class BenchmarkDriver::Output::Markdown
  NAME_LENGTH = 8

  # @param [Array<BenchmarkDriver::Metric>] metrics
  attr_writer :metrics

  # @param [Array<String>] job_names
  # @param [Array<String>] context_names
  def initialize(job_names:, context_names:)
    @context_names = context_names
    @name_length = job_names.map(&:size).max
  end

  def with_warmup(&block)
    without_stdout_buffering do
      $stdout.print 'warming up'
      block.call
    end
  ensure
    $stdout.puts
  end

  def with_benchmark(&block)
    @with_benchmark = true
    without_stdout_buffering do
      # Show header
      $stdout.puts "# #{@metrics.first.name} (#{@metrics.first.unit})\n\n"

      # Show executable names
      $stdout.print("|#{' ' * @name_length}  ")
      @context_names.each do |context_name|
        $stdout.print("|%#{NAME_LENGTH}s" % context_name) # same size as humanize
      end
      $stdout.puts('|')

      # Show header separator
      $stdout.print("|:#{'-' * (@name_length - 1)}--")
      @context_names.each do |context_name|
        $stdout.print("|:#{'-' * (NAME_LENGTH - 1)}") # same size as humanize
      end
      $stdout.puts('|')

      block.call
    end
  rescue
    @with_benchmark = false
  end

  # @param [BenchmarkDriver::Job] job
  def with_job(job, &block)
    if @with_benchmark
      $stdout.print("|%-#{@name_length}s  " % job.name)
    end
    block.call
  ensure
    if @with_benchmark
      $stdout.puts('|')
    end
  end

  # @param [BenchmarkDriver::Context] context
  def with_context(context, &block)
    block.call
  end

  # @param [Floa] value
  # @param [BenchmarkDriver::Metric] metic
  def report(value:, metric:)
    if @with_benchmark
      $stdout.print("|%#{NAME_LENGTH}s" % humanize(value))
    else
      $stdout.print '.'
    end
  end

  private

  # benchmark_driver ouputs logs ASAP. This enables sync flag for it.
  def without_stdout_buffering
    sync, $stdout.sync = $stdout.sync, true
    yield
  ensure
    $stdout.sync = sync
  end

  def humanize(value)
    if value < 0
      raise ArgumentError.new("Negative value: #{value.inspect}")
    end

    scale = (Math.log10(value) / 3).to_i
    prefix = "%6.3f" % (value.to_f / (1000 ** scale))
    suffix =
      case scale
      when 1; 'k'
      when 2; 'M'
      when 3; 'G'
      when 4; 'T'
      when 5; 'Q'
      else # < 1000 or > 10^15, no scale or suffix
        scale = 0
        return " #{prefix}"
      end
    "#{prefix}#{suffix}"
  end
end