import android.app.AppComponentFactory;
import android.content.pm.ApplicationInfo;
import android.util.Log;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.util.ArrayList;
import java.util.List;
import java.util.zip.ZipFile;

import dalvik.system.InMemoryDexClassLoader;

public class InMemoryDexClassLoaderFactory extends AppComponentFactory {

    private static ClassLoader classLoader;

    private static void readDexes(ZipFile apkFile, List<ByteBuffer> dexFiles) throws IOException {
        int secondary = 2;
        for (var dexFile = apkFile.getEntry("classes.dex"); dexFile != null;
             dexFile = apkFile.getEntry("classes" + secondary + ".dex"), secondary++) {
            var in = apkFile.getInputStream(dexFile);
            var byteBuffer = ByteBuffer.allocate(in.available());
            byteBuffer.mark();
            Channels.newChannel(in).read(byteBuffer);
            byteBuffer.reset();
            dexFiles.add(byteBuffer);
        }
    }

    @Override
    public ClassLoader instantiateClassLoader(ClassLoader cl, ApplicationInfo aInfo) {
        if (classLoader != null) return classLoader;
        var buffers = new ArrayList<ByteBuffer>();
        try (var zipFile = new ZipFile(aInfo.sourceDir)) {
            readDexes(zipFile, buffers);
        } catch (IOException e) {
            Log.e(App.TAG, "Can not load " + aInfo.sourceDir, e);
            return cl;
        }
        var dexfiles = new ByteBuffer[buffers.size()];
        buffers.toArray(dexfiles);
        classLoader = new InMemoryDexClassLoader(dexfiles, aInfo.nativeLibraryDir, cl.getParent());
        return classLoader;
    }
}