umich.ms.fileio.util.ReverseLineInputStream Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of msftbx Show documentation
MSFTBX - Mass Spectrometry File Tool Box
There is a newer version: 1.8.8
/* 
 * Copyright 2016 Dmitry Avtonomov.
 *
 * Licensed 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 umich.ms.fileio.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;

/**
 *
 * @author Dmitry Avtonomov
 */
public class ReverseLineInputStream extends InputStream {
    RandomAccessFile in;
    long currentLineStart = -1;
    long currentLineEnd = -1;
    long currentPos = -1;
    long lastPosInFile = -1;

    public ReverseLineInputStream(RandomAccessFile raf) throws IOException {
        in = raf;
        currentLineStart = raf.length();
        currentLineEnd = raf.length();
        lastPosInFile = raf.length() - 1;
        currentPos = currentLineEnd;
    }

    public void setFilePointer(long pos) {
        currentLineEnd = pos;
        currentLineStart = pos;
        currentPos = pos;
    }

    public void findPrevLine() throws IOException {
        currentLineEnd = currentLineStart;
        // There are no more lines, since we are at the beginning of the file and no lines.
        if (currentLineEnd == 0) {
            currentLineEnd = -1;
            currentLineStart = -1;
            currentPos = -1;
            return;
        }
        long filePointer = currentLineStart - 1;
        while (true) {
            filePointer--;
            // we are at start of file so this is the first line in the file.
            if (filePointer < 0) {
                break;
            }
            in.seek(filePointer);
            int readByte = in.readByte();
            // We ignore last LF in file. search back to find the previous LF.
            if (readByte == 0xA && filePointer != lastPosInFile) {
                break;
            }
        }
        // we want to start at pointer +1 so we are after the LF we found or at 0 the start of the file.
        currentLineStart = filePointer + 1;
        currentPos = currentLineStart;
    }

    @Override
    public int read() throws IOException {
        if (currentPos < currentLineEnd) {
            in.seek(currentPos++);
            int readByte = in.readByte();
            return readByte;
        } else if (currentPos < 0) {
            return -1;
        } else {
            findPrevLine();
            return read();
        }
    }
    
}