#!/bin/bash
#
# backport-change - Given a master git commit or trunk SVN revision, creates
# a backport request in Gerrit.
#
# $Id$
#
# Copyright 2013 Gerald Combs
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
#

# A more complete and likely more robust workflow can be found at
# http://www.mediawiki.org/wiki/Gerrit/Advanced_usage#Submitting_a_change_to_a_branch_for_review_.28.22backporting.22.29

export GIT_PAGER=""
TOOLS_DIR=`dirname $0`
COMMIT_MSG_HOOK=`git rev-parse --git-dir`/hooks/commit-msg

function exit_err
{
    if [ -n "$*" ] ; then
        echo -e "Error: $*\n"
    fi
    echo "Usage:"
    echo `basename $0` "<svn revision|git sha>"
    echo "SVN revisions MUST be prefixed with \"r\""
    exit 1
}

# Check if pbcopy (or similar) is available...
if [ `builtin type -p pbcopy` ] ; then
    PBCOPY="pbcopy"
fi

if [ `builtin type -p xsel` ]  ; then
    PBCOPY="xsel --clipboard --input"
fi

if [ `builtin type -p putclip` ]  ; then
    PBCOPY="putclip"
fi

#
# Make sure we have a destination
#

git ls-remote --heads gerrit &> /dev/null
if [ $? -ne 0 ] ; then exit_err "Can't find a remote named \"gerrit\"" ; fi

#
# Make sure our working directory is clean
#

git diff --quiet HEAD || exit_err "You have changes in your working directory. Please clean them up."

#
# Find our change
#

CHANGE="$1"
LONG_HASH=""

if [ -z "$CHANGE" ] ; then exit_err ; fi

if [[ $CHANGE = r* ]] ; then
    # Subversion
    SVN_REV=${CHANGE:1}
    LONG_HASH=`git log master --grep "svn path=/trunk/; revision=${SVN_REV}\$" -1 --format=format:%H`
    if [ -z "$LONG_HASH" ] ; then exit_err "Can't find SVN revision $CHANGE" ; fi
else
    # Git
    LONG_HASH=`git rev-parse $CHANGE`
    if [ -z "$LONG_HASH" ] ; then exit_err "Can't find git commit $CHANGE" ; fi
fi

#
# Make sure our upstream is valid
#

UPSTREAM_NAME=`git rev-parse --abbrev-ref --symbolic-full-name @{upstream}`
UPSTREAM_NAME=`basename $UPSTREAM_NAME`

if [ $? -ne 0 -o -z "$UPSTREAM_NAME" ] ; then exit_err "Can't find upstream branch." ; fi

if [[ $UPSTREAM_NAME != master-[0-9].[0-9]* ]] ; then
    exit_err "Can't backport to remote branch $UPSTREAM_NAME."
fi

PUSH_CMD="git push gerrit HEAD:refs/for/$UPSTREAM_NAME"

#
# On with the show
#

echo "Backporting $LONG_HASH"
git cherry-pick -x --strategy=recursive -Xtheirs $LONG_HASH

if [ $? -eq 0 ] ; then
    echo "Running diff"
    git diff
    
    # XXX We might want to install Gerrit's commit-msg hook instead, e.g.
    # scp -p -P 29418 <user>@code.wireshark.org:hooks/commit-msg .git/hooks/

    echo
    echo "Attempting push to gerrit HEAD:refs/for/$UPSTREAM_NAME"
    $PUSH_CMD

    if [ $? -ne 0 ] ; then
        # XXX - We might want to check for the commit-msg hook and if it's
        # present run git revert + git commit as described at
        # http://code.google.com/p/gerrit/issues/detail?id=843#c4
        cat <<FIN

Push failed. If the server is complaining about a missing change id
copy it and run

  git commit --amend
  # Insert the change id in your editor
  $PUSH_CMD
FIN
    fi
fi

#
# Editor modelines  -  http://www.wireshark.org/tools/modelines.html
#
# Local variables:
# c-basic-offset: 4
# tab-width: 8
# indent-tabs-mode: nil
# End:
#
# vi: set shiftwidth=4 tabstop=8 expandtab:
# :indentSize=4:tabSize=8:noTabs=true:
#