Retire vendored cacycle_diff.js for a diff-lcs-based diff view

Revisions#diff now computes an inline or side-by-side word diff
server-side (Page#diff_against, lib/html_word_diff.rb) instead of
shipping raw/escaped content to the browser for a 2008-era vendored
JS differ to mangle. View mode is picked via a `view` param, settable
either on the diff page itself or directly from the revisions#index
sticky bar next to "Diff revisions".

Also fixes a pre-existing bug in RevisionsController#diff's single-
revision branch, which set params[:start]/params[:end] instead of
params[:start_revision]/params[:end_revision].

2 files changed, 63 insertions, 0 deletions

diff --git a/test/controllers/revisions_controller_test.rb b/test/controllers/revisions_controller_test.rb
index b4dcd8f..e2fc976 100644
--- a/test/controllers/revisions_controller_test.rb
+++ b/test/controllers/revisions_controller_test.rb
@@ -59,4 +59,33 @@ class RevisionsControllerTest < ActionController::TestCase
     assert_equal @node.head, @node.pages.first
     assert_equal "first", @node.head.reload.body
   end
+
+  test "diffing two revisions renders real markup with only the changed words marked" do
+    login_as :quentin
+    post(
+      :diff, params: {
+        :node_id => @node.id,
+        :start_revision => @node.pages.first.revision,
+        :end_revision => @node.pages.last.revision
+      }
+    )
+    assert_response :success
+    assert_select "del", "first"
+    assert_select "ins", "second"
+    assert_no_match /&lt;/, response.body
+  end
+
+  test "diffing two revisions in side by side view renders two columns" do
+    login_as :quentin
+    post(
+      :diff, params: {
+        :node_id => @node.id,
+        :start_revision => @node.pages.first.revision,
+        :end_revision => @node.pages.last.revision,
+        :view => "side_by_side"
+      }
+    )
+    assert_response :success
+    assert_select ".diff_column", 2
+  end
 end
diff --git a/test/models/page_test.rb b/test/models/page_test.rb
index ad2742f..ac5691a 100644
--- a/test/models/page_test.rb
+++ b/test/models/page_test.rb
@@ -176,4 +176,38 @@ class PageTest < ActiveSupport::TestCase
     assert_not_equal first_page.id, first_page.node.head_id
     assert first_page.published_at.present?
   end
+
+  def test_diff_against_inline_keeps_tags_and_marks_only_the_changed_word
+    n = Node.root.children.create! :slug => "diff_against_test"
+    d = n.find_or_create_draft @user1
+    d.title = "Old heading"
+    d.save!
+    n.publish_draft!
+
+    d2 = n.find_or_create_draft @user1
+    d2.title = "New heading"
+    d2.save!
+
+    diff = d2.diff_against(n.head)
+
+    assert_match "<del>Old</del>", diff[:title]
+    assert_match "<ins>New</ins>", diff[:title]
+  end
+
+  def test_diff_against_side_by_side_returns_two_annotated_strings
+    n = Node.root.children.create! :slug => "diff_against_sbs_test"
+    d = n.find_or_create_draft @user1
+    d.title = "Old heading"
+    d.save!
+    n.publish_draft!
+
+    d2 = n.find_or_create_draft @user1
+    d2.title = "New heading"
+    d2.save!
+
+    old_html, new_html = d2.diff_against(n.head, view: :side_by_side)[:title]
+
+    assert_match "<del>Old</del>", old_html
+    assert_match "<ins>New</ins>", new_html
+  end
 end