#!/bin/sh
set -e

usage()
{
    cat <<EOF
Usage:
    $0                         [git-push options...] <destination> [refspec]
    $0 <--all|--mirror|--tags> [git-push options...] <destination>
EOF
}

die() { printf "Error: %s\n" "$*" >&2; exit 1; }

loudly() { (set -x; "$@"); }

quietly() { "$@" >/dev/null 2>&1; }

bad_usage()
{
    usage >&2
    exit 1
}

check_existence()
{
    (set +e;
     quietly rsync "$rsync_dest"
     case $? in
         23) return 0;;
         0) [ "$NO_ACT" ] || die "Destination already exists: '$rsync_dest'";;
         *) die "rsync returned $? when checking for destination existence.";;
     esac) || exit
}

git_init_push_checkout()
{
    TEMP_DIR=$(mktemp -d)
    trap 'rm -rf "$TEMP_DIR"' EXIT
    git init --bare "$TEMP_DIR"/.git
    loudly git push "$TEMP_DIR" "$@"

    if [ "$CHECKOUT_BRANCH" -a ! "$BARE" ]; then
        (cd "$TEMP_DIR";
        git config core.bare false
        git checkout "$CHECKOUT_BRANCH")
    fi
}

go()
{
    check_existence
    git_init_push_checkout "$@"
}

# What we want to do is push a branch, and then checkout the branch we just
# pushed. Determining the branch to checkout requires parsing the branch out of
# the git push args in $@

check_source_ref()
{
    local src="$1"
    git rev-parse --verify --quiet "$src^{commit}" >/dev/null
}

pop=$(cat <<'EOF'
i=$#;
while [ $i -gt 0 ]; do
    lastarg=$1;
    shift;
    i=$((i - 1))
    if [ $i -eq 0 ]; then
        break;
    else
        set -- "$@" "$lastarg";
    fi
done
EOF
)

parse_target()
{
    case "$1" in
        ssh://*) rsync_dest=${1#ssh://} ;;
        *:*) rsync_dest=$1 ;;
        *) die "Unrecognized git URL: '$1'" ;;
    esac
    target=$1

    case "$target" in
        *[^/].git) BARE=y ;;
        *) BARE= ;;
    esac
}

parse_refspec()
{
    local refspec="$1"
    case "$refspec" in
        *:*:*) die "expected <local-ref>:<remote-ref> but got too many colons" ;;
        ?*:?*)
            check_source_ref "${1%:*}" || die "invalid source ref: $src"
            CHECKOUT_BRANCH=${1#*:}
            ;;
        *) if check_source_ref "$1"; then CHECKOUT_BRANCH=$1; fi;;
    esac
}

current_branch() { git status -bs|sed -ne 's/^## //p'; }

REFSPEC_UNNEEDED=
arg_count=$#
for arg in "$@"; do
    case "$arg" in
        -h|--help|--usage) usage; exit;;
        --all|--mirror|--tags) REFSPEC_UNNEEDED=y;;
        --no-act) NO_ACT=y;;
        --) arg_count=$((arg_count - 1)); break;;
        -*) ;;
        *) break;;
    esac
    arg_count=$((arg_count - 1))
done

case $arg_count in
    1)
        eval "$pop"
        parse_target "$lastarg"
        b=$(current_branch)
        parse_refspec "$b:$b"
        if ! [ "$REFSPEC_UNNEEDED" ]; then
            set -- "$@" "$b"
        fi
        ;;
    2)
        eval "$pop"
        refspec=$lastarg
        parse_refspec "$refspec"
        eval "$pop"
        parse_target "$lastarg"
        set -- "$@" "$refspec"
       ;;
    *) bad_usage;;
esac

go "$@"

loudly rsync ${NO_ACT:+-n} -zrlp --info=stats1 "$TEMP_DIR"/"${BARE:+.git/}" "$rsync_dest"/