class Ecu
  class LabelListComparison

    def initialize(left, right)
      unless left.is_a?(LabelList) && right.is_a?(LabelList)
        fail "Can only merge LabelLists (left: #{left.class}, right: #{right.class})!"
      end

      @left               = left.map(&:name).zip(left).to_h
      @right              = right.map(&:name).zip(right).to_h
      @unified_headers    = left.headers + right.headers
      @unified_subheaders = left.subheaders + right.subheaders
      @names              = Hash.new
    end

    def names(criterion)
      @names[criterion] ||= \
        case criterion
        when :left_exclusive  then left.keys - right.keys
        when :right_exclusive then right.keys - left.keys
        when :common          then left.keys & right.keys
        when :nonequal        then names(:common).select { |n| left.fetch(n) != right.fetch(n) }
        when :equal           then names(:common).select { |n| left.fetch(n) == right.fetch(n) }
        else fail "Unknown criterion #{criterion}"
        end
    end

    def left_exclusive
      names(:left_exclusive).map { |name| left.fetch(name) }
    end

    def right_exclusive
      names(:right_exclusive).map { |name| right.fetch(name) }
    end

    def differences
      names(:nonequal).map { |name| [ left.fetch(name), right.fetch(name) ] }
    end

    def merge(priority: :right)
      labels = []
      left.each do |name, label|
        if names(:common).include?(name) && priority == :right
          labels << right.fetch(name)
        else
          labels << left.fetch(name)
        end
      end
      right.each do |name, label|
        next if labels.map(&:name).include?(name)
        if names(:common).include?(name) && priority == :left
          labels << left.fetch(name)
        else
          labels << right.fetch(name)
        end
      end
      LabelList.new(labels, @unified_headers, @unified_subheaders)
    end

    private

    attr_reader :left, :right

  end
end