Add Linkable concern and tests

Commit audit trail:
- https://github.com/alphagov/government-frontend/blob/a938e4bee78b794e4e5303a1bde1dfd05e94b287/app/presenters/content_item/linkable.rb
- https://github.com/alphagov/government-frontend/blob/a938e4bee78b794e4e5303a1bde1dfd05e94b287/test/presenters/content_item/linkable_test.rb

app/models/concerns/linkable.rb

@@ -0,0 +1,46 @@
+module Linkable
+  extend ActiveSupport::Concern
+
+  def from
+    organisations_ordered_by_importance + links_group(%w[worldwide_organisations people speaker])
+  end
+
+private
+
+  def organisations_ordered_by_importance
+    organisations_with_emphasised_first.map do |link|
+      ActionController::Base.helpers.link_to(link["title"], link["base_path"], class: "govuk-link")
+    end
+  end
+
+  def links(type)
+    expanded_links_from_content_item(type)
+      .select { |link| link["base_path"] || type == "world_locations" }
+      .map { |link| link_for_type(type, link) }
+  end
+
+  def organisations_with_emphasised_first
+    expanded_links_from_content_item("organisations").sort_by do |organisation|
+      is_emphasised = organisation["content_id"].in?(emphasised_organisations)
+      is_emphasised ? -1 : 1
+    end
+  end
+
+  def expanded_links_from_content_item(type)
+    return [] unless content_store_hash.dig("links", type)
+
+    content_store_hash.dig("links", type)
+  end
+
+  def emphasised_organisations
+    content_store_hash.dig("details", "emphasised_organisations") || []
+  end
+
+  def links_group(types)
+    types.flat_map { |type| links(type) }.uniq
+  end
+
+  def link_for_type(_type, link)
+    ActionController::Base.helpers.link_to(link["title"], link["base_path"], class: "govuk-link")
+  end
+end

spec/models/concerns/linkable_spec.rb

@@ -0,0 +1,51 @@
+class DummyLinkableContentItem
+  include Linkable
+  attr_accessor :content_item
+
+  def content_store_hash
+    @content_item
+  end
+
+  def initialize
+    @content_item = {
+      "base_path" => "/a/base/path",
+      "links" => {},
+    }
+  end
+end
+
+RSpec.describe Linkable, type: :model do
+  let(:item) { DummyLinkableContentItem.new }
+
+  describe "#from" do
+    context "when people links have base_paths" do
+      it "returns the correct links" do
+        item.content_item["links"]["people"] = [
+          {
+            "title" => "Winston Churchill",
+            "base_path" => "/government/people/winston-churchill",
+          },
+        ]
+
+        expected_from_links = [
+          %(<a class="govuk-link" href="/government/people/winston-churchill">Winston Churchill</a>),
+        ]
+        expect(item.from).to eq(expected_from_links)
+      end
+    end
+
+    context "when people links do not have base_paths" do
+      it "skips the links" do
+        item.content_item["links"]["people"] = [
+          {
+            "title" => "Winston Churchill",
+            "base_path" => nil,
+          },
+        ]
+
+        expected_from_links = []
+        expect(item.from).to eq(expected_from_links)
+      end
+    end
+  end
+end