package com.kryptnostic.api.v1.indexing;

import java.nio.ByteBuffer;

import cern.colt.bitvector.BitVector;

import com.google.common.base.Charsets;
import com.google.common.base.Preconditions;
import com.google.common.hash.HashFunction;
import com.google.common.hash.Hashing;
import com.kryptnostic.multivariate.PolynomialFunctions;
import com.kryptnostic.multivariate.gf2.SimplePolynomialFunction;

public class Indexes {
    private static final HashFunction hashFunction = Hashing.sha256();
    
	public static SimplePolynomialFunction generateRandomIndexingFunction( int tokenLength, int nonceLength, int locationLength ) {
		SimplePolynomialFunction outer = PolynomialFunctions.denseRandomMultivariateQuadratic( locationLength , locationLength );
		SimplePolynomialFunction inner = PolynomialFunctions.unsafeRandomManyToOneLinearCombination( tokenLength + nonceLength , locationLength );
		return outer.compose( inner );
	}

	public static BitVector computeHashAndGetBits(String token) {
	    //TODO: Make this a salted hash and persist the hash as part of the private key on the phone.
	    byte[] hash = hashFunction.hashString(token, Charsets.UTF_8).asBytes();
	    //TODO: Consider padding output to a multiple of 8
	    Preconditions.checkState( hash.length % 8 == 0 , "Output length of has function must be a multiple of 8.");
	    long [] raw = new long[ hash.length >>> 3 ];
	    ByteBuffer.wrap( hash ).asLongBuffer().get( raw );

	    return new BitVector( raw , raw.length << 6 );
	}

}

@@ -418,16 +418,46 @@
 dexes %7B%0A
+    private Indexes() %7B%7D%0A    %0A
     priv

add private constructor to enforce non-instantiability