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package com.fitbur.bytebuddy.agent;

import java.lang.instrument.Instrumentation;

/**
 * An installer class which defined the hook-in methods that are required by the Java agent specification.
 */
public class Installer {

    /**
     * A field for carrying the {@link java.lang.instrument.Instrumentation} that was loaded by the Byte Buddy
     * agent. Note that this field must never be accessed directly as the agent is injected into the VM's
     * system class loader. This way, the field of this class might be {@code null} even after the installation
     * of the Byte Buddy agent as this class might be loaded by a different class loader than the system class
     * loader.
     */
    @SuppressWarnings("unused")
    public static volatile Instrumentation instrumentation;

    /**
     * The installer provides only {@code static} hook-in methods and should not be instantiated.
     */
    private Installer() {
        throw new UnsupportedOperationException();
    }

    /**
     * Allows the installation of this agent via a command line argument.
     *
     * @param agentArguments  The unused agent arguments.
     * @param instrumentation The instrumentation instance.
     */
    public static void premain(String agentArguments, Instrumentation instrumentation) {
        Installer.instrumentation = instrumentation;
    }

    /**
     * Allows the installation of this agent via the Attach API.
     *
     * @param agentArguments  The unused agent arguments.
     * @param instrumentation The instrumentation instance.
     */
    @SuppressWarnings("unused")
    public static void agentmain(String agentArguments, Instrumentation instrumentation) {
        Installer.instrumentation = instrumentation;
    }
}