feat!: convert date to iso instead of number (#21)

The reason is that Date is an object, not a scalar value, so you can't have it serialized in JSON or Avro. The only way is to transform it to a Unix timestamp (number) or some string standard (like the ISO one).

We started with the numeric approach, but we realized that we prefer the ISO one since it's easier for humans to read.

Author: rgomezcasas

src/Primitives.ts

@@ -1,4 +1,16 @@
 /* eslint-disable @typescript-eslint/no-unsafe-function-type */
+type Year = `${number}${number}${number}${number}`;
+type Month = `${number}${number}`;
+type Day = `${number}${number}`;
+type Hour = `${number}${number}`;
+type Minute = `${number}${number}`;
+type Second = `${number}${number}`;
+type Milliseconds = `${number}${number}${number}`;
+type Timezone = "Z" | `${"+" | "-"}${number}${number}:${number}${number}`;
+
+export type ISODateTime =
+	`${Year}-${Month}-${Day}T${Hour}:${Minute}:${Second}.${Milliseconds}${Timezone}`;
+
 type Methods<T> = {
 	[P in keyof T]: T[P] extends Function ? P : never;
 }[keyof T];
@@ -9,24 +21,24 @@ type Properties<T> = Omit<MethodsAndProperties<T>, Methods<T>>;
 
 type PrimitiveTypes = string | number | boolean | undefined | null;
 
-type DateToNumber<T> = T extends Date ? number : T;
+type DateToISODateTime<T> = T extends Date ? ISODateTime : T;
 
 type ValueObjectValue<T> = T extends PrimitiveTypes
 	? T
 	: T extends Date
-		? number
+		? ISODateTime
 		: T extends { value: infer U }
-			? DateToNumber<U>
+			? DateToISODateTime<U>
 			: T extends Array<{ value: infer U }>
-				? DateToNumber<U>[]
+				? DateToISODateTime<U>[]
 				: T extends Array<infer U>
 					? Array<ValueObjectValue<U>>
 					: T extends { [K in keyof Properties<T>]: unknown }
 						? {
 								[K in keyof Properties<T>]: ValueObjectValue<Properties<T>[K]>;
 							}
 						: T extends unknown
-							? DateToNumber<T>
+							? DateToISODateTime<T>
 							: never;
 
 export type Primitives<T> = {

tests/Primitives.test.ts

@@ -1,6 +1,7 @@
 import { expectTypeOf } from "expect-type";
 
 import { Primitives } from "../src";
+import { ISODateTime } from "../src/Primitives";
 import { Course } from "./Course";
 import { DeliveryInfo } from "./DeliveryInfo";
 import { Learner } from "./Learner";
@@ -70,12 +71,12 @@ describe("Primitives", () => {
 		expectTypeOf<actualPrimitives>().toEqualTypeOf<expectedPrimitives>();
 	});
 
-	it("should get primitive number type from Date", () => {
+	it("should get primitive ISO string type from Date", () => {
 		type actualPrimitives = Primitives<Step>;
 
 		type expectedPrimitives = {
 			readonly name: string;
-			readonly publishedAt: number;
+			readonly publishedAt: ISODateTime;
 		};
 
 		expectTypeOf<actualPrimitives>().toEqualTypeOf<expectedPrimitives>();