import { checkNaturalInt } from "../_check"
import { Source } from "../_core"
import { In, Out } from "../_interfaces"
import { makeObservable } from "../_obs"
import { Transaction } from "../_tx"
import { curry2 } from "../_util"
import { dispatcherOf, Observable } from "../Observable"
import { Operator } from "./_base"

export const skip: CurriedSkip = curry2(_skip)
export interface CurriedSkip {
  <ObsType, ValueType>(n: number, observable: In<ObsType, ValueType>): Out<ObsType, ValueType>
  <ValueType>(n: number): <ObsType>(observable: In<ObsType, ValueType>) => Out<ObsType, ValueType>
}

function _skip<T>(n: number, observable: Observable<T>): Observable<T> {
  checkNaturalInt(n)
  return makeObservable(observable, new Skip(dispatcherOf(observable), n))
}

class Skip<T> extends Operator<T, T> {
  constructor(source: Source<T>, private n: number) {
    super(source)
  }

  public next(tx: Transaction, val: T): void {
    if (this.n-- <= 0) {
      this.sink.next(tx, val)
    }
  }
}