git-sorthist

#!/bin/sh

#/***************************************************************************
# *   Copyright (C) 2016-2023 Daniel Mueller (deso@posteo.net)              *
# *                                                                         *
# *   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 3 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, see <http://www.gnu.org/licenses/>. *
# ***************************************************************************/

set -u -o pipefail

if [ ${#} -ne 1 ]; then
  echo "Usage: $(basename ${0}) <sha1>"
  exit 1
fi

# We need a temporary file for our purposes.
file="$(mktemp)"

# Now, put all the dates of commits in the current branch that we want
# to rebase into this file, in a sorted fashion.
git log --date=iso --format=format:'%ad' ${1}..HEAD | sort > "${file}"

if [ ${?} -ne 0 ]; then
  echo "git log failed"
  rm -f "${file}"
  exit 1
fi

# Last we get to the real fun. Rebase everything, adjust the author
# date using the first date in the temporary file. Afterwards, remove
# this very date.
cmd=" \
  date=\"\$(head -n1 ${file} | tr -d '\n')\"; \
  GIT_AUTHOR_DATE=\"\${date}\" \
    GIT_COMMITTER_DATE=\"\${date}\" \
    GPG_SIGNATURE_TIMESTAMP=\$(date --date=\"\${date}\" +'%s') \
    git commit --amend --reuse-message=HEAD --date=\"\${date}\"; \
  sed -i '1d' \"${file}\" \
"
git rebase --interactive --keep-empty --exec="${cmd}" ${1}

if [ ${?} -eq 0 ]; then
  # The file should be empty.
  if [ ! -z "$(cat ${file})" ]; then
    echo "${file} not empty; error in script"
    exit 1
  else
    rm -f "${file}"
  fi
else
  rm -f "${file}"
fi