feat: add check answers page behaviour

app/controllers/form_controller.rb

@@ -126,7 +126,7 @@ private
       page_index = page_ids.index(@page.id)
       next_page_id = form.next_page(@page, @log, current_user)
       next_page = form.get_page(next_page_id)
-      previous_page = form.previous_page(page_ids, page_index, @log, current_user)
+      previous_page = form.previous_page(@page, @log, current_user)
 
       if next_page&.interruption_screen? || next_page_id == previous_page
         return send("#{@log.class.name.underscore}_#{next_page_id}_path", @log, { referrer: "check_answers" })

app/models/form.rb

@@ -67,7 +67,7 @@ class Form
     page_ids = subsection_for_page(page).pages.map(&:id)
     page_index = page_ids.index(page.id)
     page_id = if page.interruption_screen? && log[page.questions[0].id] == 1 && page.routed_to?(log, current_user)
-                previous_page(page_ids, page_index, log, current_user)
+                previous_page(page, log, current_user)
               else
                 page_ids[page_index + 1]
               end
@@ -88,10 +88,24 @@ class Form
     end
   end
 
-  def previous_page_redirect_path(page, log, current_user)
+  def previous_page(page, log, current_user)
     page_ids = subsection_for_page(page).pages.map(&:id)
     page_index = page_ids.index(page.id)
-    previous_page = previous_page(page_ids, page_index, log, current_user)
+    page_id = if page_index == 0
+                :check_answers
+              else
+                page_ids[page_index - 1]
+              end
+    prvs_page = get_page(page_id)
+
+    return :check_answers if prvs_page.nil?
+    return prvs_page.id if prvs_page.routed_to?(log, current_user)
+
+    previous_page(prvs_page, log, current_user)
+  end
+
+  def previous_page_redirect_path(page, log, current_user)
+    previous_page = previous_page(page, log, current_user)
     if previous_page == :check_answers
       "#{type}_log_#{subsection_for_page(page).id}_check_answers_path"
     else
@@ -217,13 +231,6 @@ class Form
     questions.select { |q| q.type == "numeric" }
   end
 
-  def previous_page(page_ids, page_index, log, current_user)
-    prev_page = get_page(page_ids[page_index - 1])
-    return prev_page.id if prev_page.routed_to?(log, current_user)
-
-    previous_page(page_ids, page_index - 1, log, current_user)
-  end
-
   def send_chain(arr, log)
     Array(arr).inject(log) { |o, a| o.public_send(*a) }
   end

app/views/form/page.html.erb

@@ -1,7 +1,11 @@
 <% content_for :title, @page.header.presence || @page.questions.first.header.html_safe %>
 
 <% content_for :before_content do %>
+  <% if url_for(:back).include?("check_answers") %>
+    <%= govuk_back_link(href: :back) %>
+  <% else %>
     <%= govuk_back_link(href: send(@log.form.previous_page_redirect_path(@page, @log, current_user), @log)) %>
+  <% end %>
 <% end %>
 
 <div data-controller="govukfrontend"></div>