/*
 This file is part of GNU Taler
 (C) 2022-2024 Taler Systems S.A.

 GNU Taler is free software; you can redistribute it and/or modify it under the
 terms of the GNU General Public License as published by the Free Software
 Foundation; either version 3, or (at your option) any later version.

 GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

 You should have received a copy of the GNU General Public License along with
 GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
 */

import { AmountJson, TalerBankConversionApi, TranslatedString } from "@gnu-taler/taler-util";
import { useState } from "preact/hooks";

export type UIField = {
  value: string | undefined;
  onUpdate: (s: string) => void;
  error: TranslatedString | undefined;
}

type FormHandler<T> = {
  [k in keyof T]?:
  T[k] extends string ? UIField :
  T[k] extends AmountJson ? UIField :
  FormHandler<T[k]>;
}

export type FormValues<T> = {
  [k in keyof T]:
  T[k] extends string ? (string | undefined) :
  T[k] extends AmountJson ? (string | undefined) :
  FormValues<T[k]>;
}

export type RecursivePartial<T> = {
  [k in keyof T]?:
  T[k] extends string ? (string) :
  T[k] extends AmountJson ? (AmountJson) :
  RecursivePartial<T[k]>;
}

export type FormErrors<T> = {
  [k in keyof T]?:
  T[k] extends string ? (TranslatedString) :
  T[k] extends AmountJson ? (TranslatedString) :
  FormErrors<T[k]>;
}

export type FormStatus<T> = {
  status: "ok",
  result: T,
  errors: undefined,
} | {
  status: "fail",
  result: RecursivePartial<T>,
  errors: FormErrors<T>,
}


function constructFormHandler<T>(form: FormValues<T>, updateForm: (d: FormValues<T>) => void, errors: FormErrors<T> | undefined): FormHandler<T> {
  const keys = (Object.keys(form) as Array<keyof T>)

  const handler = keys.reduce((prev, fieldName) => {
    const currentValue: any = form[fieldName];
    const currentError: any = errors ? errors[fieldName] : undefined;
    function updater(newValue: any) {
      updateForm({ ...form, [fieldName]: newValue })
    }
    if (typeof currentValue === "object") {
      const group = constructFormHandler(currentValue, updater, currentError)
      // @ts-expect-error asdasd
      prev[fieldName] = group
      return prev;
    }
    const field: UIField = {
      error: currentError,
      value: currentValue,
      onUpdate: updater
    }
    // @ts-expect-error asdasd
    prev[fieldName] = field
    return prev
  }, {} as FormHandler<T>)

  return handler;
}

export function useFormState<T>(defaultValue: FormValues<T>, check: (f: FormValues<T>) => FormStatus<T>): [FormHandler<T>, FormStatus<T>] {
  const [form, updateForm] = useState<FormValues<T>>(defaultValue)

  const status = check(form)
  const handler = constructFormHandler(form, updateForm, status.errors)

  return [handler, status]
}