# inspired by toy-rx: https://github.com/staltz/toy-rx
class Subscriber
  attr_writer :subscription

  def initialize(observer)
    @observer = observer
  end

  def next(value)
    @observer.next(value)
  end

  def error(error)
    @observer.error(error)
  end

  def complete
    @observer.complete
  end

  def unsubscribe
    @subscription.unsubscribe unless @subscription.nil?
  end
end

class Observable
  def initialize(&subscribe)
    @subscribe = subscribe
  end

  def self.create(&subscribe)
    fail ArgumentError, "`create` needs a subscribe block" unless block_given?
    new do |observer|
      subscriber = Subscriber.new(observer)
      subscription = subscribe.call(subscriber);
      subscriber.subscription = subscription
      subscription
    end
  end

  # XXX probably nicer to define operators in another file
  def map(&tx)
    inobservable = self
    Observable.create do |out|
      observer = {
        next: -> (x) {
          begin
            out.next(tx.call(x))
          rescue => e
            out.error(e)
          end
        },
        error: -> (e) { out.error(e) },
        complete: -> (e) { out.complete },
      };
      inobservable.subscribe(observer)
    end
  end

  def subscribe(callbacks = {}, &nextcb)
    callbacks[:next] = nextcb if block_given?
    noop = -> () {}

    klass = Class.new do
      define_method(:next,     callbacks.fetch(:next, noop))
      define_method(:error,    callbacks.fetch(:error, noop))
      define_method(:complete, callbacks.fetch(:complete, noop))
    end

    observer = klass.new
    @subscribe.call(observer)
  end
end