add a page_links action to Blacklight::Searchable

- allows client-side management of show-view result set navigation

Author: barmintor

app/controllers/concerns/blacklight/search_context.rb

@@ -17,6 +17,28 @@ def record_search_parameters opts = { only: :index }
     end
   end
 
+  # GET previous and next document json for the document specified by
+  # the counter param in current search
+  def page_links
+    counter_param = params.delete(:counter)
+    @page_link_data = {}
+    if counter_param
+      index = counter_param.to_i - 1
+      response, documents = search_service.previous_and_next_documents_for_search index, search_state.reset_search
+      if documents.detect(&:present?)
+        @page_link_data[:prev] = page_links_document_path(documents.first, index)
+        @page_link_data[:next] = page_links_document_path(documents.last, index + 2)
+      end
+      if response&.total && response.total.positive?
+        @page_link_data[:counterRaw] = counter_param
+        @page_link_data[:counterDelimited] = helpers.number_with_delimiter(counter_param.to_i)
+        @page_link_data[:totalRaw] = response.total
+        @page_link_data[:totalDelimited] = helpers.number_with_delimiter(response.total)
+      end
+    end
+    render json: @page_link_data
+  end
+
   private
 
   # sets up the session[:search] hash if it doesn't already exist
@@ -120,4 +142,14 @@ def setup_next_and_previous_documents
     logger&.warn "Unable to setup next and previous documents: #{e}"
     nil
   end
+
+  def page_links_document_path(document, counter)
+    return nil unless document
+
+    if blacklight_config.view_config(:show).route
+      search_state.url_for_document(document, counter: counter)
+    else
+      solr_document_path(document, counter: counter)
+    end
+  end
 end

lib/blacklight/routes/searchable.rb

@@ -9,6 +9,7 @@ def initialize(defaults = {})
       def call(mapper, _options = {})
         mapper.match '/', action: 'index', as: 'search', via: [:get, :post]
         mapper.get '/advanced', action: 'advanced_search', as: 'advanced_search'
+        mapper.get '/page_links', action: 'page_links', as: 'page_links'
 
         mapper.post ":id/track", action: 'track', as: 'track'
         mapper.get ":id/raw", action: 'raw', as: 'raw', defaults: { format: 'json' }

spec/controllers/catalog_controller_spec.rb

@@ -919,6 +919,21 @@ def export_as_mock
       end
     end
   end
+
+  describe "page_links" do
+    it "has prev/next docs and result set data for non-empty result sets", integration: true do
+      get :page_links, params: { f: { "format" => 'Book' }, counter: 2 }
+      expect(assigns(:page_link_data)).not_to be_empty
+      expect(assigns(:page_link_data).fetch(:prev, nil)).to end_with('counter=1')
+      expect(assigns(:page_link_data).fetch(:next, nil)).to end_with('counter=3')
+      expect(assigns(:page_link_data).fetch(:totalRaw, nil)).to be 30
+    end
+
+    it "is empty for empty result sets", integration: true do
+      get :page_links, params: { f: { "format" => 'empty-result-set' }, counter: 1 }
+      expect(assigns(:page_link_data)).to be_empty
+    end
+  end
 end
 
 # there must be at least one facet, and each facet must have at least one value

spec/routing/catalog_routing_spec.rb

@@ -23,6 +23,10 @@
     it "maps { :controller => 'catalog', :action => 'show', :id => 666 } to /catalog/666" do
       expect(get: "/catalog/666").to route_to(controller: 'catalog', action: 'show', id: "666")
     end
+
+    it "maps GET {:controller => 'catalog', :action => 'prev_next_documents'} to /catalog/page_links" do
+      expect(get: "/catalog/page_links").to route_to(controller: 'catalog', action: 'page_links')
+    end
   end
 
   describe "solr_document_path for SolrDocument", test: true do