transform.ts

// SPDX-License-Identifier: MPL-2.0

import type Distree from "./Distree.ts"
import from from "./from.ts"
import insert from "./insert.ts"

/**
 * Transforms the values of the given distree. It does not modify the passed distree, and instead returns a new distree with the transformed values.
 *
 * If `transformer` throws `undefined`, the value will be filtered out from the result.
 *
 * @param distree The distree the result based on.
 * @param transformer The function that transforms the values.
 * @returns A new distree with the transformed values.
 */
const transform = <T, U>(
	distree: Distree<T>,
	transformer: (value: T, path: string) => Distree.ItemInitializer<U>,
): Distree<U> => {
	return [...distree]
		.map(([path, value]) => {
			try {
				return [[path, transformer(value, path)] as const]
			} catch (error) {
				if (error === undefined) return []
				else throw error
			}
		})
		.flat()
		.reduce(insert, from({}))
}

export default transform