1 files changed, 80 insertions, 0 deletions
diff --git a/packages/exchange-backoffice-ui/src/handlers/useField.ts b/packages/exchange-backoffice-ui/src/handlers/useField.ts
new file mode 100644
index 000000000..3be397314
--- /dev/null
+++ b/packages/exchange-backoffice-ui/src/handlers/useField.ts
@@ -0,0 +1,80 @@
+import { TargetedEvent, useContext, useState } from "preact/compat";
+import {
+  FormContext,
+  InputArrayFieldState,
+  InputFieldState,
+} from "./FormProvider.js";
+
+export interface InputFieldHandler<Type> {
+  value: Type;
+  onChange: (s: Type) => void;
+  state: InputFieldState;
+  isDirty: boolean;
+}
+
+export function useField<T>(name: keyof T): InputFieldHandler<T[keyof T]> {
+  const {
+    initialValue,
+    value: formValue,
+    computeFormState,
+    onUpdate: notifyUpdate,
+  } = useContext(FormContext);
+  type P = typeof name;
+  type V = T[P];
+  const formState = computeFormState ? computeFormState(formValue.current) : {};
+
+  const fieldValue = readField(formValue.current, String(name)) as V;
+  const [currentValue, setCurrentValue] = useState<any | undefined>(fieldValue);
+  const fieldState =
+    readField<Partial<InputFieldState>>(formState, String(name)) ?? {};
+
+  //compute default state
+  const state = {
+    disabled: fieldState.disabled ?? false,
+    readonly: fieldState.readonly ?? false,
+    hidden: fieldState.hidden ?? false,
+    error: fieldState.error,
+    elements: "elements" in fieldState ? fieldState.elements ?? [] : [],
+  };
+
+  function onChange(value: V): void {
+    setCurrentValue(value);
+    formValue.current = setValueDeeper(
+      formValue.current,
+      String(name).split("."),
+      value,
+    );
+    if (notifyUpdate) {
+      notifyUpdate(formValue.current);
+    }
+  }
+
+  return {
+    value: fieldValue,
+    onChange,
+    isDirty: currentValue !== undefined,
+    state,
+  };
+}
+
+/**
+ * read the field of an object an support accessing it using '.'
+ *
+ * @param object
+ * @param name
+ * @returns
+ */
+function readField<T>(object: any, name: string): T | undefined {
+  return name
+    .split(".")
+    .reduce((prev, current) => prev && prev[current], object);
+}
+
+function setValueDeeper(object: any, names: string[], value: any): any {
+  if (names.length === 0) return value;
+  const [head, ...rest] = names;
+  if (object === undefined) {
+    return { [head]: setValueDeeper({}, rest, value) };
+  }
+  return { ...object, [head]: setValueDeeper(object[head] ?? {}, rest, value) };
+}