1 files changed, 86 insertions, 0 deletions
diff --git a/packages/merchant-backoffice-ui/src/components/form/useField.tsx b/packages/merchant-backoffice-ui/src/components/form/useField.tsx
new file mode 100644
index 000000000..8479d7ad8
--- /dev/null
+++ b/packages/merchant-backoffice-ui/src/components/form/useField.tsx
@@ -0,0 +1,86 @@
+/*
+ This file is part of GNU Taler
+ (C) 2021 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/>
+ */
+
+/**
+*
+* @author Sebastian Javier Marchano (sebasjm)
+*/
+
+import { ComponentChildren, VNode } from "preact";
+import { useFormContext } from "./FormProvider";
+
+interface Use<V> {
+  error?: string;
+  required: boolean;
+  value: any;
+  initial: any;
+  onChange: (v: V) => void;
+  toStr: (f: V | undefined) => string;
+  fromStr: (v: string) => V
+}
+
+export function useField<T>(name: keyof T): Use<T[typeof name]> {
+  const { errors, object, initialObject, toStr, fromStr, valueHandler } = useFormContext<T>()
+  type P = typeof name
+  type V = T[P]
+
+  const updateField = (field: P) => (value: V): void => {
+    return valueHandler((prev) => {
+      return setValueDeeper(prev, String(field).split('.'), value)
+    })
+  }
+
+  const defaultToString = ((f?: V): string => String(!f ? '' : f))
+  const defaultFromString = ((v: string): V => v as any)
+  const value = readField(object, String(name))
+  const initial = readField(initialObject, String(name))
+  const isDirty = value !== initial
+  const hasError = readField(errors, String(name))
+  return {
+    error: isDirty ? hasError : undefined,
+    required: !isDirty && hasError,
+    value,
+    initial,
+    onChange: updateField(name) as any,
+    toStr: toStr[name] ? toStr[name]! : defaultToString,
+    fromStr: fromStr[name] ? fromStr[name]! : defaultFromString,
+  }
+}
+/**
+ * read the field of an object an support accessing it using '.'
+ * 
+ * @param object 
+ * @param name 
+ * @returns 
+ */
+const readField = (object: any, name: string) => {
+  return name.split('.').reduce((prev, current) => prev && prev[current], object)
+}
+
+const setValueDeeper = (object: any, names: string[], value: any): any => {
+  if (names.length === 0) return value
+  const [head, ...rest] = names
+  return { ...object, [head]: setValueDeeper(object[head] || {}, rest, value) }
+}
+
+export interface InputProps<T> {
+  name: T;
+  label: ComponentChildren;
+  placeholder?: string;
+  tooltip?: ComponentChildren;
+  readonly?: boolean;
+  help?: ComponentChildren;
+}
+\ No newline at end of file