benchmark_ips

defmodule BenchmarkIps do
  @typedoc """
  A function with zero arity
  """
  @type zero_arity_fun :: (() -> any)

  @doc """
  Returns current time in microseconds
  """
  def now_us do
    :erlang.monotonic_time(:micro_seconds)
  end

  @doc """
  Calls the function the specified number of times
  """
  def call_times(fun, 1), do: fun.()
  def call_times(fun, times) do
    fun.()
    call_times(fun, times - 1)
  end

  @doc """
  Returns the result of running a function and the time it took to run in microseconds
  """
  def measure_in_us(fun) do
    start = now_us
    result = fun.()
    finish = now_us
    {result, finish - start}
  end

  def cycles_per_100ms(iters, time_us) do
    time_ms = time_us * 1.0e-3
    cycles_per_ms = iters / time_ms
    cycles = cycles_per_ms * 100
    cycles = round(cycles)
    if cycles <= 0 do
      1
    else
      cycles
    end
  end

  def iterations_runnable_in_duration_by_cycles(fun, cycles, target_duration_us) do
    iterations_runnable_in_duration_by_cycles(fun, cycles, now_us + target_duration_us, 0)
  end

  def iterations_runnable_in_duration_by_cycles(fun, cycles, target_end_time_us, iters) do
    if now_us < target_end_time_us do
      call_times(fun, cycles)
      iterations_runnable_in_duration_by_cycles(fun, cycles, target_end_time_us, iters + 1)
    else
      iters * cycles
    end
  end

  def bench(fun, cycles, target_duration_s) do
    target_duration_us = target_duration_s * 1.0e6

    {iters, actual_time_us} = measure_in_us(fn ->
      iterations_runnable_in_duration_by_cycles(fun, cycles, target_duration_us)
    end)

    {iters, actual_time_us}
  end

  def report(fun, options \\ []) do
    warmup_duration_s = Keyword.get(options, :warmup_duration_s, 1)
    bench_duration_s = Keyword.get(options, :bench_duration_s, 2)

    {warmup_iters, warmup_time_us} = bench(fun, 1, warmup_duration_s)

    warmup_cycles_per_100ms = cycles_per_100ms(warmup_iters, warmup_time_us)

    {actual_iters, actual_time_us} = bench(fun, warmup_cycles_per_100ms, bench_duration_s)

    iters_per_us = actual_iters / actual_time_us

    us_per_iter = 1 / iters_per_us
    iters_per_s = iters_per_us * 1.0e6

    {iters_per_s, us_per_iter}
  end

  #  def list_bench do
  #    lists = [
  #      "10k": Enum.to_list(1..10_000),
  #      "100k": Enum.to_list(1..100_000),
  #      "1m": Enum.to_list(1..1_000_000),
  #      "2m": Enum.to_list(1..2_000_000),
  #      "5m": Enum.to_list(1..5_000_000),
  #      "8m": Enum.to_list(1..5_000_000),
  #      "10m": Enum.to_list(1..10_000_000)
  #    ]
  #
  #    list_operations = [
  #      "length": fn list -> length list end,
  #      "prepend": fn list -> [1|list] end,
  #      "append": fn list -> list ++ [1] end,
  #      "access first": fn list -> hd list end,
  #      "access last": fn list -> List.last list end,
  #    ]
  #
  #    IO.puts "# Lists"
  #    report_each(lists, list_operations)
  #
  #    tuples = lists |> Enum.map(fn {label, list} -> {label, List.to_tuple(list)} end)
  #
  #    tuple_operations = [
  #      "length": fn tuple -> tuple_size(tuple) end,
  #      "prepend": fn tuple -> Tuple.insert_at(tuple, 0, 1) end,
  #      "append": fn tuple -> Tuple.insert_at(tuple, tuple_size(tuple) - 1, 1) end,
  #      "access first": fn tuple -> elem(tuple, 0) end,
  #      "access last": fn tuple -> elem(tuple, tuple_size(tuple) - 1) end,
  #    ]
  #
  #    IO.puts "\n# Tuples"
  #    report_each(tuples, tuple_operations)
  #  end
  #
  #  def report_each(collection, operations) do
  #    operations
  #    |> Enum.map(fn {label, fun} ->
  #      IO.puts "\n## #{label |> to_string |> String.capitalize}\n"
  #      IO.puts "#{String.rjust("label", 10)} #{String.rjust("i/ps", 15)} #{String.rjust("μ/i", 15)}"
  #      do_with_each(collection, fun)
  #    end)
  #  end
  #
  #  def do_with_each(collection, fun) do
  #    collection
  #    |> Enum.map(fn {label, element} ->
  #      {ips, uspi} = report(fn -> fun.(element) end)
  #      label_part = String.rjust(label |> to_string, 10)
  #      ips_part = pad_float(ips, 15)
  #      uspi_part = pad_float(uspi, 15)
  #      IO.puts "#{label_part} #{ips_part} #{uspi_part}"
  #    end)
  #  end
  #
  #  def pad_float(float, padding) do
  #    :io_lib.format("~.2f", [float]) |> hd |> to_string |> String.rjust(padding)
  #  end
end