/**

* @license

* Copyright Google LLC All Rights Reserved.

*

* Use of this source code is governed by an MIT-style license that can be

* found in the LICENSE file at https://angular.io/license

*/

/**

* A decorator that memoizes methods and getters.

*

* **Note**: Be cautious where and how to use this decorator as the size of the cache will grow unbounded.

*

* @see https://en.wikipedia.org/wiki/Memoization

*/

export function memoize<T>(

target: Object,

propertyKey: string | symbol,

descriptor: TypedPropertyDescriptor<T>,

): TypedPropertyDescriptor<T> {

const descriptorPropertyName = descriptor.get ? 'get' : 'value';

const originalMethod: unknown = descriptor[descriptorPropertyName];

if (typeof originalMethod !== 'function') {

throw new Error('Memoize decorator can only be used on methods or get accessors.');

}

const cache = new Map<string, unknown>();

return {

...descriptor,

[descriptorPropertyName]: function (this: unknown, ...args: unknown[]) {

for (const arg of args) {

if (!isJSONSerializable(arg)) {

throw new Error(

`Argument ${isNonPrimitive(arg) ? arg.toString() : arg} is JSON serializable.`,

);

}

}

const key = JSON.stringify(args);

if (cache.has(key)) {

return cache.get(key);

}

const result = originalMethod.apply(this, args);

cache.set(key, result);

return result;

},

};

}

/** Method to check if value is a non primitive. */

function isNonPrimitive(value: unknown): value is object | Function | symbol {

return (

(value !== null && typeof value === 'object') ||

typeof value === 'function' ||

typeof value === 'symbol'

);

}

/** Method to check if the values are JSON serializable */

function isJSONSerializable(value: unknown): boolean {

if (!isNonPrimitive(value)) {

// Can be seralized since it's a primitive.

return true;

}

let nestedValues: unknown[] | undefined;

if (Array.isArray(value)) {

// It's an array, check each item.

nestedValues = value;

} else if (Object.prototype.toString.call(value) === '[object Object]') {

// It's a plain object, check each value.

nestedValues = Object.values(value);

}

if (!nestedValues || nestedValues.some((v) => !isJSONSerializable(v))) {

return false;

}

return true;

}