module ActiveRecord::Import::AbstractAdapter
  NO_MAX_PACKET = 0
  QUERY_OVERHEAD = 8 #This was shown to be true for MySQL, but it's not clear where the overhead is from.

  module ClassMethods
    def get_insert_value_sets( values, sql_size, max_bytes ) # :nodoc:
      value_sets = []
      arr, current_arr_values_size, current_size = [], 0, 0
      values.each_with_index do |val,i|
        comma_bytes = arr.size
        sql_size_thus_far = sql_size + current_size + val.size + comma_bytes
        if NO_MAX_PACKET == max_bytes or sql_size_thus_far <= max_bytes
          current_size += val.bytesize
          arr << val
        else
          value_sets << arr
          arr = [ val ]
          current_size = val.bytesize
        end

        # if we're on the last iteration push whatever we have in arr to value_sets
        value_sets << arr if i == (values.size-1)
      end
      [ *value_sets ]
    end
  end

  module InstanceMethods
    def next_value_for_sequence(sequence_name)
      %{#{sequence_name}.nextval}
    end

    # +sql+ can be a single string or an array. If it is an array all
    # elements that are in position >= 1 will be appended to the final SQL.
    def insert_many( sql, values, *args ) # :nodoc:
      # the number of inserts default
      number_of_inserts = 0

      base_sql,post_sql = if sql.is_a?( String )
        [ sql, '' ]
      elsif sql.is_a?( Array )
        [ sql.shift, sql.join( ' ' ) ]
      end

      sql_size = QUERY_OVERHEAD + base_sql.size + post_sql.size

      # the number of bytes the requested insert statement values will take up
      values_in_bytes = values.sum {|value| value.size }

      # the number of bytes (commas) it will take to comma separate our values
      comma_separated_bytes = values.size-1

      # the total number of bytes required if this statement is one statement
      total_bytes = sql_size + values_in_bytes + comma_separated_bytes

      max = max_allowed_packet

      # if we can insert it all as one statement
      if NO_MAX_PACKET == max or total_bytes < max
        number_of_inserts += 1
        sql2insert = base_sql + values.join( ',' ) + post_sql
        insert( sql2insert, *args )
      else
        value_sets = self.class.get_insert_value_sets( values, sql_size, max )
        value_sets.each do |values|
          number_of_inserts += 1
          sql2insert = base_sql + values.join( ',' ) + post_sql
          insert( sql2insert, *args )
        end
      end

      number_of_inserts
    end

    def pre_sql_statements(options)
      sql = []
      sql << options[:pre_sql] if options[:pre_sql]
      sql << options[:command] if options[:command]
      sql << "IGNORE" if options[:ignore]

      #add keywords like IGNORE or DELAYED
      if options[:keywords].is_a?(Array)
        sql.concat(options[:keywords])
      elsif options[:keywords]
        sql << options[:keywords].to_s
      end

      sql
    end

    # Synchronizes the passed in ActiveRecord instances with the records in
    # the database by calling +reload+ on each instance.
    def after_import_synchronize( instances )
      instances.each { |e| e.reload }
    end

    # Returns an array of post SQL statements given the passed in options.
    def post_sql_statements( table_name, options ) # :nodoc:
      post_sql_statements = []
      if options[:on_duplicate_key_update]
        post_sql_statements << sql_for_on_duplicate_key_update( table_name, options[:on_duplicate_key_update] )
      end

      #custom user post_sql
      post_sql_statements << options[:post_sql] if options[:post_sql]

      #with rollup
      post_sql_statements << rollup_sql if options[:rollup]

      post_sql_statements
    end

    # Returns the maximum number of bytes that the server will allow
    # in a single packet
    def max_allowed_packet
      NO_MAX_PACKET
    end
  end
end