package cn.edu.bjut.chapter5;

import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class SimilarityCalculator {
	public static double calculateCosineSimilarity(String text1, String text2) {
		Map<String, Integer> vector1 = getWordFrequency(text1);
		Map<String, Integer> vector2 = getWordFrequency(text2);

		double dotProduct = 0.0;
		for (String word : vector1.keySet()) {
			if (vector2.containsKey(word)) {
				dotProduct += vector1.get(word) * vector2.get(word);
			}
		}

		double magnitude1 = calculateMagnitude(vector1);
		double magnitude2 = calculateMagnitude(vector2);

		return dotProduct / (magnitude1 * magnitude2);
	}

	private static Map<String, Integer> getWordFrequency(String text) {
		String[] words = text.toLowerCase().split("\\s+");
		Map<String, Integer> wordCount = new HashMap<String, Integer>();
		for (String word : words) {
			wordCount.put(word, wordCount.getOrDefault(word, 0) + 1);
		}

		return wordCount;
	}

	private static double calculateMagnitude(Map<String, Integer> vector) {
		double sum = 0.0;
		for (int value : vector.values()) {
			sum += value * value;
		}

		return Math.sqrt(sum);
	}

	public static double calculateJaccardSimilarity(String text1, String text2) {
		Set<String> set1 = new HashSet<String>(Arrays.asList(text1.split(",\\s*")));
		Set<String> set2 = new HashSet<String>(Arrays.asList(text2.split(",\\s*")));

		Set<String> intersection = new HashSet<String>(set1);
		intersection.retainAll(set2);

		Set<String> union = new HashSet<String>(set1);
		union.addAll(set2);

		return (double) intersection.size() / union.size();
	}

	public static int calculateLevenshteinDistance(String str1, String str2) {
		int[][] dp = new int[str1.length() + 1][str2.length() + 1];

		for (int i = 0; i <= str1.length(); i++) {
			for (int j = 0; j <= str2.length(); j++) {
				if (i == 0) {
					dp[i][j] = j;
				} else if (j == 0) {
					dp[i][j] = i;
				} else {
					int cost = (str1.charAt(i - 1) == str2.charAt(j - 1)) 
							? 0 : 1;
					dp[i][j] = Math.min(Math.min(dp[i - 1][j] + 1, 
							dp[i][j - 1] + 1), 
							dp[i - 1][j - 1] + cost);
				}
			}
		}

		return dp[str1.length()][str2.length()];
	}

	public static void main(String[] args) {
		{
			String text1 = "I love programming in Java";
			String text2 = "Java programming is amazing";

			double similarity = calculateCosineSimilarity(text1, text2);
			System.out.println("Cosine Similarity: " + similarity);
		}

		{
			String text1 = "cat, dog, mouse";
			String text2 = "dog, elephant";

			double similarity = calculateJaccardSimilarity(text1, text2);
			System.out.println("Jaccard Similarity: " + similarity);
		}

		{
			String str1 = "kitten";
			String str2 = "sitting";

			int distance = calculateLevenshteinDistance(str1, str2);
			System.out.println("Levenshtein Distance: " + distance);
		}
	}
}