package eu.mikroskeem.bytecodehackery;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Type;

import static org.objectweb.asm.Opcodes.*;

public class Main {
    private Main() throws Exception {
        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);

        /* Generate class */
        cw.visit(V1_8, ACC_PUBLIC, (getClass().getPackage().getName() +".kek.Topkek").replaceAll("\\.", "/"),
                null, "java/lang/Object", new String[]{Type.getInternalName(TestInterface.class)});

        /* Generate constructor */
        MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
        mv.visitVarInsn(ALOAD, 0);

        /* Must-have for all classes */
        mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
        mv.visitInsn(RETURN);
        mv.visitMaxs(1, 1);
        mv.visitEnd();

        /* Generate toString method */
        String toStringDesc = String.format("(%s)%s", "", Type.getDescriptor(String.class));
        mv = cw.visitMethod(ACC_PUBLIC, "toString", toStringDesc, null, null);
        mv.visitLdcInsn("TOPKEK LMAUUU");
        mv.visitInsn(ARETURN);
        mv.visitMaxs(1, 1);
        mv.visitEnd();

        /* Generate a() method */
        String aDesc = String.format("(%s)%s", "", Type.getDescriptor(String.class));
        mv = cw.visitMethod(ACC_PUBLIC, "a", aDesc, null, null);
        mv.visitLdcInsn("some a() call");
        mv.visitInsn(ARETURN);
        mv.visitMaxs(1, 1);
        mv.visitEnd();


        mv = cw.visitMethod(ACC_PUBLIC, "b", "()Ljava/util/List;", "()Ljava/util/List<Ljava/lang/String;>;", null);
        mv.visitCode();
        mv.visitTypeInsn(NEW, "java/util/ArrayList");
        mv.visitInsn(DUP);
        mv.visitMethodInsn(INVOKESPECIAL, "java/util/ArrayList", "<init>", "()V", false);
        mv.visitVarInsn(ASTORE, 1);
        mv.visitVarInsn(ALOAD, 1);
        mv.visitLdcInsn("kek");
        mv.visitMethodInsn(INVOKEINTERFACE, "java/util/List", "add", "(Ljava/lang/Object;)Z", true);
        mv.visitVarInsn(ALOAD, 1);
        mv.visitLdcInsn("ayy lmao");
        mv.visitMethodInsn(INVOKEINTERFACE, "java/util/List", "add", "(Ljava/lang/Object;)Z", true);
        mv.visitInsn(POP);
        mv.visitVarInsn(ALOAD, 1);
        mv.visitInsn(ARETURN);
        mv.visitMaxs(2, 2);
        mv.visitEnd();

        /* Class end */
        cw.visitEnd();

        /* Load that class */
        Class<?> a = GeneratedClassLoader.getLoader(this.getClass().getClassLoader())
                .defineClass(getClass().getPackage().getName() +".kek.Topkek", cw.toByteArray());

        TestInterface b = (TestInterface) a.newInstance();
        System.out.println(b.toString());
        System.out.println(b.a());
        System.out.println(b.b());
    }
    public static void main(String... a) throws Exception {
        new Main();
    }
}