pulibrary / pdc_describe / 4e4e59fc-9df4-4838-9fd4-6c7ea33cdb7c

require "diff/lcs"

module DiffTools

  class SimpleDiff

    def initialize(old_value, new_value)

      old_value = old_value.to_s.split(/\b/)

      new_value = new_value.to_s.split(/\b/)

      @changes = ::Diff::LCS.sdiff(old_value, new_value).chunk(&:action).map do |action, changes|

        {

          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