/*
 * Copyright (c) 2001 Matthew Feldt. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided the copyright notice above is
 * retained.
 *
 * THIS SOFTWARE IS PROVIDED ''AS IS'' AND WITHOUT ANY EXPRESSED OR
 * IMPLIED WARRANTIES.
 */

/**
 * Tail.java
 *
 * Java Examples In A Nutshell Copyright (c) 2000 David Flanagan
 * Exercise 3-2:
 * Write a corresponding program named Tail that prints out the last 10 lines
 * of each file specified on the command line.
 *
 * Note: contains a correction and enhancement inspired by raghu
 *
 * @author Matthew Feldt <developer@feldt.com>
 * @version 1.1, 07/25/2002 12:12
 */

package com.feldt.examples.io;
import java.io.*;


public class Tail {
	public static void main (String args[]) {
		final int NUM_LINES = 10, BUFSIZE = 1024;
		long pos, endPos, lastPos;
		int lineCounter = 0;
		byte[] buffer = new byte[BUFSIZE];
		RandomAccessFile in;

		for (int i = 0; i < args.length; i++) {
			try {
				File f = new File(args[i]);
				if (! f.exists()) fail(args[i] + ": no such file or directory.");
				if (! f.canRead()) fail(args[i] + ": read protected.");
				if (! f.isFile()) fail(args[i] + ": is not a regular file.");

				in = new RandomAccessFile(f, "r");
				endPos = in.length(); // determine file length
				lastPos = endPos; // initialize lastPos to end of file

				// guarantee a non-empty file before checking if the very 
				// last character is a newline, count one if not
				if (endPos > 0) {
					byte[] oneByte = new byte[1];
					in.seek(endPos-1);
					in.read(oneByte);
					if ((char)oneByte[0] != '\n') lineCounter++;
				}

				do {
					// seek cursor back BUFSIZE bytes or to beginning of
					// file if there aren't BUFSIZE bytes remaining
					pos = ((lastPos-BUFSIZE) > 0) ? lastPos - BUFSIZE : 0;
					in.seek(pos);

					// if there aren't BUFSIZE bytes left, adjust buffer to
					// read the remaining bytes
					if ((lastPos-pos) < BUFSIZE)
						buffer = new byte[(int)(lastPos-pos)];

					// read bytes in to buffer
					in.readFully(buffer);

					// read backwards through the buffer counting newlines
					for (int j = buffer.length-1; j >= 0; j--) {
						if ((char)buffer[j] == '\n') {
							lineCounter++;
							if (lineCounter > NUM_LINES) {
								pos += (j+1);
								break;
							}
						}
					}

					// update lastPos before looping
					lastPos = pos;
				} while((lineCounter <= NUM_LINES) && (pos != 0));

				// get here after determining where to start printing
				for (pos = lastPos; pos < endPos; pos += buffer.length) {
					in.seek(pos);
					if ((endPos-pos) < BUFSIZE)
						buffer = new byte[(int)(endPos-pos)];
					in.readFully(buffer);
					System.out.print(new String(buffer));
				}
			} catch(EOFException e) {
				System.err.println("EOFException: " + e.getMessage());
			} catch(IOException e) {
				System.err.println(e.getMessage());
			} catch(IllegalArgumentException e) {
				System.err.println(e.getMessage());
			}
		}
	}

	/** shorthand method to throw an exception with the appropriate message */
	protected static void fail(String msg) throws IllegalArgumentException {
		throw new IllegalArgumentException(msg);
	}
}