#!/bin/bash
#
# Sets up a new Java JDK
# Loosely based on https://askubuntu.com/questions/1079239/can-not-install-jdk11-using-update-alternatives-install

set +eu

function usage {
    echo "Usage: $(basename $0) [-h] JDK [PRIORITY [ALIAS]]

    Configures a new Java JDK as downloaded from https://jdk.java.net and
    untarred into /usr/lib/jvm.

    -h          prints this help and exits

    JDK         the OpenJDK directory in /usr/lib/jvm/\$JDK
    PRIORITY    an optional priority value (numeric), default: 1010
    ALIAS       an optional JDK alias

    Allows supporting multiple JDKs on the same Ubuntu installation, and the use
    of update-java-alternatives to switch between them.

    This script expects the OpenJDK root folder to be in /usr/lib/jvm and its name
    to match the first argument (JDK); it will also create .\$JDK.jinfo file in the
    /usr/lib/jvm folder (used by the update-java-alternatives command).

    See also: http://manpages.ubuntu.com/manpages/precise/man8/update-java-alternatives.8.html
    
    Author: Marco Massenzio (https://codetrips.com) (c) 2020.  All rights reserved.
    Released under the Apache 2.0 License (https://www.apache.org/licenses/LICENSE-2.0.html)
"
}

if [[ ${1:-} == "-h" ]]; then
    usage
    exit 0
fi


jdk=${1:-}
priority=${2:-1010}
alias=${3:-${jdk}}
jinfo="/usr/lib/jvm/.${jdk}.jinfo"

if [[ -z ${jdk} || ! -d /usr/lib/jvm/${jdk} ]]; then
    usage
    exit 1
fi

cat <<EOF >${jinfo}
name=${jdk}
alias=${alias}
priority=${priority}
section=main

EOF

for c in $(ls /usr/lib/jvm/${jdk}/bin); do
    bin=/usr/lib/jvm/${jdk}/bin/$c
    update-alternatives --install /usr/bin/$c $c ${bin} ${priority}
    echo "jdkhl $c ${bin}" >>${jinfo}
done

update-java-alternatives -s ${jdk}