# rev_cache.py - caching branch information per revision

#

# 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 annotations

import os

import struct

from ..node import (

    nullrev,

)

from .. import (

    encoding,

    error,

    util,

)

from ..utils import (

    stringutil,

)

calcsize = struct.calcsize

pack_into = struct.pack_into

unpack_from = struct.unpack_from

# Revision branch info cache

_rbcnames = b'rbc-names' + _rbcversion

_rbcrevs = b'rbc-revs' + _rbcversion

# [4 byte hash prefix][4 byte branch name number with sign bit indicating open]

_rbcrecfmt = b'>4sI'

_rbcrecsize = calcsize(_rbcrecfmt)

_rbcmininc = 64 * _rbcrecsize

_rbcnodelen = 4

_rbcbranchidxmask = 0x7FFFFFFF

_rbccloseflag = 0x80000000

# with atomic replacement.

REWRITE_RATIO = 0.2

class rbcrevs:

    """a byte string consisting of an immutable prefix followed by a mutable suffix"""

    def __init__(self, revs):

        self._prefix = revs

        self._rest = bytearray()

    def __len__(self):

        return len(self._prefix) + len(self._rest)

    def unpack_record(self, rbcrevidx):

        if rbcrevidx < len(self._prefix):

            return unpack_from(_rbcrecfmt, util.buffer(self._prefix), rbcrevidx)

        else:

            return unpack_from(

                _rbcrecfmt,

                util.buffer(self._rest),

                rbcrevidx - len(self._prefix),

            )

    def make_mutable(self):

        if len(self._prefix) > 0:

            entirety = bytearray()

            entirety[:] = self._prefix

            entirety.extend(self._rest)

            self._rest = entirety

            self._prefix = bytearray()

    def truncate(self, pos):

        self.make_mutable()

        del self._rest[pos:]

    def pack_into(self, rbcrevidx, node, branchidx):

        if rbcrevidx < len(self._prefix):

            self.make_mutable()

        buf = self._rest

        start_offset = rbcrevidx - len(self._prefix)

        end_offset = start_offset + _rbcrecsize

        if len(self._rest) < end_offset:

            # bytearray doesn't allocate extra space at least in Python 3.7.

            # When multiple changesets are added in a row, precise resize would

            # result in quadratic complexity. Overallocate to compensate by

            # using the classic doubling technique for dynamic arrays instead.

            # If there was a gap in the map before, less space will be reserved.

            self._rest.extend(b'\0' * end_offset)

        return pack_into(

            _rbcrecfmt,

            buf,

            start_offset,

            node,

            branchidx,

        )

    def extend(self, extension):

        return self._rest.extend(extension)

    def slice(self, begin, end):

        if begin < len(self._prefix):

            acc = bytearray()

            acc[:] = self._prefix[begin:end]

            acc.extend(

                self._rest[begin - len(self._prefix) : end - len(self._prefix)]

            )

            return acc

        return self._rest[begin - len(self._prefix) : end - len(self._prefix)]

class revbranchcache:

    """Persistent cache, mapping from revision number to branch name and close.

    This is a low level cache, independent of filtering.

    Branch names are stored in rbc-names in internal encoding separated by 0.

    rbc-names is append-only, and each branch name is only stored once and will

    thus have a unique index.

    The branch info for each revision is stored in rbc-revs as constant size

    records. The whole file is read into memory, but it is only 'parsed' on

    demand. The file is usually append-only but will be truncated if repo

    modification is detected.

    The record for each revision contains the first 4 bytes of the

    corresponding node hash, and the record is only used if it still matches.

    Even a completely trashed rbc-revs fill thus still give the right result

    while converging towards full recovery ... assuming no incorrectly matching

    node hashes.

    The record also contains 4 bytes where 31 bits contains the index of the

    branch and the last bit indicate that it is a branch close commit.

    The usage pattern for rbc-revs is thus somewhat similar to 00changelog.i

    and will grow with it but be 1/8th of its size.

    """

    def __init__(self, repo, readonly=True):

        assert repo.filtername is None

        self._repo = repo

        self._names = []  # branch names in local encoding with static index

        self._rbcrevs = rbcrevs(bytearray())

        self._rbcsnameslen = 0  # length of names read at _rbcsnameslen

        try:

            bndata = repo.cachevfs.read(_rbcnames)

            self._rbcsnameslen = len(bndata)  # for verification before writing

            if bndata:

                self._names = [

                    encoding.tolocal(bn) for bn in bndata.split(b'\0')

                ]

        except (IOError, OSError):

            if readonly:

                # don't try to use cache - fall back to the slow path

                self.branchinfo = self._branchinfo

        if self._names:

            try:

                usemmap = repo.ui.configbool(b'storage', b'revbranchcache.mmap')

                with repo.cachevfs(_rbcrevs) as fp:

                    if usemmap and repo.cachevfs.is_mmap_safe(_rbcrevs):

                        data = util.buffer(util.mmapread(fp))

                    else:

                        data = fp.read()

                self._rbcrevs = rbcrevs(data)

            except (IOError, OSError) as inst:

                repo.ui.debug(

                    b"couldn't read revision branch cache: %s\n"

                    % stringutil.forcebytestr(inst)

                )

        # remember number of good records on disk

        self._rbcrevslen = min(

            len(self._rbcrevs) // _rbcrecsize, len(repo.changelog)

        )

        if self._rbcrevslen == 0:

            self._names = []

        self._rbcnamescount = len(self._names)  # number of names read at

        # _rbcsnameslen

        self._force_overwrite = False

    def _clear(self):

        self._rbcsnameslen = 0

        del self._names[:]

        self._rbcnamescount = 0

        self._rbcrevslen = len(self._repo.changelog)

        self._rbcrevs = rbcrevs(bytearray(self._rbcrevslen * _rbcrecsize))

        util.clearcachedproperty(self, b'_namesreverse')

        self._force_overwrite = True

    def invalidate(self, rev=0):

        self._rbcrevslen = rev

        self._rbcrevs.truncate(rev)

        self._force_overwrite = True

    @util.propertycache

    def _namesreverse(self):

        return {b: r for r, b in enumerate(self._names)}

    def branchinfo(self, rev):

        """Return branch name and close flag for rev, using and updating

        persistent cache."""

        changelog = self._repo.changelog

        rbcrevidx = rev * _rbcrecsize

        # avoid negative index, changelog.read(nullrev) is fast without cache

        if rev == nullrev:

            return changelog.branchinfo(rev)

        # if requested rev isn't allocated, grow and cache the rev info

        if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:

            return self._branchinfo(rev)

        # fast path: extract data from cache, use it if node is matching

        reponode = changelog.node(rev)[:_rbcnodelen]

        cachenode, branchidx = self._rbcrevs.unpack_record(rbcrevidx)

        close = bool(branchidx & _rbccloseflag)

        if close:

            branchidx &= _rbcbranchidxmask

        if cachenode == b'\0\0\0\0':

            pass

        elif cachenode == reponode:

            try:

                return self._names[branchidx], close

            except IndexError:

                # recover from invalid reference to unknown branch

                self._repo.ui.debug(

                    b"referenced branch names not found"

                    b" - rebuilding revision branch cache from scratch\n"

                )

                self._clear()

        else:

            # rev/node map has changed, invalidate the cache from here up

            self._repo.ui.debug(

                b"history modification detected - truncating "

                b"revision branch cache to revision %d\n" % rev

            )

            truncate = rbcrevidx + _rbcrecsize

            self._rbcrevs.truncate(truncate)

            self._rbcrevslen = min(self._rbcrevslen, truncate)

        # fall back to slow path and make sure it will be written to disk

        return self._branchinfo(rev)

    def _branchinfo(self, rev):

        """Retrieve branch info from changelog and update _rbcrevs"""

        changelog = self._repo.changelog

        b, close = changelog.branchinfo(rev)

        if b in self._namesreverse:

            branchidx = self._namesreverse[b]

        else:

            branchidx = len(self._names)

            self._names.append(b)

            self._namesreverse[b] = branchidx

        reponode = changelog.node(rev)

        if close:

            branchidx |= _rbccloseflag

        self._setcachedata(rev, reponode, branchidx)

        return b, close

    def setdata(self, rev, changelogrevision):

        """add new data information to the cache"""

        branch, close = changelogrevision.branchinfo

        if branch in self._namesreverse:

            branchidx = self._namesreverse[branch]

        else:

            branchidx = len(self._names)

            self._names.append(branch)

            self._namesreverse[branch] = branchidx

        if close:

            branchidx |= _rbccloseflag

        self._setcachedata(rev, self._repo.changelog.node(rev), branchidx)

        # If no cache data were readable (non exists, bad permission, etc)

        # the cache was bypassing itself by setting:

        #

        #   self.branchinfo = self._branchinfo

        #

        # Since we now have data in the cache, we need to drop this bypassing.

        if 'branchinfo' in vars(self):

            del self.branchinfo

    def _setcachedata(self, rev, node, branchidx):

        """Writes the node's branch data to the in-memory cache data."""

        if rev == nullrev:

            return

        rbcrevidx = rev * _rbcrecsize

        self._rbcrevs.pack_into(rbcrevidx, node, branchidx)

        self._rbcrevslen = min(self._rbcrevslen, rev)

        tr = self._repo.currenttransaction()

        if tr:

            tr.addfinalize(b'write-revbranchcache', self.write)

    def write(self, tr=None):

        """Save branch cache if it is dirty."""

        repo = self._repo

        wlock = None

        step = b''

        try:

            # write the new names

            if self._rbcnamescount < len(self._names):

                wlock = repo.wlock(wait=False)

                step = b' names'

                self._writenames(repo)

            # write the new revs

            start = self._rbcrevslen * _rbcrecsize

            if self._force_overwrite or start != len(self._rbcrevs):

                step = b''

                if wlock is None:

                    wlock = repo.wlock(wait=False)

                self._writerevs(repo, start)

        except (IOError, OSError, error.Abort, error.LockError) as inst:

            repo.ui.debug(

                b"couldn't write revision branch cache%s: %s\n"

                % (step, stringutil.forcebytestr(inst))

            )

        finally:

            if wlock is not None:

                wlock.release()

    def _writenames(self, repo):

        """write the new branch names to revbranchcache"""

        f = None

        try:

            if self._rbcnamescount != 0:

                f = repo.cachevfs.open(_rbcnames, b'ab')

                if f.tell() == self._rbcsnameslen:

                    f.write(b'\0')

                else:

                    f.close()

                    f = None

                    repo.ui.debug(b"%s changed - rewriting it\n" % _rbcnames)

                    self._rbcnamescount = 0

                    self._rbcrevslen = 0

            if self._rbcnamescount == 0:

                # before rewriting names, make sure references are removed

                repo.cachevfs.unlinkpath(_rbcrevs, ignoremissing=True)

                f = repo.cachevfs.open(_rbcnames, b'wb')

            names = self._names[self._rbcnamescount :]

            from_local = encoding.fromlocal

            data = b'\0'.join(from_local(b) for b in names)

            f.write(data)

            self._rbcsnameslen = f.tell()

        finally:

            if f is not None:

                f.close()

        self._rbcnamescount = len(self._names)

    def _writerevs(self, repo, start):

        """write the new revs to revbranchcache"""

        revs = min(len(repo.changelog), len(self._rbcrevs) // _rbcrecsize)

        end = revs * _rbcrecsize

        if self._force_overwrite:

            start = 0

        with repo.cachevfs.open(_rbcrevs, b'a+b') as f:

            pass  # this make sure the file exist…

        with repo.cachevfs.open(_rbcrevs, b'r+b') as f:

            f.seek(0, os.SEEK_END)

            current_size = f.tell()

            if current_size < start:

                start = 0

            if current_size != start:

                threshold = current_size * REWRITE_RATIO

                if (max(end, current_size) - start) < threshold:

                    # end affected, let overwrite the bad value

                    dbg = b"overwriting %d bytes from %d in cache/%s"

                    dbg %= (current_size - start, start, _rbcrevs)

                    if end < current_size:

                        extra = b" leaving (%d trailing bytes)"

                        extra %= current_size - end

                        dbg += extra

                    dbg += b'\n'

                    repo.ui.debug(dbg)

                else:

                    start = 0

                    dbg = b"resetting content of cache/%s\n" % _rbcrevs

                    repo.ui.debug(dbg)

            if start > 0:

                f.seek(start)

                f.write(self._rbcrevs.slice(start, end))

            else:

                f.close()

                with repo.cachevfs.open(

                    _rbcrevs,

                    b'wb',

                    atomictemp=True,

                ) as rev_file:

                    rev_file.write(self._rbcrevs.slice(start, end))

        self._rbcrevslen = revs

        self._force_overwrite = False