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import * as ExperimentAssignments from './experiment-assignments';
import localStorage from './local-storage';
import { monotonicNow } from './timing';
import { validateExperimentAssignment, isObject } from './validations';
import type { Config, ExperimentAssignment } from '../types';
interface FetchExperimentAssignmentResponse {
variations: Record< string, unknown >;
ttl: number;
}
/**
* Exported for testing only.
* @param response The response data
*/
export function isFetchExperimentAssignmentResponse(
response: unknown
): response is FetchExperimentAssignmentResponse {
return (
isObject( response ) &&
isObject( response.variations ) &&
typeof response.ttl === 'number' &&
0 < response.ttl
);
}
function validateFetchExperimentAssignmentResponse(
response: unknown
): FetchExperimentAssignmentResponse {
if ( isFetchExperimentAssignmentResponse( response ) ) {
return response;
}
throw new Error( 'Invalid FetchExperimentAssignmentResponse' );
}
// We cache the anonId and add it to requests to ensure users that have recently
// crossed the logged-out/logged-in boundry have a consistent assignment.
//
// There can be issues otherwise as matching anonId to userId is only eventually
// consistent.
const localStorageLastAnonIdKey = 'explat-last-anon-id';
const localStorageLastAnonIdRetrievalTimeKey = 'explat-last-anon-id-retrieval-time';
const lastAnonIdExpiryTimeMs = 24 * 60 * 60 * 1000; // 24 hours
/**
* INTERNAL USE ONLY
*
* Runs the getAnonId provided cached by LocalStorage:
* - Returns the result of getAnonId if it can
* - Otherwise, within the expiry time, returns the cached anonId
*
* Exported for testing.
* @param getAnonId The getAnonId function
*/
export const localStorageCachedGetAnonId = async ( getAnonId: Config[ 'getAnonId' ] ) => {
const anonId = await getAnonId();
if ( anonId ) {
localStorage.setItem( localStorageLastAnonIdKey, anonId );
localStorage.setItem( localStorageLastAnonIdRetrievalTimeKey, String( monotonicNow() ) );
return anonId;
}
const maybeStoredAnonId = localStorage.getItem( localStorageLastAnonIdKey );
const maybeStoredRetrievalTime = localStorage.getItem( localStorageLastAnonIdRetrievalTimeKey );
if (
maybeStoredAnonId &&
maybeStoredRetrievalTime &&
monotonicNow() - parseInt( maybeStoredRetrievalTime, 10 ) < lastAnonIdExpiryTimeMs
) {
return maybeStoredAnonId;
}
return null;
};
/**
* Fetch an ExperimentAssignment
* @param config The config object providing dependecy injection.
* @param experimentName The experiment name to fetch
*/
export async function fetchExperimentAssignment(
config: Config,
experimentName: string
): Promise< ExperimentAssignment > {
const retrievedTimestamp = monotonicNow();
const { variations, ttl: responseTtl } = validateFetchExperimentAssignmentResponse(
await config.fetchExperimentAssignment( {
anonId: await localStorageCachedGetAnonId( config.getAnonId ),
experimentName,
} )
);
const ttl = Math.max( ExperimentAssignments.minimumTtl, responseTtl );
const fetchedExperimentAssignments = Object.entries( variations )
.map( ( [ experimentName, variationName ] ) => ( {
experimentName,
variationName,
retrievedTimestamp,
ttl,
} ) )
.map( validateExperimentAssignment );
if ( fetchedExperimentAssignments.length > 1 ) {
throw new Error(
'Received multiple experiment assignments while trying to fetch exactly one.'
);
}
if ( fetchedExperimentAssignments.length === 0 ) {
return ExperimentAssignments.createFallbackExperimentAssignment( experimentName, ttl );
}
const fetchedExperimentAssignment = fetchedExperimentAssignments[ 0 ];
if ( fetchedExperimentAssignment.experimentName !== experimentName ) {
throw new Error(
"Newly fetched ExperimentAssignment's experiment name does not match request."
);
}
if ( ! ExperimentAssignments.isAlive( fetchedExperimentAssignment ) ) {
throw new Error( "Newly fetched experiment isn't alive." );
}
return fetchedExperimentAssignment;
}
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