/// <reference types="node" />
import { EventEmitter } from "events";
import { Method, Body, HTTPHeaders } from "./http";
export declare type TaskType = "request" | "download";
export declare enum Events {
    Error = "error",
    Complete = "complete"
}
export declare class Task {
    type: TaskType;
    method: Method;
    url: string;
    body?: Body;
    headers?: HTTPHeaders;
    id: number;
    constructor(type: TaskType, method: Method, url: string, body?: Body, headers?: HTTPHeaders);
}
export interface Options {
    concurrency?: number;
}
declare type SubscribeFn = (task: Task) => Promise<void>;
interface IScheduler extends EventEmitter {
    subscribe(fn: SubscribeFn): void;
    push(task: Task): void;
    clear(): void;
    length: number;
}
export declare class Scheduler extends EventEmitter implements IScheduler {
    private options;
    readonly pendingQueue: Task[];
    readonly runningQueue: Task[];
    private subscriptionFn;
    constructor(options?: Options);
    /**
     * execute a task
     * @param task a task to execute
     */
    private exec;
    /**
     * Is the scheduler busy?
     */
    private get isBusy();
    /**
     * Is the scheduler can go to next task?
     */
    private get nextable();
    /**
     * Go to the next task
     */
    private next;
    /**
     * Subscribe the task
     * @param fn
     */
    subscribe(fn: SubscribeFn): void;
    /**
     * Push a new task to the pool
     * @param task a new task
     */
    push(task: Task): void;
    /**
     * Clear the pendingQueue
     */
    clear(): void;
    /**
     * Get the length for this scheduler
     */
    get length(): number;
}
export {};