add actions

src/actions.test.ts

@@ -0,0 +1,14 @@
+import { test, expect } from 'vitest';
+
+import { action } from './actions.js';
+
+test('basic action', () => {
+    const foo = action('foo', (thing: string) => ({ thing }));
+
+    expect(foo('bar')).toEqual({
+        type: 'foo',
+        payload: {
+            thing: 'bar',
+        },
+    });
+});

src/actions.ts

@@ -0,0 +1,51 @@
+export type Action<T extends string = string, TPayload = any> = {
+    type: T;
+    meta?: Record<string, unknown>;
+    payload?: TPayload;
+};
+
+export type ActionGenerator<
+    TType extends string = string,
+    TPayloadGen = (...args: any[]) => any,
+> = {
+    type: TType;
+} & (TPayloadGen extends (...args: any) => any
+    ? ReturnType<TPayloadGen> extends void
+        ? (...args: Parameters<TPayloadGen>) => {
+              type: TType;
+          }
+        : (...args: Parameters<TPayloadGen>) => {
+              type: TType;
+              payload: ReturnType<TPayloadGen>;
+          }
+    : (...args: any[]) => { type: TType; payload?: unknown });
+
+export function action<
+    TType extends string,
+    TPayload extends (...args: any) => any,
+>(
+    type: TType,
+    payloadFunction?: TPayload,
+    transformer?: Function,
+): ActionGenerator<TType, TPayload> {
+    let generator: any = function (...payloadArg:any[]) {
+        const result: Action = { type };
+
+        if (payloadFunction) {
+            result.payload = payloadFunction(...payloadArg);
+        } else {
+            if (payloadArg[0] !== undefined) result.payload = payloadArg[0];
+        }
+
+        return result;
+    };
+
+    if (transformer) {
+        const orig = generator;
+        generator = (...args: any) => transformer(orig(...args), args);
+    }
+
+    generator.type = type;
+
+    return generator;
+}