Update pagination according to mockupos

** Why are these changes being introduced:

* The GDT project has called for an update to how pagination is shown,
  across all instances of this app. The details are linked from the
  ticket below.

** Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/gdt-172

** How does this address that need:

* The visual display of the pagination links is changed, including which
  data points are included. Importantly, we are moving from a display
  that uses page numbers to one that uses result counts - so there are
  changes to the analyzer model to reflect this UI.

* We also improve the accessibility of the pagination element by using
  a nav element, and adding aria labels to make the screen reader
  output more coherent.

* Tests for both the helper and analyzer are also updated to expect the
  new markup.

** Document any side effects to this change:

* The analyzer test gets some additional assertions because of the
  calculations for the first and last record in the overall range.

* The div containing the summary of the current page is still wonky
  on a screen reader, lacking context in its output: "21 40 of 95"
  for example. I'd like to ask about this during QA, however, but
  would encourage the reviewer to listen using VoiceOver to experience
  it for yourself.

app/assets/stylesheets/partials/_pagination.scss

@@ -1,15 +1,19 @@
 .pagination-container {
+  clear: both;
+  display: flex;
+  flex-flow: row nowrap;
+  justify-content: center;
   margin-top: 3em;
 
   .previous {
-    text-align: left;
-  }
-
-  .current {
-    text-align: center;
+    border-right: 1px solid black;
+    margin-right: 0.5em;
+    padding-right: 0.5em;
   }
 
   .next {
-    text-align: right;
+    border-left: 1px solid black;
+    margin-left: 0.5em;
+    padding-left: 0.5em;
   }
 }

app/helpers/pagination_helper.rb

@@ -1,15 +1,15 @@
 module PaginationHelper
   def next_url(query_params)
     query_params[:page] = @pagination[:next]
-    link_to results_path(query_params), class: 'btn button-primary' do
-      "Next page #{content_tag(:span, '', class: 'fa fa-chevron-right')}".html_safe
+    link_to results_path(query_params), 'aria-label': 'Next page' do
+      'Next »'.html_safe
     end
   end
 
   def prev_url(query_params)
     query_params[:page] = @pagination[:prev]
-    link_to results_path(query_params), class: 'btn button-primary' do
-      "#{content_tag(:span, '', class: 'fa fa-chevron-left')} Previous page".html_safe
+    link_to results_path(query_params), 'aria-label': 'Previous page' do
+      '« Previous'.html_safe
     end
   end
 end

app/models/analyzer.rb

@@ -6,7 +6,8 @@ class Analyzer
   def initialize(enhanced_query, response)
     @pagination = {}
     @pagination[:hits] = hits(response)
-    @pagination[:page] = enhanced_query[:page]
+    @pagination[:start] = ((enhanced_query[:page] - 1) * RESULTS_PER_PAGE) + 1
+    @pagination[:end] = [enhanced_query[:page] * RESULTS_PER_PAGE, hits(response)].min
     @pagination[:prev] = enhanced_query[:page] - 1 if enhanced_query[:page] > 1
     @pagination[:next] = next_page(enhanced_query[:page], @pagination[:hits])
   end

app/views/search/_pagination.html.erb

@@ -1,19 +1,19 @@
 <% return if @pagination.nil? %>
 
-<div class="gridband layout-3c pagination-container">
-  <div class="grid-item previous">
+<nav class="pagination-container" aria-label="Pagination">
+  <div class="previous">
     <% if @pagination[:prev] %>
       <%= prev_url(@enhanced_query) %>
     <% else %>
-      First page
+      First
     <% end %>
   </div>
-  <div class="grid-item current">Page <%= @pagination[:page] %> of <%= (@pagination[:hits] / 20) + 1 %></div>
-  <div class="grid-item next">
+  <div class="current"><%= @pagination[:start] %> - <%= @pagination[:end] %> of <%= @pagination[:hits] %></div>
+  <div class="next">
     <% if @pagination[:next] %>
       <%= next_url(@enhanced_query) %>
     <% else %>
-      Last page
+      Last
     <% end %>
   </div>
-</div>
+</nav>

test/helpers/pagination_helper_test.rb

@@ -6,29 +6,29 @@ class PaginationHelperTest < ActionView::TestCase
   test 'Next links for basic search' do
     @pagination = { next: 12 }
     query_params = { q: 'popcorn' }
-    assert_equal('<a class="btn button-primary" href="/results?page=12&amp;q=popcorn">Next page <span class="fa fa-chevron-right"></span></a>', next_url(query_params))
+    assert_equal('<a aria-label="Next page" href="/results?page=12&amp;q=popcorn">Next &raquo;</a>', next_url(query_params))
   end
 
   test 'Next links for advanced search' do
     @pagination = { next: 12 }
     query_params = { q: 'popcorn', title: 'titles are cool', contributors: 'yawn' }
     assert_equal(
-      '<a class="btn button-primary" href="/results?contributors=yawn&amp;page=12&amp;q=popcorn&amp;title=titles+are+cool">Next page <span class="fa fa-chevron-right"></span></a>',
+      '<a aria-label="Next page" href="/results?contributors=yawn&amp;page=12&amp;q=popcorn&amp;title=titles+are+cool">Next &raquo;</a>',
       next_url(query_params)
     )
   end
 
   test 'Previous links for basic search' do
     @pagination = { prev: 11 }
     query_params = { q: 'popcorn' }
-    assert_equal('<a class="btn button-primary" href="/results?page=11&amp;q=popcorn"><span class="fa fa-chevron-left"></span> Previous page</a>', prev_url(query_params))
+    assert_equal('<a aria-label="Previous page" href="/results?page=11&amp;q=popcorn">&laquo; Previous</a>', prev_url(query_params))
   end
 
   test 'Previous links for advanced search' do
     @pagination = { prev: 11 }
     query_params = { q: 'popcorn', title: 'titles are cool', contributors: 'yawn' }
     assert_equal(
-      '<a class="btn button-primary" href="/results?contributors=yawn&amp;page=11&amp;q=popcorn&amp;title=titles+are+cool"><span class="fa fa-chevron-left"></span> Previous page</a>',
+      '<a aria-label="Previous page" href="/results?contributors=yawn&amp;page=11&amp;q=popcorn&amp;title=titles+are+cool">&laquo; Previous</a>',
       prev_url(query_params)
     )
   end

test/models/analyzer_test.rb

@@ -2,7 +2,8 @@
 
 class AnalyzerTest < ActiveSupport::TestCase
   test 'analyzer pagination does not include previous page value on first page of results' do
-    Analyzer.any_instance.stubs(:hits).returns(100)
+    hit_count = 95
+    Analyzer.any_instance.stubs(:hits).returns(hit_count)
     mocking_hits_so_this_is_empty = {}
 
     eq = {
@@ -14,14 +15,19 @@ class AnalyzerTest < ActiveSupport::TestCase
     pagination = Analyzer.new(eq, mocking_hits_so_this_is_empty).pagination
 
     assert pagination.key?(:hits)
+    assert pagination.key?(:start)
+    assert pagination.key?(:end)
     assert pagination.key?(:next)
-    assert pagination.key?(:page)
 
     refute pagination.key?(:prev)
+
+    assert_equal 1, pagination[:start]
+    assert_equal 20, pagination[:end]
   end
 
   test 'analyzer pagination includes all values when not on first or last page of results' do
-    Analyzer.any_instance.stubs(:hits).returns(100)
+    hit_count = 95
+    Analyzer.any_instance.stubs(:hits).returns(hit_count)
     mocking_hits_so_this_is_empty = {}
 
     eq = {
@@ -33,26 +39,35 @@ class AnalyzerTest < ActiveSupport::TestCase
     pagination = Analyzer.new(eq, mocking_hits_so_this_is_empty).pagination
 
     assert pagination.key?(:hits)
+    assert pagination.key?(:start)
+    assert pagination.key?(:end)
     assert pagination.key?(:next)
     assert pagination.key?(:prev)
-    assert pagination.key?(:page)
+
+    assert_equal 21, pagination[:start]
+    assert_equal 40, pagination[:end]
   end
 
   test 'analyzer pagination does not include last page value on last page of results' do
-    Analyzer.any_instance.stubs(:hits).returns(100)
+    hit_count = 95
+    Analyzer.any_instance.stubs(:hits).returns(hit_count)
 
     mocking_hits_so_this_is_empty = {}
     eq = {
       q: 'data',
-      page: 28
+      page: 5
     }
 
     pagination = Analyzer.new(eq, mocking_hits_so_this_is_empty).pagination
 
     assert pagination.key?(:hits)
+    assert pagination.key?(:start)
+    assert pagination.key?(:end)
     assert pagination.key?(:prev)
-    assert pagination.key?(:page)
 
-    assert_nil pagination[:next]
+    refute pagination[:next]
+
+    assert_equal 81, pagination[:start]
+    assert_equal hit_count, pagination[:end]
   end
 end