require "spreadsheet/compatibility"

module Spreadsheet
  module Excel
    ##
    # This module is used to keep track of offsets in modified Excel documents.
    # Considered internal and subject to change without notice.
    module Offset
      include Compatibility
      attr_reader :changes, :offsets
      def initialize *args
        super
        @changes = {}
        @offsets = {}
      end

      def self.append_features mod
        super
        mod.module_eval do
          class << self
            include Compatibility
            def offset *keys
              keys.each do |key|
                attr_reader key unless instance_methods.include? method_name(key)
                define_method :"#{key}=" do |value|
                  @changes.store key, true
                  instance_variable_set ivar_name(key), value
                end
                define_method :"set_#{key}" do |value, pos, len|
                  instance_variable_set ivar_name(key), value
                  @offsets.store key, [pos, len]
                  havename = "have_set_#{key}"
                  send(havename, value, pos, len) if respond_to? havename
                end
              end
            end
          end
        end
      end
    end
  end
end