import { z } from "zod/v4/mini";
import { transformFormDataToObject } from "./shared";
import type { FormDataValidatorInput, FormDataValidatorParams } from "./types";

/**
 * Transforms and validates a `FormData` instance into an object parseable with `z.object()`.
 *
 * # Important notes
 * - If parsing server side, directly use Zod's schemas instead of using the included `dom` schemas.
 * - By spec, `FormData` allows for a duplicated key (e.g, having 2 or more different values per key). This validator will only use the latest / bottom-most field value
 *
 * @example
 * ```ts
 * import { z } from "zod/v4/mini";
 * import { formData } from "@angelo/zfd/mini-formdata";
 *
 * const schema = formData({
 *   key: z.optional(z.string())
 * });
 *
 * const parsed = z.parse(schema, new FormData())
 * //    ^?: { key?: string | undefined }
 * ```
 */
export const formData = <T extends FormDataValidatorParams>(
  formSchema?: T,
): z.ZodMiniType<z.output<z.ZodMiniObject<T>>, FormDataValidatorInput> =>
  z.pipe(z.pipe(z.instanceof(FormData), z.transform(transformFormDataToObject)), z.object(formSchema));