"""File processing utilities."""

import errno
import functools
import glob as _glob
import os
import shutil
import threading


class FileError(IOError):
  """An error occurred while reading or writing a file."""


class GOSError(OSError):
  """An error occurred while finding a file or in handling pathnames."""


class _GFileBase(object):
  """Base I/O wrapper class.  Similar semantics to Python's file object."""

  # pylint: disable=protected-access
  def _error_wrapper(fn):
    """Decorator wrapping GFileBase class method errors."""
    @functools.wraps(fn)  # Preserve methods' __doc__
    def wrap(self, *args, **kwargs):
      try:
        return fn(self, *args, **kwargs)
      except ValueError, e:
        # Sometimes a ValueError is raised, e.g., a read() on a closed file.
        raise FileError(errno.EIO, e.message, self._name)
      except IOError, e:
        e.filename = self._name
        raise FileError(e)
      except OSError, e:
        raise GOSError(e)
    return wrap

  def _synchronized(fn):
    """Synchronizes file I/O for methods in GFileBase."""
    @functools.wraps(fn)
    def sync(self, *args, **kwargs):
      # Sometimes a GFileBase method is called before the instance
      # has been properly initialized.  Check that _locker is available.
      if hasattr(self, '_locker'): self._locker.lock()
      try:
        return fn(self, *args, **kwargs)
      finally:
        if hasattr(self, '_locker'): self._locker.unlock()
    return sync
  # pylint: enable=protected-access

  @_error_wrapper
  def __init__(self, name, mode, locker):
    """Create the GFileBase object with the given filename, mode, and locker.

    Args:
      name: string, the filename.
      mode: string, the mode to open the file with (e.g. "r", "w", "a+").
      locker: the thread locking object (e.g. _PythonLocker) for controlling
        thread access to the I/O methods of this class.
    """
    self._name = name
    self._mode = mode
    self._locker = locker
    self._fp = open(name, mode)

  def __enter__(self):
    """Make GFileBase usable with "with" statement."""
    return self

  def __exit__(self, unused_type, unused_value, unused_traceback):
    """Make GFileBase usable with "with" statement."""
    self.close()

  @_error_wrapper
  @_synchronized
  def __del__(self):
    # __del__ is sometimes called before initialization, in which
    # case the object is not fully constructed.  Check for this here
    # before trying to close the file handle.
    if hasattr(self, '_fp'): self._fp.close()

  @_error_wrapper
  @_synchronized
  def flush(self):
    """Flush the underlying file handle."""
    return self._fp.flush()

  @property
  @_error_wrapper
  @_synchronized
  def closed(self):
    """Returns "True" if the file handle is closed.  Otherwise False."""
    return self._fp.closed

  @_error_wrapper
  @_synchronized
  def write(self, data):
    """Write data to the underlying file handle.

    Args:
      data: The string to write to the file handle.
    """
    self._fp.write(data)

  @_error_wrapper
  @_synchronized
  def writelines(self, seq):
    """Write a sequence of strings to the underlying file handle."""
    self._fp.writelines(seq)

  @_error_wrapper
  @_synchronized
  def tell(self):
    """Return the location from the underlying file handle.

    Returns:
      An integer location (which can be used in e.g., seek).
    """
    return self._fp.tell()

  @_error_wrapper
  @_synchronized
  def seek(self, offset, whence=0):
    """Seek to offset (conditioned on whence) in the underlying file handle.

    Args:
      offset: int, the offset within the file to seek to.
      whence: 0, 1, or 2.  See python's seek() documentation for details.
    """
    self._fp.seek(offset, whence)

  @_error_wrapper
  @_synchronized
  def truncate(self, new_size=None):
    """Truncate the underlying file handle to new_size.

    Args:
      new_size: Size after truncation.  If None, the file handle is truncated
      to 0 bytes.
    """
    self._fp.truncate(new_size)

  @_error_wrapper
  @_synchronized
  def readline(self, max_length=-1):
    """Read a single line (up to max_length) from the underlying file handle.

    Args:
      max_length: The maximum number of chsaracters to read.

    Returns:
      A string, including any newline at the end, or empty string if at EOF.
    """
    return self._fp.readline(max_length)

  @_error_wrapper
  @_synchronized
  def readlines(self, sizehint=None):
    """Read lines from the underlying file handle.

    Args:
      sizehint: See the python file.readlines() documentation.

    Returns:
      A list of strings from the underlying file handle.
    """
    if sizehint is not None:
      return self._fp.readlines(sizehint)
    else:
      return self._fp.readlines()

  def __iter__(self):
    """Enable line iteration on the underlying handle (not synchronized)."""
    return self

  # Not synchronized
  @_error_wrapper
  def next(self):
    """Enable line iteration on the underlying handle (not synchronized).

    Returns:
      An line iterator from the underlying handle.

    Example:
      # read a file's lines by consuming the iterator with a list
      with open("filename", "r") as fp: lines = list(fp)
    """
    return self._fp.next()

  @_error_wrapper
  @_synchronized
  def Size(self):   # pylint: disable=invalid-name
    """Get byte size of the file from the underlying file handle."""
    cur = self.tell()
    try:
      self.seek(0, 2)
      size = self.tell()
    finally:
      self.seek(cur)
    return size

  @_error_wrapper
  @_synchronized
  def read(self, n=-1):
    """Read n bytes from the underlying file handle.

    Args:
      n: Number of bytes to read (if negative, read to end of file handle.)

    Returns:
      A string of the bytes read, up to the end of file.
    """
    return self._fp.read(n)

  @_error_wrapper
  @_synchronized
  def close(self):
    """Close the underlying file handle."""
    self._fp.close()

  # Declare wrappers as staticmethods at the end so that we can
  # use them as decorators.
  _error_wrapper = staticmethod(_error_wrapper)
  _synchronized = staticmethod(_synchronized)


class GFile(_GFileBase):
  """File I/O wrappers with thread locking."""

  def __init__(self, name, mode='r'):
    super(GFile, self).__init__(name, mode, _Pythonlocker())


class FastGFile(_GFileBase):
  """File I/O wrappers without thread locking."""

  def __init__(self, name, mode='r'):
    super(FastGFile, self).__init__(name, mode, _Nulllocker())


# locker classes.  Note that locks must be reentrant, so that multiple
# lock() calls by the owning thread will not block.
class _Pythonlocker(object):
  """A locking strategy that uses standard locks from the thread module."""

  def __init__(self):
    self._lock = threading.RLock()

  def lock(self):
    self._lock.acquire()

  def unlock(self):
    self._lock.release()


class _Nulllocker(object):
  """A locking strategy where lock() and unlock() methods are no-ops."""

  def lock(self):
    pass

  def unlock(self):
    pass


def _func_error_wrapper(fn):
  """Decorator wrapping function errors."""
  @functools.wraps(fn)  # Preserve methods' __doc__
  def wrap(*args, **kwargs):
    try:
      return fn(*args, **kwargs)
    except ValueError, e:
      raise FileError(errno.EIO, e.message)
    except IOError, e:
      raise FileError(e)
    except OSError, e:
      raise GOSError(e)
  return wrap


@_func_error_wrapper
def Exists(path):   # pylint: disable=invalid-name
  """Retruns True iff "path" exists (as a dir, file, non-broken symlink)."""
  return os.path.exists(path)


@_func_error_wrapper
def IsDirectory(path):   # pylint: disable=invalid-name
  """Return True iff "path" exists and is a directory."""
  return os.path.isdir(path)


@_func_error_wrapper
def Glob(glob):   # pylint: disable=invalid-name
  """Return a list of filenames matching the glob "glob"."""
  return _glob.glob(glob)


@_func_error_wrapper
def MkDir(path, mode=0755):   # pylint: disable=invalid-name
  """Create the directory "path" with the given mode.

  Args:
    path: The directory path
    mode: The file mode for the directory

  Returns:
    None

  Raises:
    GOSError: if the path already exists
  """
  os.mkdir(path, mode)


@_func_error_wrapper
def MakeDirs(path, mode=0755):   # pylint: disable=invalid-name
  """Recursively create the directory "path" with the given mode.

  Args:
    path: The directory path
    mode: The file mode for the created directories

  Returns:
    None


  Raises:
    GOSError: if the path already exists
  """
  os.makedirs(path, mode)


@_func_error_wrapper
def RmDir(directory):   # pylint: disable=invalid-name
  """Removes the directory "directory" iff the directory is empty.

  Args:
    directory: The directory to remove.

  Raises:
    GOSError: If the directory does not exist or is not empty.
  """
  os.rmdir(directory)


@_func_error_wrapper
def Remove(path):   # pylint: disable=invalid-name
  """Delete the (non-directory) file "path".

  Args:
    path: The file to remove.

  Raises:
    GOSError: If "path" does not exist, is a directory, or cannot be deleted.
  """
  os.remove(path)


@_func_error_wrapper
def DeleteRecursively(path):   # pylint: disable=invalid-name
  """Delete the file or directory "path" recursively.

  Args:
    path: The path to remove (may be a non-empty directory).

  Raises:
    GOSError: If the path does not exist or cannot be deleted.
  """
  if IsDirectory(path):
    shutil.rmtree(path)
  else:
    Remove(path)


@_func_error_wrapper
def ListDirectory(directory, return_dotfiles=False):  # pylint: disable=invalid-name
  """Returns a list of files in dir.

  As with the standard os.listdir(), the filenames in the returned list will be
  the basenames of the files in dir (not absolute paths).  To get a list of
  absolute paths of files in a directory, a client could do:
    file_list = gfile.ListDir(my_dir)
    file_list = [os.path.join(my_dir, f) for f in file_list]
  (assuming that my_dir itself specified an absolute path to a directory).

  Args:
    directory: the directory to list
    return_dotfiles: if True, dotfiles will be returned as well.  Even if
      this arg is True, '.' and '..' will not be returned.

  Returns:
    ['list', 'of', 'files']. The entries '.' and '..' are never returned.
    Other entries starting with a dot will only be returned if return_dotfiles
    is True.
  Raises:
    GOSError: if there is an error retrieving the directory listing.
  """
  files = os.listdir(directory)
  if not return_dotfiles:
    files = [f for f in files if not f.startswith('.')]
  return files