Extract load_search_context and a SearchContextPresenter

app/controllers/concerns/blacklight/search_context.rb

@@ -7,7 +7,7 @@ module Blacklight::SearchContext
   # own controller.
   included do
     if respond_to? :helper_method
-      helper_method :current_search_session, :search_session
+      helper_method :current_search_session, :search_session, :page_links_document_path
     end
   end
 
@@ -31,23 +31,17 @@ def searches_from_history
   # 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&.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
+    counter = if Rails::VERSION::MAJOR >= 8
+                params.expect(:counter).to_i
+              else
+                params[:counter].to_i
+              end
+
+    @search_context = load_search_context(counter, search_state.reset_search)
+
+    respond_to do |format|
+      format.json
     end
-    render json: @page_link_data
   end
 
   private
@@ -142,11 +136,9 @@ def setup_next_and_previous_documents
     return { counter: params[:counter] } if setup_next_and_previous_on_client?
     return nil unless setup_next_and_previous_on_server?
 
-    index = search_session['counter'].to_i - 1
-    response, documents = search_service.previous_and_next_documents_for_search index, search_state.reset(current_search_session.query_params)
-
-    search_session['total'] = response.total
-    { prev: documents.first, next: documents.last }
+    load_search_context(search_session['counter'].to_i, search_state.reset(current_search_session.query_params)).tap do |search_context_presenter|
+      search_session['total'] = search_context_presenter.total
+    end
   rescue Blacklight::Exceptions::InvalidRequest => e
     logger&.warn "Unable to setup next and previous documents: #{e}"
     nil
@@ -166,4 +158,11 @@ def page_links_document_path(document, counter)
 
     solr_document_path(document, counter: counter)
   end
+
+  def load_search_context(counter, context_search_state)
+    index = counter - 1
+    response, _documents = search_service.previous_and_next_documents_for_search index, context_search_state
+
+    Blacklight::SearchContextPresenter.new(response, counter: counter, view_context: view_context)
+  end
 end

app/presenters/blacklight/search_context_presenter.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module Blacklight
+  # Presenter for the search context (e.g. previous + next links) of a single document within a search result.
+  class SearchContextPresenter
+    attr_reader :response, :counter, :view_context
+
+    def initialize(response, view_context:, counter: nil)
+      @response = response
+      @counter = counter
+      @view_context = view_context
+    end
+
+    # Provide backwards-compatibility for downstream code expecting the old hash-based response.
+    delegate_missing_to :to_hash
+
+    def to_hash
+      @to_hash ||= {
+        prev: previous_document,
+        next: next_document
+      }
+    end
+
+    def total
+      response.total.to_i
+    end
+
+    def previous_document
+      return if counter && counter <= 1
+
+      response.documents.first
+    end
+
+    def next_document
+      return if counter && counter >= response.total
+
+      response.documents.last
+    end
+  end
+end

app/views/catalog/page_links.json.jbuilder

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+if @search_context.previous_document || @search_context.next_document
+  json.prev page_links_document_path(@search_context.previous_document, @search_context.counter - 1) if @search_context.previous_document
+  json.next page_links_document_path(@search_context.next_document, @search_context.counter + 1) if @search_context.next_document
+  json.counterRaw @search_context.counter
+  json.totalRaw @search_context.total
+  json.counterDelimited number_with_delimiter(@search_context.counter) if @search_context.counter
+  json.totalDelimited number_with_delimiter(@search_context.total) if @search_context.total.positive?
+end

spec/controllers/catalog_controller_spec.rb

@@ -347,9 +347,11 @@
         context 'and no exception is raised' do
           before do
             expect(search_service).to receive(:previous_and_next_documents_for_search)
-              .and_return([double(total: 5), [double("a"), mock_document, double("b")]])
+              .and_return([double(total: 5, documents: documents), documents])
           end
 
+          let(:documents) { [double("a"), mock_document, double("b")] }
+
           it "sets previous document" do
             get :show, params: { id: doc_id }
             expect(assigns[:search_context][:prev]).not_to be_nil
@@ -788,17 +790,20 @@ def export_as_mock
   end
 
   describe "page_links" do
+    render_views
+
     it "has prev/next docs and result set data for non-empty result sets", :integration 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
+      get :page_links, params: { f: { "format" => 'Book' }, counter: 2, format: 'json' }
+
+      expect(response.parsed_body).not_to be_empty
+      expect(response.parsed_body.fetch(:prev, nil)).to end_with('counter=1')
+      expect(response.parsed_body.fetch(:next, nil)).to end_with('counter=3')
+      expect(response.parsed_body.fetch(:totalRaw, nil)).to be 30
     end
 
     it "is empty for empty result sets", :integration do
-      get :page_links, params: { f: { "format" => ['empty-result-set'] }, counter: 1 }
-      expect(assigns(:page_link_data)).to be_empty
+      get :page_links, params: { f: { "format" => ['empty-result-set'] }, counter: 1, format: 'json' }
+      expect(response.parsed_body).to be_empty
     end
   end
 end