# pre-release
            [-_\.]?
            (?P(a|b|c|rc|alpha|beta|pre|preview))
            [-_\.]?
            (?P[0-9]+)?
        )?
        (?P                                         # post release
            (?:-(?P[0-9]+))
            |
            (?:
                [-_\.]?
                (?Ppost|rev|r)
                [-_\.]?
                (?P[0-9]+)?
            )
        )?
        (?P                                          # dev release
            [-_\.]?
            (?Pdev)
            [-_\.]?
            (?P[0-9]+)?
        )?
    )
    (?:\+(?P[a-z0-9]+(?:[-_\.][a-z0-9]+)*))?       # local version
"""


class Version(_BaseVersion):

    _regex = re.compile(
        r"^\s*" + VERSION_PATTERN + r"\s*$",
        re.VERBOSE | re.IGNORECASE,
    )

    def __init__(self, version):
        # Validate the version and parse it into pieces
        match = self._regex.search(version)
        if not match:
            raise InvalidVersion("Invalid version: '{0}'".format(version))

        # Store the parsed out pieces of the version
        self._version = _Version(
            epoch=int(match.group("epoch")) if match.group("epoch") else 0,
            release=tuple(int(i) for i in match.group("release").split(".")),
            pre=_parse_letter_version(
                match.group("pre_l"),
                match.group("pre_n"),
            ),
            post=_parse_letter_version(
                match.group("post_l"),
                match.group("post_n1") or match.group("post_n2"),
            ),
            dev=_parse_letter_version(
                match.group("dev_l"),
                match.group("dev_n"),
            ),
            local=_parse_local_version(match.group("local")),
        )

        # Generate a key which will be used for sorting
        self._key = _cmpkey(
            self._version.epoch,
            self._version.release,
            self._version.pre,
            self._version.post,
            self._version.dev,
            self._version.local,
        )

    def __repr__(self):
        return "".format(repr(str(self)))

    def __str__(self):
        parts = []

        # Epoch
        if self._version.epoch != 0:
            parts.append("{0}!".format(self._version.epoch))

        # Release segment
        parts.append(".".join(str(x) for x in self._version.release))

        # Pre-release
        if self._version.pre is not None:
            parts.append("".join(str(x) for x in self._version.pre))

        # Post-release
        if self._version.post is not None:
            parts.append(".post{0}".format(self._version.post[1]))

        # Development release
        if self._version.dev is not None:
            parts.append(".dev{0}".format(self._version.dev[1]))

        # Local version segment
        if self._version.local is not None:
            parts.append(
                "+{0}".format(".".join(str(x) for x in self._version.local))
            )

        return "".join(parts)

    @property
    def public(self):
        return str(self).split("+", 1)[0]

    @property
    def base_version(self):
        parts = []

        # Epoch
        if self._version.epoch != 0:
            parts.append("{0}!".format(self._version.epoch))

        # Release segment
        parts.append(".".join(str(x) for x in self._version.release))

        return "".join(parts)

    @property
    def local(self):
        version_string = str(self)
        if "+" in version_string:
            return version_string.split("+", 1)[1]

    @property
    def is_prerelease(self):
        return bool(self._version.dev or self._version.pre)

    @property
    def is_postrelease(self):
        return bool(self._version.post)


def _parse_letter_version(letter, number):
    if letter:
        # We consider there to be an implicit 0 in a pre-release if there is
        # not a numeral associated with it.
        if number is None:
            number = 0

        # We normalize any letters to their lower case form
        letter = letter.lower()

        # We consider some words to be alternate spellings of other words and
        # in those cases we want to normalize the spellings to our preferred
        # spelling.
        if letter == "alpha":
            letter = "a"
        elif letter == "beta":
            letter = "b"
        elif letter in ["c", "pre", "preview"]:
            letter = "rc"
        elif letter in ["rev", "r"]:
            letter = "post"

        return letter, int(number)
    if not letter and number:
        # We assume if we are given a number, but we are not given a letter
        # then this is using the implicit post release syntax (e.g. 1.0-1)
        letter = "post"

        return letter, int(number)


_local_version_seperators = re.compile(r"[\._-]")


def _parse_local_version(local):
    """
    Takes a string like abc.1.twelve and turns it into ("abc", 1, "twelve").
    """
    if local is not None:
        return tuple(
            part.lower() if not part.isdigit() else int(part)
            for part in _local_version_seperators.split(local)
        )


def _cmpkey(epoch, release, pre, post, dev, local):
    # When we compare a release version, we want to compare it with all of the
    # trailing zeros removed. So we'll use a reverse the list, drop all the now
    # leading zeros until we come to something non zero, then take the rest
    # re-reverse it back into the correct order and make it a tuple and use
    # that for our sorting key.
    release = tuple(
        reversed(list(
            itertools.dropwhile(
                lambda x: x == 0,
                reversed(release),
            )
        ))
    )

    # We need to "trick" the sorting algorithm to put 1.0.dev0 before 1.0a0.
    # We'll do this by abusing the pre segment, but we _only_ want to do this
    # if there is not a pre or a post segment. If we have one of those then
    # the normal sorting rules will handle this case correctly.
    if pre is None and post is None and dev is not None:
        pre = -Infinity
    # Versions without a pre-release (except as noted above) should sort after
    # those with one.
    elif pre is None:
        pre = Infinity

    # Versions without a post segment should sort before those with one.
    if post is None:
        post = -Infinity

    # Versions without a development segment should sort after those with one.
    if dev is None:
        dev = Infinity

    if local is None:
        # Versions without a local segment should sort before those with one.
        local = -Infinity
    else:
        # Versions with a local segment need that segment parsed to implement
        # the sorting rules in PEP440.
        # - Alpha numeric segments sort before numeric segments
        # - Alpha numeric segments sort lexicographically
        # - Numeric segments sort numerically
        # - Shorter versions sort before longer versions when the prefixes
        #   match exactly
        local = tuple(
            (i, "") if isinstance(i, int) else (-Infinity, i)
            for i in local
        )

    return epoch, release, pre, post, dev, local