# Copyright (C) 2015 - Mike Edgar <adgar@google.com>

#

# This extension enables removal of file content at a given revision,

# rewriting the data/metadata of successive revisions to preserve revision log

# integrity.

"""erase file content at a given revision

The censor command instructs Mercurial to erase all content of a file at a given

revision *without updating the changeset hash.* This allows existing history to

remain valid while preventing future clones/pulls from receiving the erased

data.

Typical uses for censor are due to security or legal requirements, including::

 * Passwords, private keys, crytographic material

 * Licensed data/code/libraries for which the license has expired

 * Personally Identifiable Information or other private data

Censored nodes can interrupt mercurial's typical operation whenever the excised

data needs to be materialized. Some commands, like ``hg cat``/``hg revert``,

simply fail when asked to produce censored data. Others, like ``hg verify`` and

``hg update``, must be capable of tolerating censored data to continue to

function in a meaningful way. Such commands only tolerate censored file

revisions if they are allowed by the policy specified by the "censor.allow"

config option.

"""

from mercurial.node import short

from mercurial import cmdutil, error, filelog, revlog, scmutil, util

from mercurial.i18n import _

cmdtable = {}

command = cmdutil.command(cmdtable)

testedwith = 'internal'

@command('censor',

    [('r', 'rev', '', _('censor file from specified revision'), _('REV')),

     ('t', 'tombstone', '', _('replacement tombstone data'), _('TEXT'))],

    _('-r REV [-t TEXT] [FILE]'))

def censor(ui, repo, path, rev='', tombstone='', **opts):

    if not path:

        raise util.Abort(_('must specify file path to censor'))

    if not rev:

        raise util.Abort(_('must specify revision to censor'))

    flog = repo.file(path)

    if not len(flog):

        raise util.Abort(_('cannot censor file with no history'))

    rev = scmutil.revsingle(repo, rev, rev).rev()

    try:

        ctx = repo[rev]

    except KeyError:

        raise util.Abort(_('invalid revision identifier %s') % rev)

    try:

        fctx = ctx.filectx(path)

    except error.LookupError:

        raise util.Abort(_('file does not exist at revision %s') % rev)

    fnode = fctx.filenode()

    headctxs = [repo[c] for c in repo.heads()]

    heads = [c for c in headctxs if path in c and c.filenode(path) == fnode]

    if heads:

        headlist = ', '.join([short(c.node()) for c in heads])

        raise util.Abort(_('cannot censor file in heads (%s)') % headlist,

            hint=_('clean/delete and commit first'))

    wctx = repo[None]

    wp = wctx.parents()

    if ctx.node() in [p.node() for p in wp]:

        raise util.Abort(_('cannot censor working directory'),

            hint=_('clean/delete/update first'))

    flogv = flog.version & 0xFFFF

    if flogv != revlog.REVLOGNG:

        raise util.Abort(

            _('censor does not support revlog version %d') % (flogv,))

    tombstone = filelog.packmeta({"censored": tombstone}, "")

    crev = fctx.filerev()

    if len(tombstone) > flog.rawsize(crev):

        raise util.Abort(_(

            'censor tombstone must be no longer than censored data'))

    # Using two files instead of one makes it easy to rewrite entry-by-entry

    idxread = repo.svfs(flog.indexfile, 'r')

    idxwrite = repo.svfs(flog.indexfile, 'wb', atomictemp=True)

    if flog.version & revlog.REVLOGNGINLINEDATA:

        dataread, datawrite = idxread, idxwrite

    else:

        dataread = repo.svfs(flog.datafile, 'r')

        datawrite = repo.svfs(flog.datafile, 'wb', atomictemp=True)

    # Copy all revlog data up to the entry to be censored.

    rio = revlog.revlogio()

    offset = flog.start(crev)

    for chunk in util.filechunkiter(idxread, limit=crev * rio.size):

        idxwrite.write(chunk)

    for chunk in util.filechunkiter(dataread, limit=offset):

        datawrite.write(chunk)

    def rewriteindex(r, newoffs, newdata=None):

        """Rewrite the index entry with a new data offset and optional new data.

        The newdata argument, if given, is a tuple of three positive integers:

        (new compressed, new uncompressed, added flag bits).

        """

        offlags, comp, uncomp, base, link, p1, p2, nodeid = flog.index[r]

        flags = revlog.gettype(offlags)

        if newdata:

            comp, uncomp, nflags = newdata

            flags |= nflags

        offlags = revlog.offset_type(newoffs, flags)

        e = (offlags, comp, uncomp, r, link, p1, p2, nodeid)

        idxwrite.write(rio.packentry(e, None, flog.version, r))

        idxread.seek(rio.size, 1)

    def rewrite(r, offs, data, nflags=revlog.REVIDX_DEFAULT_FLAGS):

        """Write the given full text to the filelog with the given data offset.

        Returns:

            The integer number of data bytes written, for tracking data offsets.

        """

        flag, compdata = flog.compress(data)

        newcomp = len(flag) + len(compdata)

        rewriteindex(r, offs, (newcomp, len(data), nflags))

        datawrite.write(flag)

        datawrite.write(compdata)

        dataread.seek(flog.length(r), 1)

        return newcomp

    # Rewrite censored revlog entry with (padded) tombstone data.

    pad = ' ' * (flog.rawsize(crev) - len(tombstone))

    offset += rewrite(crev, offset, tombstone + pad, revlog.REVIDX_ISCENSORED)

    # Rewrite all following filelog revisions fixing up offsets and deltas.

    for srev in xrange(crev + 1, len(flog)):

        if crev in flog.parentrevs(srev):

            # Immediate children of censored node must be re-added as fulltext.

            try:

                revdata = flog.revision(srev)

            except error.CensoredNodeError, e:

                revdata = e.tombstone

            dlen = rewrite(srev, offset, revdata)

        else:

            # Copy any other revision data verbatim after fixing up the offset.

            rewriteindex(srev, offset)

            dlen = flog.length(srev)

            for chunk in util.filechunkiter(dataread, limit=dlen):

                datawrite.write(chunk)

        offset += dlen

    idxread.close()

    idxwrite.close()

    if dataread is not idxread:

        dataread.close()

        datawrite.close()