/*
 *   This file is a part of the SteamWar software.
 *
 *   Copyright (C) 2026 SteamWar.de-Serverteam
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU Affero General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *   GNU Affero General Public License for more details.
 *
 *   You should have received a copy of the GNU Affero General Public License
 *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package de.steamwar;

import java.io.File;
import java.io.IOException;
import java.lang.instrument.Instrumentation;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;

/**
 * Java agent entry point.
 *
 * Can be used two ways:
 *   1. At JVM startup:  java -javaagent:paper-access-widener-agent.jar -jar server.jar
 *   2. Late attach:     from inside a Paper plugin via the Attach API
 *
 * On attach the agent:
 *   1. Scans all existing plugin ClassLoaders for "plugin.accesswidener" resources
 *   2. Registers a ClassFileTransformer that:
 *        a. Applies widening to every class as it loads
 *        b. Detects new plugin ClassLoaders and scans them automatically
 *   3. Retransforms any Minecraft/server classes that are already loaded
 */
public class Agent {
    private Agent() {
        throw new IllegalStateException("Utility class");
    }

    private static final Logger LOG = Logger.getLogger("AccessWidenerAgent");

    // -javaagent: startup
    public static void premain(String args, Instrumentation inst) {
        init(inst);
    }

    private static void init(Instrumentation inst) {
        LOG.info("[AccessWidener] Agent initialising.");

        List<AccessWidenerEntry> entries = new ArrayList<>();
        File file = new File(new File(".").getAbsoluteFile(), "plugins/");
        File[] files = file.listFiles();
        if (files == null) files = new File[0];
        for (File jarFile : files) {
            if (!jarFile.isFile()) continue;
            if (!jarFile.getName().endsWith(".jar")) continue;
            try {
                entries.addAll(Utils.findAndParseAccessWideners(jarFile.toPath()));
            } catch (IOException e) {
                LOG.warning("Failed to parse access wideners from " + jarFile.getAbsolutePath());
            }
        }
        LOG.info("[AccessWidener] Loaded " + entries.size() + " access wideners.");

        inst.addTransformer(new WideningTransformer(entries), false);
        LOG.info("[AccessWidener] Agent ready.");
    }
}