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/*******************************************************************************
 * Copyright (c) 2015 Jeff Martin.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the GNU Lesser General Public
 * License v3.0 which accompanies this distribution, and is available at
 * http://www.gnu.org/licenses/lgpl.html
 * <p>
 * Contributors:
 * Jeff Martin - initial API and implementation
 ******************************************************************************/
package cuchaz.enigma.analysis;

import com.google.common.collect.Lists;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

import cuchaz.enigma.Constants;
import cuchaz.enigma.mapping.ClassEntry;
import javassist.ByteArrayClassPath;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;
import javassist.bytecode.Descriptor;

public class JarClassIterator implements Iterator<CtClass> {

    private JarFile jar;
    private Iterator<JarEntry> iter;

    public JarClassIterator(JarFile jar) {
        this.jar = jar;

        // get the jar entries that correspond to classes
        List<JarEntry> classEntries = Lists.newArrayList();
        Enumeration<JarEntry> entries = this.jar.entries();
        while (entries.hasMoreElements()) {
            JarEntry entry = entries.nextElement();

            // is this a class file?
            if (entry.getName().endsWith(".class")) {
                classEntries.add(entry);
            }
        }
        this.iter = classEntries.iterator();
    }

    @Override
    public boolean hasNext() {
        return this.iter.hasNext();
    }

    @Override
    public CtClass next() {
        JarEntry entry = this.iter.next();
        try {
            return getClass(this.jar, entry);
        } catch (IOException | NotFoundException ex) {
            throw new Error("Unable to load class: " + entry.getName());
        }
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }

    public static List<ClassEntry> getClassEntries(JarFile jar) {
        List<ClassEntry> classEntries = Lists.newArrayList();
        Enumeration<JarEntry> entries = jar.entries();
        while (entries.hasMoreElements()) {
            JarEntry entry = entries.nextElement();

            // is this a class file?
            if (!entry.isDirectory() && entry.getName().endsWith(".class")) {
                classEntries.add(getClassEntry(entry));
            }
        }
        return classEntries;
    }

    public static Iterable<CtClass> classes(final JarFile jar) {
        return () -> new JarClassIterator(jar);
    }

    private static CtClass getClass(JarFile jar, JarEntry entry) throws IOException, NotFoundException {
        // read the class into a buffer
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        byte[] buf = new byte[Constants.KiB];
        int totalNumBytesRead = 0;
        InputStream in = jar.getInputStream(entry);
        while (in.available() > 0) {
            int numBytesRead = in.read(buf);
            if (numBytesRead < 0) {
                break;
            }
            bos.write(buf, 0, numBytesRead);

            // sanity checking
            totalNumBytesRead += numBytesRead;
            if (totalNumBytesRead > Constants.MiB) {
                throw new Error("Class file " + entry.getName() + " larger than 1 MiB! Something is wrong!");
            }
        }

        // get a javassist handle for the class
        String className = Descriptor.toJavaName(getClassEntry(entry).getName());
        ClassPool classPool = new ClassPool();
        classPool.appendSystemPath();
        classPool.insertClassPath(new ByteArrayClassPath(className, bos.toByteArray()));
        return classPool.get(className);
    }

    private static ClassEntry getClassEntry(JarEntry entry) {
        return new ClassEntry(entry.getName().substring(0, entry.getName().length() - ".class".length()));
    }
}