/// <reference types="node" />

import * as stream from "stream";

export type Handler<T = any, U = any> = (record: T, callback: HandlerCallback, params?: any) => U
export type HandlerCallback<T = any> = (err?: null | Error, record?: T) => void
export type Callback = (err?: null | Error, output?: string) => void

export interface Options extends stream.TransformOptions {
    /**
     * In the absence of a consumer, like a `stream.Readable`, trigger the consumption of the stream.
     */
    consume?: boolean
    /**
     * The number of transformation callbacks to run in parallel; only apply with asynchronous handlers; default to "100".
     */
    parallel?: number
    /**
     * Pass user defined parameters to the user handler as last argument.
     */
    params?: any
}
export interface State {
    finished: number
    running: number
    started: number
}
export class Transformer extends stream.Transform {
    constructor(options: Options)
    readonly options: Options
    readonly state: State
}

declare function transform<T = any, U = any>(handler: Handler<T, U>, callback?: Callback): Transformer
declare function transform<T = any, U = any>(records: Array<T>, handler: Handler<T, U>, callback?: Callback): Transformer
declare function transform<T = any, U = any>(options: Options, handler: Handler<T, U>, callback?: Callback): Transformer
declare function transform<T = any, U = any>(records: Array<T>, options: Options, handler: Handler<T, U>, callback?: Callback): Transformer

export default transform;
export { transform }