import { AsyncState, PromiseState } from './types';

/**
 * Chain a callback on AsyncState or PromiseState, similar to Promise.then().
 *
 * Note: Named `chain` instead of `then` to avoid making `async` look like a
 * PromiseLike (objects with a `then` method are treated as thenables).
 *
 * - Success/Fulfilled: calls fn with data via promiseTry (ensures async)
 * - Pending with source promise: chains .then(fn) on the promise
 * - Stale mode: uses stale data if available (even in idle/pending/error)
 * - Otherwise: rejects with AsyncNotReadyError or the state's error
 *
 * @example
 * // Chain on success state
 * async.chain(userState, user => user.name);
 *
 * // Chain on pending state (waits for resolution)
 * async.chain(loadingState, data => transform(data));
 *
 * // Chain on stale mode (uses cached data)
 * async.chain(staleState, data => data); // Returns even if pending
 */
export declare function chain<T, R>(state: AsyncState<T, any> | PromiseState<T>, fn: (data: T) => R): Promise<R>;
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