###############################################################################
#
# The MIT License (MIT)
#
# Copyright (c) Crossbar.io Technologies GmbH
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
#
###############################################################################

# Note: This code is a Python implementation of the algorithm
# "Flexible and Economical UTF-8 Decoder" by Bjoern Hoehrmann
# bjoern@hoehrmann.de, http://bjoern.hoehrmann.de/utf-8/decoder/dfa/

__all__ = ("Utf8Validator",)


# DFA transitions
UTF8VALIDATOR_DFA = (
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  # 00..1f
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  # 20..3f
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  # 40..5f
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  # 60..7f
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,  # 80..9f
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,  # a0..bf
    8, 8, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,  # c0..df
    0xa, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x4, 0x3, 0x3,  # e0..ef
    0xb, 0x6, 0x6, 0x6, 0x5, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8,  # f0..ff
    0x0, 0x1, 0x2, 0x3, 0x5, 0x8, 0x7, 0x1, 0x1, 0x1, 0x4, 0x6, 0x1, 0x1, 0x1, 0x1,  # s0..s0
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1,  # s1..s2
    1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1,  # s3..s4
    1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 3, 1, 1, 1, 1, 1, 1,  # s5..s6
    1, 3, 1, 1, 1, 1, 1, 3, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  # s7..s8
)

UTF8_ACCEPT = 0
UTF8_REJECT = 1


# use Cython implementation of UTF8 validator if available
try:
    from wsaccel.utf8validator import Utf8Validator

except ImportError:

    # Fallback to pure Python implementation - also for PyPy.
    #
    # Do NOT touch this code unless you know what you are doing!
    # https://github.com/oberstet/scratchbox/tree/master/python/utf8

    # Python 3 and above

    # convert DFA table to bytes (performance)
    UTF8VALIDATOR_DFA_S = bytes(UTF8VALIDATOR_DFA)

    class Utf8Validator(object):
        """
        Incremental UTF-8 validator with constant memory consumption (minimal state).

        Implements the algorithm "Flexible and Economical UTF-8 Decoder" by
        Bjoern Hoehrmann (http://bjoern.hoehrmann.de/utf-8/decoder/dfa/).
        """

        __slots__ = (
            '_codepoint',
            '_state',
            '_index',
        )

        def __init__(self):
            self._codepoint = None
            self._state = None
            self._index = None
            self.reset()

        def decode(self, b):
            """
            Eat one UTF-8 octet, and validate on the fly.

            Returns ``UTF8_ACCEPT`` when enough octets have been consumed, in which case
            ``self.codepoint`` contains the decoded Unicode code point.

            Returns ``UTF8_REJECT`` when invalid UTF-8 was encountered.

            Returns some other positive integer when more octets need to be eaten.
            """
            tt = UTF8VALIDATOR_DFA_S[b]
            if self._state != UTF8_ACCEPT:
                self._codepoint = (b & 0x3f) | (self._codepoint << 6)
            else:
                self._codepoint = (0xff >> tt) & b
            self._state = UTF8VALIDATOR_DFA_S[256 + self._state * 16 + tt]
            return self._state

        def reset(self):
            """
            Reset validator to start new incremental UTF-8 decode/validation.
            """
            self._state = UTF8_ACCEPT  # the empty string is valid UTF8
            self._codepoint = 0
            self._index = 0

        def validate(self, ba):
            """
            Incrementally validate a chunk of bytes provided as string.

            Will return a quad ``(valid?, endsOnCodePoint?, currentIndex, totalIndex)``.

            As soon as an octet is encountered which renders the octet sequence
            invalid, a quad with ``valid? == False`` is returned. ``currentIndex`` returns
            the index within the currently consumed chunk, and ``totalIndex`` the
            index within the total consumed sequence that was the point of bail out.
            When ``valid? == True``, currentIndex will be ``len(ba)`` and ``totalIndex`` the
            total amount of consumed bytes.
            """
            #
            # The code here is written for optimal JITting in PyPy, not for best
            # readability by your grandma or particular elegance. Do NOT touch!
            #
            l = len(ba)
            i = 0
            state = self._state
            while i < l:
                # optimized version of decode(), since we are not interested in actual code points
                state = UTF8VALIDATOR_DFA_S[256 + (state << 4) + UTF8VALIDATOR_DFA_S[ba[i]]]
                if state == UTF8_REJECT:
                    self._state = state
                    self._index += i
                    return False, False, i, self._index
                i += 1
            self._state = state
            self._index += l
            return True, state == UTF8_ACCEPT, l, self._index
