package net.i2p.util;

/*
 * free (adj.): unencumbered; not under the control of others
 * Written by jrandom in 2003 and released into the public domain 
 * with no warranty of any kind, either expressed or implied.  
 * It probably won't make your computer catch on fire, or eat 
 * your children, but it might.  Use at your own risk.
 *
 */

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

import net.i2p.I2PAppContext;
import net.i2p.crypto.EntropyHarvester;

/**
 * Singleton for whatever PRNG i2p uses.  
 *
 * @author jrandom
 */
public class RandomSource extends SecureRandom implements EntropyHarvester {

    private static final long serialVersionUID = 1L;
    protected transient final I2PAppContext _context;

    /**
     *  Deprecated - do not instantiate this directly, as you won't get the
     *  good one (Fortuna). Use getInstance() or
     *  I2PAppContext.getGlobalContext().random() to get the FortunaRandomSource
     *  instance.
     */
    public RandomSource(I2PAppContext context) {
        super();
        _context = context;
    }

    /**
     * Singleton for whatever PRNG i2p uses.  
     * Same as I2PAppContext.getGlobalContext().random();
     * use context.random() if you have a context already.
     * @return I2PAppContext.getGlobalContext().random()
     */
    public static RandomSource getInstance() {
        return I2PAppContext.getGlobalContext().random();
    }

    /**
     * According to the java docs (http://java.sun.com/j2se/1.4.1/docs/api/java/util/Random.html#nextInt(int))
     * nextInt(n) should return a number between 0 and n (including 0 and excluding n).  However, their pseudocode,
     * as well as sun's, kaffe's, and classpath's implementation INCLUDES NEGATIVE VALUES.
     * Ok, so we're going to have it return between 0 and n (including 0, excluding n), since 
     * thats what it has been used for.
     *
     * This code unused, see FortunaRandomSource override
     */
    @Override
    public int nextInt(int n) {
        if (n == 0) return 0;
        int val = super.nextInt(n);
        if (val < 0) val = 0 - val;
        if (val >= n) val = val % n;
        return val;
    }

    /**
     *  This code unused, see FortunaRandomSource override
     *
     *  @return all possible int values, positive and negative
     *  @since 0.9.54
     */
    public int signedNextInt() {
        return nextInt();
    }

    /**
     * Like the modified nextInt, nextLong(n) returns a random number from 0 through n,
     * including 0, excluding n.
     *
     * This code unused, see FortunaRandomSource override
     */
    public long nextLong(long n) {
        long v = super.nextLong();
        if (v < 0) v = 0 - v;
        if (v >= n) v = v % n;
        return v;
    }

    /**
     * Not part of java.util.SecureRandom, but added since Fortuna supports it.
     *
     * This code unused, see FortunaRandomSource override
     *
     * @since 0.8.12
     */
    public void nextBytes(byte buf[], int offset, int length) {
        // inefficient, just in case anybody actually instantiates this
        if (offset == 0 && buf.length == length) {
            nextBytes(buf);
        } else {
            byte[] tmp = new byte[length];
            nextBytes(tmp);
            System.arraycopy(tmp, 0, buf, offset, length);
        }
    }

    public EntropyHarvester harvester() { return this; }
 
    public void feedEntropy(String source, long data, int bitoffset, int bits) {
        if (bitoffset == 0)
            setSeed(data);
    }
    
    public void feedEntropy(String source, byte[] data, int offset, int len) {
        if ( (offset == 0) && (len == data.length) ) {
            setSeed(data);
        } else {
            setSeed(_context.sha().calculateHash(data, offset, len).getData());
        }
    }

    /**
     *  May block up to 10 seconds
     */
    public void loadSeed() {
        byte buf[] = new byte[1024];
        if (initSeed(buf))
            setSeed(buf);
    }

    public void saveSeed() {
        byte buf[] = new byte[1024];
        nextBytes(buf);
        writeSeed(buf);
    }
    
    private static final String SEEDFILE = "prngseed.rnd";
    
    public static final void writeSeed(byte buf[]) {
        File f = new File(I2PAppContext.getGlobalContext().getConfigDir(), SEEDFILE);
        FileOutputStream fos = null;
        try {
            fos = new SecureFileOutputStream(f);
            fos.write(buf);
        } catch (IOException ioe) {
            // ignore
        } finally {
            if (fos != null) try { fos.close(); } catch (IOException ioe) {}
        }
    }
 
    /**
     *  May block up to 10 seconds
     */
    public final boolean initSeed(byte buf[]) {
        boolean ok = false;

        final byte[] tbuf = new byte[buf.length];
        Thread t = new I2PThread(new SecureRandomInit(tbuf), "SecureRandomInit", true);
        t.start();
        try {
            t.join(10*1000);
            synchronized(tbuf) {
                for (int i = 0; i < tbuf.length; i++) {
                    if (tbuf[i] != 0) {
                        ok = true;
                        break;
                    }
                }
                if (ok)
                    System.arraycopy(tbuf, 0, buf, 0, buf.length);
                // See FortunaRandomSource constructor for fallback
                //else
                //    System.out.println("INFO: SecureRandom init failed or took too long");
            }
        } catch (InterruptedException ie) {}

        // why urandom?  because /dev/random blocks
        if (!SystemVersion.isWindows())
            ok = seedFromFile(new File("/dev/urandom"), buf) || ok;
        // we merge (XOR) in the data from /dev/urandom with our own seedfile
        File localFile = new File(_context.getConfigDir(), SEEDFILE);
        ok = seedFromFile(localFile, buf) || ok;
        return ok;
    }
    
    /**
     *  Thread to prevent hanging on init,
     *  presumably due to /dev/random blocking,
     *  which is common in VMs.
     *
     *  @since 0.9.18
     */
    private static class SecureRandomInit implements Runnable {
        private final byte[] buf;
        private static final int SZ = 64;

        public SecureRandomInit(byte[] buf) {
            this.buf = buf;
        }

        public void run() {
            byte[] buf2 = new byte[SZ];
            // do this 64 bytes at a time, so if system is low on entropy we will
            // hopefully get something before the timeout
            try {
                SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
                for (int i = 0; i < buf.length; i += SZ) {
                    sr.nextBytes(buf2);
                    synchronized(buf) {
                        System.arraycopy(buf2, 0, buf, i, Math.min(SZ, buf.length - i));
                    }
                }
            } catch (NoSuchAlgorithmException e) {}
        }
    }

    /**
     *  XORs the seed into buf
     *
     *  @param f absolute path
     *  @return success
     */
    private static final boolean seedFromFile(File f, byte buf[]) {
        if (f.exists()) {
            FileInputStream fis = null;
            try {
                fis = new FileInputStream(f);
                int read = 0;
                byte tbuf[] = new byte[buf.length];
                while (read < buf.length) {
                    int curRead = fis.read(tbuf, read, tbuf.length - read);
                    if (curRead < 0)
                        break;
                    read += curRead;
                }
                for (int i = 0; i < read; i++)
                    buf[i] ^= tbuf[i];
                return true;
            } catch (IOException ioe) {
                // ignore
            } finally {
                if (fis != null) try { fis.close(); } catch (IOException ioe) {}
            }
        }
        return false;
    }

/****
    public static void main(String args[]) {
        for (int j = 0; j < 2; j++) {
        RandomSource rs = new RandomSource(I2PAppContext.getGlobalContext());
        byte buf[] = new byte[1024];
        boolean seeded = rs.initSeed(buf);
        System.out.println("PRNG class hierarchy: ");
        Class c = rs.getClass();
        while (c != null) {
            System.out.println("\t" + c.getName());
            c = c.getSuperclass();
        }
        System.out.println("Provider: \n" + rs.getProvider());
        if (seeded) {
            System.out.println("Initialized seed: " + Base64.encode(buf));
            rs.setSeed(buf);
        }
        for (int i = 0; i < 64; i++) rs.nextBytes(buf);
        rs.saveSeed();
        }
    }
****/
}
