#ft=bash

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

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

set_link () {
    TARGET="$1"
    APP_DIR="$2"
    APP_PATH="$3"

    pushd "$(dirname "${TARGET}")" >/dev/null || exit 1
    unlink_if_set "${TARGET}"
    REL_PATH=$(relative_path "$(dirname "${TARGET}")" "${APP_DIR}/current/${APP_PATH}")
    ln -s "${REL_PATH}" "$(basename "${TARGET}")"
    popd >/dev/null || exit 1
}

get_os () {
    case $(uname -s) in
        Linux*)         echo linux;;
        Darwin*)        echo darwin;;
        Dragonfly*)     echo dragonfly;;
        FreeBSD*)       echo freebsd;;
        NetBSD*)        echo netbsd;;
        OpenBSD*)       echo openbsd;;
        SunOS*)         echo solaris;;
        Windows_NT*)    echo windows;;
        CYGWIN_NT*)     echo windows;;
        *)          >&2 echo "unsupported os"; return;
    esac
}

get_arch () {
    case $(uname -m) in
        x86_64*)    echo amd64;;
        amd64*)     echo amd64;;
        i386*)      echo 386;;
        i686*)      echo 386;;
        arm)        echo arm;;
        armv7*)     echo arm;;
        armv6*)     echo arm;;
        armv8*)     echo arm;;
        aarch64*)   echo arm64;;
        *)          >&2 echo "unsupported architecture: $(uname -m)"; exit 1;;
    esac
}

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

unlink_if_set () {
    dir="$1"
    sudo="$2"
    if [ -L "${dir}" ]; then
        # shellcheck disable=SC2086
        ${sudo} unlink "${dir}"
    fi
}

mkdir_if_missing () {
    dir="$1"
    sudo=$2
    if [ ! -d "${dir}" ]; then
        # shellcheck disable=SC2086
        $sudo mkdir -p "${dir}"
    fi
}

extract_zip () {
    url="${1}"
    dest="${2}"
    args="${3}"
    sudo="${4}"
    if [ -d "${dest}" ]; then
        return
    fi

    mkdir_if_missing "${dest}" "${sudo}"
    tmp_dir="$(mktemp -d)"
    zipfile=${tmp_dir}/release.zip
    curl --silent --location --output "${zipfile}" "${url}"
    # shellcheck disable=SC2086
    $sudo unzip -o "${zipfile}" -d "${dest}" ${args}
    rm -rf "${tmp_dir}"
}

extract_tarball () {
    url="${1}"
    dest="${2}"
    args="${3}"
    sudo="${4}"
    if [ -d "${dest}" ]; then
        return
    fi

    mkdir_if_missing "${dest}" "${sudo}"
    tmp_dir="$(mktemp -d)"
    tarball=${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"
}