Add an Alchemy::EssenceHeadline

This adds an Alchemy::EssenceHeadline. It has the following features:
When used as a preview text, it will show the level of the headline so
that content editors can see what levels they are using. There are is
also an optional `level` element.

Headlines can be configured through their content settings. One can
restrict the sizes and levels available to an element, by specifying them
like follows:

```yml
- name: MyComponent
  contents:
     - name: my_headline
       type: EssenceHeadline
       settings:
          levels: [3, 4]
          sizes: [3]
```

If, as in the previous example, `sizes` only has one option, the select
input in the element editor will not be displayed.

If `sizes` is unconfigured, the default will be an empty array, and the
essence will have no size class.

app/models/alchemy/essence_headline.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+module Alchemy
+  class EssenceHeadline < BaseRecord
+    acts_as_essence(
+      ingredient_column: :body,
+      preview_text_method: :preview_text
+    )
+
+    after_initialize :set_level_and_size
+
+    def preview_text(maxlength = 30)
+      "H#{level}: #{body}"[0..maxlength - 1]
+    end
+
+    def level_options
+      levels.map { |level| ["H#{level}", level] }
+    end
+
+    def size_options
+      sizes.map { |size| ["H#{size}", size] }
+    end
+
+    private
+
+    def content_settings
+      content&.settings || {}
+    end
+
+    def levels
+      content_settings.fetch(:levels, (1..6))
+    end
+
+    def sizes
+      content_settings.fetch(:sizes, [])
+    end
+
+    def set_level_and_size
+      self.level ||= levels.first
+      self.size ||= sizes.first
+    end
+  end
+end

app/views/alchemy/essences/_essence_headline_view.html.erb

@@ -0,0 +1 @@
+<%= content_tag "h#{content.essence.level}", content.essence.ingredient, class: "h#{content.essence.size} #{options[:classes]}" %>

db/migrate/20210406093436_add_alchemy_essence_headlines.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class AddAlchemyEssenceHeadlines < ActiveRecord::Migration[6.0]
+  def change
+    create_table :alchemy_essence_headlines do |t|
+      t.text :body
+      t.integer :level
+      t.integer :size
+      t.timestamps
+    end
+  end
+end

spec/dummy/db/migrate/20210406093436_add_alchemy_essence_headlines.rb

@@ -0,0 +1 @@
+../../../../db/migrate/20210406093436_add_alchemy_essence_headlines.rb

spec/dummy/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_03_26_105046) do
+ActiveRecord::Schema.define(version: 2021_04_06_093436) do
 
   create_table "alchemy_attachments", force: :cascade do |t|
     t.string "name"
@@ -80,6 +80,14 @@
     t.index ["attachment_id"], name: "index_alchemy_essence_files_on_attachment_id"
   end
 
+  create_table "alchemy_essence_headlines", force: :cascade do |t|
+    t.text "body"
+    t.integer "level"
+    t.integer "size"
+    t.datetime "created_at", precision: 6, null: false
+    t.datetime "updated_at", precision: 6, null: false
+  end
+
   create_table "alchemy_essence_htmls", force: :cascade do |t|
     t.text "source"
   end

spec/models/alchemy/essence_headline_spec.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Alchemy::EssenceHeadline do
+  subject(:essence) do
+    Alchemy::EssenceHeadline.new(
+      body: ingredient_value,
+      level: 2,
+      size: 3
+    )
+  end
+
+  let(:ingredient_value) { "A headline" }
+
+  it_behaves_like "an essence"
+
+  describe "#level_options" do
+    subject { essence.level_options }
+
+    it { is_expected.to eq([["H1", 1], ["H2", 2], ["H3", 3], ["H4", 4], ["H5", 5], ["H6", 6]]) }
+
+    context "when restricted through the essence settings" do
+      before do
+        expect(essence).to receive_message_chain(:content, :settings).and_return(levels: [2, 3])
+      end
+
+      it { is_expected.to eq([["H2", 2], ["H3", 3]]) }
+    end
+  end
+
+  describe "#size_options" do
+    subject { essence.size_options }
+
+    it { is_expected.to eq([]) }
+
+    context "when enabled through the essence settings" do
+      before do
+        expect(essence).to receive_message_chain(:content, :settings).and_return(sizes: [3, 4])
+      end
+
+      it { is_expected.to eq([["H3", 3], ["H4", 4]]) }
+    end
+  end
+
+  describe "initialization" do
+    describe "level" do
+      subject { Alchemy::EssenceHeadline.new.level }
+
+      it { is_expected.to eq(1) }
+    end
+
+    describe "size" do
+      let(:content) { build(:alchemy_content) }
+      let(:essence) { Alchemy::EssenceHeadline.new(content: content) }
+      subject { essence.size }
+
+      it { is_expected.to be_nil }
+
+      context "when enabled through the essence settings" do
+        before do
+          expect(content).to receive(:settings).and_return(sizes: [3, 4]).twice
+        end
+
+        it { is_expected.to eq(3) }
+      end
+    end
+  end
+end