module RecordSearch
   # Builds an index file using as source data +data_source+, which can be a
   # subclass of RecordSearch::DataSource or an object with a next method.
  def self.index(data_source, db, db_idx=nil)
     db_idx = db + '.idx' if db_idx.nil?
     records = 0

     File.open(db, 'w') do |fdb|
       File.open(db_idx, 'w') do |fidx|
         last = nil
         while record = data_source.next
           if !last.nil? && last >= record
             raise "data is not ordered! #{last} >= #{record}"
           end

           fidx.write([fdb.pos].pack('L'))
           fdb.write(record)

           last = record
           records += 1
         end
       end
     end

     records
  end

end