/* @flow */

import type EventEmitter from "events";

export type Event<V,E> =
  {type: 'value', value: V} |
  {type: 'error', value: E} |
  {type: 'end', value: void};

export type Emitter<V,E> = {
  value(value: V): boolean;
  event(event: Event<V,E>): boolean;
  error(e: E): boolean;
  end(): void;

  // Deprecated methods
  emit(value: V): boolean;
  emitEvent(event: Event<V,E>): boolean;
};

export type Subscription = {
  closed: boolean;
  unsubscribe(): void;
};

export type Observer<V,E> = {
  +value?: (value: V) => void;
  +error?: (err: E) => void;
  +end?: () => void;
};

interface ESObserver<-V,-E> {
  start?: Function,
  next?: (value: V) => any,
  error?: (error: E) => any,
  complete?: () => any,
}

/*
 * This is the interface described by https://github.com/tc39/proposal-observable
 * It provides interoperability between stream implementations, including Kefir,
 * RxJS, and zen-observable.
 */
type ESObservable<+V,+E=*> = {
  subscribe(callbacks: ESObserver<V, E>): { unsubscribe: () => void };
};

declare class Observable<+V,+E=*> {
  toProperty($?: empty): Property<V,E>;
  toProperty<V2>(getCurrent: () => V2): Property<V|V2,E>;
  changes(): Observable<V,E>;

  observe(obs: Observer<V,E>, $?: empty): Subscription;
  observe(onValue?: ?(v: V) => void, onError?: ?(err: E) => void, onEnd?: ?() => void): Subscription;
  onValue(cb: (v: V) => void): this;
  offValue(cb: (v: V) => void): this;
  onError(cb: (err: E) => void): this;
  offError(cb: (err: E) => void): this;
  onEnd(cb: () => void): this;
  offEnd(cb: () => void): this;
  onAny(cb: (event: Event<V,E>) => void): this;
  offAny(cb: (event: Event<V,E>) => void): this;
  log(name?: string): this;
  offLog(name?: string): this;
  spy(name?: string): this;
  offSpy(name?: string): this;
  setName(name: string): this;
  setName(Observable<any, any>, name: string): this;
  toPromise(PromiseConstructor?: Function): Promise<V>;
  toESObservable(): ESObservable<V,E>;

  map<V2>(cb: (v: V) => V2): Observable<V2,E>;
  filter(cb?: typeof Boolean): Observable<$NonMaybeType<V>,E>;
  filter(cb: (v: V) => any): Observable<V,E>;
  take(n: number): Observable<V,E>;
  takeWhile(cb?: (v: V) => boolean): Observable<V,E>;
  last(): Observable<V,E>;
  skip(n: number): Observable<V,E>;
  skipWhile(cb?: (v: V) => boolean): Observable<V,E>;
  skipDuplicates(comparator?: (a: V, b: V) => boolean): Observable<V,E>;

  diff($?: empty): Observable<[V, V],E>;
  diff<V2>(fn: (prev: V, next: V) => V2, $?: empty): Observable<V2,E>;
  diff<V2,V3>(fn: (prev: V | V3, next: V) => V2, seed: V3): Observable<V2,E>;
  diff<V3>(fn: null | void, seed: V3): Observable<[V | V3, V],E>;

  scan(cb: (prev: V, next: V) => V, $?: empty): Observable<V,E>;
  scan<V2>(cb: (prev: V2, next: V) => V2, seed: V2): Observable<V2,E>;

  flatten($?: empty): Observable<any,E>;
  flatten<V2>(transformer: (value: V) => V2[]): Observable<V2,E>;

  delay(n: number): Observable<V,E>;
  throttle(n: number, options?: {leading?: boolean, trailing?: boolean}): Observable<V,E>;
  debounce(n: number, options?: {immediate?: boolean}): Observable<V,E>;
  mapErrors<E2>(fn: (error: E) => E2): Observable<V,E2>;
  filterErrors(fn?: typeof Boolean): Observable<V,$NonMaybeType<E>>;
  filterErrors(fn: (error: E) => any): Observable<V,E>;
  takeErrors(n: number): Observable<V,E>;
  ignoreValues(): Observable<empty,E>;
  ignoreErrors(): Observable<V,empty>;
  ignoreEnd(): Observable<V,E>;
  beforeEnd<V2>(fn: () => V2): Observable<V|V2,E>;
  slidingWindow(max: number, min?: number): Observable<V[],E>;
  bufferWhile(predicate?: (value: V) => boolean, options?: {flushOnEnd?: boolean}): Observable<V[],E>;
  transduce(transducer: any): Observable<any,E>;
  withHandler<V2,E2>(handler: (emitter: Emitter<V2,E2>, event: Event<V,E>) => void): Observable<V2,E2>;

  combine<V2,E2>(otherObs: Observable<V2,E2>, $?: empty): Observable<[V,V2],E|E2>;
  combine<V2,V3,E2>(otherObs: Observable<V2,E2>, combinator: (v: V, v2: V2) => V3): Observable<V3,E|E2>;
  combine<V2,V3,E2,E3>(
    otherObs: Observable<V2,E2>,
    passiveObss: Observable<V3,E3>[],
    $?: empty
  ): Observable<Array<V|V2|V3>,E|E2|E3>;
  combine<V2,V3,V4,E2,E3>(
    otherObs: Observable<V2,E2>,
    passiveObss: Observable<V3,E3>[],
    combinator: (v: V, v2: V2, ...v3: V3[]) => V4
  ): Observable<V4,E|E2|E3>;

  zip<V2,E2>(otherObs: Observable<V2,E2>, $?: empty): Observable<[V,V2],E|E2>;
  zip<V2,V3,E2>(otherObs: Observable<V2,E2>, combinator: (v: V, v2: V2) => V3): Observable<V3,E|E2>;

  merge<V2,E2>(otherObs: Observable<V2,E2>): Observable<V|V2,E|E2>;
  concat<V2,E2>(otherObs: Observable<V2,E2>): Observable<V|V2,E|E2>;

  flatMap<V2,E2>(transform: (value: V) => Observable<V2,E2>): Observable<V2,E|E2>;
  flatMapLatest<V2,E2>(transform: (value: V) => Observable<V2,E2>): Observable<V2,E|E2>;
  flatMapFirst<V2,E2>(transform: (value: V) => Observable<V2,E2>): Observable<V2,E|E2>;
  flatMapConcat<V2,E2>(transform: (value: V) => Observable<V2,E2>): Observable<V2,E|E2>;
  flatMapConcurLimit<V2,E2>(transform: (value: V) => Observable<V2,E2>, limit: number): Observable<V2,E|E2>;
  flatMapErrors<V2,E2>(transform: (error: E) => Observable<V2,E2>): Observable<V|V2,E2>;

  filterBy(otherObs: Observable<any,any>): Observable<V,E>;
  skipUntilBy(otherObs: Observable<any,any>): Observable<V,E>;
  takeUntilBy(otherObs: Observable<any,any>): Observable<V,E>;
  bufferBy(otherObs: Observable<any,any>, options?: {flushOnEnd?: boolean}): Observable<V[],E>;
  bufferWhileBy(otherObs: Observable<any,any>, options?: {flushOnEnd?: boolean, flushOnChange?: boolean}): Observable<V[],E>;

  sampledBy(otherObs: Observable<any,any>, $?: empty): Observable<V,E>;
  sampledBy<V2,V3>(otherObs: Observable<V2,any>, combinator: (obsValue: V, otherObsValue: V2) => V3): Observable<V3,E>;

  bufferWithTimeOrCount(time: number, count: number, options?: {flushOnEnd: boolean}): Observable<V,E>;
}

declare class Pool<V,E=*> extends Observable<V,E> {
  plug(s: Observable<V,E>): () => void;
}

declare class Stream<+V,+E=*> extends Observable<V,E> {
}

declare class Property<+V,+E=*> extends Observable<V,E> {
}

// `$observedValuesTuple` is a helper type that describes a type for a tuple or
// array of values in relation to a tuple or array of observables. This mapping
// states that the type of each position in the new tuple type matches the type
// of the value type parameter of the observable in the same position in the
// input tuple.
type $observedValuesTuple<Obss> = $TupleMap<Obss, <V,E>(obs: Observable<V,E>) => V>

// `$observedValuesObject` is similar to `$observedValuesTuple` - except that
// `$observedValuesObject` describes an object type where the type of each
// property in the new object matches the value type parameter of the observable
// type under the same key in the input object.
type $observedValuesObject<Obss> = $ObjMap<Obss, <V,E>(obs: Observable<V,E>) => V>

declare var Kefir: {
  Observable: typeof Observable;
  Pool: typeof Pool;
  Stream: typeof Stream;
  Property: typeof Property;

  staticLand: {
    Observable: {
      ap<A,B,E1,E2>(obsF: Observable<(x: A) => B, E1>, obsV: Observable<A, E2>): Observable<B,E1|E2>;
      bimap<V1,E1,V2,E2>(fnE: (x: E1) => E2, fnV: (x: V1) => V2, obs: Observable<V1,E1>): Observable<V2,E2>;
      chain<V,V2,E,E2>(cb: (value: V) => Observable<V2,E2>, s: Observable<V,E>): Observable<V2,E|E2>;
      concat<V1,E1,V2,E2>(obs1: Observable<V1,E1>, obs2: Observable<V2,E2>): Observable<V1|V2,E1|E2>;
      empty(): Observable<*,*>;
      map<V,V2,E>(cb: (value: V) => V2, s: Observable<V,E>): Observable<V2,E>;
      of<V>(value: V): Observable<V,*>;
    };
  };

  never(): Observable<empty,empty>;
  later<V>(delay: number, value: V): Observable<V,empty>;
  interval<V>(interval: number, value: V): Observable<V,empty>;
  sequentially<V>(interval: number, values: V[]): Observable<V,empty>;
  fromPoll<V>(interval: number, f: () => V): Observable<V,empty>;
  withInterval<V,E>(interval: number, f: (emitter: Emitter<V,E>) => void): Observable<V,E>;
  fromCallback<V>(f: (cb: (value: V) => void) => void): Observable<V,empty>;
  fromNodeCallback<V,E>(f: (cb: (err: E, value: ?V) => void) => void): Observable<V,E>;
  fromEvents<V,E>(
    target: EventTarget | EventEmitter, // `EventTarget` comes from Flow's built-in dom types
    eventName: string,
    transformer?: (...args: any[]) => V
  ): Observable<V,E>;
  stream<V,E>(subscribe: (emitter: Emitter<V,E>) => ?() => void): Observable<V,E>;

  constant<V>(value: V): Property<V,empty>;
  constantError<E>(err: E): Property<empty,E>;

  fromPromise<V,E>(promise: Promise<V>): Property<V,E>;
  fromESObservable<V,E>(observable: ESObservable<V,E>): Observable<V,E>;

  combine:
    // array of observables
    & (<E, Obss: Observable<any,E>[]>(
      obss: Obss,
      $?: empty
    ) => Observable<$observedValuesTuple<Obss>, E>)

    // array of observables, combinator
    & (<V,E>(obss: Observable<any,E>[], combinator: (...args: any[]) => V) => Observable<V,E>)

    // array of observables, array of passive observables
    & (<V,V2,E,E2>(obss: Observable<V,E>[], passiveObss: Observable<V2,E2>[], $?: empty) => Observable<(V|V2)[],E|E2>)

    // array of observables, array of passive observables, combinator
    & (<V,E,E2>(obss: Observable<any,E>[], passiveObss: Observable<any,E2>[], combinator: (...args: any[]) => V) => Observable<V,E|E2>)

    // object of observables
    & (<E, Obss: { [key: string]: Observable<any, E> }>(
      obss: Obss,
      $?: empty
    ) => Observable<$observedValuesObject<Obss>, E>)

    // object of observables, combinator
    & (<V, E, Obss: { [key: string]: Observable<any,E> }>(
      obss: Obss,
      combinator: (vs: $observedValuesObject<Obss>) => V
    ) => Observable<V,E>)

    // object of observables, object of passive observables
    & (<E, E2, Obss: { [key: string]: Observable<any,E> }, PassiveObss: { [key: string]: Observable<any,E2> }>(
      obss: Obss,
      passiveObss: PassiveObss,
      $?: empty
    ) => Observable<
      $observedValuesObject<Obss> & $observedValuesObject<PassiveObss>,
      E|E2>)

    // object of observables, object of passive observables, combinator
    & (<V, E, E2, Obss: { [key: string]: Observable<any,E> }, PassiveObss: { [key: string]: Observable<any,E2> }>(
      obss: Obss,
      passiveObss: PassiveObss,
      combinator: (vs: $observedValuesObject<Obss> & $observedValuesObject<PassiveObss>) => V,
    ) => Observable<V, E|E2>);

  zip:
    & (<E, Obss: Observable<any,E>[]>(
      obss: Obss,
      $?: empty
    ) => Observable<$observedValuesTuple<Obss>, E>)
    & (<V,V2,E>(obss: Observable<any,E>[], combinator: (...args: any[]) => V2) => Observable<V2,E>);

  merge<V,E>(obss: Observable<V,E>[]): Observable<V,E>;
  concat<V,E>(obss: Observable<V,E>[]): Observable<V,E>;

  pool(): Pool<*,*>;
  repeat<V,E>(fn: (i: number) => ?Observable<V,E>): Observable<V,E>;
};

module.exports = Kefir;