#!/bin/bash

function wait_count {
  local TIME=$1
  while [ ${TIME} -gt 0 ]; do
    echo Waiting ${TIME}
    sleep 1
    let TIME=${TIME}-1
  done
}


if [ $# -ne 1 -o "$1" = "-h" -o "$1" = "--help" ]; then
  echo "Usage: $(basename $0) <base branch>"
  echo
  echo "Example: $(basename $0) master"
  echo
  echo "This tool rebases the current branch one commit at a time to the base"
  echo "branch. Doing so instead of rebasing all at once makes sure the"
  echo "changes at each step are as small as possible. Smaller changes mean a"
  echo "(sometimes much) higher chance of getting away without conflict. It"
  echo "also means that upcoming conflicts are as small as possible."
  echo
  echo "The tool stops as soon as a conflict happens. After resolving these"
  echo "you can restart or continue manually."
  echo
  echo "Manual equivalent of this tool would be something like this:"
  echo
  echo "  git checkout <branch to rebase>"
  echo "  git rebase <base branch>~1000"
  echo "  git rebase <base branch>~999"
  echo "  git rebase <base branch>~998"
  echo "  ..."

  exit 1
fi

BASE_BRANCH=${1}

COMMON_PARENT=$(git merge-base HEAD ${BASE_BRANCH})
echo
echo "Common parent is ${COMMON_PARENT}."

PARENTS=$(git rev-list --first-parent ${COMMON_PARENT}..${BASE_BRANCH} | wc -l)
echo "${PARENTS} commits to go."
let PARENTS=${PARENTS}-1

CURRENT_BRANCH=$(git status | awk '/^On branch/ { print $3 }')
echo "Will rebase current branch ${CURRENT_BRANCH} to branch ${BASE_BRANCH}."
echo
echo "IS THIS FINE?"
echo "If not, hit Ctrl-C now."
wait_count 5

while [ ${PARENTS} -ge 0 ]; do
  echo -e "Next: rebasing to \033[1m${BASE_BRANCH}~${PARENTS}\033[0m"
  if ! git rebase --rerere-autoupdate --whitespace=fix ${BASE_BRANCH}~${PARENTS}; then
    echo
    echo "Standard rebase failed."
    echo "Trying again, this time ignoring whitespace ..."
    git rebase --abort
    if ! git rebase --rerere-autoupdate -X ignore-all-space --whitespace=fix ${BASE_BRANCH}~${PARENTS}; then
      exit
    fi
  fi
  let PARENTS=${PARENTS}-1
done

echo "All rebased."