import marisa_trie
import os
import tarfile
from aufs import is_aufs_metadata, get_deleted_prefix
from util.tarlayerformat import TarLayerFormat

AUFS_METADATA = u'.wh..wh.'

AUFS_WHITEOUT = u'.wh.'
AUFS_WHITEOUT_PREFIX_LENGTH = len(AUFS_WHITEOUT)

class StreamLayerMerger(TarLayerFormat):
  """ Class which creates a generator of the combined TAR data for a set of Docker layers. """
  def __init__(self, layer_iterator):
    super(StreamLayerMerger, self).__init__(layer_iterator)

    self.path_trie = marisa_trie.Trie()
    self.path_encountered = []

    self.prefix_trie = marisa_trie.Trie()
    self.prefix_encountered = []

  def after_tar_layer(stream, current_layer):
      # Update the tries.
      self.path_trie = marisa_trie.Trie(self.path_encountered)
      self.prefix_trie = marisa_trie.Trie(self.prefix_encountered)
      
  def check_tar_info(self, tar_info):
    absolute = os.path.relpath(tar_info.name.decode('utf-8'), './')

    # Skip metadata.
    if is_aufs_metadata(absolute):
      return False

    # Add any prefix of deleted paths to the prefix list.
    deleted_prefix = get_deleted_prefix(absolute)    
    if deleted_prefix is not None:
      self.prefix_encountered.append(deleted_prefix)
      return False

    # Check if this file has already been encountered somewhere. If so,
    # skip it.
    ubsolute = unicode(absolute)
    if ubsolute in self.path_trie:
      return False

    # Check if this file is under a deleted path.
    for prefix in self.prefix_trie.iter_prefixes(ubsolute):
      if not os.path.relpath(ubsolute, prefix).startswith('..'):
        return False

    # Otherwise, add the path to the encountered list and return it.
    self.path_encountered.append(absolute)
    return True