refactor(backend): use utility function for email normalization (SCRUM-307)

Author: bernhaaard

backend/src/common/utils/email-utils.ts

@@ -0,0 +1,11 @@
+/**
+ * Utility function to normalize email addresses to lowercase
+ * Used in DTOs to ensure email case consistency
+ */
+export function normalizeEmail(value: unknown): string {
+  if (typeof value === 'string') {
+    return value.toLowerCase();
+  }
+  // If not a string, convert to string and lowercase
+  return String(value).toLowerCase();
+}

backend/src/modules/admin/dto/create-admin.dto.ts

@@ -1,6 +1,7 @@
 import { ApiProperty } from '@nestjs/swagger';
 import { IsEmail, IsString, IsNotEmpty } from 'class-validator';
 import { Transform } from 'class-transformer';
+import { normalizeEmail } from '../../../common/utils/email-utils';
 import { IsAllowedEmailDomain } from '../../../common/validators/allowed-email-domains.validator';
 
 export class CreateAdminDto {
@@ -11,9 +12,7 @@ export class CreateAdminDto {
   })
   @IsEmail()
   @IsNotEmpty()
-  @Transform(({ value }: { value: unknown }) =>
-    typeof value === 'string' ? value.toLowerCase() : (value as string),
-  )
+  @Transform(({ value }) => normalizeEmail(value))
   @IsAllowedEmailDomain({
     message: 'Email must be from an allowed domain',
   })

backend/src/modules/admin/dto/supervisors-bulk-import.dto.ts

@@ -10,6 +10,7 @@ import {
   IsArray,
 } from 'class-validator';
 import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+import { normalizeEmail } from '../../../common/utils/email-utils';
 
 export class SupervisorDto {
   @ApiProperty({
@@ -19,9 +20,7 @@ export class SupervisorDto {
   })
   @IsEmail()
   @IsNotEmpty()
-  @Transform(({ value }: { value: unknown }) =>
-    typeof value === 'string' ? value.toLowerCase() : (value as string),
-  )
+  @Transform(({ value }) => normalizeEmail(value))
   email: string;
 
   @ApiPropertyOptional({

backend/src/modules/requests/supervision/dto/create-supervision-request.dto.ts

@@ -1,6 +1,7 @@
 import { ApiPropertyOptional } from '@nestjs/swagger';
 import { IsEmail, IsOptional, IsUUID } from 'class-validator';
 import { Transform } from 'class-transformer';
+import { normalizeEmail } from '../../../../common/utils/email-utils';
 import { IsAllowedEmailDomain } from '../../../../common/validators/allowed-email-domains.validator';
 
 export class CreateSupervisionRequestDto {
@@ -19,9 +20,7 @@ export class CreateSupervisionRequestDto {
   })
   @IsOptional()
   @IsEmail()
-  @Transform(({ value }: { value: unknown }) =>
-    typeof value === 'string' ? value.toLowerCase() : (value as string),
-  )
+  @Transform(({ value }) => normalizeEmail(value))
   @IsAllowedEmailDomain({
     message: 'Email must be from an allowed domain',
   })

backend/src/modules/users/dto/create-user.dto.ts

@@ -1,6 +1,7 @@
 import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
 import { IsEmail, IsOptional, IsString, IsNotEmpty } from 'class-validator';
 import { Transform } from 'class-transformer';
+import { normalizeEmail } from '../../../common/utils/email-utils';
 
 export class CreateUserDto {
   @ApiProperty({
@@ -10,9 +11,7 @@ export class CreateUserDto {
   })
   @IsEmail()
   @IsNotEmpty()
-  @Transform(({ value }: { value: unknown }) =>
-    typeof value === 'string' ? value.toLowerCase() : (value as string),
-  )
+  @Transform(({ value }) => normalizeEmail(value))
   email: string;
 
   @ApiPropertyOptional({

backend/src/modules/users/dto/update-user.dto.ts

@@ -1,6 +1,7 @@
 import { ApiPropertyOptional } from '@nestjs/swagger';
 import { IsEmail, IsOptional, IsString } from 'class-validator';
 import { Transform } from 'class-transformer';
+import { normalizeEmail } from '../../../common/utils/email-utils';
 
 export class UpdateUserDto {
   @ApiPropertyOptional({
@@ -9,9 +10,7 @@ export class UpdateUserDto {
   })
   @IsEmail()
   @IsOptional()
-  @Transform(({ value }: { value: unknown }) =>
-    typeof value === 'string' ? value.toLowerCase() : (value as string),
-  )
+  @Transform(({ value }) => normalizeEmail(value))
   email?: string;
 
   @ApiPropertyOptional({