🐛 fix: normalize AI-generated dates to valid ISO offset datetimes

- add normalizeAiDateString() to coerce bare ISO datetimes, date-only
  strings, and fractional-second variants into offset-aware format
- apply via z.preprocess in AiEventResponseItemSchema so Zod validation
  no longer rejects AI responses missing a timezone offset
- fix system prompt to use toISOString() (unambiguous UTC) and clarify
  expected datetime format for the AI model
- install bun-types and add to tsconfig so bun:test resolves cleanly
- add 8 behaviour-driven tests covering all normalizer edge cases

bun.lock

@@ -41,6 +41,7 @@
         "@types/react": "^19",
         "@types/react-dom": "^19",
         "@typescript/native-preview": "^7.0.0-dev.20260407.1",
+        "bun-types": "^1.3.11",
         "drizzle-kit": "^0.31.4",
         "eslint": "^9",
         "eslint-config-next": "15.4.6",
@@ -521,6 +522,8 @@
 
     "buffer-from": ["buffer-from@1.1.2", "", {}, "sha512-E+XQCRwSbaaiChtv6k6Dwgc+bx+Bs6vuKJHHl5kox/BaKbhiXzqQOwK4cO22yElGp2OCmjwVhT3HmxgyPGnJfQ=="],
 
+    "bun-types": ["bun-types@1.3.11", "", { "dependencies": { "@types/node": "*" } }, "sha512-1KGPpoxQWl9f6wcZh57LvrPIInQMn2TQ7jsgxqpRzg+l0QPOFvJVH7HmvHo/AiPgwXy+/Thf6Ov3EdVn1vOabg=="],
+
     "call-bind": ["call-bind@1.0.8", "", { "dependencies": { "call-bind-apply-helpers": "^1.0.0", "es-define-property": "^1.0.0", "get-intrinsic": "^1.2.4", "set-function-length": "^1.2.2" } }, "sha512-oKlSFMcMwpUg2ednkhQ454wfWiU/ul3CkJe/PEHcTKuiX6RpbehUiFMXu13HalGZxfUwCQzZG747YXBn1im9ww=="],
 
     "call-bind-apply-helpers": ["call-bind-apply-helpers@1.0.2", "", { "dependencies": { "es-errors": "^1.3.0", "function-bind": "^1.1.2" } }, "sha512-Sp1ablJ0ivDkSzjcaJdxEunN5/XvksFJ2sMBFfq6x0ryhQV/2b/KwFe21cMpmHtPOSij8K99/wSfoEuTObmuMQ=="],

package.json

@@ -46,6 +46,7 @@
     "@types/react": "^19",
     "@types/react-dom": "^19",
     "@typescript/native-preview": "^7.0.0-dev.20260407.1",
+    "bun-types": "^1.3.11",
     "drizzle-kit": "^0.31.4",
     "eslint": "^9",
     "eslint-config-next": "15.4.6",

src/app/api/ai-event/route.ts

@@ -17,7 +17,7 @@ TypeScript type:
   description?: string,
   location?: string,
   url?: string,
-  start: string, // ISO datetime
+  start: string, // ISO 8601 datetime with timezone, e.g. "2025-04-10T10:00:00-04:00"
   end?: string,
   allDay?: boolean,
   recurrenceRule?: string // valid iCal RRULE string like FREQ=WEEKLY;BYDAY=MO;INTERVAL=1
@@ -26,7 +26,7 @@ TypeScript type:
 Rules:
   - If the user describes multiple events in one prompt, return multiple objects (one per event).
   - Always return a valid JSON array of objects, even if there's only one event.
-  - Today is ${new Date().toLocaleString()}.
+  - Today is ${new Date().toISOString()}.
   - If no time is given, assume allDay event.
   - If no end time is given (and event is not allDay), default to 1 hour after start.
   - If multiple events are described, return multiple.

src/lib/date-normalizer.ts

@@ -0,0 +1,10 @@
+import { formatISO, parseISO } from "date-fns";
+
+const ISO_DATETIME_WITH_OFFSET =
+	/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(Z|[+-]\d{2}:\d{2})$/;
+
+export const normalizeAiDateString = (input: string): string => {
+	if (ISO_DATETIME_WITH_OFFSET.test(input)) return input;
+	const parsed = parseISO(input);
+	return formatISO(parsed);
+};

src/lib/types.ts

@@ -1,5 +1,6 @@
 import { z } from "zod";
 import { MAX_IMAGE_SIZE_BYTES } from "@/lib/constants";
+import { normalizeAiDateString } from "@/lib/date-normalizer";
 
 /** Validates that a base64 data URL string decodes to binary under the max size. */
 const isValidImageSize = (val: string | undefined): boolean => {
@@ -29,14 +30,19 @@ export const AiEventRequestSchema = z
 
 export type AiEventRequest = z.infer<typeof AiEventRequestSchema>;
 
+const aiDatetime = z.preprocess(
+	(val) => (typeof val === "string" ? normalizeAiDateString(val) : val),
+	z.string().datetime({ offset: true }),
+);
+
 export const AiEventResponseItemSchema = z.object({
 	id: z.string().optional(),
 	title: z.string().min(1),
 	description: z.string().optional(),
 	location: z.string().optional(),
 	url: z.string().optional(),
-	start: z.string().datetime({ offset: true }),
+	start: aiDatetime,
-	end: z.string().datetime({ offset: true }).optional(),
+	end: aiDatetime.optional(),
 	allDay: z.boolean().optional(),
 	recurrenceRule: z.string().optional(),
 });

tests/date-normalizer.test.ts

@@ -0,0 +1,83 @@
+import { describe, expect, test } from "bun:test";
+import { normalizeAiDateString } from "@/lib/date-normalizer";
+import { AiEventResponseSchema } from "@/lib/types";
+
+describe("normalizeAiDateString", () => {
+	test("converts bare ISO datetime (no offset) to valid offset datetime accepted by Zod", () => {
+		const input = "2025-04-10T10:00:00";
+		const result = normalizeAiDateString(input);
+		expect(result).toMatch(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(Z|[+-]\d{2}:\d{2})$/);
+		expect(new Date(result).getHours()).toBe(10);
+	});
+
+	test("converts date-only string to midnight datetime with offset", () => {
+		const input = "2025-04-10";
+		const result = normalizeAiDateString(input);
+		expect(result).toMatch(/^\d{4}-\d{2}-\d{2}T00:00:00(Z|[+-]\d{2}:\d{2})$/);
+	});
+
+	test("passes through already-valid datetime with offset unchanged", () => {
+		const input = "2025-04-10T10:00:00-04:00";
+		const result = normalizeAiDateString(input);
+		expect(result).toBe("2025-04-10T10:00:00-04:00");
+	});
+
+	test("passes through datetime with Z suffix unchanged", () => {
+		const input = "2025-04-10T10:00:00Z";
+		const result = normalizeAiDateString(input);
+		expect(result).toBe("2025-04-10T10:00:00Z");
+	});
+
+	test("handles datetime with fractional seconds", () => {
+		const input = "2025-04-10T10:00:00.000Z";
+		const result = normalizeAiDateString(input);
+		expect(result).toMatch(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}/);
+		expect(new Date(result).getHours()).toBe(10);
+	});
+});
+
+describe("AiEventResponseSchema date normalization", () => {
+	test("accepts event with bare ISO datetime (no offset) by normalizing it", () => {
+		const raw = [
+			{
+				title: "Team Meeting",
+				start: "2025-04-10T10:00:00",
+				end: "2025-04-10T11:00:00",
+			},
+		];
+		const result = AiEventResponseSchema.safeParse(raw);
+		expect(result.success).toBe(true);
+		if (result.success) {
+			expect(result.data[0].start).toMatch(
+				/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(Z|[+-]\d{2}:\d{2})$/,
+			);
+		}
+	});
+
+	test("accepts event with date-only start and no end", () => {
+		const raw = [
+			{
+				title: "All-day workshop",
+				start: "2025-07-20",
+				allDay: true,
+			},
+		];
+		const result = AiEventResponseSchema.safeParse(raw);
+		expect(result.success).toBe(true);
+	});
+
+	test("accepts event with already-valid offset datetime", () => {
+		const raw = [
+			{
+				title: "Standup",
+				start: "2025-04-10T09:00:00-05:00",
+				end: "2025-04-10T09:30:00-05:00",
+			},
+		];
+		const result = AiEventResponseSchema.safeParse(raw);
+		expect(result.success).toBe(true);
+		if (result.success) {
+			expect(result.data[0].start).toBe("2025-04-10T09:00:00-05:00");
+		}
+	});
+});

tsconfig.json

@@ -20,7 +20,8 @@
 		],
 		"paths": {
 			"@/*": ["./src/*"]
-		}
+		},
+		"types": ["bun-types"]
 	},
 	"include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
 	"exclude": ["node_modules"]