module ActiveRecord::Import::MysqlAdapter
  include ActiveRecord::Import::ImportSupport
  include ActiveRecord::Import::OnDuplicateKeyUpdateSupport

  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.

  # +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.bytesize }

    # 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 = ::ActiveRecord::Import::ValueSetsBytesParser.parse(values,
        :reserved_bytes => sql_size,
        :max_bytes => 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

  # Returns the maximum number of bytes that the server will allow
  # in a single packet
  def max_allowed_packet # :nodoc:
    @max_allowed_packet ||= begin
      result = execute( "SHOW VARIABLES like 'max_allowed_packet';" )
      # original Mysql gem responds to #fetch_row while Mysql2 responds to #first
      val = result.respond_to?(:fetch_row) ? result.fetch_row[1] : result.first[1]
      val.to_i
    end
  end

  # Returns a generated ON DUPLICATE KEY UPDATE statement given the passed
  # in +args+.
  def sql_for_on_duplicate_key_update( table_name, *args ) # :nodoc:
    sql = ' ON DUPLICATE KEY UPDATE '
    arg = args.first
    if arg.is_a?( Array )
      sql << sql_for_on_duplicate_key_update_as_array( table_name, arg )
    elsif arg.is_a?( Hash )
      sql << sql_for_on_duplicate_key_update_as_hash( table_name, arg )
    elsif arg.is_a?( String )
      sql << arg
    else
      raise ArgumentError.new( "Expected Array or Hash" )
    end
    sql
  end

  def sql_for_on_duplicate_key_update_as_array( table_name, arr )  # :nodoc:
    results = arr.map do |column|
      qc = quote_column_name( column )
      "#{table_name}.#{qc}=VALUES(#{qc})"
    end
    results.join( ',' )
  end

  def sql_for_on_duplicate_key_update_as_hash( table_name, hsh ) # :nodoc:
    sql = ' ON DUPLICATE KEY UPDATE '
    results = hsh.map do |column1, column2|
      qc1 = quote_column_name( column1 )
      qc2 = quote_column_name( column2 )
      "#{table_name}.#{qc1}=VALUES( #{qc2} )"
    end
    results.join( ',')
  end

  #return true if the statement is a duplicate key record error
  def duplicate_key_update_error?(exception)# :nodoc:
    exception.is_a?(ActiveRecord::StatementInvalid) && exception.to_s.include?('Duplicate entry')
  end
end