feat: add application productivity foundations

packages/reactive/src/form.ts

@@ -0,0 +1,75 @@
+import { computed, signal, type ReadonlySignal, type Signal } from "./signal.ts";
+
+export interface FormState<T extends Record<string, unknown>> {
+  values: Signal<T>;
+  errors: Signal<Partial<Record<keyof T, string>>>;
+  submitting: Signal<boolean>;
+  dirty: ReadonlySignal<boolean>;
+  field<K extends keyof T>(
+    name: K,
+  ): {
+    value: T[K];
+    onInput(payload: { value?: unknown; checked?: boolean }): void;
+  };
+  set<K extends keyof T>(name: K, value: T[K]): void;
+  reset(next?: T): void;
+  validate(): Promise<boolean>;
+  submit<R>(operation: (values: T) => R | Promise<R>): Promise<R>;
+}
+
+export function useForm<T extends Record<string, unknown>>(
+  initial: T,
+  validator?: (
+    values: T,
+  ) => Partial<Record<keyof T, string>> | Promise<Partial<Record<keyof T, string>>>,
+): FormState<T> {
+  let baseline = structuredClone(initial);
+  const values = signal(structuredClone(initial));
+  const errors = signal<Partial<Record<keyof T, string>>>({});
+  const submitting = signal(false);
+  const dirty = computed(() => JSON.stringify(values.get()) !== JSON.stringify(baseline));
+  const set = <K extends keyof T>(name: K, value: T[K]) => {
+    values.set({ ...values.get(), [name]: value });
+    if (errors.get()[name]) errors.set({ ...errors.get(), [name]: undefined });
+  };
+  const validate = async () => {
+    errors.set((await validator?.(values.get())) ?? {});
+    return Object.values(errors.get()).every((value) => !value);
+  };
+  return {
+    values,
+    errors,
+    submitting,
+    dirty,
+    field(name) {
+      return {
+        value: values.get()[name],
+        onInput(payload) {
+          const current = values.get()[name];
+          set(
+            name,
+            (typeof current === "boolean"
+              ? Boolean(payload.checked)
+              : payload.value) as T[typeof name],
+          );
+        },
+      };
+    },
+    set,
+    reset(next = initial) {
+      baseline = structuredClone(next);
+      values.set(structuredClone(next));
+      errors.set({});
+    },
+    validate,
+    async submit(operation) {
+      if (!(await validate())) throw new Error("WRN-FORM-INVALID");
+      submitting.set(true);
+      try {
+        return await operation(values.get());
+      } finally {
+        submitting.set(false);
+      }
+    },
+  };
+}

packages/reactive/src/index.ts

@@ -17,6 +17,8 @@ export {
   createTimeline,
   urlSignal,
 } from "./advanced.ts";
+export { useForm } from "./form.ts";
+export type { FormState } from "./form.ts";
 export type {
   HistorySignal,
   ReactiveContext,