import "math/event" for Event, MultiListenerToken
import "math/util" for Util

class Observable{
  value{_value}
  value=(v){
    _event.emit([v]) //do extra list wrapping here to allow list values
    _value = v
  }
  value_no_update=(v){_value = v}

  event{_event}

  static new(value){
    var variable = new()
    variable.value_no_update = value
    return variable
  }

  construct new(){
    _event = Event.new()
  }

  //manually emit an update
  emit(){
    _event.emit([_value])
  }

  on_change(fn){
    return _event.listen(fn)
  }

  on_change(initial, fn){
    if(initial){
      fn.call(value)
    }
    return on_change(fn)
  }

  not_on_change(fn){
    _event.unlisten(fn)
  }

  on_not_null(fn){
    if(value){
      fn.call(value)
    } else {
      _event.once(fn)
    }
  }

  static any_change(observables, fn){
    var change_method = Fn.new{|whatever|
      Util.call_arg_list(fn, observables.map{|observable| observable.value.toList})
    }
    var tokens = observables.map{|observable|
      return observable.on_change(change_method)
    }
    return MultiListenerToken.new(tokens)
  }

  static any_change(observables, initial, fn){
    if(initial){
      Util.call_arg_list(fn, observables.map{|observable|observable.value}.toList)
    }
    any_change(observables, fn)
  }
}