.dependency_tracker" do
       [:erb, :slim, :haml].each do |handler|
         ActionView::DependencyTracker.register_tracker(handler, CacheDigests::TemplateTracker)
@@ -41,7 +45,7 @@ class Engine < Rails::Engine
         app.middleware.insert_before(
           0, Webpacker::DevServerProxy,
           ssl_verify_none: true,
-          webpacker: Alchemy.webpacker
+          webpacker: Alchemy.webpacker,
         )
       end
     end

lib/alchemy_cms.rb

@@ -30,6 +30,7 @@ module Alchemy
 # Require globally used Alchemy mixins
 require_relative "alchemy/ability_helper"
 require_relative "alchemy/admin/locale"
+require_relative "alchemy/admin/preview_url"
 require_relative "alchemy/auth_accessors"
 require_relative "alchemy/cache_digests/template_tracker"
 require_relative "alchemy/config"

spec/libraries/admin/preview_url_spec.rb

@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Alchemy::Admin::PreviewUrl do
+  let(:preview_url) do
+    described_class.new(routes: Alchemy::Engine.routes)
+  end
+
+  describe "#url_for" do
+    let(:page) { create(:alchemy_page) }
+
+    subject { preview_url.url_for(page) }
+
+    context "without preview configured" do
+      it "returns the admin pages preview url" do
+        is_expected.to eq "/admin/pages/#{page.id}"
+      end
+    end
+
+    context "with preview configured" do
+      context "without protocol" do
+        before do
+          stub_alchemy_config(:preview, {
+            "host" => "www.example.com",
+          })
+        end
+
+        it "returns the configured preview url" do
+          expect { subject }.to raise_error(Alchemy::Admin::PreviewUrl::MissingProtocolError)
+        end
+      end
+
+      context "as http url" do
+        before do
+          stub_alchemy_config(:preview, {
+            "host" => "http://www.example.com",
+          })
+        end
+
+        it "returns the configured preview url" do
+          is_expected.to eq "http://www.example.com/#{page.urlname}"
+        end
+      end
+
+      context "as https url" do
+        before do
+          stub_alchemy_config(:preview, {
+            "host" => "https://www.example.com",
+          })
+        end
+
+        it "returns the configured preview url with https" do
+          is_expected.to eq "https://www.example.com/#{page.urlname}"
+        end
+      end
+
+      context "and with basic auth configured" do
+        before do
+          stub_alchemy_config(:preview, {
+            "host" => "https://www.example.com",
+            "auth" => {
+              "username" => "foo",
+              "password" => "baz",
+            },
+          })
+        end
+
+        it "returns the configured preview url with userinfo" do
+          is_expected.to eq "https://foo:baz@www.example.com/#{page.urlname}"
+        end
+      end
+    end
+  end
+end