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package vmversion;

import java.io.DataInputStream;
import java.io.File;
import java.io.IOException;
import java.util.Enumeration;
import java.util.zip.ZipEntry;
import java.util.zip.ZipException;
import java.util.zip.ZipFile;

/**
 *
 * @author tom
 */
public class Main {

    private static final int CF_11 = 0x2d;
    private static final int CF_12 = 0x2e;
    private static final int CF_13 = 0x2f;
    private static final int CF_14 = 0x30;
    private static final int CF_15 = 0x31;
    private static final int CF_16 = 0x32;
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        if (args.length == 0) {
            System.err.println ("usage: VMVersion (file|folder)+");
            System.exit (1);
        }
        for (String arg : args) {
            final File file = new File (arg);            
            process (new File[] {file});
        }
    }
    
    private static final String getVersion (final short major, final short minor) {
        switch (major) {
            case CF_11:
                return "1.1";
            case CF_12:
                return "1.2";
            case CF_13:
                return "1.3";
            case CF_14:
                return "1.4";
            case CF_15:
                return "1.5";
            case CF_16:
                return "1.6";
            default:
                if (major > CF_16) {
                    return "newer than 1.6";
                }
                else {
                    return "unknown";
                }
        }
    }
    
    private static void process (final ZipFile zf) throws IOException {
        final Enumeration<? extends ZipEntry> entries = zf.entries();
        ZipEntry entry = null;
        while (entries.hasMoreElements()) {
            ZipEntry e = entries.nextElement();
            if (e.getName().endsWith(".class")) {
                entry = e;
                break;
            }
        }
        if (entry != null) {
            final DataInputStream in = new DataInputStream(zf.getInputStream(entry));
            try {
                int magic = in.readInt();
                short minor = in.readShort();
                short major = in.readShort();
                if (magic != 0xCAFEBABE) {
                    System.err.println("Invalid class file in: " + zf.getName());
                    return;
                }
                System.out.println(zf.getName()+"\t"+getVersion(major,minor));
            } finally {
                in.close();
            }
        }
    }
    
    private static void process (final File f) throws IOException {
        assert f != null;
        try {
            final ZipFile zf = new ZipFile (f);
            try {
                process (zf);
            } finally {
                zf.close();
            }
        } catch (ZipException e) {
            System.err.println("Not a zip file: " + f);
        }
    }
    
    private static void process (final File[] files) {
        if (files == null) {
            return;
        }
        for (File f : files) {
            if (!f.canRead()) {
                System.err.println("Cannot read file: " + f);
                continue;
            }
            else if (f.isDirectory()) {
                process (f.listFiles());
            }
            else {
                try {
                    process (f);
                } catch (IOException e) {
                    System.err.println("Cannot read file: " + f);
                }
            }
        }
    }

}