Total Pages should be at least one

And the link to the last page cannot be `page=0`.

lib/api/helpers/pagination.rb

@@ -11,7 +11,7 @@ module API
 
       def add_pagination_headers(paginated_data)
         header 'X-Total',       paginated_data.total_count.to_s
-        header 'X-Total-Pages', paginated_data.total_pages.to_s
+        header 'X-Total-Pages', total_pages(paginated_data).to_s
         header 'X-Per-Page',    paginated_data.limit_value.to_s
         header 'X-Page',        paginated_data.current_page.to_s
         header 'X-Next-Page',   paginated_data.next_page.to_s
@@ -26,20 +26,25 @@ module API
 
         links = []
 
-        request_params[:page] = paginated_data.current_page - 1
-        links << %(<#{request_url}?#{request_params.to_query}>; rel="prev") unless paginated_data.first_page?
+        request_params[:page] = paginated_data.prev_page
+        links << %(<#{request_url}?#{request_params.to_query}>; rel="prev") if request_params[:page]
 
-        request_params[:page] = paginated_data.current_page + 1
-        links << %(<#{request_url}?#{request_params.to_query}>; rel="next") unless paginated_data.last_page? || paginated_data.out_of_range?
+        request_params[:page] = paginated_data.next_page
+        links << %(<#{request_url}?#{request_params.to_query}>; rel="next") if request_params[:page]
 
         request_params[:page] = 1
         links << %(<#{request_url}?#{request_params.to_query}>; rel="first")
 
-        request_params[:page] = paginated_data.total_pages
+        request_params[:page] = total_pages(paginated_data)
         links << %(<#{request_url}?#{request_params.to_query}>; rel="last")
 
         links.join(', ')
       end
+
+      def total_pages(paginated_data)
+        # Ensure there is in total at least 1 page
+        [paginated_data.total_pages, 1].max
+      end
     end
   end
 end

spec/lib/api/helpers/pagination_spec.rb

@@ -107,7 +107,7 @@ describe API::Helpers::Pagination do
 
         it 'adds appropriate headers' do
           expect_header('X-Total', '0')
-          expect_header('X-Total-Pages', '0')
+          expect_header('X-Total-Pages', '1')
           expect_header('X-Per-Page', '2')
           expect_header('X-Page', '1')
           expect_header('X-Next-Page', '')
@@ -118,6 +118,7 @@ describe API::Helpers::Pagination do
             expect(val).to include('rel="last"')
             expect(val).not_to include('rel="prev"')
             expect(val).not_to include('rel="next"')
+            expect(val).not_to include('page=0')
           end
 
           subject.paginate(resource)