1 files changed, 100 insertions, 0 deletions
diff --git a/packages/demobank-ui/src/hooks/form.ts b/packages/demobank-ui/src/hooks/form.ts
new file mode 100644
index 000000000..26354b108
--- /dev/null
+++ b/packages/demobank-ui/src/hooks/form.ts
@@ -0,0 +1,100 @@
+/*
+ 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]
+}
+\ No newline at end of file