# Copyright (c) 2008 Grant Rettke (grettke@acm.org)
# 
# 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 name of the author may not be used to endorse or promote products
#    derived from this software without specific prior written permission.
# 
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS 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 AUTHOR 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.

# $LastChangedDate: 2008-04-27 21:28:21 -0500 (Sun, 27 Apr 2008) $
# $LastChangedRevision: 1697 $
# $HeadURL: svn://osiris/smoothtail/tags/1.00/smoothtail.rb $

# Smoothtail is a tail utility written for Microsoft Windows that is simple, free, and provides regex based pattern matching. It depends on Ruby 1.8.4 and File::Tail version 0.1.3.

# Believe it or not, Microsoft Windows has not got any tail utilies
# that are simultaneously:
# * good
# * free
# * easy to use
#
# To remedy this situation I wrote what is essentially a helper script
# that uses Florian Frank's <flori@ping.de> excellent File::Tail library.
#
# Combine an explanation (in the script itself) of how to add this
# tail utility to the Windows "Send To" menu with pattern matching in the tail
# itself and the result is a nice little tail utility. 

# How to install in Windows SendTo Shell
#
#   Please subsitute paths as desired
#
#   1. In explorer open C:\Documents and Settings\<user name>\SendTo
#   2. Right click the window and choose New->Shorcut.
#   3. In the location of the item paste
#       %SystemRoot%\system32\cmd.exe /k ruby <full path to location of>\smoothtail.rb
#   4. Name the shortcut "smoothtail".
#
#   You need to run this with: ruby 1.8.4 (2006-04-14) [i386-mswin32]

# 	Import the 'file-tail' library via its gem
# 	This script was written against version 0.1.3
# 	Install it by typing at the command line
#   	'gem install file-tail-0.1.3.gem'
require 'file/tail'

# At least one argument, the file name to tail, must be provided.
# Otherwise display usage and stop the program
file_name = ARGV.shift or fail "Usage: #$0 filename"

print "Please enter the desired regex pattern (or hit enter to display every line instead): "
regex_pattern = gets
regex_pattern = regex_pattern.chomp

# Create a file-tail Logfile object and get a block in which we have got a reference do it (log_file)
File::Tail::Logfile.open(file_name) do |log_file|
    
    # The start value of the sleep interval. This value
    # goes against <code>max_interval</code> if the tailed
    # file is silent for a sufficient time.
    log_file.interval = 1
    
    # The maximum interval File::Tail sleeps, before it tries
    # to take some action like reading the next few lines
    # or reopening the file.
    log_file.max_interval = 5
    
    # If this attribute is set to a true value, File::Tail persists
    # on reopening a deleted file waiting <code>max_interval</code> seconds
    # between the attempts. This is useful if logfiles are
    # moved away while rotation occurs but are recreated at
    # the same place after a while. It defaults to true.
    log_file.reopen_deleted = true
    
    # If this attribute is set to a true value, File::Tail
    # attempts to reopen it's tailed file after
    # <code>suspicious_interval</code> seconds of silence.
    log_file.reopen_suspicious = true
    
    # This attribute is the invterval in seconds before File::Tail
    # gets suspicious that something has happend to it's tailed file
    # and an attempt to reopen it is made.
    #
    # If the attribute <code>reopen_suspicious</code> is
    # set to a non true value, suspicious_interval is
    # meaningless. It defaults to 60 seconds.
    log_file.suspicious_interval = 20
    
    # Default arguments, called here for example, are (n = 0, bufsiz = nil)
    # Rewind the last <code>n</code> lines of this file, starting
    # from the end. The default is to start tailing directly from the
    # end of the file.
    #
    # The additional argument <code>bufsiz</code> is
    # used to determine the buffer size that is used to step through
    # the file backwards. It defaults to the block size of the 
    # filesystem this file belongs to or 8192 bytes if this cannot
    # be determined.
    #
    # This call starts a the last two lines of the file
    log_file.rewind(20)
    
    # If the user passed in a pattern on which to match, only print matching lines.
    # Otherwise print every line.
    work = nil
    if regex_pattern.length == 0
        work = lambda { |line| print "#{line}" }
    else
        work =
            lambda do |line|
                regex = Regexp.new(regex_pattern)
                if regex.match(line)
                    print "#{line}"
                end
            end
    end
	
	# Start tailing the file
	log_file.tail do |line|
		work.call(line)
	end # end block: tailing the file, only CTRL-C gets you out of this block
	
end # end block: the log file reference