/**
 * The unique ID of the task
 */
export type TaskId = string | number;
/**
 * The status of the task
 */
export type TaskStatus = 'idle' | 'running' | 'success' | 'error';
/**
 * The unique ID of the queue
 */
export type QueueId = number;
/**
 * Promise resolver
 */
export type Resolve<ReturnType> = (value: ReturnType) => void;
/**
 * Promise rejecter
 */
export type Reject = (error: Error) => void;
/**
 * Task status changes handler
 */
export type TaskStatusUpdateHandler<ReturnType = any> = (status: TaskStatus, task: Task<ReturnType>) => void;
/**
 * Pending task prioritization mode
 */
export type TaskPrioritizationMode = 'head' | 'tail' | 'head-with-truncation' | 'tail-with-truncation';
/**
 * Task priority
 */
export type TaskPriority = 'normal' | 'important';
/**
 * Conditional type to check if a type is a function
 */
export type IfFunction<T, U> = T extends (...args: any[]) => any ? U : never;
/**
 * The task object
 */
export interface Task<ReturnType = any> {
    taskId: TaskId;
    status: TaskStatus;
    priority: TaskPriority;
    callback: () => ReturnType | Promise<ReturnType>;
    onStatusUpdate?: TaskStatusUpdateHandler<ReturnType>;
    createdAt: number;
    queueId?: QueueId;
    result?: ReturnType;
    error?: Error;
    runAt?: number;
    finishedAt?: number;
}
/**
 * The waited task object, which has not been executed
 */
export interface WaitedTask<ReturnType = any> extends Task<ReturnType> {
    resolve: Resolve<ReturnType>;
    reject: Reject;
    promise: Promise<ReturnType>;
}
/**
 * Promise queue to schedule and execute the tasks
 */
export interface PromiseQueue {
    queueId: QueueId;
    promise: Promise<any>;
    length: number;
    taskIds: Array<TaskId>;
    parentQueue?: PromiseQueue | undefined | null;
}
/**
 * Check if the given object is TaskId
 * @param obj - Any object
 */
export declare const isTaskId: (obj: any) => obj is TaskId;
/**
 * Check if the given object is WaitedTask
 * @param obj - Any object
 */
export declare const isWaitedTask: (obj: any) => obj is WaitedTask<any>;