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"""Azure Blob Storage Implementation for accesing files on
Azure Blob Storage.
"""

from __future__ import absolute_import

from future.utils import iteritems

from apache_beam.io.azure import blobstorageio
from apache_beam.io.filesystem import BeamIOError
from apache_beam.io.filesystem import CompressedFile
from apache_beam.io.filesystem import CompressionTypes
from apache_beam.io.filesystem import FileMetadata
from apache_beam.io.filesystem import FileSystem

__all__ = ['BlobStorageFileSystem']


class BlobStorageFileSystem(FileSystem):
  """An Azure Blob Storage ``FileSystem`` implementation for accesing files on
  Azure Blob Storage.
  """

  CHUNK_SIZE = blobstorageio.MAX_BATCH_OPERATION_SIZE
  AZURE_FILE_SYSTEM_PREFIX = 'azfs://'

  @classmethod
  def scheme(cls):
    """URI scheme for the FileSystem
    """
    return 'azfs'

  def join(self, basepath, *paths):
    """Join two or more pathname components for the filesystem

    Args:
      basepath: string path of the first component of the path
      paths: path components to be added

    Returns: full path after combining all the passed components
    """
    if not basepath.startswith(BlobStorageFileSystem.AZURE_FILE_SYSTEM_PREFIX):
      raise ValueError(
          'Basepath %r must be an Azure Blob Storage path.' % basepath)

    path = basepath
    for p in paths:
      path = path.rstrip('/') + '/' + p.lstrip('/')
    return path

  def split(self, path):
    """Splits the given path into two parts.

    Splits the path into a pair (head, tail) such that tail contains the last
    component of the path and head contains everything up to that.
    For file-systems other than the local file-system, head should include the
    prefix.

    Args:
      path: path as a string

    Returns:
      a pair of path components as strings.
    """
    path = path.strip()
    if not path.startswith(BlobStorageFileSystem.AZURE_FILE_SYSTEM_PREFIX):
      raise ValueError('Path %r must be Azure Blob Storage path.' % path)

    prefix_len = len(BlobStorageFileSystem.AZURE_FILE_SYSTEM_PREFIX)
    last_sep = path[prefix_len:].rfind('/')
    if last_sep >= 0:
      last_sep += prefix_len

    if last_sep > 0:
      return (path[:last_sep], path[last_sep + 1:])
    elif last_sep < 0:
      return (path, '')
    else:
      raise ValueError('Invalid path: %s' % path)

  def mkdirs(self, path):
    """Recursively create directories for the provided path.

    Args:
      path: string path of the directory structure that should be created

    Raises:
      IOError: if leaf directory already exists.
    """
    pass

  def has_dirs(self):
    """Whether this FileSystem supports directories."""
    return False

  def _list(self, dir_or_prefix):
    """List files in a location.
    Listing is non-recursive (for filesystems that support directories).
    Args:
      dir_or_prefix: (string) A directory or location prefix (for filesystems
        that don't have directories).
    Returns:
      Generator of ``FileMetadata`` objects.
    Raises:
      ``BeamIOError``: if listing fails, but not if no files were found.
    """
    try:
      for path, size in \
          iteritems(blobstorageio.BlobStorageIO().list_prefix(dir_or_prefix)):
        yield FileMetadata(path, size)
    except Exception as e:  # pylint: disable=broad-except
      raise BeamIOError("List operation failed", {dir_or_prefix: e})

  def _path_open(
      self,
      path,
      mode,
      mime_type='application/octet-stream',
      compression_type=CompressionTypes.AUTO):
    """Helper functions to open a file in the provided mode.
    """
    compression_type = FileSystem._get_compression_type(path, compression_type)
    mime_type = CompressionTypes.mime_type(compression_type, mime_type)
    raw_file = blobstorageio.BlobStorageIO().open(
        path, mode, mime_type=mime_type)
    if compression_type == CompressionTypes.UNCOMPRESSED:
      return raw_file
    return CompressedFile(raw_file, compression_type=compression_type)

  def create(
      self,
      path,
      mime_type='application/octet-stream',
      compression_type=CompressionTypes.AUTO):
    # type: (...) -> BinaryIO

    """Returns a write channel for the given file path.

    Args:
      path: string path of the file object to be written to the system
      mime_type: MIME type to specify the type of content in the file object
      compression_type: Type of compression to be used for this object

    Returns: file handle with a close function for the user to use
    """
    return self._path_open(path, 'wb', mime_type, compression_type)

  def open(
      self,
      path,
      mime_type='application/octet-stream',
      compression_type=CompressionTypes.AUTO):
    # type: (...) -> BinaryIO

    """Returns a read channel for the given file path.

    Args:
      path: string path of the file object to be read
      mime_type: MIME type to specify the type of content in the file object
      compression_type: Type of compression to be used for this object

    Returns: file handle with a close function for the user to use
    """
    return self._path_open(path, 'rb', mime_type, compression_type)

  def copy(self, source_file_names, destination_file_names):
    """Recursively copy the file tree from the source to the destination

    Args:
      source_file_names: list of source file objects that needs to be copied
      destination_file_names: list of destination of the new object

    Raises:
      ``BeamIOError``: if any of the copy operations fail
    """
    if not len(source_file_names) == len(destination_file_names):
      message = 'Unable to copy unequal number of sources and destinations.'
      raise BeamIOError(message)
    src_dest_pairs = list(zip(source_file_names, destination_file_names))
    return blobstorageio.BlobStorageIO().copy_paths(src_dest_pairs)

  def rename(self, source_file_names, destination_file_names):
    """Rename the files at the source list to the destination list.
    Source and destination lists should be of the same size.

    Args:
      source_file_names: List of file paths that need to be moved
      destination_file_names: List of destination_file_names for the files

    Raises:
      ``BeamIOError``: if any of the rename operations fail
    """
    if not len(source_file_names) == len(destination_file_names):
      message = 'Unable to rename unequal number of sources and destinations.'
      raise BeamIOError(message)
    src_dest_pairs = list(zip(source_file_names, destination_file_names))
    results = blobstorageio.BlobStorageIO().rename_files(src_dest_pairs)
    # Retrieve exceptions.
    exceptions = {(src, dest): error
                  for (src, dest, error) in results if error is not None}
    if exceptions:
      raise BeamIOError("Rename operation failed.", exceptions)

  def exists(self, path):
    """Check if the provided path exists on the FileSystem.

    Args:
      path: string path that needs to be checked.

    Returns: boolean flag indicating if path exists
    """
    try:
      return blobstorageio.BlobStorageIO().exists(path)
    except Exception as e:  # pylint: disable=broad-except
      raise BeamIOError("Exists operation failed", {path: e})

  def size(self, path):
    """Get size in bytes of a file on the FileSystem.

    Args:
      path: string filepath of file.

    Returns: int size of file according to the FileSystem.

    Raises:
      ``BeamIOError``: if path doesn't exist.
    """
    try:
      return blobstorageio.BlobStorageIO().size(path)
    except Exception as e:  # pylint: disable=broad-except
      raise BeamIOError("Size operation failed", {path: e})

  def last_updated(self, path):
    """Get UNIX Epoch time in seconds on the FileSystem.

    Args:
      path: string path of file.

    Returns: float UNIX Epoch time

    Raises:
      ``BeamIOError``: if path doesn't exist.
    """
    try:
      return blobstorageio.BlobStorageIO().last_updated(path)
    except Exception as e:  # pylint: disable=broad-except
      raise BeamIOError("Last updated operation failed", {path: e})

  def checksum(self, path):
    """Fetch checksum metadata of a file on the
    :class:`~apache_beam.io.filesystem.FileSystem`.

    Args:
      path: string path of a file.

    Returns: string containing checksum

    Raises:
      ``BeamIOError``: if path isn't a file or doesn't exist.
    """
    try:
      return blobstorageio.BlobStorageIO().checksum(path)
    except Exception as e:  # pylint: disable=broad-except
      raise BeamIOError("Checksum operation failed", {path, e})

  def delete(self, paths):
    """Deletes files or directories at the provided paths.
    Directories will be deleted recursively.

    Args:
      paths: list of paths that give the file objects to be deleted

    Raises:
      ``BeamIOError``: if any of the delete operations fail
    """
    results = blobstorageio.BlobStorageIO().delete_paths(paths)
    # Retrieve exceptions.
    exceptions = {
        path: error
        for (path, error) in results.items() if error is not None
    }

    if exceptions:
      raise BeamIOError("Delete operation failed", exceptions)
