#ft=sh

bail () {
    >&2 echo "ERROR: $1"
    exit 1
}

must_be_root () {
    if [ "$(id --user)" != 0 ]; then
        bail "must run as root"
    fi
}

get_os () {
    case $(uname -s) in
        Linux*)     echo linux;;
        Darwin*)    echo darwin;;
        *)          bail "unsupported os: $(uname -s)" ;;
    esac
}

get_arch () {
    case $(uname -m) in
        x86_64*)    echo amd64;;
        amd64*)     echo amd64;;
        *)          bail "unsupported architecture: $(uname -m)" ;;
    esac
}

set_current_link () {
    prefix="${1}"
    version="${2}"
    sudo="${3}"
    current="${prefix}/current"
    if [ -s "${current}" ] ; then
        $sudo unlink "${current}"
    fi
    $sudo ln --symbolic --relative "${prefix}/${version}" "${current}"
}

extract_tarball () {
    url="${1}"
    dest="${2}"
    args="${3}"
    sudo="${4}"

    if [ -d "${dest}" ]; then
        return
    fi
    $sudo mkdir -p "${dest}"

    tmp_dir="$(mktemp --directory)"
    tarball=${tmp_dir}/release.tar.gz
    curl --silent --location --output "${tarball}" "${url}"
    # shellcheck disable=SC2086
    $sudo tar xf "${tarball}" --directory "${dest}" ${args}
    rm -rf "${tmp_dir}"
}

relative_path() {
    # both $1 and $2 are absolute paths beginning with /
    # $1 must be a canonical path; that is none of its directory
    # components may be ".", ".." or a symbolic link
    #
    # returns relative path to $2/$target from $1/$src
    src=$1
    target=$2

    common_part=$src
    result=

    while [ "${target#"$common_part"}" = "$target" ]; do
        # no match, means that candidate common part is not correct
        # go up one level (reduce common part)
        common_part=$(dirname "$common_part")
        # and record that we went back, with correct / handling
        if [ -z "$result" ]; then
            result=..
        else
            result=../$result
        fi
    done

    if [ "$common_part" = / ]; then
        # special case for root (no common path)
        result=$result/
    fi

    # since we now have identified the common part,
    # compute the non-common part
    forward_part=${target#"$common_part"}

    # and now stick all parts together
    if [ -n "$result" ] && [ -n "$forward_part" ]; then
        result=$result$forward_part
    elif [ -n "$forward_part" ]; then
        # extra slash removal
        result=${forward_part#?}
    fi

    printf '%s' "$result"
}