/*
 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit http://www.davidflanagan.com/javaexamples2.
 */
package com.davidflanagan.examples.io;
import java.io.*;

/**
 * This class is a BufferedReader that filters out all lines that
 * do not contain the specified pattern.
 **/
public class GrepReader extends BufferedReader {
    String pattern;  // The string we are going to be matching.
    
    /** Pass the stream to our superclass, and remember the pattern ourself */
    public GrepReader(Reader in, String pattern) {
        super(in);
        this.pattern = pattern;
    }
    
    /**
     * This is the filter: call our superclass's readLine() to get the
     * actual lines, but only return lines that contain the pattern.
     * When the superclass readLine() returns null (EOF), we return null.
     **/
    public final String readLine() throws IOException {
        String line;
        do { line = super.readLine(); }
        while ((line != null)&& line.indexOf(pattern) == -1);
        return line;
    }
    
    /**
     * This class demonstrates the use of the GrepReader class.
     * It prints the lines of a file that contain a specified substring.
     **/
    public static class Test {
        public static void main(String args[]) {
            try {
                if (args.length != 2) 
                    throw new IllegalArgumentException("Wrong number of args");
                GrepReader in=new GrepReader(new FileReader(args[1]), args[0]);
                String line;
                while((line = in.readLine()) != null) System.out.println(line);
                in.close();
            }
            catch (Exception e) { 
                System.err.println(e);
                System.out.println("Usage: java GrepReader$Test" +
				   " <pattern> <file>");
            }
        }
    }
}