class ActiveRecord::Base

def self.synchronize(instances, keys=[self.primary_key])
  return if instances.empty?
  conditions = {}
  order = ""
  key_values = keys.map { |key| instances.map(&"#{key}".to_sym) }
  keys.zip(key_values).each { |key, values| conditions[key] = values }
  order = keys.map{ |key| "#{key} ASC" }.join(",")
  klass = instances.first.class
  fresh_instances = klass.where(conditions).order(order)
  instances.each do |instance|
    matched_instance = fresh_instances.detect do |fresh_instance|
      keys.all?{ |key| fresh_instance.send(key) == instance.send(key) }
    end
    if matched_instance
      instance.send :clear_aggregation_cache
      instance.send :clear_association_cache
      instance.instance_variable_set :@attributes, matched_instance.instance_variable_get(:@attributes)
      if instance.respond_to?(:clear_changes_information)
        instance.clear_changes_information                  # Rails 4.1 and higher
      else
        instance.changed_attributes.clear                   # Rails 3.1, 3.2
      end
      # Since the instance now accurately reflects the record in
      # the database, ensure that instance.persisted? is true.
      instance.instance_variable_set '@new_record', false
      instance.instance_variable_set '@destroyed', false
    end
  end
end

def add_special_rails_stamps( column_names, array_of_attributes, options )
  AREXT_RAILS_COLUMNS[:create].each_pair do |key, blk|
    if self.column_names.include?(key)
      value = blk.call
      if index=column_names.index(key) || index=column_names.index(key.to_sym)
        # replace every instance of the array of attributes with our value
        array_of_attributes.each{ |arr| arr[index] = value if arr[index].nil? }
      else
        column_names << key
        array_of_attributes.each { |arr| arr << value }
      end
    end
  end
  AREXT_RAILS_COLUMNS[:update].each_pair do |key, blk|
    if self.column_names.include?(key)
      value = blk.call
      if index=column_names.index(key) || index=column_names.index(key.to_sym)
         # replace every instance of the array of attributes with our value
         array_of_attributes.each{ |arr| arr[index] = value }
      else
        column_names << key
        array_of_attributes.each { |arr| arr << value }
      end
      if supports_on_duplicate_key_update?
        connection.add_column_for_on_duplicate_key_update(key, options)
      end
    end
  end
end

def establish_connection_with_activerecord_import(*args)
  conn = establish_connection_without_activerecord_import(*args)
  if !ActiveRecord.const_defined?(:Import) || !ActiveRecord::Import.respond_to?(:load_from_connection_pool)
    require "activerecord-import/base"
  end
  ActiveRecord::Import.load_from_connection_pool connection_pool
  conn
end

def find_associated_objects_for_import(associated_objects_by_class, model)
  associated_objects_by_class[model.class.name]||={}
  association_reflections =
    model.class.reflect_on_all_associations(:has_one) +
    model.class.reflect_on_all_associations(:has_many)
  association_reflections.each do |association_reflection|
    associated_objects_by_class[model.class.name][association_reflection.name]||=[]
    association = model.association(association_reflection.name)
    association.loaded!
    # Wrap target in an array if not already
    association = Array(association.target)
    changed_objects = association.select {|a| a.new_record? || a.changed?}
    changed_objects.each do |child|
      child.send("#{association_reflection.foreign_key}=", model.id)
    end
    associated_objects_by_class[model.class.name][association_reflection.name].concat changed_objects
  end
  associated_objects_by_class
end

def import(*args)
  if args.first.is_a?( Array ) and args.first.first.is_a? ActiveRecord::Base
    options = {}
    options.merge!( args.pop ) if args.last.is_a?(Hash)
    models = args.first
    import_helper(models, options)
  else
    import_helper(*args)
  end
end

def import_associations(models, options)
  # now, for all the dirty associations, collect them into a new set of models, then recurse.
  # notes:
  #    does not handle associations that reference themselves
  #    should probably take a hash to associations to follow.
  associated_objects_by_class={}
  models.each {|model| find_associated_objects_for_import(associated_objects_by_class, model) }
  associated_objects_by_class.each_pair do |class_name, associations|
    associations.each_pair do |association_name, associated_records|
      associated_records.first.class.import(associated_records, options) unless associated_records.empty?
    end
  end
end

def import_from_table( options ) # :nodoc:
end

def import_helper( *args )
  options = { :validate=>true, :timestamps=>true, :primary_key=>primary_key }
  options.merge!( args.pop ) if args.last.is_a? Hash
  # Don't modify incoming arguments
  if options[:on_duplicate_key_update]
    options[:on_duplicate_key_update] = options[:on_duplicate_key_update].dup
  end
  is_validating = options[:validate]
  is_validating = true unless options[:validate_with_context].nil?
  # assume array of model objects
  if args.last.is_a?( Array ) and args.last.first.is_a? ActiveRecord::Base
    if args.length == 2
      models = args.last
      column_names = args.first
    else
      models = args.first
      column_names = self.column_names.dup
    end
    array_of_attributes = models.map do |model|
      # this next line breaks sqlite.so with a segmentation fault
      # if model.new_record? || options[:on_duplicate_key_update]
        column_names.map do |name|
          name = name.to_s
          if respond_to?(:defined_enums) && defined_enums.has_key?(name) # ActiveRecord 5
            model.read_attribute(name)
          elsif model.class.column_defaults[name].is_a?(Integer)
            model.read_attribute(name)
          else
            model.read_attribute_before_type_cast(name)
          end
        end
      # end
    end
    # supports empty array
  elsif args.last.is_a?( Array ) and args.last.empty?
    return ActiveRecord::Import::Result.new([], 0, []) if args.last.empty?
    # supports 2-element array and array
  elsif args.size == 2 and args.first.is_a?( Array ) and args.last.is_a?( Array )
    column_names, array_of_attributes = args
  else
    raise ArgumentError.new( "Invalid arguments!" )
  end
  # dup the passed in array so we don't modify it unintentionally
  column_names = column_names.dup
  array_of_attributes = array_of_attributes.dup
  # Force the primary key col into the insert if it's not
  # on the list and we are using a sequence and stuff a nil
  # value for it into each row so the sequencer will fire later
  if !column_names.include?(primary_key) && connection.prefetch_primary_key? && sequence_name
     column_names << primary_key
     array_of_attributes.each { |a| a << nil }
  end
  # record timestamps unless disabled in ActiveRecord::Base
  if record_timestamps && options.delete( :timestamps )
     add_special_rails_stamps column_names, array_of_attributes, options
  end
  return_obj = if is_validating
    import_with_validations( column_names, array_of_attributes, options )
  else
    (num_inserts, ids) = import_without_validations_or_callbacks( column_names, array_of_attributes, options )
    ActiveRecord::Import::Result.new([], num_inserts, ids)
  end
  if options[:synchronize]
    sync_keys = options[:synchronize_keys] || [self.primary_key]
    synchronize( options[:synchronize], sync_keys)
  end
  return_obj.num_inserts = 0 if return_obj.num_inserts.nil?
  # if we have ids, then set the id on the models and mark the models as clean.
  if support_setting_primary_key_of_imported_objects?
    set_ids_and_mark_clean(models, return_obj)
    # if there are auto-save associations on the models we imported that are new, import them as well
    if options[:recursive]
      import_associations(models, options)
    end
  end
  return_obj
end

def import_with_validations( column_names, array_of_attributes, options={} )
  failed_instances = []
  # create instances for each of our column/value sets
  arr = validations_array_for_column_names_and_attributes( column_names, array_of_attributes )
  # keep track of the instance and the position it is currently at. if this fails
  # validation we'll use the index to remove it from the array_of_attributes
  arr.each_with_index do |hsh,i|
    instance = new do |model|
      hsh.each_pair{ |k,v| model.send("#{k}=", v) }
    end
    if not instance.valid?(options[:validate_with_context])
      array_of_attributes[ i ] = nil
      failed_instances << instance
    end
  end
  array_of_attributes.compact!
  (num_inserts, ids) = if array_of_attributes.empty? || options[:all_or_none] && failed_instances.any?
                  [0,[]]
                else
                  import_without_validations_or_callbacks( column_names, array_of_attributes, options )
                end
  ActiveRecord::Import::Result.new(failed_instances, num_inserts, ids)
end

def import_without_validations_or_callbacks( column_names, array_of_attributes, options={} )
  column_names = column_names.map(&:to_sym)
  scope_columns, scope_values = scope_attributes.to_a.transpose
  unless scope_columns.blank?
    scope_columns.zip(scope_values).each do |name, value|
      name_as_sym = name.to_sym
      next if column_names.include?(name_as_sym)
      is_sti = (name_as_sym == inheritance_column.to_sym && self < base_class)
      value = value.first if is_sti
      column_names << name_as_sym
      array_of_attributes.each { |attrs| attrs << value }
    end
  end
  columns = column_names.each_with_index.map do |name, i|
    column = columns_hash[name.to_s]
    raise ActiveRecord::Import::MissingColumnError.new(name.to_s, i) if column.nil?
    column
  end
  columns_sql = "(#{column_names.map{|name| connection.quote_column_name(name) }.join(',')})"
  insert_sql = "INSERT #{options[:ignore] ? 'IGNORE ':''}INTO #{quoted_table_name} #{columns_sql} VALUES "
  values_sql = values_sql_for_columns_and_attributes(columns, array_of_attributes)
  ids = []
  if not supports_import?
    number_inserted = 0
    values_sql.each do |values|
      connection.execute(insert_sql + values)
      number_inserted += 1
    end
  else
    # generate the sql
    post_sql_statements = connection.post_sql_statements( quoted_table_name, options )
    # perform the inserts
    (number_inserted,ids) = connection.insert_many( [ insert_sql, post_sql_statements ].flatten,
                                              values_sql,
                                              "#{self.class.name} Create Many Without Validations Or Callbacks" )
  end
  [number_inserted, ids]
end

def set_ids_and_mark_clean(models, import_result)
  unless models.nil?
    import_result.ids.each_with_index do |id, index|
      model = models[index]
      model.id = id.to_i
      if model.respond_to?(:clear_changes_information) # Rails 4.0 and higher
        model.clear_changes_information
      else  # Rails 3.1
        model.instance_variable_get(:@changed_attributes).clear
      end
      model.instance_variable_set(:@new_record, false)
    end
  end
end

def support_setting_primary_key_of_imported_objects?
  connection.respond_to?(:support_setting_primary_key_of_imported_objects?) && connection.support_setting_primary_key_of_imported_objects?
end

def supports_import?(*args)
  connection.respond_to?(:supports_import?) && connection.supports_import?(*args)
end

def supports_on_duplicate_key_update?
  connection.supports_on_duplicate_key_update?
end

def synchronize(instances, key=[ActiveRecord::Base.primary_key])
  self.class.synchronize(instances, key)
end

def validations_array_for_column_names_and_attributes( column_names, array_of_attributes ) # :nodoc:
  array_of_attributes.map do |attributes|
    Hash[attributes.each_with_index.map {|attr, c| [column_names[c], attr] }]
  end
end

def values_sql_for_columns_and_attributes(columns, array_of_attributes)   # :nodoc:
  # connection gets called a *lot* in this high intensity loop.
  # Reuse the same one w/in the loop, otherwise it would keep being re-retreived (= lots of time for large imports)
  connection_memo = connection
  array_of_attributes.map do |arr|
    my_values = arr.each_with_index.map do |val,j|
      column = columns[j]
      # be sure to query sequence_name *last*, only if cheaper tests fail, because it's costly
      if val.nil? && column.name == primary_key && !sequence_name.blank?
         connection_memo.next_value_for_sequence(sequence_name)
      elsif column
        if respond_to?(:type_caster) && type_caster.respond_to?(:type_cast_for_database) # Rails 5.0 and higher
          connection_memo.quote(type_caster.type_cast_for_database(column.name, val))
        elsif column.respond_to?(:type_cast_from_user)                      # Rails 4.2 and higher
          connection_memo.quote(column.type_cast_from_user(val), column)
        else                                                                # Rails 3.1, 3.2, and 4.1
          connection_memo.quote(column.type_cast(val), column)
        end
      end
    end
    "(#{my_values.join(',')})"
  end
end