/*
 * Copyright 2013 Eediom Inc.
 * 
 * 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 org.araqne.log.api;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

public class TextFileReader {
	private String charsetName;
	private RandomAccessFile raf;
	private ByteArrayOutputStream bos = new ByteArrayOutputStream();

	private byte[] buf = new byte[80960];
	private int bufpos = 0;
	private int buflen = 0;
	private long readBytes;
	private boolean closed;
	private final boolean needLastNewLine;

	public TextFileReader(File file, long offset, String charsetName) throws IOException {
		this(file, offset, charsetName, false);
	}

	public TextFileReader(File file, long offset, String charsetName, boolean needLastNewLine) throws IOException {
		this.charsetName = charsetName;
		this.raf = new RandomAccessFile(file, "r");
		this.raf.seek(offset);
		this.readBytes += offset;
		this.needLastNewLine = needLastNewLine;
	}

	public String readLine() throws IOException {
		if (closed)
			throw new IOException("Already closed");

		long bytes = 0;
		if (buflen < 0)
			buflen = 0;

		bos.reset();
		String line = null;
		boolean lineEnd = false;
		while (!lineEnd) {
			if (buflen < 0) {
				if (bos.size() == 0)
					return null;
				else if (needLastNewLine) {
					// back file pointer to last newline
					raf.seek(readBytes);
					raf.getFD().sync();
					return null;
				} else
					return bos.toString(charsetName);
			}

			while (true) {
				if (bufpos >= buflen) {
					buflen = raf.read(buf, 0, buf.length);
					if (buflen < 0)
						break;

					bufpos = 0;
				}

				boolean found = false;
				int begin = bufpos;
				while (bufpos < buflen) {
					byte b = buf[bufpos++];
					bytes++;
					if (b == 0xa) {
						found = true;
						break;
					}
				}

				int len = bufpos - begin;
				bos.write(buf, begin, len);
				if (found)
					break;
			}

			if (bos.size() == 0) {
				if (!needLastNewLine) {
					readBytes += bytes;
					bytes = 0;
				}
				return null;
			}

			line = bos.toString(charsetName);
			lineEnd = line.endsWith("\n");
			if (lineEnd || !needLastNewLine) {
				readBytes += bytes;
				bytes = 0;
			}
		}

		int len = line.length();

		if (line.endsWith("\r\n"))
			return line.substring(0, len - 2);
		return line.substring(0, len - 1);
	}

	public long getPosition() throws IOException {
		if (closed)
			throw new IOException("Already closed");
		return readBytes;
	}

	public void close() {
		if (closed)
			return;

		closed = true;
		buf = null;
		bos = null;

		try {
			raf.close();
			raf = null;
		} catch (IOException e) {
		}
	}
}