# Copyright 2016-present Facebook. All Rights Reserved.

#

# revmap: trivial hg hash - linelog rev bidirectional map

#

# 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 bisect

import io

import os

import struct

from mercurial.node import hex

from mercurial import (

    error as hgerror,

    pycompat,

)

from . import error

# the revmap file format is straightforward:

#

#    8 bytes: header

#    1 byte : flag for linelog revision 1

#    ? bytes: (optional) '\0'-terminated path string

#             only exists if (flag & renameflag) != 0

#   20 bytes: hg hash for linelog revision 1

#    1 byte : flag for linelog revision 2

#    ? bytes: (optional) '\0'-terminated path string

#   20 bytes: hg hash for linelog revision 2

#   ....

#

# the implementation is kinda stupid: __init__ loads the whole revmap.

# no laziness. benchmark shows loading 10000 revisions is about 0.015

# seconds, which looks enough for our use-case. if this implementation

# becomes a bottleneck, we can change it to lazily read the file

# from the end.

# whether the changeset is in the side branch. i.e. not in the linear main

# branch but only got referenced by lines in merge changesets.

sidebranchflag = 1

# whether the changeset changes the file path (ie. is a rename)

renameflag = 2

# len(mercurial.node.nullid)

_hshlen = 20

class revmap(object):

    """trivial hg bin hash - linelog rev bidirectional map

    also stores a flag (uint8) for each revision, and track renames.

    """

    HEADER = b'REVMAP1\0'

    def __init__(self, path=None):

        """create or load the revmap, optionally associate to a file

        if path is None, the revmap is entirely in-memory. the caller is

        responsible for locking. concurrent writes to a same file is unsafe.

        the caller needs to make sure one file is associated to at most one

        revmap object at a time."""

        self.path = path

        self._rev2hsh = [None]

        self._rev2flag = [None]

        self._hsh2rev = {}

        # since rename does not happen frequently, do not store path for every

        # revision. self._renamerevs can be used for bisecting.

        self._renamerevs = [0]

        self._renamepaths = ['']

        self._lastmaxrev = -1

        if path:

            if os.path.exists(path):

                self._load()

            else:

                # write the header so "append" can do incremental updates

                self.flush()

    def copyfrom(self, rhs):

        """copy the map data from another revmap. do not affect self.path"""

        self._rev2hsh = rhs._rev2hsh[:]

        self._rev2flag = rhs._rev2flag[:]

        self._hsh2rev = rhs._hsh2rev.copy()

        self._renamerevs = rhs._renamerevs[:]

        self._renamepaths = rhs._renamepaths[:]

        self._lastmaxrev = -1

    @property

    def maxrev(self):

        """return max linelog revision number"""

        return len(self._rev2hsh) - 1

    def append(self, hsh, sidebranch=False, path=None, flush=False):

        """add a binary hg hash and return the mapped linelog revision.

        if flush is True, incrementally update the file.

        """

        if hsh in self._hsh2rev:

            raise error.CorruptedFileError('%r is in revmap already' % hex(hsh))

        if len(hsh) != _hshlen:

            raise hgerror.ProgrammingError('hsh must be %d-char long' % _hshlen)

        idx = len(self._rev2hsh)

        flag = 0

        if sidebranch:

            flag |= sidebranchflag

        if path is not None and path != self._renamepaths[-1]:

            flag |= renameflag

            self._renamerevs.append(idx)

            self._renamepaths.append(path)

        self._rev2hsh.append(hsh)

        self._rev2flag.append(flag)

        self._hsh2rev[hsh] = idx

        if flush:

            self.flush()

        return idx

    def rev2hsh(self, rev):

        """convert linelog revision to hg hash. return None if not found."""

        if rev > self.maxrev or rev < 0:

            return None

        return self._rev2hsh[rev]

    def rev2flag(self, rev):

        """get the flag (uint8) for a given linelog revision.

        return None if revision does not exist.

        """

        if rev > self.maxrev or rev < 0:

            return None

        return self._rev2flag[rev]

    def rev2path(self, rev):

        """get the path for a given linelog revision.

        return None if revision does not exist.

        """

        if rev > self.maxrev or rev < 0:

            return None

        idx = bisect.bisect_right(self._renamerevs, rev) - 1

        return self._renamepaths[idx]

    def hsh2rev(self, hsh):

        """convert hg hash to linelog revision. return None if not found."""

        return self._hsh2rev.get(hsh)

    def clear(self, flush=False):

        """make the map empty. if flush is True, write to disk"""

        # rev 0 is reserved, real rev starts from 1

        self._rev2hsh = [None]

        self._rev2flag = [None]

        self._hsh2rev = {}

        self._rev2path = ['']

        self._lastmaxrev = -1

        if flush:

            self.flush()

    def flush(self):

        """write the state down to the file"""

        if not self.path:

            return

        if self._lastmaxrev == -1: # write the entire file

            with open(self.path, 'wb') as f:

                f.write(self.HEADER)

                for i in pycompat.xrange(1, len(self._rev2hsh)):

                    self._writerev(i, f)

        else: # append incrementally

            with open(self.path, 'ab') as f:

                for i in pycompat.xrange(self._lastmaxrev + 1,

                                         len(self._rev2hsh)):

                    self._writerev(i, f)

        self._lastmaxrev = self.maxrev

    def _load(self):

        """load state from file"""

        if not self.path:

            return

        # use local variables in a loop. CPython uses LOAD_FAST for them,

        # which is faster than both LOAD_CONST and LOAD_GLOBAL.

        flaglen = 1

        hshlen = _hshlen

        with open(self.path, 'rb') as f:

            if f.read(len(self.HEADER)) != self.HEADER:

                raise error.CorruptedFileError()

            self.clear(flush=False)

            while True:

                buf = f.read(flaglen)

                if not buf:

                    break

                flag = ord(buf)

                rev = len(self._rev2hsh)

                if flag & renameflag:

                    path = self._readcstr(f)

                    self._renamerevs.append(rev)

                    self._renamepaths.append(path)

                hsh = f.read(hshlen)

                if len(hsh) != hshlen:

                    raise error.CorruptedFileError()

                self._hsh2rev[hsh] = rev

                self._rev2flag.append(flag)

                self._rev2hsh.append(hsh)

        self._lastmaxrev = self.maxrev

    def _writerev(self, rev, f):

        """append a revision data to file"""

        flag = self._rev2flag[rev]

        hsh = self._rev2hsh[rev]

        f.write(struct.pack('B', flag))

        if flag & renameflag:

            path = self.rev2path(rev)

            if path is None:

                raise error.CorruptedFileError('cannot find path for %s' % rev)

            f.write(path + b'\0')

        f.write(hsh)

    @staticmethod

    def _readcstr(f):

        """read a C-language-like '\0'-terminated string"""

        buf = ''

        while True:

            ch = f.read(1)

            if not ch: # unexpected eof

                raise error.CorruptedFileError()

            if ch == '\0':

                break

            buf += ch

        return buf

    def __contains__(self, f):

        """(fctx or (node, path)) -> bool.

        test if (node, path) is in the map, and is not in a side branch.

        f can be either a tuple of (node, path), or a fctx.

        """

        if isinstance(f, tuple): # f: (node, path)

            hsh, path = f

        else: # f: fctx

            hsh, path = f.node(), f.path()

        rev = self.hsh2rev(hsh)

        if rev is None:

            return False

        if path is not None and path != self.rev2path(rev):

            return False

        return (self.rev2flag(rev) & sidebranchflag) == 0

def getlastnode(path):

    """return the last hash in a revmap, without loading its full content.

    this is equivalent to `m = revmap(path); m.rev2hsh(m.maxrev)`, but faster.

    """

    hsh = None

    try:

        with open(path, 'rb') as f:

            f.seek(-_hshlen, io.SEEK_END)

            if f.tell() > len(revmap.HEADER):

                hsh = f.read(_hshlen)

    except IOError:

        pass

    return hsh