Make routes and parts dynamic

We can now define arbitrary routes (and their equivalent arbitrary
parts) by simply declaring a different `"part": "/route"` property
under the `forms`. In this case we only want one route and part -
topical event about pages - but you can imagine how we'd extend
this to support all possible Corporate Information Pages, for
example.

Author: ChrisBAshton

app/models/configurable_document_type.rb

@@ -87,12 +87,24 @@ def properties
     @schema["attributes"] || {}
   end
 
+  def parts
+    parts = []
+    @forms.each_value.flat_map do |form|
+      next unless form["fields"]
+
+      form["fields"].each do |_, field|
+        parts << field["part"] if field["part"]
+      end
+    end
+    parts.uniq
+  end
+
   def fields_for_part(part_key)
     @forms.each_value.flat_map do |form|
       next unless form["fields"]
 
-      form["fields"].select { |_, field| field["part_of"] == part_key }.map do |key, field|
-        { "key" => key, "part_name" => field["part_name"] }
+      form["fields"].select { |_, field| field["part"] == part_key }.map do |key, field|
+        { "key" => key, "part_name" => field["part_name"], "part" => part_key }
       end
     end
   end

app/models/configurable_document_types/topical_event.json

@@ -38,23 +38,23 @@
           "title": "Title",
           "block": "default_string",
           "attribute_path": ["block_content", "about_title"],
-          "part_of": "about_page_parts",
+          "part": "/about",
           "part_name": "title",
           "translatable": true
         },
         "about_summary": {
           "title": "Summary",
           "block": "default_textarea",
           "attribute_path": ["block_content", "about_summary"],
-          "part_of": "about_page_parts",
+          "part": "/about",
           "part_name": "summary",
           "translatable": true
         },
         "about_body": {
           "title": "Body",
           "block": "govspeak",
           "attribute_path": ["block_content", "about_body"],
-          "part_of": "about_page_parts",
+          "part": "/about",
           "part_name": "body",
           "translatable": true
         }
@@ -224,9 +224,6 @@
   },
   "settings": {
     "base_path_prefix": "/government/topical-events",
-    "additional_routes": [
-      "/about"
-    ],
     "publishing_api_schema_name": "topical_event",
     "publishing_api_document_type": "topical_event",
     "rendering_app": "frontend",

app/models/standard_edition.rb

@@ -107,7 +107,7 @@ def base_path
   end
 
   def additional_routes
-    type_instance.settings["additional_routes"] || []
+    type_instance.parts
   end
 
   def type_instance

app/presenters/publishing_api/payload_builder/block_content.rb

@@ -57,9 +57,9 @@ def social_media_links(attribute)
       end
 
       def parts(_attribute)
-        # TODO: make more abstract by passing a parameter to the 'parts' method
-        # so that we're not hardcoding this only for 'about page' usage.
-        PayloadBuilder::MultipleParts.for(item, "about_page_parts")
+        item.type_instance.parts.map do |part|
+          PayloadBuilder::MultipleParts.for(item, part)
+        end
       end
     end
   end

app/presenters/publishing_api/payload_builder/multiple_parts.rb

@@ -1,15 +1,15 @@
 module PublishingApi
   module PayloadBuilder
     class MultipleParts
-      attr_reader :item, :part_of
+      attr_reader :item, :part
 
-      def self.for(item, part_of)
-        new(item, part_of).call
+      def self.for(item, part)
+        new(item, part).call
       end
 
-      def initialize(item, part_of)
+      def initialize(item, part)
         @item = item
-        @part_of = part_of
+        @part = part
       end
 
       def call
@@ -19,11 +19,13 @@ def call
     private
 
       def parts
-        item.type_instance.fields_for_part(part_of).map do |field|
-          {
-            field["part_name"].to_sym => item.block_content&.public_send(field["key"]),
-          }
+        hash = {
+          slug: part.gsub("/", ""),
+        }
+        item.type_instance.fields_for_part(part).each_with_object(hash) do |field, obj|
+          obj[field["part_name"].to_sym] = item.block_content&.public_send(field["key"])
         end
+        hash
       end
     end
   end

test/unit/app/models/configurable_document_type_test.rb

@@ -165,15 +165,15 @@ class ConfigurableDocumentTypeTest < ActiveSupport::TestCase
                 "title" => "Title",
                 "block" => "default_string",
                 "attribute_path" => %w[block_content about_title],
-                "part_of" => "about_page_parts",
+                "part" => "/about",
                 "part_name" => "title",
                 "translatable" => true,
               },
               "about_summary" => {
                 "title" => "Summary",
                 "block" => "default_textarea",
                 "attribute_path" => %w[block_content about_summary],
-                "part_of" => "about_page_parts",
+                "part" => "/about",
                 "part_name" => "summary",
                 "translatable" => true,
               },
@@ -189,13 +189,15 @@ class ConfigurableDocumentTypeTest < ActiveSupport::TestCase
       {
         "key" => "about_title",
         "part_name" => "title",
+        "part" => "/about",
       },
       {
         "key" => "about_summary",
         "part_name" => "summary",
+        "part" => "/about",
       },
     ]
-    assert_equal expected_fields, document_type.fields_for_part("about_page_parts")
+    assert_equal expected_fields, document_type.fields_for_part("/about")
   end
 
   test "#form creates a flattened hash of fields if no form key is provided" do