require 'yajl'
require 'geokit'
require 'socket'
require 'ruby-units'
require 'json/pure'

class GPSPipe
  attr_accessor :host, :port

  def initialize(host='127.0.0.1', port='2947')
    @host = host
    @port = port
    # Hash that stores history for distance calculation
    @history = {'TPV' => []} # defaultize the hash
  end

  # Opens a connection to gpsd and streams from it
  def stream()
    TCPSocket.open(@host, @port) do |socket|
      socket.write "?WATCH={\"enable\":true,\"json\":true}"
      socket.each_line do |line|
        parsed = handle_data(line)
        yield parsed if parsed
      end
    end
  end

private
  def handle_data(data)
    data = JSON.parse(data.chomp)
    case data["class"]
      when "VERSION", "DEVICES", "WATCH"
        data
      when "SKY"
        # TODO
      when "TPV"
        moved?(data) ? data : nil
      else
        raise ArgumentError, 'Unknown input: %s' % data
    end
  end

  def cleanup_history!
    @history.each_value do |value|
      raise "History is bogus" if value.length > 4
      value.shift if value.length > 3
    end
  end

  def has_moved?(data)
    # Remove old items from history, append item to history and return the history
    cleanup_history!
    h = @history['TPV']
    h << data

    # Check that we moved 1m away from history coordinates
    minimum_distance = Unit.new("0.2 meters")
    now     = GeoKit::LatLng.new(h.last['lat'], h.last['lon'])
    matches = h[0..-2].select { |test|
      previous = GeoKit::LatLng.new(test['lat'], test['lon'])
      distance = Unit.new("%s miles" % previous.distance_to(now))

      distance > minimum_distance
    }

    # Return true if our distance changed compard to *all* items in history
    # If we really moved, then we aren't just jumping between 2 coordinates.
    matches.length == h.length-1
  end
end

gpspipe = GPSPipe.new()
gpspipe.stream do |output|
  p output
end