import java.io.*;
import java.util.ArrayList;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.Random;
import java.util.zip.DataFormatException;
import java.util.zip.Deflater;
import java.util.zip.Inflater;

public class Test {
    private static final int bucketSize = 1<<17;//in real world should not be const, but we bored horribly
    static final int zipLevel = 2;//feel free to experiement, higher compression (5+)is likely to be total waste


 static void writes(long[] a, File file, boolean sync) throws IOException{
        byte[] bucket = new byte[Math.min(bucketSize,  Math.max(1<<13, Integer.highestOneBit(a.length >>3)))];//128KB bucket
        byte[] zipOut = new byte[bucket.length];

        final FileOutputStream fout = new FileOutputStream(file);
        FileChannel channel = fout.getChannel();
        try{

            ByteBuffer buf = ByteBuffer.wrap(bucket);
            //unfortunately java.util.zip doesn't support Direct Buffer - that would be the perfect fit
            ByteBuffer out = ByteBuffer.wrap(zipOut);
            out.putLong(a.length);//write length aka header
            if (a.length==0){
                doWrite(channel, out, 0);
                return;
            }

            Deflater deflater = new Deflater(zipLevel, false);
            try{
                for (int i=0;i<a.length;){
                    i = puts(a, buf, i);
                    buf.flip();
                    deflater.setInput(bucket, buf.position(), buf.limit());

                    if (i==a.length)
                        deflater.finish();

                    //hacking and using bucket here is tempting since it's copied twice but well
                    for (int n; (n= deflater.deflate(zipOut, out.position(), out.remaining()))>0;){
                        doWrite(channel, out, n);
                    }
                    buf.clear();
                }

            }finally{
                deflater.end();
            }
        }finally{
            if (sync)
                fout.getFD().sync();
            channel.close();
        }
    }

    static long[] reads(File file) throws IOException, DataFormatException{
        FileChannel channel = new FileInputStream(file).getChannel();
        try{
            byte[] in = new byte[(int)Math.min(bucketSize, channel.size())];
            ByteBuffer buf = ByteBuffer.wrap(in);
            System.out.println("Read channel size: " + in.length);
            channel.read(buf);
            buf.flip();
            long[] a = new long[(int)buf.getLong()];
            System.out.println("Read length: " + a.length);
            if (a.length==0)
                return a;
            int i=0;
            byte[] inflated = new byte[Math.min(1<<17, a.length*8)];
            ByteBuffer longBuffer = ByteBuffer.wrap(inflated);
            Inflater inflater = new Inflater(false);
            try{
                do{
                    if (!buf.hasRemaining()){
                        buf.clear();
                        channel.read(buf);
                        buf.flip();
                    }
                    inflater.setInput(in, buf.position(), buf.remaining());
                    buf.position(buf.position()+buf.remaining());//simulate all read

                    for (;;){
                        int n = inflater.inflate(inflated,longBuffer.position(), longBuffer.remaining());
                        if (n==0)
                            break;
                        longBuffer.position(longBuffer.position()+n).flip();
                        for (;longBuffer.remaining()>7 && i<a.length;i++){//need at least 4 bytes to form an int
                            a[i] = longBuffer.getLong();
                        }
                        longBuffer.compact();
                    }

                }while (channel.position()<channel.size() && i<a.length);
            }finally{
                inflater.end();
            }
            //          System.out.printf("read ints: %d - channel.position:%d %n", i, channel.position());
            return a;
        }finally{
            channel.close();
        }
    }

    private static void doWrite(FileChannel channel, ByteBuffer out, int n) throws IOException {
        out.position(out.position()+n).flip();
        while (out.hasRemaining())
            channel.write(out);
        out.clear();
    }
    private static int puts(long[] a, ByteBuffer buf, int i) {
        for (;buf.hasRemaining() && i<a.length;){
            buf.putLong(a[i++]);
        }
        return i;
    }





    private static long[] generateRandom(int len){
        Random r = new Random(17);
        long[] n = new long [len];
        for (int i=0;i<len;i++){
            n[i]= r.nextBoolean()?0: r.nextInt(1<<23);//limit bounds to have any sensible compression
        }
        return n;
    }
    public static void main(String[] args) throws Throwable{
        File file = new File("xxx.xxx");
        long[] n = generateRandom(3000000); //{0,2,4,1,2,3};
        long start = System.nanoTime();
        writes(n, file, false);
        long elapsed = System.nanoTime() - start;//elapsed will be fairer if the sync is true

        System.out.printf("File length: %d, for %d ints, ratio %.2f in %.2fms %n", file.length(), n.length, ((double)file.length())/8/n.length, java.math.BigDecimal.valueOf(elapsed, 6) );

        long[] m = reads(file);

        //compare, Arrays.equals doesn't return position, so it sucks/kinda
        for (int i=0; i<n.length; i++){
            if (m[i]!=n[i]){
                System.err.printf("Failed at %d%n",i);
                break;
            }
        }
        System.out.printf("All done!");
    };

}