defmodule ExTmpFs do
  @moduledoc """
    This module provide some functions for the wrapper of TmpFs System.
    He use System.cmd, so use sudo is preferable.
  """

  # TODO Make documentation

  @type size_type :: :O | :K | :M | :G
  @type size :: [size: non_neg_integer, type: size_type]

  @doc """
    Mount and create the directory to mount a tmpfs device.

    ## Parameters

      - path: Path.t
      - size: size

    ## examples

       sudo iex -S mix
       iex> {:ok, ref} = ExTmpFs.mount(".tmp", [size: 1, size_type: :G])
  """
  @spec mount(path :: Path.t, size :: size) :: {:ok, atom} | {:error, term}
  def mount(path, size) do
    name = ((path |> Path.basename) <> (path |> Comeonin.Bcrypt.hashpwsalt |> String.slice(0,5))) |> String.to_atom
    case ConCache.get(:cache_extmpfs, {:tmpfs, name}) do
      nil ->
        case File.mkdir_p(path) do
          :ok ->
            case System.cmd("mount", ["-t", "tmpfs", "-o", "size=#{size[:size]}#{size[:size_type]}", "tmpfs", path], [stderr_to_stdout: true]) do
              {_nil, 0} ->
                ConCache.put(:cache_extmpfs, {:tmpfs, name}, path)
                {:ok, name}
              {_reason, 1} -> {:error, "incorrect invocation or permissions"}
              {_reason, 2} -> {:error, "system error (out of memory, cannot fork, no more loop devices)"}
              {_reason, 4} -> {:error, "internal mount bug"}
              {_reason, 8} -> {:error, "user interrupt"}
              {_reason, 16} -> {:error, "problems writing or locking /etc/mtab"}
              {_reason, 32} -> {:error, "mount failure"}
              {_reason, 64} -> {:error, "some mount succeeded"}
              {reason, _integer} -> {:error, reason}
            end
          _error = file_error -> {:error, file_error}
        end
      _ -> {:error, "Name already choosed"}
    end
  end

  @doc """
    Umount and destroy the directory of mounting tmpfs device.

    ## Parameters

      - name: atom

    ## examples

       sudo iex -S mix
       iex> {:ok, ref} = ExTmpFs.mount(".tmp", [size: 1, size_type: :G])
       iex> :ok = ExTmpFs.umount(ref)
  """
  @spec umount(name :: atom) :: :ok | {:error, term}
  def umount(name) do
    case ConCache.get(:cache_extmpfs, {:tmpfs, name}) do
      nil -> {:error, "incorrect name for tmpfs partition"}
      path ->
        ConCache.delete(:cache_extmpfs, {:tmpfs, name})
        case System.cmd("umount", [path], [stderr_to_stdout: true]) do
          {_nil, 0} ->
            File.rmdir(path)
            :ok
          {_reason, _value} -> {:error, "some umount errors"}
        end
    end
  end
end