defmodule Profiler do
  @moduledoc """
  This sampling profiler is intendend for shell and remote shell usage.
  Most commands here print their results to the screen for human inspection.

  Example usage:
  ```
  iex(2)> Profiler.profile("<0.187.0>")
  100% {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}
    100% {IEx.Evaluator, :init, 4, [file: 'lib/iex/evaluator.ex', line: 27]}
      100% {IEx.Evaluator, :loop, 1, [file: 'lib/iex/evaluator.ex', line: 103]}
          100% {IEx.Evaluator, :eval, 3, [file: 'lib/iex/evaluator.ex', line: 217]}
            100% {IEx.Evaluator, :do_eval, 3, [file: 'lib/iex/evaluator.ex', line: 239]}
                100% {IEx.Evaluator, :handle_eval, 5, [file: 'lib/iex/evaluator.ex', line: 258]}
                  100% {:elixir, :eval_forms, 3, [file: 'src/elixir.erl', line: 263]}
                      100% {:elixir, :recur_eval, 3, [file: 'src/elixir.erl', line: 278]}
                        100% {:erl_eval, :do_apply, 6, [file: 'erl_eval.erl', line: 680]}
                            100% {Profiler, :profile, 2, [file: 'lib/profiler.ex', line: 120]}
                              100% {Enum, :reduce_range_inc, 4, [file: 'lib/enum.ex', line: 3371]}
                                  100% {Profiler, :"-profile/2-fun-0-", 3, [file: 'lib/profiler.ex', line: 121]}
  ```
  """

  @doc """
    Times the given function and prints the result.
    Example usage:
    ```
    iex(1)> Profiler.time(fn() -> Process.sleep 1000 end)
    timer: 1004
    :ok
    ```
  """
  @spec time(fun(), String.t()) :: any()
  def time(fun, msg \\ "timer") do
    t1 = Time.utc_now()
    ret = fun.()
    t2 = Time.utc_now()
    IO.puts("#{msg}: #{Time.diff(t2, t1, :millisecond)}ms")
    ret
  end

  @doc """
    Processes lists all processes ordered by reductions withing the given
    timeout. For that it takes an initial snapshot, sleeps the given timeout
    and takes a second snapshot.

    ```
    iex(1)> Profiler.processes
    [<0.187.0>,{'Elixir.IEx.Evaluator',init,4},1339]
    [<0.132.0>,tls_client_ticket_store,32]
    [<0.182.0>,{'Elixir.Logger.Watcher',init,1},1]
    [<0.181.0>,'Elixir.Logger.BackendSupervisor',1]
    [<0.180.0>,{'Elixir.Logger.Watcher',init,1},1]
    [<0.179.0>,'Elixir.Logger',1]
    [<0.178.0>,'Elixir.Logger.Supervisor',1]
    [<0.177.0>,{application_master,start_it,4},1]
    [<0.176.0>,{application_master,init,4},1]
    [<0.161.0>,'Elixir.Hex.UpdateChecker',1]
    :ok
    ```
  """
  @spec processes(:infinity | non_neg_integer) :: :ok
  def processes(timeout \\ 5000) do
    pids = :erlang.processes()
    info1 = Enum.map(pids, &:erlang.process_info/1)
    Process.sleep(timeout)
    info2 = Enum.map(pids, &:erlang.process_info/1)

    info =
      Enum.zip([pids, info1, info2])
      |> Enum.reject(fn {_pid, info1, info2} -> info1 == :undefined or info2 == :undefined end)
      |> Enum.map(fn {pid, info1, info2} ->
        name =
          if info2[:registered_name] == nil do
            if info2[:dictionary] == nil or info2[:dictionary][:"$initial_call"] == nil do
              info2[:initial_call]
            else
              info2[:dictionary][:"$initial_call"]
            end
          else
            info2[:registered_name]
          end

        [
          {:pid, pid},
          {:reductionsd, info2[:reductions] - info1[:reductions]},
          {:name, name}
          | info2
        ]
      end)
      |> Enum.sort(&(&1[:reductionsd] > &2[:reductionsd]))
      |> Enum.take(10)

    for n <- info do
      :io.format("~p~n", [[n[:pid], n[:name], n[:reductionsd]]])
    end

    :ok
  end

  @doc """
    Arguments are the same as for profile() but this sampling profiler does not
    analyze stacktrace but instead just samples the current function and prints
    the result.

    The first number shows the total number of samples that have been recorded
    per function call.
    ```
    iex(2)> Profiler.profile_simple 197
    {10000, {Profiler, :"-profile_simple/2-fun-0-", 3}}
    ```
  """
  @spec profile_simple(any, integer) :: :ok
  def profile_simple(pid, n \\ 10000) do
    pid = to_pid(pid)

    samples =
      for _ <- 1..n do
        {:current_function, what} = :erlang.process_info(pid, :current_function)
        Process.sleep(1)
        {Time.utc_now(), what}
      end

    ret =
      Enum.reduce(samples, %{}, fn {_time, what}, map ->
        Map.update(map, what, 1, fn n -> n + 1 end)
      end)

    ret = Enum.map(ret, fn {k, v} -> {v, k} end) |> Enum.sort()
    for n <- ret, do: IO.puts("#{inspect(n)}")
    :ok
  end

  @doc """
    This runs the sampling profiler for the given amount of milliseconds or
    10 seconds by default. The sampling profiler will collect stack traces
    of the given process pid or process name and print the collected samples
    based on frequency.

    For pid there are three different input formats allowed:

    1. Native pid()
    2. An atom that is resolved using whereis(name)
    3. A string of the format "<a.b.c>" or "0.b.c" or just "b" in which
       case the pid is interpreted as "<0.b.0>"
    4  An integer, in which case the pid is interpreted as "<0.\#{int}.0>"

    In this example the profiler is used to profile itself. The first percentage
    number shows how many samples were found in the given function call.
    Indention indicates the call stack:
    ```
    iex(2)> Profiler.profile(187)
    100% {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}
      100% {IEx.Evaluator, :init, 4, [file: 'lib/iex/evaluator.ex', line: 27]}
        100% {IEx.Evaluator, :loop, 1, [file: 'lib/iex/evaluator.ex', line: 103]}
            100% {IEx.Evaluator, :eval, 3, [file: 'lib/iex/evaluator.ex', line: 217]}
              100% {IEx.Evaluator, :do_eval, 3, [file: 'lib/iex/evaluator.ex', line: 239]}
                  100% {IEx.Evaluator, :handle_eval, 5, [file: 'lib/iex/evaluator.ex', line: 258]}
                    100% {:elixir, :eval_forms, 3, [file: 'src/elixir.erl', line: 263]}
                        100% {:elixir, :recur_eval, 3, [file: 'src/elixir.erl', line: 278]}
                          100% {:erl_eval, :do_apply, 6, [file: 'erl_eval.erl', line: 680]}
                              100% {Profiler, :profile, 2, [file: 'lib/profiler.ex', line: 120]}
                                100% {Enum, :reduce_range_inc, 4, [file: 'lib/enum.ex', line: 3371]}
                                    100% {Profiler, :"-profile/2-fun-0-", 3, [file: 'lib/profiler.ex', line: 121]}
    ```


  """
  @spec profile(String.t() | atom() | pid(), integer()) :: :ok
  def profile(pid, n \\ 10000) do
    pid = to_pid(pid)
    :erlang.system_flag(:backtrace_depth, 30)

    samples =
      for _ <- 1..n do
        {:current_stacktrace, what} = :erlang.process_info(pid, :current_stacktrace)
        Process.sleep(1)
        {Time.utc_now(), what}
      end

    ret =
      Enum.reduce(samples, %{}, fn {_time, what}, map ->
        Map.update(map, what, 1, fn n -> n + 1 end)
      end)

    ret2 = Enum.map(ret, fn {k, v} -> {v, Enum.reverse(k)} end) |> Enum.sort()

    tree =
      Enum.reduce(ret2, %{}, &update/2)
      |> Enum.sort_by(fn {_key, {count, _subtree}} -> count end)

    print(tree)
    # ret2
    :ok
  end

  defp print(tree) do
    sum = Enum.reduce(tree, 0, fn {_, {count, _}}, sum -> sum + count end)
    print(0, tree, sum / 20)
  end

  defp print(level, tree, min) do
    prefix = level * 3

    for {key, {count, subtree}} <- tree do
      if count > min do
        count = round(count * 5 / min) |> Integer.to_string()
        IO.puts("#{count |> String.pad_leading(4 + prefix)}% #{inspect(key)}")
        print(level + 1, subtree, min)
      end
    end
  end

  defp update({_count, []}, map) do
    map
  end

  defp update({count, [head | list]}, map) do
    {nil, map} =
      Map.get_and_update(map, head, fn
        {c, tree} ->
          {nil, {c + count, update({count, list}, tree)}}

        nil ->
          {nil, {count, update({count, list}, %{})}}
      end)

    map
  end

  defp to_pid(pid) when is_binary(pid) do
    case String.first(pid) do
      "0" -> "<#{pid}>"
      "<" -> pid
      _ -> "<0.#{pid}.0>"
    end
    |> :erlang.binary_to_list()
    |> :erlang.list_to_pid()
  end

  defp to_pid(pid) when is_atom(pid) do
    :erlang.whereis(pid)
  end

  defp to_pid(pid) when is_integer(pid) do
    to_pid("<0.#{pid}.0>")
  end

  defp to_pid(pid) do
    pid
  end
end