function defaultUseWorkerNumber(prev: number, totalWorkers: number) {
    return prev + 1;
}

export class WorkerMultiDispatch<POST = any, RETURN = any> {
    private symbol = Symbol('WorkerMultiDispatch');
    private workers: Worker[] = [];
    private terminated = false;
    private prevWorkerNumber = 0;
    private getUseWorkerNumber = defaultUseWorkerNumber;
    private finalizationRegistry: FinalizationRegistry<symbol>;

    constructor(workerConstructor: () => Worker, concurrency: number, getUseWorkerNumber = defaultUseWorkerNumber) {
        this.getUseWorkerNumber = getUseWorkerNumber;
        for (let i = 0; i < concurrency; i++) {
            this.workers.push(workerConstructor());
        }

        this.finalizationRegistry = new FinalizationRegistry(() => {
            this.terminate();
        });
        this.finalizationRegistry.register(this, this.symbol);

        if (_DEV_) console.log('WorkerMultiDispatch: Created', this);
    }

    public postMessage(message: POST, options?: Transferable[] | StructuredSerializeOptions, useWorkerNumber: typeof defaultUseWorkerNumber = this.getUseWorkerNumber) {
        let workerNumber = useWorkerNumber(this.prevWorkerNumber, this.workers.length);
        workerNumber = Math.abs(Math.round(workerNumber)) % this.workers.length;
        if (_DEV_) console.log('WorkerMultiDispatch: Posting message to worker', workerNumber, useWorkerNumber);
        this.prevWorkerNumber = workerNumber;

        // 不毛だがunionをoverloadに突っ込めない
        // https://stackoverflow.com/questions/66507585/overload-signatures-union-types-and-no-overload-matches-this-call-error
        // https://github.com/microsoft/TypeScript/issues/14107
        if (Array.isArray(options)) {
            this.workers[workerNumber].postMessage(message, options);
        } else {
            this.workers[workerNumber].postMessage(message, options);
        }
        return workerNumber;
    }

    public addListener(callback: (this: Worker, ev: MessageEvent<RETURN>) => any, options?: boolean | AddEventListenerOptions) {
        this.workers.forEach(worker => {
            worker.addEventListener('message', callback, options);
        });
    }

    public removeListener(callback: (this: Worker, ev: MessageEvent<RETURN>) => any, options?: boolean | AddEventListenerOptions) {
        this.workers.forEach(worker => {
            worker.removeEventListener('message', callback, options);
        });
    }

    public terminate() {
        this.terminated = true;
        if (_DEV_) console.log('WorkerMultiDispatch: Terminating', this);
        this.workers.forEach(worker => {
            worker.terminate();
        });
        this.workers = [];
        this.finalizationRegistry.unregister(this);
    }

    public isTerminated() {
        return this.terminated;
    }
    public getWorkers() {
        return this.workers;
    }
    public getSymbol() {
        return this.symbol;
    }
}