Add link_to_previous_page helper for sinatra

lib/kaminari/helpers/sinatra_helpers.rb

@@ -93,6 +93,18 @@ def paginate(scope, options = {}, &block)
         paginator.to_s
       end
 
+      def link_to_previous_page(scope, name, options = {})
+        params = options.delete(:params) || (Rack::Utils.parse_query(env['QUERY_STRING']).symbolize_keys rescue {})
+        param_name = options.delete(:param_name) || Kaminari.config.param_name
+        placeholder = options.delete(:placeholder)
+        query = params.merge(param_name => (scope.current_page - 1))
+        unless scope.first_page?
+          link_to name, env['PATH_INFO'] + (query.empty? ? '' : "?#{query.to_query}"), options.reverse_merge(:rel => 'previous')
+        else
+          placeholder
+        end
+      end
+
       # A simple "Twitter like" pagination link that creates a link to the next page.
       # Works on Sinatra.
       #

spec/helpers/sinatra_helpers_spec.rb

@@ -12,6 +12,17 @@
   </div>
 EOT
 
+  ERB_TEMPLATE_FOR_PREVIOUS_PAGE = <<EOT
+  <div>
+  <ul>
+  <% @users.each do |user| %>
+    <li class="user_info"><%= user.id %></li>
+  <% end %>
+  </ul>
+  <%= link_to_previous_page(@users, "Previous!", {:id => 'previous_page_link'}.merge(@options || {})) %>
+  </div>
+EOT
+
   ERB_TEMPLATE_FOR_NEXT_PAGE = <<EOT
   <div>
   <ul>
@@ -125,6 +136,48 @@
       end
     end
 
+    describe '#link_to_previous_page' do
+      before do
+        mock_app do
+          register Kaminari::Helpers::SinatraHelpers
+          get '/users' do
+            @page = params[:page] || 2
+            @users = User.page(@page)
+            erb ERB_TEMPLATE_FOR_PREVIOUS_PAGE
+          end
+
+          get '/users_placeholder' do
+            @page = params[:page] || 2
+            @options = {:placeholder => %{<span id='no_previous_page'>No Previous Page</span>}}
+            @users = User.page(@page)
+            erb ERB_TEMPLATE_FOR_PREVIOUS_PAGE
+          end
+        end
+      end
+
+      context 'having more page' do
+        it 'should have a more page link' do
+          get '/users'
+          last_document.search('a#previous_page_link').should be_present
+          last_document.search('a#previous_page_link').text.should match(/Previous!/)
+        end
+      end
+
+      context 'the first page' do
+        it 'should not have a more page link' do
+          get '/users?page=1'
+          last_document.search('a#previous_page_link').should be_empty
+        end
+
+        it 'should have a no more page notation using placeholder' do
+          get '/users_placeholder?page=1'
+          last_document.search('a#previous_page_link').should be_empty
+          last_document.search('span#no_previous_page').should be_present
+          last_document.search('span#no_previous_page').text.should match(/No Previous Page/)
+        end
+      end
+    end
+
     describe '#link_to_next_page' do
       before do
         mock_app do