declare function fastq<C, T = any, R = any>(
  context: C,
  worker: fastq.worker<C, T, R>,
  concurrency: number
): fastq.queue<T, R>;
declare function fastq<C, T = any, R = any>(
  worker: fastq.worker<C, T, R>,
  concurrency: number
): fastq.queue<T, R>;

declare namespace fastq {
  type worker<C, T = any, R = any> = (
    this: C,
    task: T,
    cb: fastq.done<R>
  ) => void;
  type asyncWorker<C, T = any, R = any> = (this: C, task: T) => Promise<R>;
  type done<R = any> = (err: Error | null, result?: R) => void;
  type errorHandler<T = any> = (err: Error, task: T) => void;

  interface queue<T = any, R = any> {
    /** Add a task at the end of the queue. `done(err, result)` will be called when the task was processed. */
    push(task: T, done?: done<R>): void;
    /** Add a task at the beginning of the queue. `done(err, result)` will be called when the task was processed. */
    unshift(task: T, done?: done<R>): void;
    /** Pause the processing of tasks. Currently worked tasks are not stopped. */
    pause(): any;
    /** Resume the processing of tasks. */
    resume(): any;
    running(): number;
    /** Returns `false` if there are tasks being processed or waiting to be processed. `true` otherwise. */
    idle(): boolean;
    /** Returns the number of tasks waiting to be processed (in the queue). */
    length(): number;
    /** Returns all the tasks be processed (in the queue). Returns empty array when there are no tasks */
    getQueue(): T[];
    /** Removes all tasks waiting to be processed, and reset `drain` to an empty function. */
    kill(): any;
    /** Same than `kill` but the `drain` function will be called before reset to empty. */
    killAndDrain(): any;
    /** Set a global error handler. `handler(err, task)` will be called each time a task is completed, `err` will be not null if the task has thrown an error. */
    error(handler: errorHandler<T>): void;
    /** Property that returns the number of concurrent tasks that could be executed in parallel. It can be altered at runtime. */
    concurrency: number;
    /** Property (Read-Only) that returns `true` when the queue is in a paused state. */
    readonly paused: boolean;
    /** Function that will be called when the last item from the queue has been processed by a worker. It can be altered at runtime. */
    drain(): any;
    /** Function that will be called when the last item from the queue has been assigned to a worker. It can be altered at runtime. */
    empty: () => void;
    /** Function that will be called when the queue hits the concurrency limit. It can be altered at runtime. */
    saturated: () => void;
  }

  interface queueAsPromised<T = any, R = any> extends queue<T, R> {
    /** Add a task at the end of the queue. The returned `Promise` will be fulfilled (rejected) when the task is completed successfully (unsuccessfully). */
    push(task: T): Promise<R>;
    /** Add a task at the beginning of the queue. The returned `Promise` will be fulfilled (rejected) when the task is completed successfully (unsuccessfully). */
    unshift(task: T): Promise<R>;
    /** Wait for the queue to be drained. The returned `Promise` will be resolved when all tasks in the queue have been processed by a worker. */
    drained(): Promise<void>;
  }

  function promise<C, T = any, R = any>(
    context: C,
    worker: fastq.asyncWorker<C, T, R>,
    concurrency: number
  ): fastq.queueAsPromised<T, R>;
  function promise<C, T = any, R = any>(
    worker: fastq.asyncWorker<C, T, R>,
    concurrency: number
  ): fastq.queueAsPromised<T, R>;
}

export = fastq;