defmodule CollectableStreamer do
  @moduledoc ~S"""
  A module for accessing command output line by line.

  ## Example

      iex> import ExUnit.CaptureIO
      iex> callback = fn line -> IO.puts("Received line: #{line}") end
      iex> streamer = CollectableStreamer.new(callback)
      iex> capture_io(fn -> System.cmd("echo", ["Hello, World!"], into: streamer) end)
      "Received line: Hello, World!\n"
  """

  @behaviour Collectable

  defstruct [:callback]

  def new(callback) when is_function(callback, 1) do
    %__MODULE__{callback: callback}
  end

  def into(streamer) do
    {
      streamer,
      fn
        streamer, {:cont, item} ->
          trimmed = String.replace_suffix(item, "\n", "")
          streamer.callback.(trimmed)
          streamer

        streamer, :done ->
          streamer

        _streamer, :halt ->
          :ok
      end
    }
  end

  defimpl Collectable do
    def into(streamer) do
      CollectableStreamer.into(streamer)
    end
  end
end