1 files changed, 124 insertions, 0 deletions
diff --git a/packages/bank-ui/src/hooks/form.ts b/packages/bank-ui/src/hooks/form.ts
new file mode 100644
index 000000000..fae11c05c
--- /dev/null
+++ b/packages/bank-ui/src/hooks/form.ts
@@ -0,0 +1,124 @@
+/*
+ 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, 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: unknown = form[fieldName];
+    const currentError: unknown = errors ? errors[fieldName] : undefined;
+    function updater(newValue: unknown) {
+      updateForm({ ...form, [fieldName]: newValue });
+    }
+    if (typeof currentValue === "object") {
+      // @ts-expect-error FIXME better typing
+      const group = constructFormHandler(currentValue, updater, currentError);
+      // @ts-expect-error FIXME better typing
+      prev[fieldName] = group;
+      return prev;
+    }
+    const field: UIField = {
+      // @ts-expect-error FIXME better typing
+      error: currentError,
+      // @ts-expect-error FIXME better typing
+      value: currentValue,
+      onUpdate: updater,
+    };
+    // @ts-expect-error FIXME better typing
+    prev[fieldName] = field;
+    return prev;
+  }, {} as FormHandler<T>);
+
+  return handler;
+}
+
+/**
+ * FIXME: Consider sending this to web-utils
+ * 
+ * 
+ * @param defaultValue 
+ * @param check 
+ * @returns 
+ */
+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];
+}