A small helper utility to create a new Astro collections loader

defineLoader.ts

import { AstroError } from "astro/errors";
import { z } from "astro/zod";

import type { Loader, LoaderContext } from "astro/loaders";

interface CustomLoader<T extends z.ZodTypeAny> extends Omit<Loader, "load"> {
	load: (ctx: LoaderContext, options: z.infer<T>) => ReturnType<Loader["load"]>;
	options?: T;
}

function defineLoader<T extends z.ZodTypeAny = never>(
	options: CustomLoader<T>,
): (userOptions: z.infer<T>) => Loader {
	return (userOptions) => ({
		load: async (ctx) => {
			if (options.options) {
				const parsedOptions = options.options.safeParse(userOptions);
				if (!parsedOptions.success) {
					throw new AstroError(
						"Invalid loader options",
						Object.entries(parsedOptions.error.flatten().fieldErrors)
							.map(([field, error]) => `${field}: ${error?.join(", ")}`)
							.join("\n"),
					);
				}
			}

			return options.load(ctx, userOptions);
		},
		name: options.name,
		schema: options.schema,
	});
}