piotrmurach/tty-prompt

# frozen_string_literal: true

module TTY
  class Prompt
    # A class responsible for string comparison
    class Distance
      # Calculate the optimal string alignment distance
      #
      # @api public
      def distance(first, second)
        distances = []
        rows      = first.to_s.length
        cols      = second.to_s.length

        0.upto(rows) do |index|
          distances << [index] + [0] * cols
        end
        distances[0] = 0.upto(cols).to_a

        1.upto(rows) do |first_index|
          1.upto(cols) do |second_index|
            first_char  = first[first_index - 1]
            second_char = second[second_index - 1]
            cost        = first_char == second_char ? 0 : 1

            distances[first_index][second_index] = [
              distances[first_index - 1][second_index], # deletion
              distances[first_index][second_index - 1],     # insertion
              distances[first_index - 1][second_index - 1]  # substitution
            ].min + cost

            if first_index > 1 && second_index > 1
              first_previous_char = first[first_index - 2]
              second_previous_char = second[second_index - 2]
              if first_char == second_previous_char && second_char == first_previous_char
                distances[first_index][second_index] = [
                  distances[first_index][second_index],
                  distances[first_index - 2][second_index - 2] + 1 # transposition
                ].min
              end
            end

          end
        end
        distances[rows][cols]
      end
    end # Distance
  end # Prompt
end # TTY