48 lines
1.6 KiB
TypeScript
48 lines
1.6 KiB
TypeScript
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// Copyright 2021 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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import { defaultMemoize } from 'reselect';
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import { strictAssert } from './assert';
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// The difference between the function below and `defaultMemoize` from
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// `reselect` is that it supports multiple "root" states. `reselect` is designed
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// to interact with a single redux store and by default it memoizes only the
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// last result of the selector (matched by its arguments). This works well when
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// applied to singular entities living in the redux's state, but we need to
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// apply selector to multitide of conversations and messages.
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//
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// The way it works is that it adds an extra memoization step that uses the
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// first argument ("root") as a key in a weak map, and then applies the default
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// `reselect`'s memoization function to the rest of the arguments. This way
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// we essentially get a weak map of selectors by the "root".
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// eslint-disable-next-line @typescript-eslint/ban-types
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export function memoizeByRoot<F extends Function>(
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fn: F,
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equalityCheck?: <T>(a: T, b: T, index: number) => boolean
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): F {
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// eslint-disable-next-line @typescript-eslint/ban-types
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const cache = new WeakMap<object, Function>();
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const wrap = (root: unknown, ...rest: Array<unknown>): unknown => {
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strictAssert(
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typeof root === 'object' && root !== null,
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'Root is not object'
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);
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let partial = cache.get(root);
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if (!partial) {
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partial = defaultMemoize((...args: Array<unknown>): unknown => {
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return fn(root, ...args);
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}, equalityCheck);
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cache.set(root, partial);
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}
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return partial(...rest);
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};
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return (wrap as unknown) as F;
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}
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