#! /bin/sh -e

fail () {
  echo >&2 "$0: $*"
  exit 1
}

usage () {
  echo "usage: $0 [-c] [UPSTREAM BUILDABLE]"
}

fail_usage () {
  usage >&2
  exit 1
}

## Parse the command-line.
bogusp=nil createp=nil
unset head new
while getopts "ch" opt; do
  case $opt in
    h) usage; exit 0 ;;
    c) createp=t ;;
    *) bogusp=t ;;
  esac
done
shift $(( $OPTIND - 1 ))
case $# in 0) ;; 1) bogusp=t ;; *) head=$1 new=$2; shift 2 ;; esac
case $# in 0) ;; *) bogusp=t ;; esac
case $bogusp in nil) ;; *) fail_usage ;; esac

## Get the current branch name.
case ${head+t} in
  t) ;;
  *)
    head=$(git symbolic-ref HEAD)
    case $head in
      refs/heads/*) head=${head#refs/heads/} ;;
      *) fail "HEAD is not at a branch head" ;;
    esac
    case $head in
      buildable/*) fail "upstream is already a buildable branch" ;;
    esac
    ;;
esac

## Get the output branch name.
case ${new+t} in
  t) ;;
  *)
    new=buildable/$head
    ;;
esac
case $createp in
  t)
    if git rev-parse $new -- >/dev/null 2>&1; then
      fail "branch $new already exists"
    fi
    old=0000000000000000000000000000000000000000
    ;;
  nil)
    old=$(git rev-parse $new --)
    ;;
esac

## Make a temporary place.
git=$(git rev-parse --git-dir)
git=$(cd $git && pwd)
dir=$(mktemp -d)
trap "cd; rm -rf \"$dir\"" EXIT INT TERM
cd "$dir"
mkdir work tmp

## Make a nice clean checkout.
GIT_INDEX_FILE=$dir/idx; export GIT_INDEX_FILE
GIT_DIR=$git; export GIT_DIR
GIT_WORK_TREE=$dir/work; export GIT_WORK_TREE
git read-tree "$head^{}"
git checkout-index --all

## Go in, and set stuff up.  The business with `RELEASE' is kinda scungy.
## Sorry 'bout that.
cd work
if ! ver=$(git describe --abbrev=4 "$head^{}" 2>/dev/null); then
  ver=UNKNOWN
fi
echo "$ver" >RELEASE
mdw-setup
rm -rf autom4te.cache/ RELEASE

## Pick through newly added symlinks and snap them to real files.
git ls-files -o | while read f; do
  if [ -L "$f" ]; then
    cp "$f" ../tmp/snap
    mv ../tmp/snap "$f"
  fi
done

## Add the new files to the tree.
commit () {
  tree=$1; shift
  case $createp in
    t) git commit-tree -p "$head^{}" "$@" $tree ;;
    nil) git commit-tree -p "$new" -p "$head^{}" "$@" $tree ;;
  esac
}
git ls-files -oz | xargs -0r git add -f
tree=$(git write-tree)
commit=$(commit $tree -m "Update automatically managed build utilities.")
git update-ref "refs/heads/$new" $commit $old