// Measures the value a JavaBean getter returns on a freshly constructed object.
// XMLEncoder shares equal Integer and Boolean objects: an int written once as
// the result of a getter (`<void id="Integer0" property="iconTextGap"/>`) is
// later referenced by id — e.g. as a node's x coordinate. Decoding such a file
// needs these defaults; they are measured here, not guessed.
//
// The same holds for static constants: the first Integer 0 in a file may be
// written as `SwingConstants.CENTER`, and every later 0 refers to it.
//
// Usage: java -cp filius.jar:lib/*:classes GetterDefaults <output json> <fqcn#property | fqcn::FIELD>...

import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.io.FileOutputStream;
import java.lang.reflect.Method;
import java.nio.charset.StandardCharsets;
import java.util.Map;
import java.util.TreeMap;

public class GetterDefaults {

    public static void main(String[] args) throws Exception {
        Map<String, Object> result = new TreeMap<>();
        for (int index = 1; index < args.length; index++) {
            String key = args[index];
            if (key.contains("::")) {
                String className = key.substring(0, key.indexOf("::"));
                String field = key.substring(key.indexOf("::") + 2);
                String simpleName = className.substring(className.lastIndexOf('.') + 1);
                result.put(simpleName + "." + field, Class.forName(className).getField(field).get(null));
                continue;
            }
            String className = key.substring(0, key.indexOf('#'));
            String property = key.substring(key.indexOf('#') + 1);
            String simpleName = className.substring(className.lastIndexOf('.') + 1);
            try {
                // Constructed many times: a constructor may roll its value (Gnutella's
                // peer limit is 3, 4 or 5 at random). Such a value is no default and is
                // written as {"random": [the values seen]}.
                java.util.TreeSet<String> seen = new java.util.TreeSet<>();
                Object value = null;
                for (int attempt = 0; attempt < 64; attempt++) {
                    value = className.equals("java.lang.ThreadGroup")
                            // A Thread's uncaughtExceptionHandler is its group; XMLDecoder runs
                            // in the main thread, so that is the group asked.
                            ? read(Thread.currentThread().getThreadGroup(), property)
                            : read(Class.forName(className).getDeclaredConstructor().newInstance(), property);
                    seen.add(String.valueOf(value));
                }
                result.put(simpleName + "#" + property, seen.size() == 1 ? value : Map.of("random", new java.util.ArrayList<>(seen)));
            } catch (Throwable error) {
                Throwable cause = error.getCause() != null ? error.getCause() : error;
                result.put(simpleName + "#" + property, Map.of("error", cause.toString()));
            }
        }
        try (FileOutputStream out = new FileOutputStream(args[0])) {
            out.write((FlsOracle.Json.write(result, "") + "\n").getBytes(StandardCharsets.UTF_8));
        }
        System.out.println("getter defaults: " + result.size());
        System.exit(0);
    }

    static Object read(Object target, String property) throws Exception {
        Method getter = null;
        for (PropertyDescriptor descriptor : Introspector.getBeanInfo(target.getClass()).getPropertyDescriptors()) {
            if (descriptor.getName().equals(property)) getter = descriptor.getReadMethod();
        }
        if (getter == null) getter = target.getClass().getMethod(property);
        Object value = getter.invoke(target);
        if (value == null || value instanceof Number || value instanceof Boolean || value instanceof String) return value;
        return Map.of("class", value.getClass().getName());
    }
}