import re

_hexdig = '0123456789ABCDEFabcdef'
_hextobyte = None


def unquote_to_bytes(string):
    """unquote_to_bytes('abc%20def') -> b'abc def'."""
    # Note: strings are encoded as UTF-8. This is only an issue if it contains
    # unescaped non-ASCII characters, which URIs should not.
    if not string:
        # Is it a string-like object?
        string.split
        return b''
    if isinstance(string, str):
        string = string.encode('utf-8')
    bits = string.split(b'%')
    if len(bits) == 1:
        return string
    res = [bits[0]]
    append = res.append
    # Delay the initialization of the table to not waste memory
    # if the function is never called
    global _hextobyte
    if _hextobyte is None:
        _hextobyte = {(a + b).encode(): bytes([int(a + b, 16)])
                      for a in _hexdig for b in _hexdig}
    for item in bits[1:]:
        try:
            append(_hextobyte[item[:2]])
            append(item[2:])
        except KeyError:
            append(b'%')
            append(item)
    return b''.join(res)


_asciire = re.compile('([\x00-\x7f]+)')


def unquote(string, encoding='utf-8', errors='replace'):
    """Replace %xx escapes by their single-character equivalent. The optional
    encoding and errors parameters specify how to decode percent-encoded
    sequences into Unicode characters, as accepted by the bytes.decode()
    method.
    By default, percent-encoded sequences are decoded with UTF-8, and invalid
    sequences are replaced by a placeholder character.

    unquote('abc%20def') -> 'abc def'.
    """
    if '%' not in string:
        string.split
        return string
    if encoding is None:
        encoding = 'utf-8'
    if errors is None:
        errors = 'replace'
    bits = _asciire.split(string)
    res = [bits[0]]
    append = res.append
    for i in range(1, len(bits), 2):
        append(unquote_to_bytes(bits[i]).decode(encoding, errors))
        append(bits[i + 1])
    return ''.join(res)


def _noop(obj):
    return obj


def _decode_args(args, encoding='ascii',
                 errors='strict'):
    return tuple(x.decode(encoding, errors) if x else '' for x in args)


def _coerce_args(*args):
    # Invokes decode if necessary to create str args
    # and returns the coerced inputs along with
    # an appropriate result coercion function
    #   - noop for str inputs
    #   - encoding function otherwise
    str_input = isinstance(args[0], str)
    for arg in args[1:]:
        # We special-case the empty string to support the
        # "scheme=''" default argument to some functions
        if arg and isinstance(arg, str) != str_input:
            raise TypeError("Cannot mix str and non-str arguments")
    if str_input:
        return args + (_noop,)
    return _decode_args(args) + (_encode_result,)


def parse_args(qs, keep_blank_values=False, strict_parsing=False, multi=False):
    """Parse a query given as a string argument.

    Arguments:

    qs: percent-encoded query string to be parsed

    keep_blank_values: flag indicating whether blank values in
        percent-encoded queries should be treated as blank strings.  A
        true value indicates that blanks should be retained as blank
        strings.  The default false value indicates that blank values
        are to be ignored and treated as if they were  not included.

    strict_parsing: flag indicating what to do with parsing errors. If
        false (the default), errors are silently ignored. If true,
        errors raise a ValueError exception.

    encoding and errors: specify how to decode percent-encoded sequences
        into Unicode characters, as accepted by the bytes.decode() method.

    Returns a list, as G-d intended.
    """
    qs, _coerce_result = _coerce_args(qs)
    pairs = [s2 for s1 in qs.split('&') for s2 in s1.split(';')]
    r = {}
    for name_value in pairs:
        if not name_value and not strict_parsing:
            continue
        nv = name_value.split('=', 1)
        if len(nv) != 2:
            if strict_parsing:
                raise ValueError("bad query field: %r" % (name_value,))
            # Handle case of a control-name with no equal sign
            if keep_blank_values:
                nv.append('')
            else:
                continue
        if len(nv[1]) or keep_blank_values:
            name = nv[0].replace('+', ' ')
            name = unquote(name)
            name = _coerce_result(name)
            value = nv[1].replace('+', ' ')
            value = unquote_to_bytes(value)
            value = _coerce_result(value)
            if multi:
                r.setdefault(name, [])
                r[name].append(value)
            else:
                r[name] = value
    return r
