# frozen_string_literal: true

class ChunkedWriter
  DEFAULT_CHECK_INTERVAL = 1_000_000
  DEFAULT_MAX_FILE_SIZE_BYTES = (50 * 1024 * 1024).freeze # 50MB

  def initialize(**opts, &finisher)
    @finisher = finisher
    @check_interval = opts.fetch(:check_interval, DEFAULT_CHECK_INTERVAL)
    @max_file_size_bytes = opts.fetch(:max_file_size_bytes, DEFAULT_MAX_FILE_SIZE_BYTES)
    @rows_written_since_last_check = 0
  end

  def write(bytes)
    current_writer.write(bytes).tap { rotate_files_if_necessary }
  end

  def finish
    current_writer.finish # write the gzip footer
    current_file.rewind # yield the file ready for reading
    finisher.call(current_file)
    current_file.close! # close and delete the file
  end

  private

  attr_reader :finisher, :check_interval, :max_file_size_bytes

  def rotate_files_if_necessary
    @rows_written_since_last_check += 1
    return unless @rows_written_since_last_check > check_interval
    @rows_written_since_last_check = 0

    # flush buffers to the output file, so the size can be measured accurately
    current_writer.flush
    return if current_file.size < max_file_size_bytes

    rotate_files
  end

  def rotate_files
    finish
    @current_file = nil
    @current_writer = nil
  end

  def current_writer
    @current_writer ||= Zlib::GzipWriter.new(current_file)
  end

  def current_file
    @current_file ||= Tempfile.new.tap(&:binmode)
  end
end