From a90299578bdef705b4ae0e43600760d5fc0529fe Mon Sep 17 00:00:00 2001
From: tim-s-ccs <timothy.south@crowncommercial.gov.uk>
Date: Mon, 7 Feb 2022 09:46:25 +0000
Subject: [PATCH] Update some of the rules of casting

---
 src/utils/cast.ts       |  8 ++++++--
 test/utils/cast.test.ts | 22 ++++++++++++++++++++--
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/utils/cast.ts b/src/utils/cast.ts
index 17198a7..01e99a8 100644
--- a/src/utils/cast.ts
+++ b/src/utils/cast.ts
@@ -1,8 +1,12 @@
-const cast = (input: string, targetType: NumberConstructor|StringConstructor|BooleanConstructor): any => {
+const cast = (input: string|undefined, targetType: NumberConstructor|StringConstructor|BooleanConstructor): string|number|boolean|undefined => {
+  if (input === undefined) return undefined
+
   switch(targetType) {
   case Number:
     if (input.length > 0) {
-      return Number(input)
+      const number = Number(input)
+
+      return isNaN(number) ? undefined : number
     } else {
       return undefined
     }
diff --git a/test/utils/cast.test.ts b/test/utils/cast.test.ts
index 8fad408..3a3938f 100644
--- a/test/utils/cast.test.ts
+++ b/test/utils/cast.test.ts
@@ -4,16 +4,22 @@ import { expect } from 'chai'
 
 describe('cast', () => {
   describe('when casting to \'Number\'', () => {
+    it('returns \'undefined\' when the input is undefined', () => {
+      const result = cast(undefined, Number)
+
+      expect(result).to.eq(undefined)
+    })
+
     it('returns \'undefined\' when the input is \'\'', () => {
       const result = cast('', Number)
 
       expect(result).to.eq(undefined)
     })
 
-    it('returns \'NaN\' when the input is a random string', () => {
+    it('returns \'undefined\' when the input is a random string', () => {
       const result = cast('something', Number)
 
-      expect(result).to.be.NaN
+      expect(result).to.eq(undefined)
     })
 
     it('returns an integer when the input is an integer as a string', () => {
@@ -32,6 +38,12 @@ describe('cast', () => {
   })
 
   describe('when casting to \'String\'', () => {
+    it('returns \'undefined\' when the input is undefined', () => {
+      const result = cast(undefined, String)
+
+      expect(result).to.eq(undefined)
+    })
+
     it('returns an empty string when the input is is \'\'', () => {
       const result = cast('', String)
 
@@ -54,6 +66,12 @@ describe('cast', () => {
   })
 
   describe('when casting to \'Boolean\'', () => {
+    it('returns \'undefined\' when the input is undefined', () => {
+      const result = cast(undefined, Boolean)
+
+      expect(result).to.eq(undefined)
+    })
+
     it('returns true when the input is is \'true\'', () => {
       const result = cast('true', Boolean)