pivotal/LicenseFinder

# frozen_string_literal: true

module CommonPathHelper
  def self.longest_common_paths(paths)
    [].tap do |common_paths|
      # organize by matching root paths
      paths_with_roots = paths.group_by { |path| path.split('/').first }
      paths_with_roots.each do |common_root, full_paths|
        # use the shortest path as the 'template'
        shortest_path = full_paths.min_by { |path| path.split('/').length }
        longest_common_path = common_root

        # iterate through each subpath of the 'template'
        shortest_path.split('/').each_with_index do |subpath, i|
          potential_path = i.zero? ? longest_common_path : [longest_common_path, subpath].join('/')

          # check each for the existence of the subsequent subpath
          mismatch = full_paths.any? { |path| !path.start_with?(potential_path) }
          break if mismatch

          longest_common_path = potential_path
        end

        longest_common_path = full_paths if longest_common_path.split('/').length == 1
        (common_paths << longest_common_path).flatten!
      end
    end
  end
end