module EmeterGomDaemon
  class Daemon

    Defaults = {
      :logfile => '-',
      :interval => 5,
      :threshold => 5, # in percent
      :nagios_port => 9918,
      :stealth => false,
    }

    # option precedence is: 
    #   1. commands line options
    #   2. GOM Sensor node values
    #   3. built-in Default values (see #Defaults)
    #
    def initialize sensor_url, options = {}
      @sensor_url = sensor_url
      @gom, @sensor_path = (Gom::Remote::Connection.init @sensor_url)

      @options = Defaults.merge(gnode(@sensor_path)).merge(options)
      puts "options: #{@options.inspect}"

      redirect_to logfile
    end

    def logfile
      @logfile ||= @options[:logfile]
    end

    def interval 
      @interval ||= Integer(@options[:interval])
    end

    def emeter_ip
      @emeter_ip ||= @options[:emeter_ip]
    end

    def nagios_port
      @nagios_port ||= @options[:nagios_port]
    end

    def threshold
      @threshold ||= Float(@options[:threshold])
    end

    def stealth?
      @stealth ||= @options[:stealth]
    end

    def run
      run_nagios_thread # become visible to nagios
      gom_checkin
      loop do
        begin
          tic
        rescue Exception => e
          callstack = "#{e.backtrace.join "\n    "}"
          puts " ## #{self} - #{e}\n -> #{callstack}"
        ensure
          sleep interval
        end
      end
    ensure
      stop_nagios_thread
    end

    private

    def tic 
      old = @current_value || 0
      readout = poll
      _, _, _, @current_value = readout
      change_in_percent = 100 * (1 - (@current_value / old)).abs
      if threshold < change_in_percent
        t = Time.now
        puts "#{t} :: #{readout.inspect}"
        puts "#{t} :: #{@current_value}"
        @gom.write "#{@sensor_path}:current_value", @current_value
      end
    end

    def poll
      # expected: '172.20.10.24;WEBIO-042BFF;Sensor 1 0..50A;0,150 A'
      line = (open "http://#{emeter_ip}/Single1").read
      ip, id, name, val = (line.split /;/)
      [ip, id, name, (val.sub! /,/, '.').to_f]
    end

    private

    def redirect_to logfile
      (@logfile_fd && @logfile_fd.close) rescue nil
      puts " -- redirecting stdout/stderr to: #{logfile}"
      if logfile == '-'
        if @stdout
          $stderr, $stdout = @stdout, @stderr
        end
      else
        @stderr, @stdout = $stdout, $stderr
        @logfile_fd = File.open(logfile, File::WRONLY|File::APPEND|File::CREAT)
        @logfile_fd.sync = true
        $stderr = $stdout = @logfile_fd
      end
      # first line after redirect
      puts " -- e-meter daemon logile redirect at #{Time.now}"
    end

    # push own ip and monitoring port back to GOM node
    def gom_checkin
      if stealth?
        puts "skipping gom check-in in stealth mode"
      else
        @gom.write "#{@sensor_path}:daemon_ip", @gom.callback_ip
        @gom.write "#{@sensor_path}:nagios_port", nagios_port
      end
    end

    def stop_nagios_thread
      @nagios_thread or return 
      puts ' -- killing nagios thread...'
      @nagios_thread.kill
      @nagios_thread = nil
      puts '    and gone.'
      self
    end

    def run_nagios_thread
      @nagios_thread .nil? or (raise "already running!")
      port = nagios_port
      @nagios_thread = Thread.new do
        infinity = Proc.new do |env| 
          [200, {"Content-Type" => "text/plain"}, env.inspect]
        end
        puts " -- running nagios server on port: #{port}"
        Rack::Handler::Mongrel.run infinity, :Port => port
      end
      self
    end

    # 
    # TODO: The GOM helper stuff is experimental and being tested here. Once
    # it's prove i'll move it into the gom-script gem
    #

    #def gattr name
    #  (Gom::Remote.connection.read "#{@sensor_path}:#{name}.txt")
    #rescue NameError
    #  nil
    #end

    def gnode path
      json = (Gom::Remote.connection.read "#{path}.json")
      (JSON.parse json)["node"]["entries"].select do |entry|
        # 1. select attribute entries
        entry.has_key? "attribute"
      end.inject({}) do |h, a|
        # 2. make it a key, value list
        kv = a["attribute"]
        h.update(kv["name"].to_sym => kv["value"])
      end
    end
  end
end