"""Module with functions which are supposed to be as fast as possible"""
from stat import S_ISDIR
from git.compat import (
    byte_ord,
    defenc,
    xrange,
    text_type,
    bchr
)

__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 = b''
        for i in xrange(6):
            mode_str = bchr(((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 byte_ord(mode_str[0]) == ord_zero:
            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, text_type):
            name = name.encode(defenc)
        write(b''.join((mode_str, b' ', name, b'\0', 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 (as bytes)
    :return: list(tuple(binsha, mode, tree_relative_path), ...)"""
    ord_zero = ord('0')
    space_ord = ord(' ')
    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 byte_ord(data[i]) != space_ord:
            # move existing mode integer up one level being 3 bits
            # and add the actual ordinal value of the character
            mode = (mode