# storageutil.py - Storage functionality agnostic of backend implementation.

#

# Copyright 2018 Gregory Szorc <gregory.szorc@gmail.com>

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import hashlib

import re

from ..i18n import _

from ..node import (

    bin,

    nullid,

    nullrev,

)

from .. import (

    error,

    pycompat,

)

_nullhash = hashlib.sha1(nullid)

def hashrevisionsha1(text, p1, p2):

    """Compute the SHA-1 for revision data and its parents.

    This hash combines both the current file contents and its history

    in a manner that makes it easy to distinguish nodes with the same

    content in the revision graph.

    """

    # As of now, if one of the parent node is null, p2 is null

    if p2 == nullid:

        # deep copy of a hash is faster than creating one

        s = _nullhash.copy()

        s.update(p1)

    else:

        # none of the parent nodes are nullid

        if p1 < p2:

            a = p1

            b = p2

        else:

            a = p2

            b = p1

        s = hashlib.sha1(a)

        s.update(b)

    s.update(text)

    return s.digest()

METADATA_RE = re.compile(b'\x01\n')

def parsemeta(text):

    """Parse metadata header from revision data.

    Returns a 2-tuple of (metadata, offset), where both can be None if there

    is no metadata.

    """

    # text can be buffer, so we can't use .startswith or .index

    if text[:2] != b'\x01\n':

        return None, None

    s = METADATA_RE.search(text, 2).start()

    mtext = text[2:s]

    meta = {}

    for l in mtext.splitlines():

        k, v = l.split(b': ', 1)

        meta[k] = v

    return meta, s + 2

def packmeta(meta, text):

    """Add metadata to fulltext to produce revision text."""

    keys = sorted(meta)

    metatext = b''.join(b'%s: %s\n' % (k, meta[k]) for k in keys)

    return b'\x01\n%s\x01\n%s' % (metatext, text)

def iscensoredtext(text):

    meta = parsemeta(text)[0]

    return meta and b'censored' in meta

def filtermetadata(text):

    """Extract just the revision data from source text.

    Returns ``text`` unless it has a metadata header, in which case we return

    a new buffer without hte metadata.

    """

    if not text.startswith(b'\x01\n'):

        return text

    offset = text.index(b'\x01\n', 2)

    return text[offset + 2:]

def filerevisioncopied(store, node):

    """Resolve file revision copy metadata.

    Returns ``False`` if the file has no copy metadata. Otherwise a

    2-tuple of the source filename and node.

    """

    if store.parents(node)[0] != nullid:

        return False

    meta = parsemeta(store.revision(node))[0]

    # copy and copyrev occur in pairs. In rare cases due to old bugs,

    # one can occur without the other. So ensure both are present to flag

    # as a copy.

    if meta and b'copy' in meta and b'copyrev' in meta:

        return meta[b'copy'], bin(meta[b'copyrev'])

    return False

def filedataequivalent(store, node, filedata):

    """Determines whether file data is equivalent to a stored node.

    Returns True if the passed file data would hash to the same value

    as a stored revision and False otherwise.

    When a stored revision is censored, filedata must be empty to have

    equivalence.

    When a stored revision has copy metadata, it is ignored as part

    of the compare.

    """

    if filedata.startswith(b'\x01\n'):

        revisiontext = b'\x01\n\x01\n' + filedata

    else:

        revisiontext = filedata

    p1, p2 = store.parents(node)

    computednode = hashrevisionsha1(revisiontext, p1, p2)

    if computednode == node:

        return True

    # Censored files compare against the empty file.

    if store.iscensored(store.rev(node)):

        return filedata == b''

    # Renaming a file produces a different hash, even if the data

    # remains unchanged. Check if that's the case.

    if store.renamed(node):

        return store.read(node) == filedata

    return False

def iterrevs(storelen, start=0, stop=None):

    """Iterate over revision numbers in a store."""

    step = 1

    if stop is not None:

        if start > stop:

            step = -1

        stop += step

        if stop > storelen:

            stop = storelen

    else:

        stop = storelen

    return pycompat.xrange(start, stop, step)

def fileidlookup(store, fileid, identifier):

    """Resolve the file node for a value.

    ``store`` is an object implementing the ``ifileindex`` interface.

    ``fileid`` can be:

    * A 20 byte binary node.

    * An integer revision number

    * A 40 byte hex node.

    * A bytes that can be parsed as an integer representing a revision number.

    ``identifier`` is used to populate ``error.LookupError`` with an identifier

    for the store.

    Raises ``error.LookupError`` on failure.

    """

    if isinstance(fileid, int):

        try:

            return store.node(fileid)

        except IndexError:

            raise error.LookupError(fileid, identifier, _('no match found'))

    if len(fileid) == 20:

        try:

            store.rev(fileid)

            return fileid

        except error.LookupError:

            pass

    if len(fileid) == 40:

        try:

            rawnode = bin(fileid)

            store.rev(rawnode)

            return rawnode

        except TypeError:

            pass

    try:

        rev = int(fileid)

        if b'%d' % rev != fileid:

            raise ValueError

        try:

            return store.node(rev)

        except (IndexError, TypeError):

            pass

    except (ValueError, OverflowError):

        pass

    raise error.LookupError(fileid, identifier, _('no match found'))

def resolvestripinfo(minlinkrev, tiprev, headrevs, linkrevfn, parentrevsfn):

    """Resolve information needed to strip revisions.

    Finds the minimum revision number that must be stripped in order to

    strip ``minlinkrev``.

    Returns a 2-tuple of the minimum revision number to do that and a set

    of all revision numbers that have linkrevs that would be broken

    by that strip.

    ``tiprev`` is the current tip-most revision. It is ``len(store) - 1``.

    ``headrevs`` is an iterable of head revisions.

    ``linkrevfn`` is a callable that receives a revision and returns a linked

    revision.

    ``parentrevsfn`` is a callable that receives a revision number and returns

    an iterable of its parent revision numbers.

    """

    brokenrevs = set()

    strippoint = tiprev + 1

    heads = {}

    futurelargelinkrevs = set()

    for head in headrevs:

        headlinkrev = linkrevfn(head)

        heads[head] = headlinkrev

        if headlinkrev >= minlinkrev:

            futurelargelinkrevs.add(headlinkrev)

    # This algorithm involves walking down the rev graph, starting at the

    # heads. Since the revs are topologically sorted according to linkrev,

    # once all head linkrevs are below the minlink, we know there are

    # no more revs that could have a linkrev greater than minlink.

    # So we can stop walking.

    while futurelargelinkrevs:

        strippoint -= 1

        linkrev = heads.pop(strippoint)

        if linkrev < minlinkrev:

            brokenrevs.add(strippoint)

        else:

            futurelargelinkrevs.remove(linkrev)

        for p in parentrevsfn(strippoint):

            if p != nullrev:

                plinkrev = linkrevfn(p)

                heads[p] = plinkrev

                if plinkrev >= minlinkrev:

                    futurelargelinkrevs.add(plinkrev)

    return strippoint, brokenrevs