guard/rb-fsevent

# -*- encoding: utf-8 -*-

require 'otnetstring'

class FSEvent
  class << self
    class_eval <<-END
      def root_path
        "#{File.expand_path(File.join(File.dirname(__FILE__), '..', '..'))}"
      end
    END
    class_eval <<-END
      def watcher_path
        "#{File.join(FSEvent.root_path, 'bin', 'fsevent_watch')}"
      end
    END
  end

  attr_reader :paths, :callback

  def initialize args = nil, &block
    watch(args, &block) unless args.nil?
  end

  def watch(watch_paths, options=nil, &block)
    @paths      = watch_paths.kind_of?(Array) ? watch_paths : [watch_paths]
    @callback   = block

    if options.kind_of?(Hash)
      @options  = parse_options(options)
    elsif options.kind_of?(Array)
      @options  = options
    else
      @options  = []
    end
  end

  def run
    @pipe    = open_pipe
    @running = true

    # please note the use of IO::select() here, as it is used specifically to
    # preserve correct signal handling behavior in ruby 1.8.
    while @running && IO::select([@pipe], nil, nil, nil)
      # managing the IO ourselves allows us to be careful and never pass an
      # incomplete message to OTNetstring.parse()
      message = String.new
      length = String.new
      byte = nil

      reading_length = true
      found_length = false

      while reading_length
        byte = @pipe.read_nonblock(1)
        if "#{byte}" =~ /\d/
          length << byte
          found_length = true
        elsif found_length == false
          next
        else
          reading_length = false
        end
      end
      length = Integer(length, 10)
      type = byte

      message << "#{length}#{type}"
      message << @pipe.read(length)

      decoded = OTNetstring.parse(message)
      modified_paths = decoded["events"].map {|event| event["path"]}
      # passing the full info as a second block param feels icky, but such is
      # the trap of backward compatibility.
      case callback.arity
        when 1
          callback.call(modified_paths)
        when 2
          callback.call(modified_paths, decoded)
      end
    end
  rescue Interrupt, IOError, Errno::EBADF
  ensure
    stop
  end

  def stop
    unless @pipe.nil?
      Process.kill('KILL', @pipe.pid) if process_running?(@pipe.pid)
      @pipe.close
    end
  rescue IOError, Errno::EBADF
  ensure
    @running = false
  end

  def process_running?(pid)
    begin
      Process.kill(0, pid)
      true
    rescue Errno::ESRCH
      false
    end
  end

  if RUBY_VERSION < '1.9'
    def open_pipe
      IO.popen("'#{self.class.watcher_path}' #{options_string} #{shellescaped_paths}")
    end

    private

    def options_string
      @options.join(' ')
    end

    def shellescaped_paths
      @paths.map {|path| shellescape(path)}.join(' ')
    end

    # for Ruby 1.8.6  support
    def shellescape(str)
      # An empty argument will be skipped, so return empty quotes.
      return "''" if str.empty?

      str = str.dup

      # Process as a single byte sequence because not all shell
      # implementations are multibyte aware.
      str.gsub!(/([^A-Za-z0-9_\-.,:\/@\n])/n, "\\\\\\1")

      # A LF cannot be escaped with a backslash because a backslash + LF
      # combo is regarded as line continuation and simply ignored.
      str.gsub!(/\n/, "'\n'")

      return str
    end
  else
    def open_pipe
      IO.popen([self.class.watcher_path] + @options + @paths)
    end
  end

  private

  def parse_options(options={})
    opts = ['--format=otnetstring']
    opts.concat(['--since-when', options[:since_when]]) if options[:since_when]
    opts.concat(['--latency', options[:latency]]) if options[:latency]
    opts.push('--no-defer') if options[:no_defer]
    opts.push('--watch-root') if options[:watch_root]
    opts.push('--file-events') if options[:file_events]
    # ruby 1.9's IO.popen(array-of-stuff) syntax requires all items to be strings
    opts.map {|opt| "#{opt}"}
  end

end