import {
  EventStream,
  EventStreamSeed,
  Observer,
  Property,
  PropertySeed,
  Event,
  isValue,
  valueEvent,
  AtomSeed,
  Subscribe,
  isProperty,
  isEventStream,
  isEventStreamSeed,
  isPropertySeed,
  Desc,
} from "./abstractions"
import { cachedFn } from "./cachedFn"
import { StatelessEventStream } from "./eventstream"
import { EventStreamSeedImpl } from "./eventstream"
import { PropertySeedImpl } from "./property"
import { StatelessProperty } from "./property"
import { In } from "./transform"

export type MapResult<A, B, O> = O extends Property<any>
  ? Property<B>
  : O extends PropertySeed<any>
  ? PropertySeed<B>
  : O extends EventStream<any>
  ? EventStream<B>
  : EventStreamSeed<B>

export interface MapOp<A, B> {
  <O>(o: In<O, A>): MapResult<A, B, O>
}
export function map<A, B>(fn: (value: A) => B): MapOp<A, B>
export function map<A, B>(sampledProperty: Property<B>): MapOp<A, B>
export function map<A, B>(x: ((value: A) => B) | Property<B>): any {
  return (o: any) => {
    const desc = [o, "map", [x]] as Desc
    let fn = isProperty(x) ? () => x.get() : x
    if (isEventStream<A>(o)) {
      return new StatelessEventStream(
        desc,
        mapSubscribe(o.subscribe.bind(o), fn),
        o.getScope()
      )
    } else if (isEventStreamSeed<A>(o)) {
      const source = o.consume()
      return new EventStreamSeedImpl(
        desc,
        mapSubscribe(source.subscribe.bind(source), fn)
      )
    } else if (isProperty<A>(o)) {
      fn = cachedFn(fn)
      return new StatelessProperty(
        desc,
        () => fn(o.get()),
        mapSubscribe(o.onChange.bind(o), fn),
        o.getScope()
      )
    } else if (isPropertySeed<A>(o)) {
      const source = o.consume()
      fn = cachedFn(fn)
      return new PropertySeedImpl(
        desc,
        () => fn(source.get()),
        mapSubscribe(source.onChange.bind(source), fn)
      )
    }
    throw Error("Unknown observable")
  }
}

export function mapSubscribe<A, B>(
  subscribe: Subscribe<A>,
  fn: (value: A) => B
): Subscribe<B> {
  return (onValue, onEnd) => subscribe(mapObserver(onValue, fn), onEnd)
}

export function mapObserver<A, B>(
  observer: Observer<B>,
  fn: (value: A) => B
): Observer<A> {
  return (event: A) => observer(fn(event))
}

export function mapEvent<A, B>(event: Event<A>, fn: (value: A) => B): Event<B> {
  if (isValue(event)) {
    return valueEvent(fn(event.value))
  } else {
    return event
  }
}