/**
 * Search for all the sub-objects (even deep-nested ones) that have the given key-value pair(filter).
 *
 * @param data - The data on which search is to be performed.
 * @param key - The key of the key-value pair to search.
 * @param value - The value of the key-value pait to search.
 * @returns The list of sub-objects from the given object, having the given key-value pair.
 *
 * @internal
 */
export function findByFilter<T>(data: NonNullable<unknown>, key: string, value: string): T[] {
	/**
	 * The list containing all the objects matching given filter.
	 */
	let res: T[] = [];

	/**
	 * If the data is an array, recursively run the function of each element of the array and merge the results.
	 */
	if (Array.isArray(data)) {
		/**
		 * findByFilter returns an array.
		 * map() also returns an array.
		 * Therefore, map(item =\> findByFilter(.......)) returns an array of arrays.
		 * Therefore, using ... operator to spread the 2-D array in 1-D array.
		 */
		res = res.concat(...data.map((item) => findByFilter<T>(item as NonNullable<unknown>, key, value)));
	}
	// If the data is an object
	else if (data != null && typeof data == 'object') {
		/**
		 * If the object includes the key and the value specified by the key matches the filter, add it to the result.
		 */
		if (Object.keys(data).includes(key) && data[key as keyof typeof data] == value) {
			res.push(data as T);
		}

		/**
		 * Recursively run the function on each value specified by each key in the object, for subsequent matches.
		 */
		for (const [, v] of Object.entries(data)) {
			res = res.concat(findByFilter<T>(v as NonNullable<unknown>, key, value));
		}
	}

	return res;
}

/**
 * Searches for the key which has the given value in the given object.
 *
 * @param data - The data on which search is to be performed.
 * @param value - The value to search.
 * @returns The key with the given value.
 *
 * @internal
 */
export function findKeyByValue(data: NonNullable<unknown>, value: string): string | undefined {
	// Finding the key-value pairs that have the given value
	const kvPair = Object.entries(data).filter(([, v]) => v == value)[0];

	// If a match is found
	if (kvPair) {
		return kvPair[0];
	}
	// If no match is found
	else {
		return undefined;
	}
}