#!/usr/bin/env bash

# Usage: subtree-hash ROOT_HASH [SUBDIR ...]

subtree_hash()
{
    root_hash="$1"
    if test "$#" -eq 1; then
        echo $root_hash
    else
        subdir="$2"
        subtree_info="$(git ls-tree "$root_hash" | grep -E "	$subdir\$")" || true
        if test "$(echo "$subtree_info" | wc -l)" -ne 1; then
            echo "Didn't find just one matching line in subtree $root_hash" 1>&2
            return 1
        fi

        subtree_hash="$(echo "$subtree_info" | cut -d' ' -f 3 | cut -d$'\t' -f 1)" || true
        if test -z "$subtree_hash"; then
            echo "Unable to find subtree hash in git output: $subtree_info" 1>&2
            return 1
        fi

        shift 2 || exit $?
        subtree_hash "$subtree_hash" "$@" || exit $?
    fi
}

subtree_hash "$@"