#!/usr/bin/ruby

unless ARGV.size == 2
	puts "Usage: #{File.basename($0)} <file> <command>"
	exit 1
end

file = ARGV.shift
command = ARGV.shift

unless test(?f, file)
	puts "Invalid file: #{file}"
	exit 1
end

mt = File.stat(file).mtime

pid = nil

puts "+++ Watching ..."
begin
	loop do
		Process.wait(-1, Process::WNOHANG) rescue nil
		mt_new = File.stat(file).mtime rescue next
		unless mt_new == mt
			puts "+++ File (#{file}) changed ... launching command."
			if pid
				Process.kill(9, pid) if (Process.kill(0, pid) rescue nil)
				pid = nil
			end
			pid = fork do
				Kernel.exec("sh", "-c", command)
			end
			puts "+++ Watching ..."
			mt = mt_new
		end
		sleep 0.5
	end
rescue Interrupt
end