proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/TailFilter.java

/*
 *  The Apache Software License, Version 1.1
 *
 *  Copyright (c) 2002 The Apache Software Foundation.  All rights
 *  reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *  notice, this list of conditions and the following disclaimer.
 *
 *  2. Redistributions in binary form must reproduce the above copyright
 *  notice, this list of conditions and the following disclaimer in
 *  the documentation and/or other materials provided with the
 *  distribution.
 *
 *  3. The end-user documentation included with the redistribution, if
 *  any, must include the following acknowlegement:
 *  "This product includes software developed by the
 *  Apache Software Foundation (http://www.apache.org/)."
 *  Alternately, this acknowlegement may appear in the software itself,
 *  if and wherever such third-party acknowlegements normally appear.
 *
 *  4. The names "The Jakarta Project", "Ant", and "Apache Software
 *  Foundation" must not be used to endorse or promote products derived
 *  from this software without prior written permission. For written
 *  permission, please contact apache@apache.org.
 *
 *  5. Products derived from this software may not be called "Apache"
 *  nor may "Apache" appear in their names without prior written
 *  permission of the Apache Group.
 *
 *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 *  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *  DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 *  ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 *  USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 *  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 *  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 *  OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 *  SUCH DAMAGE.
 *  ====================================================================
 *
 *  This software consists of voluntary contributions made by many
 *  individuals on behalf of the Apache Software Foundation.  For more
 *  information on the Apache Software Foundation, please see
 *  <http://www.apache.org/>.
 */
package org.apache.tools.ant.filters;

import java.io.IOException;
import java.io.Reader;

import org.apache.tools.ant.types.Parameter;

/**
 * Read the last n lines.  Default is last 10 lines.
 *
 * Example:
 * =======
 *
 * &lt;tailfilter lines=&quot;3&quot;/&gt;
 *
 * Or:
 *
 * &lt;filterreader classname=&quot;org.apache.tools.ant.filters.TailFilter&quot;&gt;
 *    &lt;param name=&quot;lines&quot; value=&quot;3&quot;/&gt;
 * &lt;/filterreader&gt;
 *
 * @author <a href="mailto:umagesh@apache.org">Magesh Umasankar</a>
 */
public final class TailFilter
    extends BaseParamFilterReader
    implements ChainableReader
{
    /** The name that param recognizes to set the number of lines. */
    private static final String LINES_KEY = "lines";

    /** Number of lines currently read in. */
    private long linesRead = 0;

    /** Default number of lines returned. */
    private long lines = 10;

    /** Buffer to hold in characters read ahead. */
    private char[] buffer = new char[4096];

    /** The character position that has been returned from the buffer. */
    private int returnedCharPos = -1;

    /** Has read ahead been completed? */
    private boolean completedReadAhead = false;

    /** Current index position on the buffer. */
    private int bufferPos = 0;

    /**
     * This constructor is a dummy constructor and is
     * not meant to be used by any class other than Ant's
     * introspection mechanism. This will close the filter
     * that is created making it useless for further operations.
     */
    public TailFilter() {
        super();
    }

    /**
     * Create a new filtered reader.
     *
     * @param in  a Reader object providing the underlying stream.
     */
    public TailFilter(final Reader in) {
        super(in);
    }

    /**
     * Read ahead and keep in buffer last n lines only at any given
     * point.  Grow buffer as needed.
     */
    public final int read() throws IOException {
        if (!getInitialized()) {
            initialize();
            setInitialized(true);
        }

        if (!completedReadAhead) {
            int ch = -1;
            while ((ch = in.read()) != -1) {
                if (buffer.length == bufferPos) {
                    if (returnedCharPos != -1) {
                        final char[] tmpBuffer = new char[buffer.length];
                        System.arraycopy(buffer, returnedCharPos + 1, tmpBuffer,
                                         0, buffer.length - (returnedCharPos + 1));
                        buffer = tmpBuffer;
                        bufferPos = bufferPos - (returnedCharPos + 1);
                        returnedCharPos = -1;
                    } else {
                        final char[] tmpBuffer = new char[buffer.length * 2];
                        System.arraycopy(buffer, 0, tmpBuffer, 0, bufferPos);
                        buffer = tmpBuffer;
                    }
                }

                if (ch == '\n' || ch == -1) {
                    ++linesRead;

                    if (linesRead == lines) {
                        int i = 0;
                        for (i = returnedCharPos + 1;
                            buffer[i] != 0 && buffer[i] != '\n'; i++) {
                        }
                        returnedCharPos = i;
                        --linesRead;
                    }
                }
                if (ch == -1) {
                    break;
                }

                buffer[bufferPos] = (char) ch;
                bufferPos++;
            }
            completedReadAhead = true;
        }

        ++returnedCharPos;
        if (returnedCharPos >= bufferPos) {
            return -1;
        } else {
            return buffer[returnedCharPos];
        }
    }

    /**
     * Set number of lines to be returned.
     */
    public final void setLines(final long lines) {
        this.lines = lines;
    }

    /**
     * Get number of lines to be returned.
     */
    private final long getLines() {
        return lines;
    }

    /**
     * Create a new TailFilter using the passed in
     * Reader for instantiation.
     */
    public final Reader chain(final Reader rdr) {
        TailFilter newFilter = new TailFilter(rdr);
        newFilter.setLines(getLines());
        newFilter.setInitialized(true);
        return newFilter;
    }

    /**
     * Scan for the lines parameter.
     */
    private final void initialize() {
        Parameter[] params = getParameters();
        if (params != null) {
            for (int i = 0; i < params.length; i++) {
                if (LINES_KEY.equals(params[i].getName())) {
                    setLines(new Long(params[i].getValue()).longValue());
                    break;
                }
            }
        }
    }
}