#! /bin/sh
set -ex
if [ "$1" = "-f" ];then
  force=true
  shift
elif [ -n "$(/bin/ls *.patch 2>/dev/null|tee /proc/self/fd/2)" ];then
  echo >&2 "Some *.patch files exist!"
  exit 1
else
  force=false
fi
if [ $# != 1 ] || ! echo "$1" | grep -q '-';then
  echo >&2 "Syntax: $0 branch-list-delimited-by-dashes"
  exit 1
fi
base="master"
for elem in $(echo "$1"|tr '-' ' ');do
  if [ "$base" = "master" ];then
    next="$elem"
  else
    next="$base-$elem"
  fi
  git checkout "$next"
  git merge "$base"
  if $force;then
    echo -e '/^--- /,$d\nw'|ed "$next".patch
  else
    rm -f "$next".patch
  fi
  git diff "$base" "$next"|diffdecvs >>"$next".patch
  base="$next"
done
git checkout master
echo OK