import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.nio.file.Files;
import java.util.Enumeration;
import java.util.jar.Attributes;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.jar.JarOutputStream;
import java.util.jar.Manifest;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.commons.ClassRemapper;
import org.objectweb.asm.commons.Remapper;

/**
 * Baut die Agent-Datei: eigene Klassen + ASM, dabei org/objectweb/asm nach
 * de/aeromc/capes/asm umbenannt. So kann das ASM von Fabric/Forge (das auf
 * demselben Klassenpfad liegt) nie mit unserem verwechselt werden.
 *
 * Aufruf: java Shade <ziel.jar> <klassenordner> <asm.jar>
 */
public class Shade {
    static final Remapper UMBENENNEN = new Remapper() {
        @Override
        public String map(String name) {
            return name.startsWith("org/objectweb/asm/") ? "de/aeromc/capes/asm/" + name.substring(18) : name;
        }
    };

    static byte[] umbenennen(byte[] klasse) {
        ClassReader r = new ClassReader(klasse);
        ClassWriter w = new ClassWriter(0);
        r.accept(new ClassRemapper(w, UMBENENNEN), 0);
        return w.toByteArray();
    }

    static byte[] lies(InputStream in) throws Exception {
        ByteArrayOutputStream b = new ByteArrayOutputStream();
        byte[] p = new byte[8192];
        int n;
        while ((n = in.read(p)) > 0) b.write(p, 0, n);
        return b.toByteArray();
    }

    public static void main(String[] a) throws Exception {
        Manifest mf = new Manifest();
        Attributes at = mf.getMainAttributes();
        at.put(Attributes.Name.MANIFEST_VERSION, "1.0");
        at.putValue("Premain-Class", "de.aeromc.capes.Agent");
        at.putValue("Agent-Class", "de.aeromc.capes.Agent");
        at.putValue("Can-Retransform-Classes", "false");
        at.putValue("Implementation-Title", "AeroMC Umhang-Agent");
        try (JarOutputStream out = new JarOutputStream(new FileOutputStream(a[0]), mf)) {
            // eigene Klassen
            File basis = new File(a[1]);
            for (File f : Files.walk(basis.toPath()).map(p -> p.toFile()).filter(f -> f.getName().endsWith(".class")).toArray(File[]::new)) {
                String name = basis.toPath().relativize(f.toPath()).toString().replace('\\', '/');
                out.putNextEntry(new JarEntry(name));
                out.write(umbenennen(Files.readAllBytes(f.toPath())));
                out.closeEntry();
            }
            // ASM (umbenannt), ohne Modul-Infos und Signaturen
            try (JarFile asm = new JarFile(a[2])) {
                Enumeration<JarEntry> e = asm.entries();
                while (e.hasMoreElements()) {
                    JarEntry je = e.nextElement();
                    String n = je.getName();
                    if (!n.startsWith("org/objectweb/asm/") || !n.endsWith(".class")) continue;
                    byte[] neu = umbenennen(lies(asm.getInputStream(je)));
                    out.putNextEntry(new JarEntry("de/aeromc/capes/asm/" + n.substring(18)));
                    out.write(neu);
                    out.closeEntry();
                }
            }
        }
    }
}