Change file name and use module to organize

app/lib/diff_tools.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require "diff/lcs"
+
+module DiffTools
+  class SimpleDiff
+    def initialize(old_value, new_value)
+      old_value ||= ""
+      new_value ||= ""
+      @changes = ::Diff::LCS.sdiff(old_value, new_value).chunk(&:action).map do |action, changes|
+        {
+          action: action,
+          old: changes.map(&:old_element).join,
+          new: changes.map(&:new_element).join
+        }
+      end
+    end
+
+    def to_html
+      @changes.map do |chunk|
+        old_html = DiffTools.value_to_html(chunk[:old])
+        new_html = DiffTools.value_to_html(chunk[:new])
+        if chunk[:action] == "="
+          new_html
+        else
+          (old_html.empty? ? "" : "<del>#{old_html}</del>") + \
+            (new_html.empty? ? "" : "<ins>#{new_html}</ins>")
+        end
+      end.join
+    end
+  end
+
+  def self.value_to_html(value)
+    too_many_words_re = /
+      ((?:\S+\s+){3}) # group 1: Three words, including trailing space
+      (.+)            # group 2: Drop this
+      ((?:\s+\S+){3}) # group 3: Three words, including leading space
+    /x
+    ellipsis = value.gsub(too_many_words_re, '\1...\3')
+    CGI.escapeHTML(ellipsis)
+  end
+end

app/models/work_activity.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require_relative "../lib/simple_diff"
+require_relative "../lib/diff_tools"
 
 # rubocop:disable Metrics/ClassLength
 class WorkActivity < ApplicationRecord
@@ -199,7 +199,7 @@ def created_at_html
 
     def change_value_html(value)
       if value["action"] == "changed"
-        SimpleDiff.new(value["from"], value["to"]).to_html
+        DiffTools::SimpleDiff.new(value["from"], value["to"]).to_html
       else
         "old change"
       end

spec/lib/diff_spec.rb

@@ -1,34 +1,34 @@
 # frozen_string_literal: true
 
-require_relative "../../app/lib/simple_diff"
+require_relative "../../app/lib/diff_tools"
 
-RSpec.describe SimpleDiff do
+RSpec.describe DiffTools::SimpleDiff do
   it "handles complete change" do
-    expect(SimpleDiff.new("cat", "dog").to_html).to eq "<del>cat</del><ins>dog</ins>"
+    expect(DiffTools::SimpleDiff.new("cat", "dog").to_html).to eq "<del>cat</del><ins>dog</ins>"
   end
   it "handles single character change" do
-    expect(SimpleDiff.new("cat", "bat").to_html).to eq "<del>c</del><ins>b</ins>at"
+    expect(DiffTools::SimpleDiff.new("cat", "bat").to_html).to eq "<del>c</del><ins>b</ins>at"
   end
   it "handles nil old" do
-    expect(SimpleDiff.new(nil, "dog").to_html).to eq "<ins>dog</ins>"
+    expect(DiffTools::SimpleDiff.new(nil, "dog").to_html).to eq "<ins>dog</ins>"
   end
   it "handles nil new" do
-    expect(SimpleDiff.new("dog", nil).to_html).to eq "<del>dog</del>"
+    expect(DiffTools::SimpleDiff.new("dog", nil).to_html).to eq "<del>dog</del>"
   end
   it "handles addition" do
-    expect(SimpleDiff.new("dog", "In the dog house").to_html).to eq "<ins>In the </ins>dog<ins> house</ins>"
+    expect(DiffTools::SimpleDiff.new("dog", "In the dog house").to_html).to eq "<ins>In the </ins>dog<ins> house</ins>"
   end
   it "handles deletion" do
-    expect(SimpleDiff.new("The cow jumped", "cow").to_html).to eq "<del>The </del>cow<del> jumped</del>"
+    expect(DiffTools::SimpleDiff.new("The cow jumped", "cow").to_html).to eq "<del>The </del>cow<del> jumped</del>"
   end
   it "handles mixed" do
-    expect(SimpleDiff.new("quick brown", "brown fox").to_html).to eq "<del>quick </del>brown<ins> fox</ins>"
+    expect(DiffTools::SimpleDiff.new("quick brown", "brown fox").to_html).to eq "<del>quick </del>brown<ins> fox</ins>"
   end
   it "encodes html" do
-    expect(SimpleDiff.new("1 < 2", "2 > 1").to_html).to eq "<del>1</del><ins>2</ins> <del>&lt;</del><ins>&gt;</ins> <del>2</del><ins>1</ins>"
+    expect(DiffTools::SimpleDiff.new("1 < 2", "2 > 1").to_html).to eq "<del>1</del><ins>2</ins> <del>&lt;</del><ins>&gt;</ins> <del>2</del><ins>1</ins>"
   end
   it "abbreviates really long strings" do
-    expect(SimpleDiff.new(
+    expect(DiffTools::SimpleDiff.new(
       "This does not repeat the entire string if its just a tiny typo in the middle that changes.",
       "This does not repeat the entire string if it's just a tiny typo in the middle that changes."
     ).to_html).to eq "This does not ... string if it<ins>&#39;</ins>s just a ... middle that changes."