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import { OFF_LOGGER } from '../../logger/off-logger.ts';
import { withPrefix } from '../../logger/prefixed-logger.ts';
import { createDeferredValue } from './deferred-value.ts';
import { delay } from './delay.ts';
/**
* Configuration options for polling operations.
*
* @template T The type of value that the polling operation returns
* @template V The type of value to return when a timeout occurs
*/
export type PollingOptions<T, V> = {
/**
* Whether to invoke the operation immediately or instead wait for the first interval.
*/
readonly invokeImmediately?: boolean;
/**
* Maximum time in milliseconds to poll before auto-stopping.
*/
readonly timeout?: number;
/**
* Value to return when a timeout occurs.
*/
readonly timeoutValue?: V;
/**
* Maximum number of times to call the operation before auto-stopping.
*/
readonly retryLimit?: number;
/**
* Function that evaluates each result and returns true if polling should stop.
*
* @param result The result returned by the operation
* @param invocationIndex The current invocation count (0-based)
* @returns `true` to stop polling, `false` to continue
*/
readonly interrupt?: (result: T, invocationIndex: number) => boolean;
/**
* Logger to capture polling events and errors.
*/
readonly logger?: Logger;
};
/**
* Polls a function at regular intervals until a condition is met, a timeout occurs, maximum retries are reached, or
* it's manually stopped. Returns both a method to stop polling and a promise that resolves with the last result.
*
* The polling operation handles both synchronous and asynchronous (Promise-returning) functions. If the operation
* throws an error or rejects, polling continues but the error is logged. If a previous asynchronous operation is still
* resolving when the next interval occurs, that polling iteration is skipped.
*
* @example Simple polling at regular intervals
*
* ```ts
* // Poll every 5 seconds until manually stopped
* const closeable = startPolling(() => fetchLatestData(), 5_000);
*
* // Stop polling after 30 seconds
* await delay(30_000).then(close);
*
* // Get the final result
* const finalData = await wait;
* ```
*
* @example Basic polling until a condition is met
*
* ```ts
* const { wait, close } = startPolling(() => fetchStatus(), 1000, {
* interrupt: (status) => status === 'completed',
* });
*
* // Later get the final result
* const finalStatus = await wait;
* ```
*
* @example Polling with timeout
*
* ```ts
* const { wait } = startPolling(() => checkJobStatus(jobId), 2000, {
* timeout: 30000, // Stop after 30 seconds
* interrupt: (status) => ['completed', 'failed'].includes(status),
* logger: console,
* });
*
* const finalStatus = await wait;
* if (finalStatus === 'completed') {
* // Job finished successfully
* } else {
* // Either timed out or job failed
* }
* ```
*
* @example Polling with maximum retries
*
* ```ts
* const { wait } = startPolling(() => checkJobStatus(jobId), 2000, {
* retryLimit: 5, // Stop after 5 attempts
* logger: console,
* });
*
* const finalStatus = await wait;
* ```
*
* @example Manual control of polling
*
* ```ts
* const poll = startPolling(() => fetchDataPoints(), 5000);
*
* // Stop polling after some external event
* eventEmitter.on('stop-polling', () => {
* poll.close();
* });
*
* // Get the last result when polling stops
* const lastDataPoints = await poll.wait;
* ```
*
* @param operation Function to execute on each poll interval. Can return a value or a Promise.
* @param interval Time in milliseconds between poll attempts
* @param options Optional configuration for polling behavior
* @returns An object with a `close()` method to manually stop polling and a `wait` Promise that resolves with the last
* result when polling stops
*/
export const startPolling = <T, const V = undefined>(
operation: () => T | Promise<T>,
interval: number,
options?: PollingOptions<T, V>,
): { readonly wait: Promise<T | V | undefined>; readonly close: () => Promise<void> } => {
const deferred = createDeferredValue<T | V | undefined>();
interval = Math.max(0, Math.ceil(interval));
let resolving = false;
let invocationIndex = -1;
let active = true;
let lastResult: T | V | undefined;
const logger = withPrefix(options?.logger ?? OFF_LOGGER, 'poll', { fallbackPrefix: 'emitnlog' });
const polledOperation = (): void => {
if (resolving || !active) {
return;
}
invocationIndex++;
// Check if we've reached the maximum number of retries
if (options?.retryLimit !== undefined && invocationIndex >= options.retryLimit) {
logger.d`reached maximum retries (${options.retryLimit})`;
void close();
return;
}
try {
logger.d`invoking the operation for the ${invocationIndex + 1} time`;
const result = operation();
if (result instanceof Promise) {
resolving = true;
void result
.then((value) => {
lastResult = value;
if (options?.interrupt && options.interrupt(value, invocationIndex)) {
void close();
}
})
.catch((error: unknown) => {
logger.args(error).e`the operation rejected with an error: ${error}`;
})
.finally(() => {
resolving = false;
});
return;
}
lastResult = result;
if (options?.interrupt && options.interrupt(result, invocationIndex)) {
void close();
return;
}
} catch (error) {
logger.args(error).e`the operation threw an error: ${error}`;
}
};
const close = async (): Promise<void> => {
if (active) {
active = false;
logger.d`closing the poll after ${invocationIndex + 1} invocations`;
clearInterval(intervalId);
deferred.resolve(lastResult);
}
await deferred.promise;
};
if (options?.invokeImmediately) {
polledOperation();
// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
Iif (!active) {
return { close, wait: deferred.promise };
}
}
const intervalId = setInterval(polledOperation, interval);
if (options?.timeout && options.timeout >= 0) {
void delay(options.timeout).then(() => {
if (active) {
if ('timeoutValue' in options) {
lastResult = options.timeoutValue;
}
logger.d`timeout for the operation reached after ${options.timeout}ms`;
void close();
}
});
}
return { close, wait: deferred.promise };
};
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