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].

1 files changed, 16 insertions, 0 deletions

diff --git a/app/models/page.rb b/app/models/page.rb
index 1a98e08..ea04cd6 100644
--- a/app/models/page.rb
+++ b/app/models/page.rb
@@ -175,6 +175,22 @@ class Page < ApplicationRecord
     self.save
   end
 
+  def diff_against other, view: :inline
+    if view == :side_by_side
+      {
+        title:    HtmlWordDiff.side_by_side(other.title.to_s,    title.to_s),
+        abstract: HtmlWordDiff.side_by_side(other.abstract.to_s, abstract.to_s),
+        body:     HtmlWordDiff.side_by_side(other.body.to_s,     body.to_s)
+      }
+    else
+      {
+        title:    HtmlWordDiff.inline(other.title.to_s,    title.to_s),
+        abstract: HtmlWordDiff.inline(other.abstract.to_s, abstract.to_s),
+        body:     HtmlWordDiff.inline(other.body.to_s,     body.to_s)
+      }
+    end
+  end
+
   def public?
     published_at.nil? ? true : published_at < Time.now
   end