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Filename : grange.py
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# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license

# Copyright (C) 2012-2017 Nominum, Inc.
#
# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose with or without fee is hereby granted,
# provided that the above copyright notice and this permission notice
# appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

"""DNS GENERATE range conversion."""

from typing import Tuple

import dns


def from_text(text: str) -> Tuple[int, int, int]:
    """Convert the text form of a range in a ``$GENERATE`` statement to an
    integer.

    *text*, a ``str``, the textual range in ``$GENERATE`` form.

    Returns a tuple of three ``int`` values ``(start, stop, step)``.
    """

    start = -1
    stop = -1
    step = 1
    cur = ""
    state = 0
    # state   0   1   2
    #         x - y / z

    if text and text[0] == "-":
        raise dns.exception.SyntaxError("Start cannot be a negative number")

    for c in text:
        if c == "-" and state == 0:
            start = int(cur)
            cur = ""
            state = 1
        elif c == "/":
            stop = int(cur)
            cur = ""
            state = 2
        elif c.isdigit():
            cur += c
        else:
            raise dns.exception.SyntaxError("Could not parse %s" % (c))

    if state == 0:
        raise dns.exception.SyntaxError("no stop value specified")
    elif state == 1:
        stop = int(cur)
    else:
        assert state == 2
        step = int(cur)

    assert step >= 1
    assert start >= 0
    if start > stop:
        raise dns.exception.SyntaxError("start must be <= stop")

    return (start, stop, step)