watch.rb

#!/usr/bin/env ruby
require 'tempfile'
require 'fileutils'

# Signals
trap("SIGINT") { exit }

# Setup
TARGET_FOLDER = ARGV[0]
TARGET_URL    = ARGV[1]

if TARGET_FOLDER.nil? || TARGET_URL.nil?
  puts "Usage: #{$0} TARGET_FOLDER TARGET_URL"
  exit
end

# Apple script wrapper class
class AppleScript

  def initialize(content)
    @file = Tempfile.new('applescript')
    @file.write(content)
    @file.close
    FileUtils.chmod(0755, @file.path)
 end

  def run(*args)
    %x[#{@file.path} #{args.join(" ")}]
  end

end

# Watcher wrapper class
class Watcher
  EXTENSIONS = %w( htm html css js jpg jpeg gif png php asp rb )

  def initialize(path)
    @directory = path
    @file_list = build_file_list
    @callbacks = {}
  end

  # Register callback to run on file change
  def on_change(&block)
    @callbacks[:change] = block
  end

  # Run the watcher event loop
  def run!
    loop do
      new_file_list = build_file_list

      unless (diff = @file_list - new_file_list).empty?
        @file_list = new_file_list

        sleep 0.5

        diff.each do |meta|
          @callbacks[:change].call(meta[0])
        end
      end

      sleep 0.5
    end
  end

  def build_file_list
    list = EXTENSIONS.map do |ext|
      Dir[File.join(@directory, "**", "*.#{ext}")]
    end

    list.flatten!
    list.collect do |file|
      [file, File.stat(file).mtime.to_i]
    end
  end
end

script_content = <<-APPLESCRIPT
#!/usr/bin/osascript
on run argv
    set theUrl to "about:blank"
    if (count of argv) > 0 then
        set theUrl to item 1 of argv
        if not (theUrl starts with "http://" or theUrl starts with "https://") then
            set theUrl to "http://" & theUrl
        end if
    end if
    tell application "Google Chrome"
        set found to false
        set theWindowIndex to 0
        repeat with theWindow in every window
            set theTabIndex to 0
            repeat with theTab in every tab of theWindow
                set theTabIndex to theTabIndex + 1
                if theTab's URL starts with theUrl then
                    set found to true
                    tell application "Google Chrome" to set active tab index of theWindow to theTabIndex
                    tell theTab to reload
                end if
            end repeat
        end repeat
        if not found then
            set URL of (active tab of (make new window)) to theUrl
        end if
    end tell
end run
APPLESCRIPT

# Run it
script  = AppleScript.new(script_content)
watcher = Watcher.new(TARGET_FOLDER)

watcher.on_change do |path|
  puts "- #{path} changed."
  script.run(TARGET_URL)
end

watcher.run!