var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
import { AsyncSerialScheduler } from "./_scheduler";
import Observable from "./observable";
import unsubscribe from "./unsubscribe";
function scan(accumulator, seed) {
    return (observable) => {
        return new Observable(observer => {
            let accumulated;
            let index = 0;
            const scheduler = new AsyncSerialScheduler(observer);
            const subscription = observable.subscribe({
                complete() {
                    scheduler.complete();
                },
                error(error) {
                    scheduler.error(error);
                },
                next(value) {
                    scheduler.schedule((next) => __awaiter(this, void 0, void 0, function* () {
                        const prevAcc = index === 0
                            ? (typeof seed === "undefined" ? value : seed)
                            : accumulated;
                        accumulated = yield accumulator(prevAcc, value, index++);
                        next(accumulated);
                    }));
                }
            });
            return () => unsubscribe(subscription);
        });
    };
}
export default scan;
