/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package pt.ist.socialsoftware.edition.ldod.social.aware;

import java.util.Arrays;

public class JaroWinklerDistance {
	/**
	 * Represents a failed index search.
	 */
	public static final int INDEX_NOT_FOUND = -1;

	/**
	 * Find the Jaro Winkler Distance which indicates the similarity score between
	 * two CharSequences.
	 *
	 * <pre>
	 * distance.apply(null, null)          = IllegalArgumentException
	 * distance.apply("","")               = 0.0
	 * distance.apply("","a")              = 0.0
	 * distance.apply("aaapppp", "")       = 0.0
	 * distance.apply("frog", "fog")       = 0.93
	 * distance.apply("fly", "ant")        = 0.0
	 * distance.apply("elephant", "hippo") = 0.44
	 * distance.apply("hippo", "elephant") = 0.44
	 * distance.apply("hippo", "zzzzzzzz") = 0.0
	 * distance.apply("hello", "hallo")    = 0.88
	 * distance.apply("ABC Corporation", "ABC Corp") = 0.93
	 * distance.apply("D N H Enterprises Inc", "D &amp; H Enterprises, Inc.") = 0.95
	 * distance.apply("My Gym Children's Fitness Center", "My Gym. Childrens Fitness") = 0.92
	 * distance.apply("PENNSYLVANIA", "PENNCISYLVNIA")    = 0.88
	 * </pre>
	 *
	 * @param left
	 *            the first String, must not be null
	 * @param right
	 *            the second String, must not be null
	 * @return result distance
	 * @throws IllegalArgumentException
	 *             if either String input {@code null}
	 */
	public Double apply(final CharSequence left, final CharSequence right) {
		final double defaultScalingFactor = 0.1;

		if (left == null || right == null) {
			throw new IllegalArgumentException("Strings must not be null");
		}

		final int[] mtp = matches(left, right);
		final double m = mtp[0];
		if (m == 0) {
			return 0D;
		}
		final double j = (m / left.length() + m / right.length() + (m - mtp[1]) / m) / 3;
		final double jw = j < 0.7D ? j : j + Math.min(defaultScalingFactor, 1D / mtp[3]) * mtp[2] * (1D - j);
		return jw;
	}

	/**
	 * This method returns the Jaro-Winkler string matches, transpositions, prefix,
	 * max array.
	 *
	 * @param first
	 *            the first string to be matched
	 * @param second
	 *            the second string to be matched
	 * @return mtp array containing: matches, transpositions, prefix, and max length
	 */
	protected static int[] matches(final CharSequence first, final CharSequence second) {
		CharSequence max, min;
		if (first.length() > second.length()) {
			max = first;
			min = second;
		} else {
			max = second;
			min = first;
		}
		final int range = Math.max(max.length() / 2 - 1, 0);
		final int[] matchIndexes = new int[min.length()];
		Arrays.fill(matchIndexes, -1);
		final boolean[] matchFlags = new boolean[max.length()];
		int matches = 0;
		for (int mi = 0; mi < min.length(); mi++) {
			final char c1 = min.charAt(mi);
			for (int xi = Math.max(mi - range, 0), xn = Math.min(mi + range + 1, max.length()); xi < xn; xi++) {
				if (!matchFlags[xi] && c1 == max.charAt(xi)) {
					matchIndexes[mi] = xi;
					matchFlags[xi] = true;
					matches++;
					break;
				}
			}
		}
		final char[] ms1 = new char[matches];
		final char[] ms2 = new char[matches];
		for (int i = 0, si = 0; i < min.length(); i++) {
			if (matchIndexes[i] != -1) {
				ms1[si] = min.charAt(i);
				si++;
			}
		}
		for (int i = 0, si = 0; i < max.length(); i++) {
			if (matchFlags[i]) {
				ms2[si] = max.charAt(i);
				si++;
			}
		}
		int transpositions = 0;
		for (int mi = 0; mi < ms1.length; mi++) {
			if (ms1[mi] != ms2[mi]) {
				transpositions++;
			}
		}
		int prefix = 0;
		for (int mi = 0; mi < min.length(); mi++) {
			if (first.charAt(mi) == second.charAt(mi)) {
				prefix++;
			} else {
				break;
			}
		}
		return new int[] { matches, transpositions / 2, prefix, max.length() };
	}
}
