import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.net.URL;

import java.util.function.Function;

import org.graalvm.options.OptionDescriptor;

import org.graalvm.options.OptionDescriptors;

import org.graalvm.polyglot.Context;

import org.graalvm.polyglot.Engine;

import org.graalvm.polyglot.Instrument;

import org.graalvm.polyglot.Source;

import org.graalvm.polyglot.Value;

@SuppressWarnings("unchecked")

public class Embedding {

public static void main(String... args) throws Exception {

ByteArrayOutputStream out = new ByteArrayOutputStream();

try (Context ctx = Context.newBuilder().out(out).err(out).build()) {

Engine eng = ctx.getEngine();

Instrument instrument = eng.getInstruments().get("agentscript");

assert instrument != null : "AgentScript instrument found";

OptionDescriptors ops = instrument.getOptions();

assert ops != null : "Options found";

OptionDescriptor script = ops.get("agentscript");

assert script != null : "agent script: " + script;

Value fib = ctx.eval("js", "(function fib(n) {\n" +

" if (n <= 2) return 1;\n" +

" return fib(n - 1) + fib(n - 2);\n" +

"})"

);

int fib10 = fib.execute(10).asInt();

assert fib10 == 55 : "fib(10) == " + fib10;

assert out.size() == 0 : "No output yet: " + out.toString("UTF-8");

try (AutoCloseable c = registerAgent(instrument)) {

int fib11 = fib.execute(11).asInt();

assert fib11 == 89 : "fib(11) == " + fib11;

String txt = out.toString("UTF-8");

assert txt.contains("calling fib with 5") : "Expecting debug output:\n" + txt;

}

out.reset();

assert out.size() == 0 : "Empty again";

int fib12 = fib.execute(12).asInt();

assert fib12 == 144 : "fib(12) == " + fib12;

assert out.size() == 0 : "No output again:\n" + out.toString("UTF-8");

}

System.out.println("Everything is OK!");

}

private static AutoCloseable registerAgent(Instrument instrument) throws InterruptedException, IOException {

Function<Source,?> api = instrument.lookup(Function.class);

assert api != null : "Instrument exposes a function like API";

ClassLoader l = api.getClass().getClassLoader();

assert l == null : "No special loader found: " + l;

URL agentScript = Embedding.class.getResource("agent-embedding.js");

assert agentScript != null : "Script found";

Source src = Source.newBuilder("js", agentScript).internal(true).build();

Object[] handle = { null };

Thread register = new Thread("register agent") {

@Override

public void run() {

handle[0] = api.apply(src);

}

};

register.start();

register.join();

assert handle[0] != null : "Enabling agent script returns its closable handle";

return (AutoCloseable) handle[0];

}

}