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.find( :all, :conditions=>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.clear_aggregation_cache
      instance.clear_association_cache
      instance.instance_variable_set '@attributes', matched_instance.attributes
      # 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)
         # 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
    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)
         # 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?
        if options[:on_duplicate_key_update]
          options[:on_duplicate_key_update] << key.to_sym if options[:on_duplicate_key_update].is_a?(Array)
          options[:on_duplicate_key_update][key.to_sym] = key.to_sym if options[:on_duplicate_key_update].is_a?(Hash)
        else
          options[:on_duplicate_key_update] = [ key.to_sym ]
        end
      end
    end
  end
end

def establish_connection_with_activerecord_import(*args)
  establish_connection_without_activerecord_import(*args)
  ActiveSupport.run_load_hooks(:active_record_connection_established, connection_pool)
end

def import( *args )
  options = { :validate=>true, :timestamps=>true }
  options.merge!( args.pop ) if args.last.is_a? Hash
  is_validating = options.delete( :validate )
  # 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|
          model.send( "#{name}_before_type_cast" )
        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
  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 = import_without_validations_or_callbacks( column_names, array_of_attributes, options )
    ActiveRecord::Import::Result.new([], num_inserts)
  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?
  return_obj
end

def import_from_table( options ) # :nodoc:
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?
      array_of_attributes[ i ] = nil
      failed_instances << instance
    end    
  end
  array_of_attributes.compact!
  num_inserts = 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)
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|
      next if column_names.include?(name.to_sym)
      column_names << name
      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)
  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 = connection.insert_many( [ insert_sql, post_sql_statements ].flatten, 
                                              values_sql,
                                              "#{self.class.name} Create Many Without Validations Or Callbacks" )
  end
  number_inserted
end

def supports_import?(*args)
  connection.supports_import?(*args)
rescue NoMethodError
  false
end

def supports_on_duplicate_key_update?
  connection.supports_on_duplicate_key_update?
rescue NoMethodError
  false
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)
      else
        if serialized_attributes.include?(column.name)
          connection_memo.quote(serialized_attributes[column.name].dump(val), column)
        else
          connection_memo.quote(val, column)
        end
      end
    end
    "(#{my_values.join(',')})"
  end
end