add session helper module

server/@types/express/index.d.ts

@@ -8,9 +8,9 @@ export declare module 'express-session' {
   }
 
   interface ApplicationData {
-    type: ApplicationType
-    prisonerName: string
-    date: Date
+    type?: ApplicationType
+    prisonerName?: string
+    date?: Date
     additionalData?: AdditionalApplicationData
   }
 

server/routes/applications/applicationTypeRoutes.ts

@@ -2,6 +2,7 @@ import { Request, Response, Router } from 'express'
 import { APPLICATION_TYPES } from '../../constants/applicationTypes'
 import asyncMiddleware from '../../middleware/asyncMiddleware'
 import AuditService, { Page } from '../../services/auditService'
+import { updateSessionData } from '../../utils/session'
 
 export default function applicationTypeRoutes({ auditService }: { auditService: AuditService }): Router {
   const router = Router()
@@ -36,11 +37,7 @@ export default function applicationTypeRoutes({ auditService }: { auditService:
         return
       }
 
-      req.session.applicationData = {
-        type: selectedAppType,
-        prisonerName: '',
-        date: new Date(),
-      }
+      updateSessionData(req, { type: selectedAppType })
 
       res.redirect(`/log/prisoner-details`)
     }),

server/routes/applications/prisonerDetailsRoutes.ts

@@ -1,6 +1,7 @@
 import { Request, Response, Router } from 'express'
 import asyncMiddleware from '../../middleware/asyncMiddleware'
 import AuditService, { Page } from '../../services/auditService'
+import { updateSessionData } from '../../utils/session'
 
 export default function prisonerDetailsRoutes({ auditService }: { auditService: AuditService }): Router {
   const router = Router()
@@ -32,11 +33,10 @@ export default function prisonerDetailsRoutes({ auditService }: { auditService:
         return
       }
 
-      req.session.applicationData = {
-        ...req.session.applicationData,
+      updateSessionData(req, {
         prisonerName: req.body.prisonerName,
         date: req.body.date,
-      }
+      })
 
       res.redirect(`/log/swap-vos-pin-credit-details`)
     }),

server/routes/applications/swapVosPinCreditDetailsRoutes.ts

@@ -1,7 +1,8 @@
 import { Request, Response, Router } from 'express'
+import { APPLICATION_TYPES } from '../../constants/applicationTypes'
 import asyncMiddleware from '../../middleware/asyncMiddleware'
 import AuditService, { Page } from '../../services/auditService'
-import { APPLICATION_TYPES } from '../../constants/applicationTypes'
+import { updateSessionData } from '../../utils/session'
 
 export default function swapVosPinCreditDetailsRoutes({ auditService }: { auditService: AuditService }): Router {
   const router = Router()
@@ -30,13 +31,12 @@ export default function swapVosPinCreditDetailsRoutes({ auditService }: { auditS
   router.post(
     '/log/swap-vos-pin-credit-details',
     asyncMiddleware(async (req: Request, res: Response) => {
-      req.session.applicationData = {
-        ...req.session.applicationData,
+      updateSessionData(req, {
         additionalData: {
           ...req.session.applicationData?.additionalData,
           swapVOsToPinCreditDetails: req.body.swapVosPinCreditDetails,
         },
-      }
+      })
 
       res.redirect(`/log/swap-vos-pin-credit-details/confirm`)
     }),

server/utils/session.test.ts

@@ -0,0 +1,71 @@
+import { Request } from 'express'
+import { SessionData } from 'express-session'
+import { updateSessionData } from './session'
+
+describe(updateSessionData.name, () => {
+  let req: Request
+
+  beforeEach(() => {
+    req = {
+      session: {} as SessionData,
+    } as Request
+  })
+
+  it('should initialize applicationData if it does not exist', () => {
+    updateSessionData(req, { prisonerName: 'John Doe' })
+
+    expect(req.session.applicationData).toEqual({
+      prisonerName: 'John Doe',
+    })
+  })
+
+  it('should update an existing field without removing other fields', () => {
+    req.session.applicationData = {
+      type: { name: 'Swap VOs', value: 'swap-vos' },
+      prisonerName: 'Jane Doe',
+    }
+
+    updateSessionData(req, { prisonerName: 'John Doe' })
+
+    expect(req.session.applicationData).toEqual({
+      type: { name: 'Swap VOs', value: 'swap-vos' },
+      prisonerName: 'John Doe',
+    })
+  })
+
+  it('should add new fields while keeping existing ones', () => {
+    req.session.applicationData = {
+      type: { name: 'Swap VOs', value: 'swap-vos' },
+    }
+
+    updateSessionData(req, { prisonerName: 'John Doe', date: new Date('2024-02-05') })
+
+    expect(req.session.applicationData).toEqual({
+      type: { name: 'Swap VOs', value: 'swap-vos' },
+      prisonerName: 'John Doe',
+      date: new Date('2024-02-05'),
+    })
+  })
+
+  it('should not overwrite nested objects but merge updates', () => {
+    req.session.applicationData = {
+      type: { name: 'Swap VOs', value: 'swap-vos' },
+      additionalData: { swapVOsToPinCreditDetails: 'Old value' },
+    }
+
+    updateSessionData(req, {
+      additionalData: { swapVOsToPinCreditDetails: 'New value' },
+    })
+
+    expect(req.session.applicationData).toEqual({
+      type: { name: 'Swap VOs', value: 'swap-vos' },
+      additionalData: { swapVOsToPinCreditDetails: 'New value' },
+    })
+  })
+
+  it('should handle undefined session gracefully', () => {
+    req.session = undefined
+
+    expect(() => updateSessionData(req, { prisonerName: 'John Doe' })).toThrow()
+  })
+})

server/utils/session.ts

@@ -0,0 +1,14 @@
+import { Request } from 'express'
+import { SessionData } from 'express-session'
+
+// eslint-disable-next-line import/prefer-default-export
+export const updateSessionData = (req: Request, updates: Partial<SessionData['applicationData']>) => {
+  if (!req.session.applicationData) {
+    req.session.applicationData = {} as SessionData['applicationData']
+  }
+
+  req.session.applicationData = {
+    ...req.session.applicationData,
+    ...updates,
+  }
+}