#!/bin/bash
set -e

RELPATH="$1"
REMOTE="$2"
MAINTBRANCH="$3"
DEVBRANCH="$4"
TMPBRANCH=$MAINTBRANCH-$DEVBRANCH-$(date "+%Y-%m-%d-%H-%M-%S")

if [ -z "$RELPATH" -o  -z "$REMOTE" -o  -z "$MAINTBRANCH" -o  -z "$DEVBRANCH" ] ; then
  PROG=$(basename $0)
  echo "Merge any changes from the maintenance-branch into the development-branch."
  echo "If there are no conflicts, then push the changes."
  echo ""
  echo "Usage: $PROG <relpath> <remote> <maintenance-branch> <development-branch>"
  echo ""
  echo "Example: $PROG drupal upstream 7.x-4.3 7.x-master"
  exit 1
fi

pushd "$RELPATH" >> /dev/null
  ## OS X: mktemp requires "-t prefix" argument
  ## GNU: mktemp accepts optional -t pattern" argument
  ## The string "merge-forward-XXXXXX" works as a prefix or pattern
  TMPFILE=$(mktemp -t merge-forward-XXXXXX)

  set -x
  git fetch $REMOTE
  git checkout -b $TMPBRANCH $REMOTE/$DEVBRANCH
  git merge $REMOTE/$MAINTBRANCH | tee $TMPFILE
  set +x

  if grep -q CONFLICT "$TMPFILE" ; then
    echo ""
    echo "==> Conflicted merge. Please resolve conflicts and then push with:"
    echo ""
    echo "git push $REMOTE $TMPBRANCH:$DEVBRANCH"
  elif grep -q "Already up-to-date." "$TMPFILE" ; then
    echo ""
    echo "==> No update needed"
    echo ""
  else
    echo ""
    echo "==> Clean merge; proceeding with push"
    echo ""
    set -x
    git push $REMOTE $TMPBRANCH:$DEVBRANCH
    git fetch $REMOTE
    git checkout $REMOTE/$DEVBRANCH
    git branch -d $TMPBRANCH
    set +x
  fi

  /bin/rm -f "$TMPFILE"
popd  >> /dev/null