melbourne_metro_trains.rb

class MelbourneMetroTrains < SiriProxy::Plugin
  trigger /when is my next train/ do |data|
    respond_with_next_train data
  end

  contextual_trigger :map_show, /map/ do |data|
    show_map Map.new(@train_details.station.coordinates) # Automatic bounding box

    available_transitions.clear
  end

  def respond_with_next_train(data)
    if default_station.nil?
      return if ask_and_store_default_station == false
    end

    train_details = fetch_train_details(data.current_location, default_station)

    if train_details
      say "Your next #{train_details.line} train to #{default_station} departs from #{train_details.source} at #{train_details.time}"    

      @train_details = train_details
      available_transitions << :map_show
    else
      say "Sorry, I'm unable to retrieve your train details."
    end
  end

  def ask_and_store_default_station
    say "I don't know where you usually go in the #{morning_or_afternoon}"
    station = ask("What is the station?", all_stations)

    if station.nil?
      false
    else
      true
    end
  end

  private

  def all_stations
    # Static or dynamic list of stations
  end
end

plugin.rb

class SiriProxy::Plugin

  def self.trigger(regex, &block)
    @triggers ||= {}
    @triggers[regex] = block
  end

  def self.triggers
    @triggers
  end

  def self.contextual_trigger(name, regex, &block)
    @contextual_triggers ||= {}
    @contextual_triggers[[name, regex]] = block # This is a hack, haven't thought about it yet
  end

  def self.contextual_triggers
    @contextual_triggers
  end

  def available_transactions
    @available_transactions ||= []
  end

protected

  def say(text)
    connection.say(text)
  end

  def ask(prompt, valid_options = nil)
    say(text)

    input = nil # Scope
    while true
      input = prompt_speech
      return nil if input.cancel?

      if valid_options && !valid_options.include?(input)
        say("I'm sorry, I could not find '#{input}'.")
        next
      end

      break
    end

    input
  end

  def show_map(coords, bonuds = nil)
    # Magical show map here
  end

  def prompt_speech
    connection.prompt_speech
  end
end