# 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

import struct

from ..i18n import _

from ..node import (

    bin,

    nullid,

    nullrev,

)

from .. import (

    dagop,

    error,

    mdiff,

    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('%d' % 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

def emitrevisions(store, nodes, nodesorder, resultcls, deltaparentfn=None,

                  candeltafn=None, rawsizefn=None, revdifffn=None, flagsfn=None,

                  sendfulltext=False,

                  revisiondata=False, assumehaveparentrevisions=False,

                  deltaprevious=False):

    """Generic implementation of ifiledata.emitrevisions().

    Emitting revision data is subtly complex. This function attempts to

    encapsulate all the logic for doing so in a backend-agnostic way.

    ``store``

       Object conforming to ``ifilestorage`` interface.

    ``nodes``

       List of revision nodes whose data to emit.

    ``resultcls``

       A type implementing the ``irevisiondelta`` interface that will be

       constructed and returned.

    ``deltaparentfn`` (optional)

       Callable receiving a revision number and returning the revision number

       of a revision that the internal delta is stored against. This delta

       will be preferred over computing a new arbitrary delta.

       If not defined, a delta will always be computed from raw revision

       data.

    ``candeltafn`` (optional)

       Callable receiving a pair of revision numbers that returns a bool

       indicating whether a delta between them can be produced.

       If not defined, it is assumed that any two revisions can delta with

       each other.

    ``rawsizefn`` (optional)

       Callable receiving a revision number and returning the length of the

       ``store.revision(rev, raw=True)``.

       If not defined, ``len(store.revision(rev, raw=True))`` will be called.

    ``revdifffn`` (optional)

       Callable receiving a pair of revision numbers that returns a delta

       between them.

       If not defined, a delta will be computed by invoking mdiff code

       on ``store.revision()`` results.

       Defining this function allows a precomputed or stored delta to be

       used without having to compute on.

    ``flagsfn`` (optional)

       Callable receiving a revision number and returns the integer flags

       value for it. If not defined, flags value will be 0.

    ``sendfulltext``

       Whether to send fulltext revisions instead of deltas, if allowed.

    ``nodesorder``

    ``revisiondata``

    ``assumehaveparentrevisions``

    ``deltaprevious``

       See ``ifiledata.emitrevisions()`` interface documentation.

    """

    fnode = store.node

    frev = store.rev

    if nodesorder == 'nodes':

        revs = [frev(n) for n in nodes]

        revs = set(frev(n) for n in nodes)

        revs = dagop.linearize(revs, store.parentrevs)

    prevrev = None

    if deltaprevious or assumehaveparentrevisions:

        prevrev = store.parentrevs(revs[0])[0]

    # Set of revs available to delta against.

    available = set()

    for rev in revs:

        if rev == nullrev:

            continue

        node = fnode(rev)

        p1rev, p2rev = store.parentrevs(rev)

        if deltaparentfn:

            deltaparentrev = deltaparentfn(rev)

        else:

            deltaparentrev = nullrev

        # Forced delta against previous mode.

        if deltaprevious:

            baserev = prevrev

        # We're instructed to send fulltext. Honor that.

        elif sendfulltext:

            baserev = nullrev

        # There is a delta in storage. We try to use that because it

        # amounts to effectively copying data from storage and is

        # therefore the fastest.

        elif deltaparentrev != nullrev:

            # Base revision was already emitted in this group. We can

            # always safely use the delta.

            if deltaparentrev in available:

                baserev = deltaparentrev

            # Base revision is a parent that hasn't been emitted already.

            # Use it if we can assume the receiver has the parent revision.

            elif (assumehaveparentrevisions

                  and deltaparentrev in (p1rev, p2rev)):

                baserev = deltaparentrev

            # No guarantee the receiver has the delta parent. Send delta

            # against last revision (if possible), which in the common case

            # should be similar enough to this revision that the delta is

            # reasonable.

            elif prevrev is not None:

                baserev = prevrev

            else:

                baserev = nullrev

        # Storage has a fulltext revision.

        # Let's use the previous revision, which is as good a guess as any.

        # There is definitely room to improve this logic.

        elif prevrev is not None:

            baserev = prevrev

        else:

            baserev = nullrev

        # But we can't actually use our chosen delta base for whatever

        # reason. Reset to fulltext.

        if baserev != nullrev and (candeltafn and not candeltafn(baserev, rev)):

            baserev = nullrev

        revision = None

        delta = None

        baserevisionsize = None

        if revisiondata:

            if store.iscensored(baserev) or store.iscensored(rev):

                try:

                    revision = store.revision(node, raw=True)

                except error.CensoredNodeError as e:

                    revision = e.tombstone

                if baserev != nullrev:

                    if rawsizefn:

                        baserevisionsize = rawsizefn(baserev)

                    else:

                        baserevisionsize = len(store.revision(baserev,

                                                              raw=True))

            elif baserev == nullrev and not deltaprevious:

                revision = store.revision(node, raw=True)

                available.add(rev)

            else:

                if revdifffn:

                    delta = revdifffn(baserev, rev)

                else:

                    delta = mdiff.textdiff(store.revision(baserev, raw=True),

                                           store.revision(rev, raw=True))

                available.add(rev)

        yield resultcls(

            node=node,

            p1node=fnode(p1rev),

            p2node=fnode(p2rev),

            basenode=fnode(baserev),

            flags=flagsfn(rev) if flagsfn else 0,

            baserevisionsize=baserevisionsize,

            revision=revision,

            delta=delta)

        prevrev = rev

def deltaiscensored(delta, baserev, baselenfn):

    """Determine if a delta represents censored revision data.

    ``baserev`` is the base revision this delta is encoded against.

    ``baselenfn`` is a callable receiving a revision number that resolves the

    length of the revision fulltext.

    Returns a bool indicating if the result of the delta represents a censored

    revision.

    """

    # Fragile heuristic: unless new file meta keys are added alphabetically

    # preceding "censored", all censored revisions are prefixed by

    # "\1\ncensored:". A delta producing such a censored revision must be a

    # full-replacement delta, so we inspect the first and only patch in the

    # delta for this prefix.

    hlen = struct.calcsize(">lll")

    if len(delta) <= hlen:

        return False

    oldlen = baselenfn(baserev)

    newlen = len(delta) - hlen

    if delta[:hlen] != mdiff.replacediffheader(oldlen, newlen):

        return False

    add = "\1\ncensored:"

    addlen = len(add)

    return newlen >= addlen and delta[hlen:hlen + addlen] == add