defmodule File do
  @moduledoc ~S"""
  This module contains functions to manipulate files.

  Some of those functions are low-level, allowing the user
  to interact with the file or IO devices, like `open/2`,
  `copy/3` and others. This module also provides higher
  level functions that work with filenames and have their naming
  based on UNIX variants. For example, one can copy a file
  via `cp/3` and remove files and directories recursively
  via `rm_rf/1`

  ## Encoding

  In order to write and read files, one must use the functions
  in the `IO` module. By default, a file is opened in binary mode
  which requires the functions `IO.binread/2` and `IO.binwrite/2`
  to interact with the file. A developer may pass `:utf8` as an
  option when opening the file, then the slower `IO.read/2` and
  `IO.write/2` functions must be used as they are responsible for
  doing the proper conversions and data guarantees.

  Note that filenames when given as char lists in Elixir are
  always treated as UTF-8. In particular, we expect that the
  shell and the operating system are configured to use UTF8
  encoding. Binary filenames are considering raw and passed
  to the OS as is.

  ## API

  Most of the functions in this module return `:ok` or
  `{:ok, result}` in case of success, `{:error, reason}`
  otherwise. Those function are also followed by a variant
  that ends with `!` which returns the result (without the
  `{:ok, result}` tuple) in case of success or raises an
  exception in case it fails. For example:

      File.read("hello.txt")
      #=> {:ok, "World"}

      File.read("invalid.txt")
      #=> {:error, :enoent}

      File.read!("hello.txt")
      #=> "World"

      File.read!("invalid.txt")
      #=> raises File.Error

  In general, a developer should use the former in case he wants
  to react if the file does not exist. The latter should be used
  when the developer expects his software to fail in case the
  file cannot be read (i.e. it is literally an exception).

  ## Processes and raw files

  Every time a file is opened, Elixir spawns a new process. Writing
  to a file is equivalent to sending messages to that process that
  writes to the file descriptor.

  This means files can be passed between nodes and message passing
  guarantees they can write to the same file in a network.

  However, you may not always want to pay the price for this abstraction.
  In such cases, a file can be opened in `:raw` mode. The options `:read_ahead`
  and `:delayed_write` are also useful when operating large files or
  working with files in tight loops.

  Check http://www.erlang.org/doc/man/file.html#open-2 for more information
  about such options and other performance considerations.
  """

  alias :file, as: F

  @type posix :: :file.posix()
  @type io_device :: :file.io_device()
  @type stat_options :: [time: :local | :universal | :posix]
  @type mode :: :append | :binary | :compressed | :delayed_write | :exclusive |
    :raw | :read | :read_ahead | :sync | :write |
    {:encoding , :latin1 | :unicode | :utf16 | :utf32 | :utf8 |
      {:utf16, :big | :little} | {:utf32, :big | :little}} |
    {:read_ahead, pos_integer} |
    {:delayed_write, non_neg_integer, non_neg_integer}

  @doc """
  Returns `true` if the path is a regular file.

  ## Examples

      File.regular? __ENV__.file #=> true

  """
  @spec regular?(Path.t) :: boolean
  def regular?(path) do
    :elixir_utils.read_file_type(IO.chardata_to_string(path)) == {:ok, :regular}
  end

  @doc """
  Returns `true` if the path is a directory.
  """
  @spec dir?(Path.t) :: boolean
  def dir?(path) do
    :elixir_utils.read_file_type(IO.chardata_to_string(path)) == {:ok, :directory}
  end

  @doc """
  Returns `true` if the given path exists.
  It can be regular file, directory, socket,
  symbolic link, named pipe or device file.

  ## Examples

      File.exists?("test/")
      #=> true

      File.exists?("missing.txt")
      #=> false

      File.exists?("/dev/null")
      #=> true

  """
  @spec exists?(Path.t) :: boolean
  def exists?(path) do
    match?({:ok, _}, F.read_file_info(IO.chardata_to_string(path)))
  end

  @doc """
  Tries to create the directory `path`. Missing parent directories are not created.
  Returns `:ok` if successful, or `{:error, reason}` if an error occurs.

  Typical error reasons are:

    * `:eacces`  - missing search or write permissions for the parent
       directories of `path`
    * `:eexist`  - there is already a file or directory named `path`
    * `:enoent`  - a component of `path` does not exist
    * `:enospc`  - there is a no space left on the device
    * `:enotdir` - a component of `path` is not a directory;
       on some platforms, `:enoent` is returned instead
  """
  @spec mkdir(Path.t) :: :ok | {:error, posix}
  def mkdir(path) do
    F.make_dir(IO.chardata_to_string(path))
  end

  @doc """
  Same as `mkdir/1`, but raises an exception in case of failure. Otherwise `:ok`.
  """
  @spec mkdir!(Path.t) :: :ok | no_return
  def mkdir!(path) do
    path = IO.chardata_to_string(path)
    case mkdir(path) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "make directory", path: path
    end
  end

  @doc """
  Tries to create the directory `path`. Missing parent directories are created.
  Returns `:ok` if successful, or `{:error, reason}` if an error occurs.

  Typical error reasons are:

    * `:eacces`  - missing search or write permissions for the parent
                   directories of `path`
    * `:enospc`  - there is a no space left on the device
    * `:enotdir` - a component of `path` is not a directory
  """
  @spec mkdir_p(Path.t) :: :ok | {:error, posix}
  def mkdir_p(path) do
    do_mkdir_p(IO.chardata_to_string(path))
  end

  defp do_mkdir_p("/") do
    :ok
  end

  defp do_mkdir_p(path) do
    if dir?(path) do
      :ok
    else
      parent = Path.dirname(path)
      if parent == path do
        # Protect against infinite loop
        {:error, :einval}
      else
        _ = do_mkdir_p(parent)
        case :file.make_dir(path) do
          {:error, :eexist} = error ->
            if dir?(path), do: :ok, else: error
          other ->
            other
        end
      end
    end
  end

  @doc """
  Same as `mkdir_p/1`, but raises an exception in case of failure. Otherwise `:ok`.
  """
  @spec mkdir_p!(Path.t) :: :ok | no_return
  def mkdir_p!(path) do
    path = IO.chardata_to_string(path)
    case mkdir_p(path) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "make directory (with -p)", path: path
    end
  end

  @doc """
  Returns `{:ok, binary}`, where `binary` is a binary data object that contains the contents
  of `path`, or `{:error, reason}` if an error occurs.

  Typical error reasons:

    * `:enoent`  - the file does not exist
    * `:eacces`  - missing permission for reading the file,
                   or for searching one of the parent directories
    * `:eisdir`  - the named file is a directory
    * `:enotdir` - a component of the file name is not a directory;
                   on some platforms, `:enoent` is returned instead
    * `:enomem`  - there is not enough memory for the contents of the file

  You can use `:file.format_error/1` to get a descriptive string of the error.
  """
  @spec read(Path.t) :: {:ok, binary} | {:error, posix}
  def read(path) do
    F.read_file(IO.chardata_to_string(path))
  end

  @doc """
  Returns binary with the contents of the given filename or raises
  `File.Error` if an error occurs.
  """
  @spec read!(Path.t) :: binary | no_return
  def read!(path) do
    path = IO.chardata_to_string(path)
    case read(path) do
      {:ok, binary} ->
        binary
      {:error, reason} ->
        raise File.Error, reason: reason, action: "read file", path: path
    end
  end

  @doc """
  Returns information about the `path`. If it exists, it
  returns a `{:ok, info}` tuple, where info is a
  `File.Stat` struct. Returns `{:error, reason}` with
  the same reasons as `read/1` if a failure occurs.

  ## Options

  The accepted options are:

    * `:time` - `:local | :universal | :posix`; default: `:local`

  """
  @spec stat(Path.t, stat_options) :: {:ok, File.Stat.t} | {:error, posix}
  def stat(path, opts \\ []) do
    case F.read_file_info(IO.chardata_to_string(path), opts) do
      {:ok, fileinfo} ->
        {:ok, File.Stat.from_record(fileinfo)}
      error ->
        error
    end
  end

  @doc """
  Same as `stat/2` but returns the `File.Stat` directly and
  throws `File.Error` if an error is returned.
  """
  @spec stat!(Path.t, stat_options) :: File.Stat.t | no_return
  def stat!(path, opts \\ []) do
    path = IO.chardata_to_string(path)
    case stat(path, opts) do
      {:ok, info}      -> info
      {:error, reason} ->
        raise File.Error, reason: reason, action: "read file stats", path: path
    end
  end

  @doc """
  Writes the given `File.Stat` back to the filesystem at the given
  path. Returns `:ok` or `{:error, reason}`.
  """
  @spec write_stat(Path.t, File.Stat.t, stat_options) :: :ok | {:error, posix}
  def write_stat(path, stat, opts \\ []) do
    F.write_file_info(IO.chardata_to_string(path), File.Stat.to_record(stat), opts)
  end

  @doc """
  Same as `write_stat/3` but raises an exception if it fails.
  Returns `:ok` otherwise.
  """
  @spec write_stat!(Path.t, File.Stat.t, stat_options) :: :ok | no_return
  def write_stat!(path, stat, opts \\ []) do
    path = IO.chardata_to_string(path)
    case write_stat(path, stat, opts) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "write file stats", path: path
    end
  end

  @doc """
  Updates modification time (mtime) and access time (atime) of
  the given file. File is created if it doesn’t exist.
  """
  @spec touch(Path.t, :calendar.datetime) :: :ok | {:error, posix}
  def touch(path, time \\ :calendar.local_time) do
    path = IO.chardata_to_string(path)
    case F.change_time(path, time) do
      {:error, :enoent} -> touch_new(path, time)
      other -> other
    end
  end

  defp touch_new(path, time) do
    case write(path, "", [:append]) do
      :ok -> F.change_time(path, time)
      {:error, _reason} = error -> error
    end
  end

  @doc """
  Same as `touch/2` but raises an exception if it fails.
  Returns `:ok` otherwise.
  """
  @spec touch!(Path.t, :calendar.datetime) :: :ok | no_return
  def touch!(path, time \\ :calendar.local_time) do
    path = IO.chardata_to_string(path)
    case touch(path, time) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "touch", path: path
    end
  end

  @doc """
  Creates a symbolic link `new` to the file or directory `existing`.

  Returns `:ok` if successful, `{:error, reason}` otherwise.
  If the operating system does not support symlinks, returns
  `{:error, :enotsup}`.
  """
  def ln_s(existing, new) do
    F.make_symlink(existing, new)
  end

  @doc """
  Copies the contents of `source` to `destination`.

  Both parameters can be a filename or an io device opened
  with `open/2`. `bytes_count` specifies the number of
  bytes to copy, the default being `:infinity`.

  If file `destination` already exists, it is overwritten
  by the contents in `source`.

  Returns `{:ok, bytes_copied}` if successful,
  `{:error, reason}` otherwise.

  Compared to the `cp/3`, this function is more low-level,
  allowing a copy from device to device limited by a number of
  bytes. On the other hand, `cp/3` performs more extensive
  checks on both source and destination and it also preserves
  the file mode after copy.

  Typical error reasons are the same as in `open/2`,
  `read/1` and `write/3`.
  """
  @spec copy(Path.t, Path.t, pos_integer | :infinity) :: {:ok, non_neg_integer} | {:error, posix}
  def copy(source, destination, bytes_count \\ :infinity) do
    F.copy(IO.chardata_to_string(source), IO.chardata_to_string(destination), bytes_count)
  end

  @doc """
  The same as `copy/3` but raises an `File.CopyError` if it fails.
  Returns the `bytes_copied` otherwise.
  """
  @spec copy!(Path.t, Path.t, pos_integer | :infinity) :: non_neg_integer | no_return
  def copy!(source, destination, bytes_count \\ :infinity) do
    source = IO.chardata_to_string(source)
    destination = IO.chardata_to_string(destination)
    case copy(source, destination, bytes_count) do
      {:ok, bytes_count} -> bytes_count
      {:error, reason} ->
        raise File.CopyError, reason: reason, action: "copy",
          source: source, destination: destination
    end
  end

  @doc """
  Copies the contents in `source` to `destination` preserving its mode.

  If a file already exists in the destination, it invokes a
  callback which should return `true` if the existing file
  should be overwritten, `false` otherwise. It defaults to return `true`.

  It returns `:ok` in case of success, returns
  `{:error, reason}` otherwise.

  If you want to copy contents from an io device to another device
  or do a straight copy from a source to a destination without
  preserving modes, check `copy/3` instead.

  Note: The command `cp` in Unix systems behaves differently depending
  if `destination` is an existing directory or not. We have chosen to
  explicitly disallow this behaviour. If destination is a directory, an
  error will be returned.
  """
  @spec cp(Path.t, Path.t, (Path.t, Path.t -> boolean)) :: :ok | {:error, posix}
  def cp(source, destination, callback \\ fn(_, _) -> true end) do
    source = IO.chardata_to_string(source)
    destination = IO.chardata_to_string(destination)

    case do_cp_file(source, destination, callback, []) do
      {:error, reason, _} -> {:error, reason}
      _ -> :ok
    end
  end

  @doc """
  The same as `cp/3`, but raises `File.CopyError` if it fails.
  Returns the list of copied files otherwise.
  """
  @spec cp!(Path.t, Path.t, (Path.t, Path.t -> boolean)) :: :ok | no_return
  def cp!(source, destination, callback \\ fn(_, _) -> true end) do
    source = IO.chardata_to_string(source)
    destination = IO.chardata_to_string(destination)

    case cp(source, destination, callback) do
      :ok -> :ok
      {:error, reason} ->
        raise File.CopyError, reason: reason, action: "copy recursively",
          source: source, destination: destination
    end
  end

  @doc ~S"""
  Copies the contents in source to destination.

  If the source is a file, it copies `source` to
  `destination`. If the source is a directory, it copies
  the contents inside source into the destination.

  If a file already exists in the destination,
  it invokes a callback which should return
  `true` if the existing file should be overwritten,
  `false` otherwise. It defaults to return `true`.

  If a directory already exists in the destination
  where a file is meant to be (or otherwise), this
  function will fail.

  This function may fail while copying files,
  in such cases, it will leave the destination
  directory in a dirty state, where already
  copied files won't be removed.

  It returns `{:ok, files_and_directories}` in case of
  success with all files and directories copied in no
  specific order, `{:error, reason, file}` otherwise.

  Note: The command `cp` in Unix systems behaves differently
  depending if `destination` is an existing directory or not.
  We have chosen to explicitly disallow this behaviour.

  ## Examples

      # Copies "a.txt" to "tmp"
      File.cp_r "a.txt", "tmp.txt"

      # Copies all files in "samples" to "tmp"
      File.cp_r "samples", "tmp"

      # Same as before, but asks the user how to proceed in case of conflicts
      File.cp_r "samples", "tmp", fn(source, destination) ->
        IO.gets("Overwriting #{destination} by #{source}. Type y to confirm.") == "y"
      end

  """
  @spec cp_r(Path.t, Path.t, (Path.t, Path.t -> boolean)) :: {:ok, [binary]} | {:error, posix, binary}
  def cp_r(source, destination, callback \\ fn(_, _) -> true end) when is_function(callback) do
    source = IO.chardata_to_string(source)
    destination = IO.chardata_to_string(destination)

    case do_cp_r(source, destination, callback, []) do
      {:error, _, _} = error -> error
      res -> {:ok, res}
    end
  end

  @doc """
  The same as `cp_r/3`, but raises `File.CopyError` if it fails.
  Returns the list of copied files otherwise.
  """
  @spec cp_r!(Path.t, Path.t, (Path.t, Path.t -> boolean)) :: [binary] | no_return
  def cp_r!(source, destination, callback \\ fn(_, _) -> true end) do
    source = IO.chardata_to_string(source)
    destination = IO.chardata_to_string(destination)

    case cp_r(source, destination, callback) do
      {:ok, files} -> files
      {:error, reason, file} ->
        raise File.CopyError, reason: reason, action: "copy recursively",
          source: source, destination: destination, on: file
    end
  end

  # src may be a file or a directory, dest is definitely
  # a directory. Returns nil unless an error is found.
  defp do_cp_r(src, dest, callback, acc) when is_list(acc) do
    case :elixir_utils.read_link_type(src) do
      {:ok, :regular} ->
        do_cp_file(src, dest, callback, acc)
      {:ok, :symlink} ->
        case F.read_link(src) do
          {:ok, link} -> do_cp_link(link, src, dest, callback, acc)
          {:error, reason} -> {:error, reason, src}
        end
      {:ok, :directory} ->
        case F.list_dir(src) do
          {:ok, files} ->
            case mkdir(dest) do
              success when success in [:ok, {:error, :eexist}] ->
                Enum.reduce(files, [dest|acc], fn(x, acc) ->
                  do_cp_r(Path.join(src, x), Path.join(dest, x), callback, acc)
                end)
              {:error, reason} -> {:error, reason, dest}
            end
          {:error, reason} -> {:error, reason, src}
        end
      {:ok, _} -> {:error, :eio, src}
      {:error, reason} -> {:error, reason, src}
    end
  end

  # If we reach this clause, there was an error while
  # processing a file.
  defp do_cp_r(_, _, _, acc) do
    acc
  end

  defp copy_file_mode!(src, dest) do
    write_stat!(dest, %{stat!(dest) | mode: stat!(src).mode})
  end

  # Both src and dest are files.
  defp do_cp_file(src, dest, callback, acc) do
    case F.copy(src, {dest, [:exclusive]}) do
      {:ok, _} ->
        copy_file_mode!(src, dest)
        [dest|acc]
      {:error, :eexist} ->
        if callback.(src, dest) do
          # If rm/1 fails, copy/2 will fail
          _ = rm(dest)
          case copy(src, dest) do
            {:ok, _} ->
              copy_file_mode!(src, dest)
              [dest|acc]
            {:error, reason} -> {:error, reason, src}
          end
        else
          acc
        end
      {:error, reason} -> {:error, reason, src}
    end
  end

  # Both src and dest are files.
  defp do_cp_link(link, src, dest, callback, acc) do
    case F.make_symlink(link, dest) do
      :ok ->
        [dest|acc]
      {:error, :eexist} ->
        if callback.(src, dest) do
          # If rm/1 fails, iF.make_symlink/2 will fail
          _ = rm(dest)
          case F.make_symlink(link, dest) do
            :ok -> [dest|acc]
            {:error, reason} -> {:error, reason, src}
          end
        else
          acc
        end
      {:error, reason} -> {:error, reason, src}
    end
  end

  @doc """
  Writes `content` to the file `path`.

  The file is created if it does not exist. If it exists, the previous
  contents are overwritten. Returns `:ok` if successful, or `{:error, reason}`
  if an error occurs.

  **Warning:** Every time this function is invoked, a file descriptor is opened
  and a new process is spawned to write to the file. For this reason, if you are
  doing multiple writes in a loop, opening the file via `File.open/2` and using
  the functions in `IO` to write to the file will yield much better performance
  then calling this function multiple times.

  Typical error reasons are:

    * `:enoent`  - a component of the file name does not exist
    * `:enotdir` - a component of the file name is not a directory;
                   on some platforms, enoent is returned instead
    * `:enospc`  - there is a no space left on the device
    * `:eacces`  - missing permission for writing the file or searching one of
                   the parent directories
    * `:eisdir`  - the named file is a directory

  Check `File.open/2` for other available options.
  """
  @spec write(Path.t, iodata, [mode]) :: :ok | {:error, posix}
  def write(path, content, modes \\ []) do
    F.write_file(IO.chardata_to_string(path), content, modes)
  end

  @doc """
  Same as `write/3` but raises an exception if it fails, returns `:ok` otherwise.
  """
  @spec write!(Path.t, iodata, [mode]) :: :ok | no_return
  def write!(path, content, modes \\ []) do
    path = IO.chardata_to_string(path)
    case F.write_file(path, content, modes) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "write to file", path: path
    end
  end

  @doc """
  Tries to delete the file `path`.

  Returns `:ok` if successful, or `{:error, reason}` if an error occurs.
  Note the file is deleted even if in read-only mode.

  Typical error reasons are:

    * `:enoent`  - the file does not exist
    * `:eacces`  - missing permission for the file or one of its parents
    * `:eperm`   - the file is a directory and user is not super-user
    * `:enotdir` - a component of the file name is not a directory;
                   on some platforms, enoent is returned instead
    * `:einval`  - filename had an improper type, such as tuple

  ## Examples

      File.rm('file.txt')
      #=> :ok

      File.rm('tmp_dir/')
      #=> {:error, :eperm}

  """
  @spec rm(Path.t) :: :ok | {:error, posix}
  def rm(path) do
    path = IO.chardata_to_string(path)
    case F.delete(path) do
      :ok ->
        :ok
      {:error, :eacces} = e ->
        change_mode_windows(path) || e
      {:error, _} = e ->
        e
    end
  end

  defp change_mode_windows(path) do
    if match? {:win32, _}, :os.type do
      case F.read_file_info(IO.chardata_to_string(path)) do
        {:ok, file_info} when elem(file_info, 3) in [:read, :none] ->
          change_mode_windows(path, file_info)
        _ ->
          nil
      end
    end
  end

  defp change_mode_windows(path, file_info) do
    case File.chmod(path, (elem(file_info, 7) + 0o200)) do
      :ok -> F.delete(path)
      {:error, _reason} = error -> error
    end
  end

  @doc """
  Same as `rm/1`, but raises an exception in case of failure. Otherwise `:ok`.
  """
  @spec rm!(Path.t) :: :ok | no_return
  def rm!(path) do
    path = IO.chardata_to_string(path)
    case rm(path) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "remove file", path: path
    end
  end

  @doc """
  Tries to delete the dir at `path`.
  Returns `:ok` if successful, or `{:error, reason}` if an error occurs.

  ## Examples

      File.rmdir('tmp_dir')
      #=> :ok

      File.rmdir('file.txt')
      #=> {:error, :enotdir}

  """
  @spec rmdir(Path.t) :: :ok | {:error, posix}
  def rmdir(path) do
    F.del_dir(IO.chardata_to_string(path))
  end

  @doc """
  Same as `rmdir/1`, but raises an exception in case of failure. Otherwise `:ok`.
  """
  @spec rmdir!(Path.t) :: :ok | {:error, posix}
  def rmdir!(path) do
    path = IO.chardata_to_string(path)
    case rmdir(path) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "remove directory", path: path
    end
  end

  @doc """
  Remove files and directories recursively at the given `path`.
  Symlinks are not followed but simply removed, non-existing
  files are simply ignored (i.e. doesn't make this function fail).

  Returns `{:ok, files_and_directories}` with all files and
  directories removed in no specific order, `{:error, reason, file}`
  otherwise.

  ## Examples

      File.rm_rf "samples"
      #=> {:ok, ["samples", "samples/1.txt"]}

      File.rm_rf "unknown"
      #=> {:ok, []}

  """
  @spec rm_rf(Path.t) :: {:ok, [binary]} | {:error, posix, binary}
  def rm_rf(path) do
    do_rm_rf(IO.chardata_to_string(path), {:ok, []})
  end

  defp do_rm_rf(path, {:ok, _} = entry) do
    case safe_list_dir(path) do
      {:ok, files} when is_list(files) ->
        res =
          Enum.reduce files, entry, fn(file, tuple) ->
            do_rm_rf(Path.join(path, file), tuple)
          end

        case res do
          {:ok, acc} ->
            case rmdir(path) do
              :ok -> {:ok, [path|acc]}
              {:error, :enoent} -> res
              {:error, reason} -> {:error, reason, path}
            end
          reason ->
            reason
        end
      {:ok, :directory} -> do_rm_directory(path, entry)
      {:ok, :regular} -> do_rm_regular(path, entry)
      {:error, reason} when reason in [:enoent, :enotdir] -> entry
      {:error, reason} -> {:error, reason, path}
    end
  end

  defp do_rm_rf(_, reason) do
    reason
  end

  defp do_rm_regular(path, {:ok, acc} = entry) do
    case rm(path) do
      :ok -> {:ok, [path|acc]}
      {:error, :enoent} -> entry
      {:error, reason} -> {:error, reason, path}
    end
  end

  # On windows, symlinks are treated as directory and must be removed
  # with rmdir/1. But on Unix, we remove them via rm/1. So we first try
  # to remove it as a directory and, if we get :enotdir, we fallback to
  # a file removal.
  defp do_rm_directory(path, {:ok, acc} = entry) do
    case rmdir(path) do
      :ok -> {:ok, [path|acc]}
      {:error, :enotdir} -> do_rm_regular(path, entry)
      {:error, :enoent} -> entry
      {:error, reason} -> {:error, reason, path}
    end
  end

  defp safe_list_dir(path) do
    case :elixir_utils.read_link_type(path) do
      {:ok, :symlink} ->
        case :elixir_utils.read_file_type(path) do
          {:ok, :directory} -> {:ok, :directory}
          _ -> {:ok, :regular}
        end
      {:ok, :directory} ->
        F.list_dir(path)
      {:ok, _} ->
        {:ok, :regular}
      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc """
  Same as `rm_rf/1` but raises `File.Error` in case of failures,
  otherwise the list of files or directories removed.
  """
  @spec rm_rf!(Path.t) :: [binary] | no_return
  def rm_rf!(path) do
    path = IO.chardata_to_string(path)
    case rm_rf(path) do
      {:ok, files} -> files
      {:error, reason, _} ->
        raise File.Error, reason: reason, path: path,
          action: "remove files and directories recursively from"
    end
  end

  @doc ~S"""
  Opens the given `path` according to the given list of modes.

  In order to write and read files, one must use the functions
  in the `IO` module. By default, a file is opened in binary mode
  which requires the functions `IO.binread/2` and `IO.binwrite/2`
  to interact with the file. A developer may pass `:utf8` as an
  option when opening the file and then all other functions from
  `IO` are available, since they work directly with Unicode data.

  The allowed modes:

    * `:read` - the file, which must exist, is opened for reading.

    * `:write` - the file is opened for writing. It is created if it does not
      exist.

      If the file does exists, and if write is not combined with read, the file
      will be truncated.

    * `:append` - the file will be opened for writing, and it will be created
      if it does not exist. Every write operation to a file opened with append
      will take place at the end of the file.

    * `:exclusive` - the file, when opened for writing, is created if it does
      not exist. If the file exists, open will return `{:error, :eexist}`.

    * `:char_list` - when this term is given, read operations on the file will
      return char lists rather than binaries.

    * `:compressed` - makes it possible to read or write gzip compressed files.

      The compressed option must be combined with either read or write, but not
      both. Note that the file size obtained with `stat/1` will most probably
      not match the number of bytes that can be read from a compressed file.

    * `:utf8` - this option denotes how data is actually stored in the disk
      file and makes the file perform automatic translation of characters to
      and from utf-8.

      If data is sent to a file in a format that cannot be converted to the
      utf-8 or if data is read by a function that returns data in a format that
      cannot cope with the character range of the data, an error occurs and the
      file will be closed.

  Check http://www.erlang.org/doc/man/file.html#open-2 for more information about
  other options like `:read_ahead` and `:delayed_write`.

  This function returns:

    * `{:ok, io_device}` - the file has been opened in the requested mode.

      `io_device` is actually the pid of the process which handles the file.
      This process is linked to the process which originally opened the file.
      If any process to which the `io_device` is linked terminates, the file
      will be closed and the process itself will be terminated.

      An `io_device` returned from this call can be used as an argument to the
      `IO` module functions.

    * `{:error, reason}` - the file could not be opened.

  ## Examples

      {:ok, file} = File.open("foo.tar.gz", [:read, :compressed])
      IO.read(file, :line)
      File.close(file)

  """
  @spec open(Path.t, [mode | :ram]) :: {:ok, io_device} | {:error, posix}
  @spec open(Path.t, (io_device -> res)) :: {:ok, res} | {:error, posix} when res: var
  def open(path, modes \\ [])

  def open(path, modes) when is_list(modes) do
    F.open(IO.chardata_to_string(path), open_defaults(modes, true))
  end

  def open(path, function) when is_function(function) do
    open(path, [], function)
  end

  @doc """
  Similar to `open/2` but expects a function as last argument.

  The file is opened, given to the function as argument and
  automatically closed after the function returns, regardless
  if there was an error when executing the function.

  It returns `{:ok, function_result}` in case of success,
  `{:error, reason}` otherwise.

  This function expects the file to be closed with success,
  which is usually the case unless the `:delayed_write` option
  is given. For this reason, we do not recommend passing
  `:delayed_write` to this function.

  ## Examples

      File.open("file.txt", [:read, :write], fn(file) ->
        IO.read(file, :line)
      end)

  """
  @spec open(Path.t, [mode | :ram], (io_device -> res)) :: {:ok, res} | {:error, posix} when res: var
  def open(path, modes, function) do
    case open(path, modes) do
      {:ok, device} ->
        try do
          {:ok, function.(device)}
        after
          :ok = close(device)
        end
      other -> other
    end
  end

  @doc """
  Same as `open/2` but raises an error if file could not be opened.

  Returns the `io_device` otherwise.
  """
  @spec open!(Path.t, [mode]) :: io_device | no_return
  def open!(path, modes \\ []) do
    path = IO.chardata_to_string(path)
    case open(path, modes) do
      {:ok, device}    -> device
      {:error, reason} ->
        raise File.Error, reason: reason, action: "open", path: path
    end
  end

  @doc """
  Same as `open/3` but raises an error if file could not be opened.

  Returns the function result otherwise.
  """
  @spec open!(Path.t, [mode | :ram], (io_device -> res)) :: res | no_return when res: var
  def open!(path, modes, function) do
    path = IO.chardata_to_string(path)
    case open(path, modes, function) do
      {:ok, device}    -> device
      {:error, reason} ->
        raise File.Error, reason: reason, action: "open", path: path
    end
  end

  @doc """
  Gets the current working directory.

  In rare circumstances, this function can fail on Unix. It may happen
  if read permission does not exist for the parent directories of the
  current directory. For this reason, returns `{:ok, cwd}` in case
  of success, `{:error, reason}` otherwise.
  """
  @spec cwd() :: {:ok, binary} | {:error, posix}
  def cwd() do
    case F.get_cwd do
      {:ok, base} -> {:ok, IO.chardata_to_string(fix_drive_letter(base))}
      {:error, _} = error -> error
    end
  end

  defp fix_drive_letter([l, ?:, ?/ | rest] = original) when l in ?A..?Z do
    case :os.type() do
      {:win32, _} -> [l+?a-?A, ?:, ?/ | rest]
      _ -> original
    end
  end

  defp fix_drive_letter(original), do: original

  @doc """
  The same as `cwd/0`, but raises an exception if it fails.
  """
  @spec cwd!() :: binary | no_return
  def cwd!() do
    case cwd() do
      {:ok, cwd} -> cwd
      {:error, reason} ->
          raise File.Error, reason: reason, action: "get current working directory"
    end
  end

  @doc """
  Sets the current working directory.

  Returns `:ok` if successful, `{:error, reason}` otherwise.
  """
  @spec cd(Path.t) :: :ok | {:error, posix}
  def cd(path) do
    F.set_cwd(IO.chardata_to_string(path))
  end

  @doc """
  The same as `cd/1`, but raises an exception if it fails.
  """
  @spec cd!(Path.t) :: :ok | no_return
  def cd!(path) do
    path = IO.chardata_to_string(path)
    case F.set_cwd(path) do
      :ok -> :ok
      {:error, reason} ->
          raise File.Error, reason: reason, action: "set current working directory to", path: path
    end
  end

  @doc """
  Changes the current directory to the given `path`,
  executes the given function and then revert back
  to the previous path regardless if there is an exception.

  Raises an error if retrieving or changing the current
  directory fails.
  """
  @spec cd!(Path.t, (() -> res)) :: res | no_return when res: var
  def cd!(path, function) do
    old = cwd!
    cd!(path)
    try do
      function.()
    after
      cd!(old)
    end
  end

  @doc """
  Returns list of files in the given directory.

  It returns `{:ok, [files]}` in case of success,
  `{:error, reason}` otherwise.
  """
  @spec ls(Path.t) :: {:ok, [binary]} | {:error, posix}
  def ls(path \\ ".") do
    case F.list_dir(IO.chardata_to_string(path)) do
      {:ok, file_list} -> {:ok, Enum.map(file_list, &IO.chardata_to_string/1)}
      {:error, _} = error -> error
    end
  end

  @doc """
  The same as `ls/1` but raises `File.Error`
  in case of an error.
  """
  @spec ls!(Path.t) :: [binary] | no_return
  def ls!(path \\ ".") do
    path = IO.chardata_to_string(path)
    case ls(path) do
      {:ok, value} -> value
      {:error, reason} ->
        raise File.Error, reason: reason, action: "list directory", path: path
    end
  end

  @doc """
  Closes the file referenced by `io_device`. It mostly returns `:ok`, except
  for some severe errors such as out of memory.

  Note that if the option `:delayed_write` was used when opening the file,
  `close/1` might return an old write error and not even try to close the file.
  See `open/2`.
  """
  @spec close(io_device) :: :ok | {:error, posix | :badarg | :terminated}
  def close(io_device) do
    F.close(io_device)
  end

  @doc """
  Returns a `File.Stream` for the given `path` with the given `modes`.

  The stream implements both `Enumerable` and `Collectable` protocols,
  which means it can be used both for read and write.

  The `line_or_byte` argument configures how the file is read when
  streaming, by `:line` (default) or by a given number of bytes.

  Operating the stream can fail on open for the same reasons as
  `File.open!/2`. Note that the file is automatically opened only and
  every time streaming begins. There is no need to pass `:read` and
  `:write` modes, as those are automatically set by Elixir.

  ## Raw files

  Since Elixir controls when the streamed file is opened, the underlying
  device cannot be shared and as such it is convenient to open the file
  in raw mode for performance reasons. Therefore, Elixir **will** open
  streams in `:raw` mode with the `:read_ahead` option unless an encoding
  is specified.

  One may also consider passing the `:delayed_write` option if the stream
  is meant to be written to under a tight loop.
  """
  def stream!(path, modes \\ [], line_or_bytes \\ :line) do
    modes = open_defaults(modes, true)
    File.Stream.__build__(IO.chardata_to_string(path), modes, line_or_bytes)
  end

  @doc """
  Changes the unix file `mode` for a given `file`.
  Returns `:ok` on success, or `{:error, reason}`
  on failure.
  """
  @spec chmod(Path.t, non_neg_integer) :: :ok | {:error, posix}
  def chmod(path, mode) do
    F.change_mode(IO.chardata_to_string(path), mode)
  end

  @doc """
  Same as `chmod/2`, but raises an exception in case of failure. Otherwise `:ok`.
  """
  @spec chmod!(Path.t, non_neg_integer) :: :ok | no_return
  def chmod!(path, mode) do
    path = IO.chardata_to_string(path)
    case chmod(path, mode) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "change mode for", path: path
    end
  end

  @doc """
  Changes the user group given by the group id `gid`
  for a given `file`. Returns `:ok` on success, or
  `{:error, reason}` on failure.
  """
  @spec chgrp(Path.t, non_neg_integer) :: :ok | {:error, posix}
  def chgrp(path, gid) do
    F.change_group(IO.chardata_to_string(path), gid)
  end

  @doc """
  Same as `chgrp/2`, but raises an exception in case of failure. Otherwise `:ok`.
  """
  @spec chgrp!(Path.t, non_neg_integer) :: :ok | no_return
  def chgrp!(path, gid) do
    path = IO.chardata_to_string(path)
    case chgrp(path, gid) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "change group for", path: path
    end
  end

  @doc """
  Changes the owner given by the user id `uid`
  for a given `file`. Returns `:ok` on success,
  or `{:error, reason}` on failure.
  """
  @spec chown(Path.t, non_neg_integer) :: :ok | {:error, posix}
  def chown(path, uid) do
    F.change_owner(IO.chardata_to_string(path), uid)
  end

  @doc """
  Same as `chown/2`, but raises an exception in case of failure. Otherwise `:ok`.
  """
  @spec chown!(Path.t, non_neg_integer) :: :ok | no_return
  def chown!(path, uid) do
    path = IO.chardata_to_string(path)
    case chown(path, uid) do
      :ok -> :ok
      {:error, reason} ->
        raise File.Error, reason: reason, action: "change owner for", path: path
    end
  end

  ## Helpers

  @read_ahead 64*1024

  defp open_defaults([:char_list|t], _add_binary) do
    open_defaults(t, false)
  end

  defp open_defaults([:utf8|t], add_binary) do
    open_defaults([{:encoding, :utf8}|t], add_binary)
  end

  defp open_defaults([:read_ahead|t], add_binary) do
    open_defaults([{:read_ahead, @read_ahead}|t], add_binary)
  end

  defp open_defaults([h|t], add_binary) do
    [h|open_defaults(t, add_binary)]
  end

  defp open_defaults([], true),  do: [:binary]
  defp open_defaults([], false), do: []
end
