From d8970acf4e45d3912d32c2c8b2d2f88d4512f0b5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dafydd=20Ll=C5=B7r=20Pearson?= <DafyddLlyr@gmail.com>
Date: Fri, 2 Aug 2024 16:20:21 +0100
Subject: [PATCH] fix: Better type narrowing in calculationSchema

---
 app/schemas/calculationSchema.ts | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/app/schemas/calculationSchema.ts b/app/schemas/calculationSchema.ts
index 99d0319e..cfb5274b 100644
--- a/app/schemas/calculationSchema.ts
+++ b/app/schemas/calculationSchema.ts
@@ -1,6 +1,9 @@
 import { z } from "zod";
 import { parse as parsePostcode, fix as fixPostcode } from "postcode";
 
+// Type not exported by postcode lib directly
+type ValidPostcode = Extract<ReturnType<typeof parsePostcode>, { valid: true }>;
+
 const HouseTypeEnum = z.enum(['D', 'S', 'T', 'F']);
 
 /**
@@ -12,12 +15,12 @@ export const calculationSchema = z.object({
     .min(1, "housePostcode is required")
     .refine(fixPostcode, "Invalid postcode")
     .transform(parsePostcode)
-    .refine((postcode) => postcode.valid, { message: "Invalid postcode" }),
+    .refine((postcode): postcode is ValidPostcode => postcode.valid),
   houseSize: z.coerce.number().positive("houseSize must be a positive integer"),
   houseAge: z.coerce.number().positive("houseAge must be a positive integer"),
   houseBedrooms: z.coerce
     .number()
-    .positive("houseBedroomsmust be a positive integer"),
+    .positive("houseBedrooms must be a positive integer"),
   houseType: HouseTypeEnum.refine(
     (value) => HouseTypeEnum.options.includes(value),
     {