defmodule Benchee.Formatters.CSV do

  @moduledoc """
  Functionality for converting Benchee benchmarking results to CSV so that
  they can be written to file and opened in a spreadsheet tool for graph
  generation for instance.
  """

  @column_descriptors ["Name", "Iterations per Second", "Average",
                       "Standard Deviation", "Standard Deviation Ratio",
                       "Median"]

  @doc """
  Transforms the statistical results `Benche.statistics` to be written
  somewhere, such as a file through `IO.write/2`.

  ## Examples

      iex> [{"My Job", %{average: 200.0, ips: 5000.0, std_dev: 20, std_dev_ratio: 0.1, median: 190.0}}]
      iex> |> Benchee.Formatters.CSV.format
      iex> |> Enum.take(2)
      ["Name,Iterations per Second,Average,Standard Deviation,Standard Deviation Ratio,Median\\r\\n",
       "My Job,5.0e3,200.0,20,0.1,190.0\\r\\n"]

  """
  def format(jobs) do
    sorted = Benchee.Statistics.sort(jobs)
    [@column_descriptors | job_csvs(sorted)]
    |> CSV.encode
  end

  defp job_csvs(jobs) do
    Enum.map(jobs, &to_csv/1)
  end

  defp to_csv({name, %{ips:           ips,
                       average:       average,
                       std_dev:       std_dev,
                       std_dev_ratio: std_dev_ratio,
                       median:        median}}) do
    [name, ips, average, std_dev, std_dev_ratio, median]
  end
end