1 files changed, 74 insertions, 0 deletions

diff --git a/lib/html_word_diff.rb b/lib/html_word_diff.rb
new file mode 100644
index 0000000..aa0cb86
--- /dev/null
+++ b/lib/html_word_diff.rb
@@ -0,0 +1,74 @@
+require 'diff/lcs'
+require 'cgi'
+
+module HtmlWordDiff
+  TOKEN_REGEXP = /<[^>]*>|[[:space:]]+|[[:alnum:]]+|[^[:space:][:alnum:]<>]/
+
+  def self.inline(old_html, new_html)
+    html = +''
+    each_change(old_html, new_html) do |action, old_token, new_token|
+      case action
+      when '='
+        html << new_token
+      when '-'
+        html << wrap_removed(old_token)
+      when '+'
+        html << wrap_inserted(new_token)
+      when '!'
+        html << wrap_removed(old_token)
+        html << wrap_inserted(new_token)
+      end
+    end
+    html
+  end
+
+  def self.side_by_side(old_html, new_html)
+    old_out = +''
+    new_out = +''
+    each_change(old_html, new_html) do |action, old_token, new_token|
+      case action
+      when '='
+        old_out << old_token
+        new_out << new_token
+      when '-'
+        old_out << wrap_removed(old_token)
+      when '+'
+        new_out << wrap_inserted(new_token)
+      when '!'
+        old_out << wrap_removed(old_token)
+        new_out << wrap_inserted(new_token)
+      end
+    end
+    [old_out, new_out]
+  end
+
+  def self.each_change(old_html, new_html)
+    Diff::LCS.sdiff(tokenize(old_html), tokenize(new_html)).each do |change|
+      yield change.action, change.old_element, change.new_element
+    end
+  end
+
+  def self.tokenize(html)
+    html.to_s.scan(TOKEN_REGEXP)
+  end
+
+  def self.tag_token?(token)
+    token.to_s.match?(/\A<[^>]*>\z/)
+  end
+
+  def self.wrap_removed(token)
+    if tag_token?(token)
+      %(<del class="diff_structural" title="removed: #{CGI.escapeHTML(token)}">\u00b6</del>)
+    else
+      "<del>#{token}</del>"
+    end
+  end
+
+  def self.wrap_inserted(token)
+    if tag_token?(token)
+      %(<ins class="diff_structural" title="added: #{CGI.escapeHTML(token)}">\u00b6</ins>)
+    else
+      "<ins>#{token}</ins>"
+    end
+  end
+end