"""Module with functions which are supposed to be as fast as possible"""

from stat import S_ISDIR

__all__ = ('tree_to_stream', 'tree_entries_from_data', 'traverse_trees_recursive',
			'traverse_tree_recursive')


				

def tree_to_stream(entries, write):
	"""Write the give list of entries into a stream using its write method
	:param entries: **sorted** list of tuples with (binsha, mode, name)
	:param write: write method which takes a data string"""
	ord_zero = ord('0')
	bit_mask = 7			# 3 bits set
	
	for binsha, mode, name in entries:
		mode_str = ''
		for i in xrange(6):
			mode_str = chr(((mode >> (i*3)) & bit_mask) + ord_zero) + mode_str
		# END for each 8 octal value
		
		# git slices away the first octal if its zero
		if mode_str[0] == '0':
			mode_str = mode_str[1:]
		# END save a byte

		# here it comes:  if the name is actually unicode, the replacement below
		# will not work as the binsha is not part of the ascii unicode encoding - 
		# hence we must convert to an utf8 string for it to work properly.
		# According to my tests, this is exactly what git does, that is it just
		# takes the input literally, which appears to be utf8 on linux.
		if isinstance(name, unicode):
			name = name.encode("utf8")
		write("%s %s\0%s" % (mode_str, name, binsha)) 
	# END for each item


def tree_entries_from_data(data):
	"""Reads the binary representation of a tree and returns tuples of Tree items
	:param data: data block with tree data
	:return: list(tuple(binsha, mode, tree_relative_path), ...)"""
	ord_zero = ord('0')
	len_data = len(data)
	i = 0
	out = list()
	while i < len_data:
		mode = 0
		
		# read mode
		# Some git versions truncate the leading 0, some don't
		# The type will be extracted from the mode later
		while data[i] != ' ':
			# move existing mode integer up one level being 3 bits
			# and add the actual ordinal value of the character
			mode = (mode << 3) + (ord(data[i]) - ord_zero)
			i += 1
		# END while reading mode
		
		# byte is space now, skip it
		i += 1
		
		# parse name, it is NULL separated
		
		ns = i
		while data[i] != '\0':
			i += 1
		# END while not reached NULL
		
		# default encoding for strings in git is utf8
		# Only use the respective unicode object if the byte stream was encoded
		name = data[ns:i]
		name_enc = name.decode("utf-8")
		if len(name) > len(name_enc):
			name = name_enc
		# END handle encoding
		
		# byte is NULL, get next 20
		i += 1
		sha = data[i:i+20]
		i = i + 20
		out.append((sha, mode, name))
	# END for each byte in data stream
	return out
	
	
def _find_by_name(tree_data, name, is_dir, start_at):
	"""return data entry matching the given name and tree mode
	or None.
	Before the item is returned, the respective data item is set 
	None in the tree_data list to mark it done"""
	try:
		item = tree_data[start_at]
		if item and  item[2] == name and S_ISDIR(item[1]) == is_dir:
			tree_data[start_at] = None
			return item
	except IndexError:
		pass
	# END exception handling
	for index, item in enumerate(tree_data):
		if item and item[2] == name and S_ISDIR(item[1]) == is_dir:
			tree_data[index] = None
			return item
		# END if item matches
	# END for each item
	return None

def _to_full_path(item, path_prefix):
	"""Rebuild entry with given path prefix"""
	if not item:
		return item
	return (item[0], item[1], path_prefix+item[2])
	
def traverse_trees_recursive(odb, tree_shas, path_prefix):
	"""
	:return: list with entries according to the given binary tree-shas. 
		The result is encoded in a list
		of n tuple|None per blob/commit, (n == len(tree_shas)), where 
		* [0] == 20 byte sha
		* [1] == mode as int
		* [2] == path relative to working tree root
		The entry tuple is None if the respective blob/commit did not 
		exist in the given tree.
	:param tree_shas: iterable of shas pointing to trees. All trees must 
		be on the same level. A tree-sha may be None in which case None
	:param path_prefix: a prefix to be added to the returned paths on this level, 
		set it '' for the first iteration
	:note: The ordering of the returned items will be partially lost"""
	trees_data = list()
	nt = len(tree_shas)
	for tree_sha in tree_shas:
		if tree_sha is None:
			data = list()
		else:
			data = tree_entries_from_data(odb.stream(tree_sha).read())
		# END handle muted trees
		trees_data.append(data)
	# END for each sha to get data for
	
	out = list()
	out_append = out.append
	
	# find all matching entries and recursively process them together if the match
	# is a tree. If the match is a non-tree item, put it into the result.
	# Processed items will be set None
	for ti, tree_data in enumerate(trees_data):
		for ii, item in enumerate(tree_data):
			if not item:
				continue
			# END skip already done items
			entries = [ None for n in range(nt) ]
			entries[ti] = item
			sha, mode, name = item							# its faster to unpack
			is_dir = S_ISDIR(mode)							# type mode bits
			
			# find this item in all other tree data items
			# wrap around, but stop one before our current index, hence 
			# ti+nt, not ti+1+nt
			for tio in range(ti+1, ti+nt):
				tio = tio % nt
				entries[tio] = _find_by_name(trees_data[tio], name, is_dir, ii)
			# END for each other item data
			
			# if we are a directory, enter recursion
			if is_dir:
				out.extend(traverse_trees_recursive(odb, [((ei and ei[0]) or None) for ei in entries], path_prefix+name+'/'))
			else:
				out_append(tuple(_to_full_path(e, path_prefix) for e in entries))
			# END handle recursion
			
			# finally mark it done
			tree_data[ii] = None
		# END for each item
		
		# we are done with one tree, set all its data empty
		del(tree_data[:])
	# END for each tree_data chunk
	return out
	
def traverse_tree_recursive(odb, tree_sha, path_prefix):
	"""
	:return: list of entries of the tree pointed to by the binary tree_sha. An entry
		has the following format:
		* [0] 20 byte sha
		* [1] mode as int
		* [2] path relative to the repository
	:param path_prefix: prefix to prepend to the front of all returned paths"""
	entries = list()
	data = tree_entries_from_data(odb.stream(tree_sha).read())
	
	# unpacking/packing is faster than accessing individual items
	for sha, mode, name in data:
		if S_ISDIR(mode):
			entries.extend(traverse_tree_recursive(odb, sha, path_prefix+name+'/'))
		else:
			entries.append((sha, mode, path_prefix+name))
	# END for each item
	
	return entries

