Implement Server-Side Price Filtering

This commit modifies the `seats#index` HTML to take the `?maximum` query
parameter into account when deciding which `Seat` records are emphasized
or de-emphasized based on their section's price.

First, extend the price filtering `<form>` element to declare the
[`action` attribute] to the current page, and the [`method` attribute to
`GET`][get]. To declare these methods, and to integrate with Rails' CSRF
protection, declare the `<form>` using the [`form_with`
helper][form_with].

Unfortunately, Turbolinks does not support `<form>` submission redirects
for `GET` requests:

> The Turbolinks Rails engine performs this optimization automatically
> for non-GET XHR requests that redirect with the `redirect_to` helper.

To counteract that constraint, this commit passes the `local: true`
option to the `form_with` call, [opting-out of remote form submission
through unobtrusive JavaScript][local] and (transitively) Turbolinks.

Next, determine which `<input type="radio">` element to denote as
[`checked`][checked] based on whether or not its `value` attribute
matches the value of the `maximum` query parameter. If no query
parameter is provided, ensure that the last `<input type="radio">`
element is `checked`.

Render the `Section` records as a [`<g>`][g] element to group them
together. When rendering the `<g>` element, declare its
[`opacity`][opacity] based on whether its `price` is within the bounds
of the price filter.

Additionally, set [`aria-hidden="true"`][aria-hidden] for `<g>`
elements that do not match the filter criteria, so that we can exclude
them from the accessibility tree.

[action]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/form#Attributes
[get]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/GET
[form_with]: https://api.rubyonrails.org/v5.2/classes/ActionView/Helpers/FormHelper.html#method-i-form_with
[checked]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Input/radio#checked
[turbolinks-get]: https://github.com/turbolinks/turbolinks/tree/v5.2.0#redirecting-after-a-form-submission
[local]: https://api.rubyonrails.org/v5.2/classes/ActionView/Helpers/FormHelper.html#method-i-form_with-label-form_with+options
[g]: https://developer.mozilla.org/en-US/docs/Web/SVG/Element/g
[opacity]: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/opacity
[aria-hidden]: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques#States_and_properties

app/views/seats/index.html.erb

@@ -109,7 +109,14 @@
         </svg>
 
         <% sections.each do |section| %>
-          <g>
+          <g
+            <% if params.fetch(:maximum, Float::INFINITY).to_f >= section.price %>
+              opacity="1.0"
+            <% else %>
+              opacity="0.3"
+              aria-hidden="true"
+            <% end %>
+          >
             <% section.seats.each do |seat| %>
               <a
                 href="<%= venue_floor_seat_path(venue, floor, seat.row_number) %>"
@@ -135,7 +142,11 @@
     </div>
 
     <div class="syos-frame__sidebar">
-      <form>
+      <%= form_with(
+        url: venue_floor_seats_path(venue, floor),
+        method: :get,
+        local: true,
+      ) do |form| %>
         <fieldset class="syos-u-margin-bottom-6">
           <legend class="syos-u-margin-bottom-2 syos-inline-stack">
             <h2 class="syos-inline-stack__item">
@@ -153,7 +164,8 @@
                 type="radio"
                 name="maximum"
                 value="<%= maximum %>"
-                <% if next_maximum.nil? %>
+                <% if params[:maximum].to_i == maximum ||
+                    [params[:maximum], next_maximum].none? %>
                   checked
                 <% end %>
               >
@@ -177,7 +189,7 @@
 
           <input type="submit" class="syos-button syos-u-margin-top-2" value="Apply Filters">
         </fieldset>
-      </form>
+      <% end %>
 
       <div id="cart-summary">
         <h2 class="syos-u-margin-bottom-2">

test/controllers/seats_controller_test.rb

@@ -21,4 +21,51 @@ class SeatsControllerTest < ActionDispatch::IntegrationTest
 
     assert_equal Cart.last.token, cookies[:cart_token]
   end
+
+  test "#index when including sections when filtering by price" do
+    maximum = 10_00
+    price = maximum
+    venue = create(:benedum_center)
+    floor = create(:orchestra, venue: venue)
+    section = create(:section, floor: floor, price: price)
+    create(:seat, section: section)
+
+    get venue_floor_seats_path(venue, floor, maximum: maximum)
+
+    assert_select %{g[opacity="1.0"]}
+    assert_select %{g:not([aria-hidden])}
+  end
+
+  test "#index when excluding sections when filtering by price" do
+    maximum = 5_00
+    price = 10_00
+    venue = create(:benedum_center)
+    floor = create(:orchestra, venue: venue)
+    section = create(:section, floor: floor, price: price)
+    create(:seat, section: section)
+
+    get venue_floor_seats_path(venue, floor, maximum: maximum)
+
+    assert_select %{g[opacity="0.3"]}
+    assert_select %{g[aria-hidden="true"]}
+  end
+
+  test "#index with a ?maximum query parameter" do
+    venue = create(:benedum_center)
+    floor = create(:orchestra, venue: venue)
+    maximum = 10_00
+
+    get venue_floor_seats_path(venue, floor, maximum: maximum)
+
+    assert_select %{input[type="radio"][value="#{maximum}"][checked]}
+  end
+
+  test "#index without a ?maximum query parameter" do
+    venue = create(:benedum_center)
+    floor = create(:orchestra, venue: venue)
+
+    get venue_floor_seats_path(venue, floor)
+
+    assert_select %{input[type="radio"][value="1500"][checked]}
+  end
 end