feature: show discount code usage

app/views/admin/discount_codes/_card.html.haml

@@ -0,0 +1,6 @@
+.row
+  .col-12
+    .card
+      .card-header Usage
+      .card-body
+        = bar_chart Registration.where(id: discount_code.registrations.pluck(:id)).joins(:participant).group('participants.email').count

app/views/admin/discount_codes/_discount_code.html.haml

@@ -10,6 +10,10 @@
         class: "btn btn-sm btn-outline-primary" do
         %i.fa.fa-edit
         Edit
+      = link_to admin_discount_code_path(discount_code),
+        class: "btn btn-sm btn-outline-tertiary" do
+        %i.fa.fa-eye
+        Show
       - unless discount_code.used?
         = link_to admin_discount_code_path(discount_code),
           method: :delete,

app/views/admin/discount_codes/index.html.haml

@@ -1,11 +1,13 @@
 = content_for :admin_area_title do
   Discount Codes
+  = link_to new_admin_discount_code_path, class: "ml-4 btn btn-sm btn-success" do
+    %i.fa.fa-plus
+    New
 .row
   .col
+    .card
+      .card-header
+        Usage Summary
+      = column_chart Registration.joins(:discount_code).group('discount_codes.code').count
+
     = render "table"
-.row.mt-3
-  .col-12
-    .float-right
-      = link_to new_admin_discount_code_path, class: "btn btn-sm btn-success" do
-        %i.fa.fa-plus
-        Create New Discount Code

app/views/admin/discount_codes/show.html.haml

@@ -1 +1,10 @@
-= render "admin/registrations/card", registration: @registration.decorate
+= content_for :admin_area_title do
+  Discount Code ##{@discount_code.id}
+%nav{"aria-label" => "breadcrumb"}
+  %ol.breadcrumb
+    %li.breadcrumb-item
+      %a{href: admin_discount_codes_path} Discount Codes
+    %li.breadcrumb-item.active{"aria-current" => "page"} ##{@discount_code.id}
+.row
+  .col-12
+    = render "card", discount_code: @discount_code