# frozen_string_literal: true

module Micro::Attributes
  module Diff
    class Changes
      TO = 'to'.freeze
      FROM = 'from'.freeze
      FROM_TO_ERROR = 'pass the attribute name with the :from and :to values'.freeze

      attr_reader :from, :to, :differences

      def initialize(from:, to:)
        raise ArgumentError, "expected an instance of #{from.class}" unless to.is_a?(from.class)
        @from, @to = from, to
        @differences = diff(from.attributes, to.attributes).freeze
      end

      def empty?
        @differences.empty?
      end
      alias_method :blank?, :empty?

      def present?
        !empty?
      end

      def changed?(name = nil, from: nil, to: nil)
        if name.nil?
          return present? if from.nil? && to.nil?
          raise ArgumentError, FROM_TO_ERROR
        elsif from.nil? && to.nil?
          differences.has_key?(name.to_s)
        else
          result = @differences[name.to_s]
          result ? result[FROM] == from && result[TO] == to : false
        end
      end

      private

      def diff(from_attributes, to_attributes)
        @from_attributes, @to_attributes = from_attributes, to_attributes
        @from_attributes.each_with_object({}) do |(from_key, from_val), acc|
          to_value = @to_attributes[from_key]
          acc[from_key] = {FROM => from_val, TO => to_value}.freeze if from_val != to_value
        end
      end

      private_constant :TO, :FROM, :FROM_TO_ERROR
    end
  end
end