64 lines
3 KiB
TypeScript
64 lines
3 KiB
TypeScript
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/*
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Copyright 2024 New Vector Ltd
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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import { xxHash32 } from "js-xxhash";
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/**
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* The PhasedRolloutFeature class is used to manage the phased rollout of a new feature.
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*
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* It uses a hash of the user's identifier and the feature name to determine if a feature is enabled for a specific user.
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* The rollout percentage determines the probability that a user will be enabled for the feature.
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* The feature will be enabled for all users if the rollout percentage is 100, and for no users if the percentage is 0.
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* If a user is enabled for a feature at x% rollout, it will also be for any greater than x percent.
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*
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* The process ensures a uniform distribution of enabled features across users.
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*
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* @property featureName - The name of the feature to be rolled out.
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* @property rolloutPercentage - The int percentage (0..100) of users for whom the feature should be enabled.
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*/
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export class PhasedRolloutFeature {
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public readonly featureName: string;
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private readonly rolloutPercentage: number;
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private readonly seed: number;
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public constructor(featureName: string, rolloutPercentage: number) {
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this.featureName = featureName;
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if (!Number.isInteger(rolloutPercentage) || rolloutPercentage < 0 || rolloutPercentage > 100) {
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throw new Error("Rollout percentage must be an integer between 0 and 100");
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}
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this.rolloutPercentage = rolloutPercentage;
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// We add the feature name for the seed to ensure that the hash is different for each feature
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this.seed = Array.from(featureName).reduce((sum, char) => sum + char.charCodeAt(0), 0);
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}
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/**
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* Returns true if the feature should be enabled for the given user.
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* @param userIdentifier - Some unique identifier for the user, e.g. their user ID or device ID.
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*/
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public isFeatureEnabled(userIdentifier: string): boolean {
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/*
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* We use a hash function to convert the unique user ID string into an integer.
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* This integer can then be used as a basis for deciding whether the user should have access to the new feature.
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* We need some hash with good uniform distribution properties, security is not a concern here.
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* We use xxHash32, which is fast and has good distribution properties.
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*/
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const hash = xxHash32(userIdentifier, this.seed);
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// We use the hash modulo 100 to get a number between 0 and 99.
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// Modulo is simple and effective and the distribution should be uniform enough for our purposes.
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return hash % 100 < this.rolloutPercentage;
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}
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}
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