import gleam/erlang/process
import gleam/list
import gleam/otp/actor
import sensors

pub type Subscriber =
  process.Subject(sensors.SensorReading)

pub type Message {
  Subscribe(subscriber: Subscriber)
  Proc
}

pub type Subscribers =
  List(Subscriber)

fn handle_message(
  subscribers: Subscribers,
  message: Message,
) -> actor.Next(Subscribers, Message) {
  case message {
    Subscribe(subscriber) -> {
      let new_subscribers = [subscriber, ..subscribers]
      actor.continue(new_subscribers)
    }
    Proc -> {
      list.each(subscribers, fn(subscriber) {
        process.send(
          subscriber,
          sensors.SensorReading(sensors.Temperature, 26.6),
        )
      })
      actor.continue(subscribers)
    }
  }
}

// Subscribe to receive ticks from the dummy actor
pub fn subscribe(actor_ref: process.Subject(Message)) -> Subscriber {
  let mailbox = process.new_subject()
  process.send(actor_ref, Subscribe(mailbox))
  mailbox
}

// Start the actor
pub fn start() -> Result(process.Subject(Message), actor.StartError) {
  let assert Ok(started) =
    actor.new([])
    |> actor.on_message(handle_message)
    |> actor.start
  Ok(started.data)
}