Extract state selector to cell. [#47]

app/cells/state_selector/show.haml

@@ -0,0 +1,7 @@
+= form_with url: url, local: true, class: 'state-selector' do |form|
+  %p
+    = label_tag :states, _('Choose one or more states:')
+    - locale_state_options = states_for_menu.sort_by {|state| _(state.name)}.map {|state| [_(state.name), state.abbr]}
+    = select_tag :states, options_for_select(locale_state_options, @states&.map(&:abbr)), multiple: true
+  %p
+    = submit_tag _('Go')

app/cells/state_selector_cell.rb

@@ -0,0 +1,22 @@
+class StateSelectorCell < Cell::ViewModel
+  include ActionView::Helpers::FormHelper
+  include ActionView::Helpers::FormOptionsHelper
+
+  attr_reader :states, :url
+
+  def initialize(states, options)
+    super
+    @states = states
+    @url = options[:url]
+  end
+
+  def show
+    render
+  end
+
+  private
+
+  def states_for_menu
+    @states_for_menu ||= State.all
+  end
+end

app/helpers/application_helper.rb

@@ -1,5 +1,2 @@
 module ApplicationHelper
-  def states
-    State.all
-  end
 end

app/views/layouts/application.html.haml

@@ -13,7 +13,7 @@
       %h1
         = link_to '/' do
           = h(_ '%{span}COVID-19%{_span} Tracking Charts by U.S. State') % {span: '<span class="accent">'.html_safe, _span: '</span>'.html_safe}
-    %nav= render 'shared/state_selector', states: states # TODO: consider Cells or something here
+    %nav= cell(:state_selector, @states, url: choose_states_path)
 
     %main
       - if content_for :page_title

spec/cells/state_selector_cell_spec.rb

@@ -0,0 +1,71 @@
+require 'rails_helper'
+
+RSpec.describe StateSelectorCell, type: :cell do
+  let(:states) { [] }
+  let(:url) { nil }
+  let(:options) { {url: url} }
+
+  subject { described_class.new states, options }
+
+  context 'constructor' do
+    it { is_expected.to be_a_kind_of Cell::ViewModel }
+
+    it 'includes form helpers' do
+      ['FormHelper', 'FormOptionsHelper'].each do |helper|
+        expect(subject).to be_a_kind_of "ActionView::Helpers::#{helper}".constantize
+      end
+    end
+  end
+
+  context '#states' do
+    let(:states) { State.all.sample rand(2..5) }
+
+    it 'returns the given states' do
+      expect(subject.states).to be == states
+    end
+  end
+
+  context '#url' do
+    let(:url) { File.join *Faker::Lorem.words(rand 2..5) }
+
+    it 'returns the given URL' do
+      expect(subject.url).to be == url
+    end
+  end
+
+  context '#show' do
+    controller Class.new(ApplicationController) # see https://github.com/trailblazer/rspec-cells#url-helpers
+
+    let(:url) { File.join *Faker::Lorem.words(rand 2..5) }
+    let(:menu) { 'select[multiple][name="states[]"]' }
+
+    subject { Capybara.string cell(described_class, states, options).call }
+
+    it 'renders a form that will submit to the given URL' do
+      expect(subject).to have_selector "form[action='#{url}']"
+    end
+
+    it 'renders a multi-select with all the states as options, sorted by nam,e' do
+      subject.find menu do |menu|
+        selector = './/' + State.all.sort_by(&:name).map {|state| "option[@value='#{state.abbr}'][text()='#{state.name}']"}.join('/following-sibling::')
+        expect(menu).to have_xpath selector
+      end
+    end
+
+    context 'states given' do
+      let(:states) { State.all.sample rand(2..5) }
+
+      it 'marks all the states given as selected' do
+        subject.find(menu) do |menu|
+          expect(menu.all('option[selected]').map &:text).to match_array states.map(&:name)
+        end
+       end
+    end
+
+    context 'no states given' do
+      it 'marks no states as selected' do
+        expect(subject.find menu).not_to have_css 'option[selected]'
+      end
+    end
+  end
+end