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package io.atleon.core;

import com.google.common.hash.HashCode;
import com.google.common.hash.HashFunction;
import com.google.common.hash.Hashing;

import java.util.function.Function;

public abstract class NumberHashGroupExtractor implements Function {

    private final HashFunction hashFunction = Hashing.murmur3_32();

    private final int modulus;

    public NumberHashGroupExtractor(int modulus) {
        this.modulus = modulus;
    }

    public static  NumberHashGroupExtractor
    composed(Function extractor, int modulus) {
        return new Composed<>(extractor, modulus);
    }

    @Override
    public Integer apply(T t) {
        Number number = extractNumber(t);
        HashCode hash = hashFunction.hashLong(number == null ? 0L : number.longValue());
        return Math.abs(hash.asInt() % modulus);
    }

    protected abstract Number extractNumber(T t);

    private static final class Composed extends NumberHashGroupExtractor {

        private final Function extractor;

        public Composed(Function extractor, int modulus) {
            super(modulus);
            this.extractor = extractor;
        }

        @Override
        protected Number extractNumber(T t) {
            return extractor.apply(t);
        }
    }
}