package edu.uci.ics.hivesterix.runtime.factory.hashfunction;

import edu.uci.ics.hivesterix.serde.lazy.LazyUtils;
import edu.uci.ics.hivesterix.serde.lazy.LazyUtils.VInt;
import edu.uci.ics.hyracks.api.dataflow.value.IBinaryHashFunction;
import edu.uci.ics.hyracks.api.dataflow.value.IBinaryHashFunctionFactory;

public class HiveStingBinaryHashFunctionFactory implements
		IBinaryHashFunctionFactory {
	private static final long serialVersionUID = 1L;

	public static HiveStingBinaryHashFunctionFactory INSTANCE = new HiveStingBinaryHashFunctionFactory();

	private HiveStingBinaryHashFunctionFactory() {
	}

	@Override
	public IBinaryHashFunction createBinaryHashFunction() {
		// TODO Auto-generated method stub
		return new IBinaryHashFunction() {
			private VInt len = new VInt();

			@Override
			public int hash(byte[] bytes, int offset, int length) {
				LazyUtils.readVInt(bytes, offset, len);
				if (len.value + len.length != length)
					throw new IllegalStateException(
							"parse string: length mismatch, expected "
									+ (len.value + len.length) + " but get "
									+ length);
				return hashBytes(bytes, offset + len.length, length
						- len.length);
			}

			public int hashBytes(byte[] bytes, int offset, int length) {
				int value = 1;
				int end = offset + length;
				for (int i = offset; i < end; i++)
					value = value * 31 + (int) bytes[i];
				return value;
			}
		};
	}

}