import {
  endEvent,
  EventStream,
  EventStreamSeed,
  isEventStream,
  isValue,
} from "./abstractions"
import { applyScope } from "./applyscope"
import { EventStreamSeedImpl } from "./eventstream"
import { nop } from "./util"

export function merge<A>(a: EventStream<A>, b: EventStream<A>): EventStream<A>
export function merge<A, B>(
  a: EventStream<A>,
  b: EventStream<B>
): EventStream<A | B>
export function merge<A, B, C>(
  a: EventStream<A>,
  b: EventStream<B>,
  c: EventStream<C>
): EventStream<A | B | C>
export function merge<A, B, C, D>(
  a: EventStream<A>,
  b: EventStream<B>,
  c: EventStream<C>,
  d: EventStream<D>
): EventStream<A | B | C | D>
export function merge<A, B, C, D, E>(
  a: EventStream<A>,
  b: EventStream<B>,
  c: EventStream<C>,
  d: EventStream<D>,
  e: EventStream<E>
): EventStream<A | B | C | D | E>
export function merge<A>(
  a: EventStreamSeed<A>,
  b: EventStreamSeed<A>
): EventStreamSeed<A>
export function merge<A, B>(
  a: EventStreamSeed<A>,
  b: EventStreamSeed<B>
): EventStreamSeed<A | B>
export function merge<A, B, C>(
  a: EventStreamSeed<A>,
  b: EventStreamSeed<B>,
  c: EventStreamSeed<C>
): EventStreamSeed<A | B | C>
export function merge<A, B, C, D>(
  a: EventStreamSeed<A>,
  b: EventStreamSeed<B>,
  c: EventStreamSeed<C>,
  d: EventStreamSeed<D>
): EventStreamSeed<A | B | C | D>
export function merge<A, B, C, D, E>(
  a: EventStreamSeed<A>,
  b: EventStreamSeed<B>,
  c: EventStreamSeed<C>,
  d: EventStreamSeed<D>,
  e: EventStreamSeed<E>
): EventStreamSeed<A | B | C | D | E>
export function merge<A>(streams: EventStream<A>[]): EventStream<A>
export function merge<A>(streams: EventStreamSeed<A>[]): EventStreamSeed<A>
export function merge<A>(...args: any[]) {
  let streams: (EventStream<any> | EventStreamSeed<any>)[]
  if (args[0] instanceof Array) {
    streams = args[0]
  } else {
    streams = args
  }

  const sources = streams.map((s) => s.consume())
  const seed = new EventStreamSeedImpl<A>(
    ["merge", streams],
    (onValue, onEnd = nop) => {
      let endCount = 0
      const unsubs = sources.map((s) =>
        s.subscribe(
          (event) => {
            onValue(event)
          },
          () => {
            endCount++
            if (endCount === sources.length) {
              onEnd()
            }
          }
        )
      )
      return () => unsubs.forEach((f) => f())
    }
  )
  if (sources.every(isEventStream)) {
    return applyScope(sources[0].getScope())(seed)
  }
  return seed
}