import { DocumentSnapshot, QuerySnapshot } from './snapshot';
import { MetaType } from './metaTypeCreator';
import { Query, DocumentReference } from './refs';
import { Unsubscribe, SnapshotListenOptions, FirestoreError } from './alias';
export declare type OnSnapshot = {
    /**
     * Attaches a listener for `DocumentSnapshot` events. You may either pass
     * individual `onNext` and `onError` callbacks or pass a single observer
     * object with `next` and `error` callbacks.
     *
     * NOTE: Although an `onCompletion` callback can be provided, it will
     * never be called because the snapshot stream is never-ending.
     *
     * @param reference - A reference to the document to listen to.
     * @param onNext - A callback to be called every time a new `DocumentSnapshot`
     * is available.
     * @param onError - An optional callback to be called if the listen fails or is
     * cancelled. No further callbacks will occur.
     * @param options - Options controlling the listen behavior.
     * @returns An unsubscribe function that can be called to cancel
     * the snapshot listener.
     */
    <T extends MetaType, Ref extends Query<T> | DocumentReference<T>>(reference: Ref extends never ? Ref : Query<T> | DocumentReference<T>, onNext: (snapshot: Ref extends DocumentReference<T> ? DocumentSnapshot<T> : QuerySnapshot<T>) => void, onError?: (error: FirestoreError) => void, options?: SnapshotListenOptions): Unsubscribe;
    /**
     * Attaches a listener for `DocumentSnapshot` events. You may either pass
     * individual `onNext` and `onError` callbacks or pass a single observer
     * object with `next` and `error` callbacks.
     *
     * NOTE: Although an `onCompletion` callback can be provided, it will
     * never be called because the snapshot stream is never-ending.
     *
     * @param reference - A reference to the document to listen to.
     * @param onNext - A callback to be called every time a new `DocumentSnapshot`
     * is available.
     * @param options - Options controlling the listen behavior.
     * @returns An unsubscribe function that can be called to cancel
     * the snapshot listener.
     */
    <T extends MetaType, Ref extends Query<T> | DocumentReference<T>>(reference: Ref extends never ? Ref : Query<T> | DocumentReference<T>, onNext: (snapshot: Ref extends DocumentReference<T> ? DocumentSnapshot<T> : QuerySnapshot<T>) => void, options?: SnapshotListenOptions): Unsubscribe;
};