find.ts

import type { IsomorphicIterable, Maybe, Unary } from "@vangware/types";
import { whenIsIterable } from "@vangware/utils";
import type { ReducerOutput } from "./types/ReducerOutput.js";

/**
 * Returns the value of the first item in the iterable or asynchronous iterable
 * where predicate is `true`, `undefined` otherwise.
 *
 * @category Reducers
 * @example
 * ```
 * const findEven = find((number: number) => number % 2 === 0);
 * findEven([1, 2, 3, 4]); // 2
 * findEven([1, 3, 5, 7]); // undefined
 * ```
 * @param predicate Predicate function to search for item.
 * @returns Curried function with `predicate` set in context.
 */
export const find = <Item>(predicate: Unary<Item, boolean>) =>
	whenIsIterable(iterable => {
		// eslint-disable-next-line functional/no-loop-statements
		for (const item of iterable) {
			// eslint-disable-next-line functional/no-conditional-statements
			if (predicate(item as Item)) {
				return item;
			}
		}

		return undefined;
	})(async (iterable: AsyncIterable<Item>) => {
		// eslint-disable-next-line functional/no-loop-statements
		for await (const item of iterable) {
			// eslint-disable-next-line functional/no-conditional-statements
			if (predicate(item)) {
				return item;
			}
		}

		return undefined;
	}) as <Iterable extends IsomorphicIterable<Item>>(
		iterable: Iterable,
	) => ReducerOutput<Iterable, Maybe<Item>>;