Weather-O-Rama Inc.’s next generation, Internet-based Weather Monitoring Station

weather_o_rama.rb

module Subject
  def register_observer()
    raise NotImplementedError
  end

  def remove_observer()
    raise NotImplementedError
  end

  def notify_observers()
    raise NotImplementedError
  end
end

module Observer
  def update()
    raise NotImplementedError
  end
end

module DisplayElement
  def display()
    raise NotImplementedError
  end

  # UTF-8 encoding table and Unicode characters
  # http://www.utf8-chartable.de/unicode-utf8-table.pl?start=9472&unicodeinhtml=dec
  def box(title, body, width=78)
    lines = []
    lines << "╔%s╗" % ( "[ #{title} ]".center(width, "═") )
    lines << "║%s║" % ( "░" * width                       )
    lines << "║%s║" % ( " #{body} ".center(width, "░")    )
    lines << "║%s║" % ( "░" * width                       )
    lines << "╚%s╝" % ( "═" * width                       )
    lines.join("\n")
  end
end

###

class WeatherData
  include Subject

  attr_reader :temperature, :humidity, :pressure
  attr_reader :observers

  def initialize
    @observers = []
  end

  def register_observer(observer)
    observers.push(observer)
  end

  def remove_observer(observer)
    observers.delete(observer)
  end

  def notify_observers()
    observers.each(&:update)
  end

  def measurements_changed()
    notify_observers()
  end

  def set_measurements(temperature, humidity, pressure)
    @temperature = temperature
    @humidity    = humidity
    @pressure    = pressure
    measurements_changed()
  end
end

class CurrentConditionsDisplay
  include Observer
  include DisplayElement

  attr_reader :temperature, :humidity
  attr_reader :weather_data

  def initialize(weather_data)
    @weather_data = weather_data
    @weather_data.register_observer(self)
  end

  def update()
    @temperature = weather_data.temperature
    @humidity    = weather_data.humidity
    display()
  end

  def display()
    title = "Current Conditions"
    body  = "#{temperature} F degrees and #{humidity}% humidity"
    puts box(title, body)
  end
end

class ForecastDisplay
  include Observer
  include DisplayElement

  attr_reader :current_pressure, :last_pressure
  attr_reader :weather_data

  def initialize(weather_data)
    @current_pressure = 29.92
    @weather_data     = weather_data
    @weather_data.register_observer(self)
  end

  def update()
    @last_pressure    = current_pressure
    @current_pressure = weather_data.pressure
    display()
  end

  def display()
    title = "Forecast"
    body  = if current_pressure > last_pressure
              "Improving weather on the way!"
            elsif current_pressure < last_pressure
              "Watch out for cooler, rainy weather"
            else
              "More of the same"
            end
    puts box(title, body)
  end
end

class StatisticsDisplay
  include Observer
  include DisplayElement

  attr_reader :max_temp, :min_temp, :temp_sum, :num_readings
  attr_reader :weather_data

  def initialize(weather_data)
    @max_temp     = 0
    @min_temp     = 200
    @temp_sum     = 0
    @num_readings = 0
    @weather_data = weather_data
    @weather_data.register_observer(self)
  end

  def update()
    @temp_sum     += weather_data.temperature
    @num_readings += 1

    if weather_data.temperature > @max_temp
      @max_temp = weather_data.temperature
    end

    if weather_data.temperature < @min_temp
      @min_temp = weather_data.temperature
    end

    display()
  end

  def display()
    title = "Statistics"
    body  = "Avg/Max/Min temperature = %s/%s/%s"
    body  = body % [temp_sum/num_readings, max_temp, min_temp]
    puts box(title, body)
  end
end

class HeatIndexDisplay
  include Observer
  include DisplayElement

  attr_reader :heat_index
  attr_reader :weather_data

  def initialize(weather_data)
    @weather_data = weather_data
    @weather_data.register_observer(self)
  end

  def update()
    @heat_index = compute_heat_index(
                    weather_data.temperature,
                    weather_data.humidity
                  )
    display()
  end

  # The Heat Index Equation
  # http://www.hpc.ncep.noaa.gov/html/heatindex_equation.shtml
  def compute_heat_index(t, rh)
    -42.379 + 2.04901523*t + 10.14333127*rh - 0.22475541*t*rh -
      0.00683783*t*t - 0.05481717*rh*rh + 0.00122874*t*t*rh +
      0.00085282*t*rh*rh - 0.00000199*t*t*rh*rh
  end

  def display()
    title = "Heat Index"
    body  = "Heat index is %.2f" % @heat_index
    puts box(title, body)
  end
end

###

class WeatherStation
  def self.start()
    weather_data = WeatherData.new

    current_display    = CurrentConditionsDisplay.new(weather_data)
    forecase_display   = ForecastDisplay.new(weather_data)
    statistics_display = StatisticsDisplay.new(weather_data)
    heat_display       = HeatIndexDisplay.new(weather_data)

    weather_data.set_measurements(80, 65, 30.4)
    weather_data.set_measurements(82, 70, 29.2)
    weather_data.set_measurements(78, 90, 29.2)
  end
end

if $0 == __FILE__
  WeatherStation.start()
end