import java.io.IOException;

import org.apache.lucene.analysis.WhitespaceAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;

public class Exec {
        public static double computeAngle(String[] doc1, String[] doc2) {
                // assume words are unique and only occur once

                int dotProduct = 0;
                double denominator;

                for (int i = 0; i < doc1.length; i++) {
                        String word = doc1[i];
                        for (int j = 0; j < doc2.length; j++) {
                                if (word.equals(doc2[j])) {
                                        dotProduct += 1;
                                        break;
                                }
                        }
                }
                denominator = Math.sqrt(doc1.length) * Math.sqrt(doc2.length);
                double ratio = dotProduct / denominator;
                return Math.acos(ratio);
        }

        // For simple, only to get one document which must be belong to the matching
        // document
        public static Document docsLike(IndexReader reader, IndexSearcher searcher,
                        int id) throws IOException {
                Document doc = reader.document(id);
                String[] s1 = (doc.get("subjects")).split(" ");

                int matchid = 0;
                double bestAngle = Double.MAX_VALUE;

                for (int i = 0; i < reader.maxDoc(); i++) {
                        if (i != id) {
                                Document tempdoc = reader.document(i);
                                String[] s2 = (tempdoc.get("subjects")).split(" ");
                                double angle = computeAngle(s1, s2);
                                // System.out.print("***"+angle);
                                if (angle < bestAngle) {
                                        bestAngle = angle;
                                        matchid = i;
                                }
                        }
                }
                // System.out.println("/n***********"+bestAngle+"***********"+matchid);
                return reader.document(matchid);
        }

        public static void main(String[] args) throws IOException {

                IndexReader reader;
                IndexSearcher searcher;

                // Writer
                Directory directory = new RAMDirectory();
                IndexWriter writer = new IndexWriter(directory,
                                new WhitespaceAnalyzer(), true);
                writer.setUseCompoundFile(true);

                String[] isbns = new String[] { "1", "2", "3", "4", "5", "6", "7", "8",
                                "9", "10", "11" };

                String[] titles = new String[] { "Modern Art of Education",
                                "Imperial Secrets of Health", "Tao Te Ching",
                                "G.del, Escher, Bach", "Mindstorms",
                                "Java Development with Ant", "JUnit in Action",
                                "Lucene in Action", "Tapestry in Action",
                                "Extreme Programming Explained", "The Pragmatic Programmer" };
                String[] pubmonths = new String[] { "198106", "199401", "198810",
                                "197903", "198001", "200208", "200310", "200406", "199910",
                                "200403", "199910" };
                String[] categories = new String[] { "/education/pedagogy",
                                "/health/alternative/chinese", "/philosophy/eastern",
                                "/technology/computers/ai",
                                "/technology/computers/programming/education",
                                "/technology/computers/programming",
                                "/technology/computers/programming",
                                "/technology/computers/programming",
                                "/technology/computers/programming",
                                "/technology/computers/programming/methodology",
                                "/technology/computers/programming" };
                String[] subjects = new String[] {
                                "education philosophy psychology practice Waldorf",
                                "diet chinese medicine qi gong health herbs",
                                "taoism chinese ideas",
                                "artificial intelligence number theory mathematics music",
                                "children computers powerful ideas LOGO education",
                                "apache jakarta ant build tool junit java development",
                                "junit unit testing mock objects",
                                "lucene search programming",
                                "tapestry web user interface components",
                                "extreme programming agile test driven development methodology",
                                "pragmatic agile methodology developer tools" };

                for (int i = 0; i < titles.length; i++) {
                        Document doc = new Document();
                        doc.add(Field.Keyword("isbns", isbns[i]));
                        doc.add(Field.Text("titles", titles[i]));
                        doc.add(Field.Text("pubmonths", pubmonths[i]));
                        doc.add(Field.Text("categories", categories[i]));
                        doc.add(Field.Text("subjects", subjects[i], true));
                        writer.addDocument(doc);
                }
                writer.optimize();
                writer.close();

                // Reader
                reader = IndexReader.open(directory);
                searcher = new IndexSearcher(reader);
                int numDocs = reader.maxDoc();

                for (int i = 0; i < numDocs; i++) {
                        System.out.println();
                        Document doc = reader.document(i);
                        System.out.println(doc.get("titles"));
                        Document docs = docsLike(reader, searcher, i);
                        System.out.println("  -> " + docs.get("titles"));
                }
        }
}