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package ciir.umass.edu.stats;

import java.util.Map;
import java.util.Random;

/**
 * Randomized permutation test. Adapted from Michael Bendersky's Python script.
 * @author vdang
 *
 */
public class RandomPermutationTest extends SignificanceTest {

    public static int nPermutation = 10000;
    private static String[] pad = new String[] { "", "0", "00", "000", "0000", "00000", "000000", "0000000", "00000000", "000000000" };

    /**
     * Run the randomization test
     * @param baseline
     * @param target
     * @return
     */
    @Override
    public double test(final Map target, final Map baseline) {
        final double[] b = new double[baseline.keySet().size()];//baseline
        final double[] t = new double[target.keySet().size()];//target
        int c = 0;
        for (final String key : baseline.keySet()) {
            b[c] = baseline.get(key).doubleValue();
            t[c] = target.get(key).doubleValue();
            c++;
        }
        final double trueDiff = Math.abs(BasicStats.mean(b) - BasicStats.mean(t));
        double pvalue = 0.0;
        final double[] pb = new double[baseline.keySet().size()];//permutation of baseline
        final double[] pt = new double[target.keySet().size()];//permutation of target
        for (int i = 0; i < nPermutation; i++) {
            final char[] bits = randomBitVector(b.length).toCharArray();
            for (int j = 0; j < b.length; j++) {
                if (bits[j] == '0') {
                    pb[j] = b[j];
                    pt[j] = t[j];
                } else {
                    pb[j] = t[j];
                    pt[j] = b[j];
                }
            }
            final double pDiff = Math.abs(BasicStats.mean(pb) - BasicStats.mean(pt));
            if (pDiff >= trueDiff) {
                pvalue += 1.0;
            }
        }
        return pvalue / nPermutation;
    }

    /**
     * Generate a random bit vector of a certain size
     * @param size
     * @return
     */
    private String randomBitVector(final int size) {
        final Random r = new Random();
        String output = "";
        for (int i = 0; i < (size / 10) + 1; i++) {
            final int x = (int) ((1 << 10) * r.nextDouble());
            final String s = Integer.toBinaryString(x);
            if (s.length() == 11) {
                output += s.substring(1);
            } else {
                output += pad[10 - s.length()] + s;
            }
        }
        return output;
    }
}