/**
 * The input of a {@link PipelineStage}, either another {@link PipelineStage}, an array, an iterable or a promise.
 */
export type PipelineInput<T> = PipelineStage<T> | StreamPipelineInput<T> | Iterable<T> | PromiseLike<T> | ArrayLike<T>;
/**
 * An input of a {@link PipelineStage} which produces items in stream/async way.
 * Usefull for connecting a Node.JS stream into a pipeline of iterators.
 */
export interface StreamPipelineInput<T> {
    /**
     * Produces a new value and inject it into the pipeline
     * @param value - New value produced
     */
    next(value: T): void;
    /**
     * Close the pipeline input
     */
    complete(): void;
    /**
     * Report an error that occurs during execution
     * @param err - The error to report
     */
    error(err?: any): void;
}
export type PipelineObserver<T> = {
    next: (value: T) => void;
    error: (err: any) => void;
    complete: () => void;
};
export type PipelineSubscription = {
    [Symbol.dispose](): void;
};
export declare function createSubscription(): {
    [Symbol.dispose](): void;
};
export type PipelineObserverOrNext<T> = Partial<PipelineObserver<T>> | PipelineObserver<T>["next"] | undefined | null;
export declare function createObserver<T>(observerOrNext?: PipelineObserverOrNext<T>): Partial<PipelineObserver<T>>;
/**
 * A step in a pipeline. Data can be consumed in a pull-based or push-bashed fashion.
 */
export interface PipelineStage<T> {
    /**
     * Subscribes to the items emitted by the stage, in a push-based fashion
     * @param  onData - Function invoked on each item produced by the stage
     * @param  onError - Function invoked in cas of an error
     * @param  onEnd - Function invoked when the stage ends
     */
    subscribe(observerOrNext?: PipelineObserverOrNext<T>, onError?: PipelineObserver<T>["error"], onComplete?: PipelineObserver<T>["complete"]): PipelineSubscription;
    /**
     * Invoke a callback on each item produced by the stage
     * @param  cb - Function invoked on each item produced by the stage
     */
    forEach(cb: (value: T) => void): void;
    pipe<N>(fn: (source: PipelineStage<T>) => PipelineStage<N>): PipelineStage<N>;
    [Symbol.asyncIterator](): AsyncIterator<T>;
}
/**
 * Abstract representation used to apply transformations on a pipeline of iterators.
 * Concrete subclasses are used by the framework to build the query execution pipeline.
 * @abstract
 */
export declare abstract class PipelineEngine {
    /**
     * Creates a PipelineStage that emits no items
     * @return A PipelineStage that emits no items
     */
    abstract empty<T>(): PipelineStage<T>;
    /**
     * Converts the arguments to a PipelineStage
     * @param  values - Values to convert
     * @return A PipelineStage that emits the values
     */
    abstract of<T>(...values: T[]): PipelineStage<T>;
    /**
     * Creates a PipelineStage from an Array, an array-like object, a Promise, an iterable object, or an Observable-like object.
     * @param  value - Source object
     * @return A PipelineStage that emits the values contains in the object
     */
    abstract from<T>(value: PipelineInput<T>): PipelineStage<T>;
    /**
     * Creates a PipelineStage from a something that emits values asynchronously, using a {@link StreamPipelineInput} to feed values/errors into the pipeline.
     * @param  cb - Callback invoked with a {@link StreamPipelineInput} used to feed values inot the pipeline.
     * @return A PipelineStage that emits the values produces asynchronously
     */
    abstract fromAsync<T>(cb: (input: StreamPipelineInput<T>) => void): PipelineStage<T>;
    /**
     * Clone a PipelineStage
     * @param  stage - PipelineStage to clone
     * @return Cloned PipelineStage
     */
    abstract clone<T>(stage: PipelineStage<T>): PipelineStage<T>;
    /**
     * Handle errors raised in the pipeline as follows:
     * 1) Default: raise the error
     * 2) Use a handler function to returns a new PipelineStage in case of error
     * @param   input - Source PipelineStage
     * @param   handler - Function called in case of error to generate a new PipelineStage
     * @return Output PipelineStage
     */
    abstract catch<T, O>(input: PipelineStage<T>, handler?: (err: Error) => PipelineStage<O>): PipelineStage<T | O>;
    /**
     * Creates an output PipelineStage which concurrently emits all values from every given input PipelineStage.
     * @param  inputs - Inputs PipelineStage
     * @return Output PipelineStage
     */
    abstract merge<T>(...inputs: Array<PipelineStage<T> | PipelineInput<T>>): PipelineStage<T>;
    /**
     * Applies a given `mapper` function to each value emitted by the source PipelineStage, and emits the resulting values as a PipelineStage.
     * @param  input  - Source PipelineStage
     * @param  mapper - The function to apply to each value emitted by the source PipelineStage
     * @return A PipelineStage that emits the values from the source PipelineStage transformed by the given `mapper` function.
     */
    abstract map<F, T>(input: PipelineStage<F>, mapper: (value: F) => T): PipelineStage<T>;
    /**
     * Projects each source value to a PipelineStage which is merged in the output PipelineStage.
     * @param  input  - Input PipelineStage
     * @param  mapper - Transformation function
     * @return Output PipelineStage
     */
    abstract mergeMap<F, T>(input: PipelineStage<F>, mapper: (value: F) => PipelineStage<T>): PipelineStage<T>;
    abstract mergeMapAsync<F, T>(input: PipelineStage<F>, predicate: (value: F) => PipelineStage<T> | Promise<PipelineStage<T>>): PipelineStage<T>;
    /**
     * Do something after the PipelineStage has produced all its results
     * @param  input    - Input PipelineStage
     * @param  callback - Function invoked after the PipelineStage has produced all its results
     * @return Output PipelineStage
     */
    abstract finalize<T>(input: PipelineStage<T>, callback: () => void): PipelineStage<T>;
    /**
     * Maps each source value to an array of values which is merged in the output PipelineStage.
     * @param  input  - Input PipelineStage
     * @param  mapper - Transformation function
     * @return Output PipelineStage
     */
    flatMap<F, T>(input: PipelineStage<F>, mapper: (value: F) => T[]): PipelineStage<T>;
    /**
     * Flatten the output of a pipeline stage that emits array of values into single values.
     * @param  input  - Input PipelineStage
     * @return Output PipelineStage
     */
    flatten<T>(input: PipelineStage<T[]>): PipelineStage<T>;
    /**
     * Filter items emitted by the source PipelineStage by only emitting those that satisfy a specified predicate.
     * @param  input     - Input PipelineStage
     * @param  predicate - Predicate function
     * @return Output PipelineStage
     */
    abstract filter<T>(input: PipelineStage<T>, predicate: (value: T) => boolean): PipelineStage<T>;
    abstract filterAsync<T>(input: PipelineStage<T>, predicate: (value: T) => boolean | Promise<boolean>): PipelineStage<T>;
    /**
     * Applies an accumulator function over the source PipelineStage, and returns the accumulated result when the source completes, given an optional initial value.
     * @param  input   - Input PipelineStage
     * @param  reducer - Accumulator function
     * @return A PipelineStage that emits a single value that is the result of accumulating the values emitted by the source PipelineStage.
     */
    abstract reduce<F, T>(input: PipelineStage<F>, reducer: (acc: T, value: F) => T, initial: T): PipelineStage<T>;
    /**
     * Emits only the first `count` values emitted by the source PipelineStage.
     * @param  input - Input PipelineStage
     * @param  count - How many items to take
     * @return A PipelineStage that emits only the first count values emitted by the source PipelineStage, or all of the values from the source if the source emits fewer than count values.
     */
    abstract limit<T>(input: PipelineStage<T>, count: number): PipelineStage<T>;
    /**
     * Returns a PipelineStage that skips the first count items emitted by the source PipelineStage.
     * @param  input  - Input PipelineStage
     * @param  count  - How many items to skip
     * @return A PipelineStage that skips values emitted by the source PipelineStage.
     */
    abstract skip<T>(input: PipelineStage<T>, count: number): PipelineStage<T>;
    /**
     * Apply a callback on every item emitted by the source PipelineStage
     * @param  input - Input PipelineStage
     * @param  cb    - Callback
     */
    abstract forEach<T>(input: PipelineStage<T>, cb: (value: T) => void): void;
    /**
     * Emits given values if the source PipelineStage completes without emitting any next value, otherwise mirrors the source PipelineStage.
     * @param  input        - Input PipelineStage
     * @param  defaultValue - The default values used if the source Observable is empty.
     * @return A PipelineStage that emits either the specified default values if the source PipelineStage emits no items, or the values emitted by the source PipelineStage.
     */
    abstract defaultValues<T>(input: PipelineStage<T>, ...values: T[]): PipelineStage<T>;
    /**
     * Buffers the source PipelineStage values until the size hits the maximum bufferSize given.
     * @param  input - Input PipelineStage
     * @param  count - The maximum size of the buffer emitted.
     * @return A PipelineStage of arrays of buffered values.
     */
    abstract bufferCount<T>(input: PipelineStage<T>, count: number): PipelineStage<T[]>;
    /**
     * Creates a PipelineStage which collect all items from the source PipelineStage into an array, and then emits this array.
     * @param  input - Input PipelineStage
     * @return A PipelineStage which emits all values emitted by the source PipelineStage as an array
     */
    abstract collect<T>(input: PipelineStage<T>): PipelineStage<T[]>;
    /**
     * Returns a PipelineStage that emits all items emitted by the source PipelineStage that are distinct by comparison from previous items.
     * @param  input - Input PipelineStage
     * @param  selector - Optional function to select which value you want to check as distinct.
     * @return A PipelineStage that emits items from the source PipelineStage with distinct values.
     */
    distinct<T, K>(input: PipelineStage<T>, selector?: (value: T) => T | K): PipelineStage<T>;
    /**
     * Emits only the first value (or the first value that meets some condition) emitted by the source PipelineStage.
     * @param  input - Input PipelineStage
     * @return A PipelineStage of the first item that matches the condition.
     */
    first<T>(input: PipelineStage<T>): PipelineStage<T>;
    /**
     * Returns a PipelineStage that emits the items you specify as arguments after it finishes emitting items emitted by the source PipelineStage.
     * @param  input  - Input PipelineStage
     * @param  values - Values to append
     * @return A PipelineStage that emits the items emitted by the source PipelineStage and then emits the additional values.
     */
    endWith<T>(input: PipelineStage<T>, values: T[]): PipelineStage<T>;
    /**
     * Perform a side effect for every emission on the source PipelineStage, but return a PipelineStage that is identical to the source.
     * @param  input - Input PipelineStage
     * @param  cb    - Callback invoked on each item
     * @return A PipelineStage identical to the source, but runs the specified PipelineStage or callback(s) for each item.
     */
    tap<T>(input: PipelineStage<T>, cb: (value: T) => void): PipelineStage<T>;
    /**
     * Find the smallest value produced by a pipeline of iterators.
     * It takes a ranking function as input, which is invoked with (x, y)
     * and must returns True if x < y and False otherwise.
     * Warning: this function needs to materialize all values of the pipeline.
     * @param  input - Input PipelineStage
     * @param  comparator - (optional) Ranking function
     * @return A pipeline stage that emits the lowest value found
     */
    min<T>(input: PipelineStage<T>, ranking?: (x: T, y: T) => boolean): PipelineStage<T>;
    /**
     * Find the smallest value produced by a pipeline of iterators.
     * It takes a ranking function as input, which is invoked with (x, y)
     * and must returns True if x > y and False otherwise.
     * Warning: this function needs to materialize all values of the pipeline.
     * @param  input - Input PipelineStage
     * @param  comparator - (optional) Ranking function
     * @return A pipeline stage that emits the highest value found
     */
    max<T>(input: PipelineStage<T>, ranking?: (x: T, y: T) => boolean): PipelineStage<T>;
    /**
     * Groups the items produced by a pipeline according to a specified criterion,
     * and emits the resulting groups
     * @param  input - Input PipelineStage
     * @param  keySelector - A function that extracts the grouping key for each item
     * @param  elementSelector - (optional) A function that transforms items before inserting them in a group
     */
    groupBy<T, K, R>(input: PipelineStage<T>, keySelector: (value: T) => K, elementSelector?: (value: T) => R): PipelineStage<[K, R[]]>;
    /**
     * Peek values from the input pipeline stage, and use them to decide
     * between two candidate pipeline stages to continue the pipeline.
     * @param input - Input pipeline stage
     * @param count - How many items to peek from the input?
     * @param predicate - Predicate function invoked with the values
     * @param ifCase - Callback invoked if the predicate function evaluates to True
     * @param elseCase - Callback invoked if the predicate function evaluates to False
     * @return A pipeline stage
     */
    peekIf<T, O>(input: PipelineStage<T>, count: number, predicate: (values: T[]) => boolean, ifCase: (values: T[]) => Promise<PipelineStage<O>>, elseCase: (values: T[]) => Promise<PipelineStage<O>>): PipelineStage<O>;
}