Done the required changes

pom.xml

@@ -51,20 +51,20 @@
 			<scope>runtime</scope>
 			<optional>true</optional>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>io.jsonwebtoken</groupId>
 			<artifactId>jjwt-api</artifactId>
 			<version>0.11.5</version>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>io.jsonwebtoken</groupId>
 			<artifactId>jjwt-impl</artifactId>
 			<version>0.11.5</version>
 			<scope>runtime</scope>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>io.jsonwebtoken</groupId>
 			<artifactId>jjwt-jackson</artifactId>
@@ -93,13 +93,13 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-security</artifactId>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>org.springframework.security</groupId>
 			<artifactId>spring-security-test</artifactId>
 			<scope>test</scope>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>org.springframework.security</groupId>
 			<artifactId>spring-security-oauth2-client</artifactId>

src/main/java/com/libraryman_api/book/BookController.java

@@ -100,4 +100,4 @@ public BookDto updateBook(@PathVariable int id, @RequestBody BookDto bookDtoDeta
     public void deleteBook(@PathVariable int id) {
         bookService.deleteBook(id);
     }
-}
+}

src/main/java/com/libraryman_api/borrowing/BorrowingService.java

@@ -349,4 +349,4 @@ public BorrowingsDto EntityToDto(Borrowings borrowings) {
         borrowingsDto.setBook(bookService.EntityToDto(borrowings.getBook()));
         return borrowingsDto;
     }
-}
+}

src/main/java/com/libraryman_api/email/EmailService.java

@@ -17,62 +17,88 @@
 import org.springframework.stereotype.Service;
 
 /**
- * Service class for sending emails asynchronously.
- * This class handles the construction and sending of MIME email messages.
+ * Unified service class for sending emails asynchronously.
+ * Handles both general email sending and notifications.
  */
 @Service
 public class EmailService implements EmailSender {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(EmailService.class);
+
     private final NotificationRepository notificationRepository;
     private final JavaMailSender mailSender;
-    @Value("${spring.mail.properties.domain_name}")
+
+    @Value("${spring.mail.properties.domain_name}") // Domain name from application properties
     private String domainName;
 
-    /**
-     * Constructs a new {@code EmailService} with the specified {@link NotificationRepository} and {@link JavaMailSender}.
-     *
-     * @param notificationRepository the repository for managing notification entities
-     * @param mailSender             the mail sender for sending email messages
-     */
     public EmailService(NotificationRepository notificationRepository, JavaMailSender mailSender) {
         this.notificationRepository = notificationRepository;
         this.mailSender = mailSender;
     }
 
     /**
-     * Sends an email asynchronously to the specified recipient.
-     * If the email is successfully sent, the notification status is updated to SENT.
-     * If the email fails to send, the notification status is updated to FAILED and an exception is thrown.
+     * Sends a general email asynchronously.
      *
-     * @param to           the recipient's email address
-     * @param email        the content of the email to send
-     * @param subject      the subject of the email
-     * @param notification the {@link Notifications} object representing the email notification
+     * @param to      recipient's email
+     * @param body    email content (HTML supported)
+     * @param subject subject of the email
      */
-    @Override
     @Async
-    public void send(String to, String email, String subject, Notifications notification) {
+    public void sendEmail(String to, String body, String subject) {
+        sendEmail(to, body, subject, null); // Default 'from' to null
+    }
+
+    /**
+     * Sends a general email asynchronously.
+     *
+     * @param to      recipient's email
+     * @param body    email content (HTML supported)
+     * @param subject subject of the email
+     * @param from    sender's email address (overrides default if provided)
+     */
+    @Async
+    public void sendEmail(String to, String body, String subject, String from) {
         try {
             MimeMessage mimeMessage = mailSender.createMimeMessage();
             MimeMessageHelper helper = new MimeMessageHelper(mimeMessage, "utf-8");
-            helper.setText(email, true);
+
+            helper.setText(body, true); // true = enable HTML content
             helper.setTo(to);
             helper.setSubject(subject);
-            helper.setFrom(domainName);
+            helper.setFrom(from != null ? from : domainName); // Use provided sender or default domain
+
             mailSender.send(mimeMessage);
+        } catch (MessagingException e) {
+            LOGGER.error("Failed to send email", e);
+            throw new IllegalStateException("Failed to send email", e);
+        }
+    }
+
+    /**
+     * Sends a notification email and updates notification status.
+     *
+     * @param to           recipient's email
+     * @param email        email content
+     * @param subject      subject of the email
+     * @param notification notification entity to update status
+     */
+    @Override
+    @Async
+    public void send(String to, String email, String subject, Notifications notification) {
+        try {
+            sendEmail(to, email, subject); // Reuse sendEmail method for notifications
 
             // Update notification status to SENT
             notification.setNotificationStatus(NotificationStatus.SENT);
             notificationRepository.save(notification);
-        } catch (MessagingException e) {
-            LOGGER.error("Failed to send email", e);
+        } catch (Exception e) {
+            LOGGER.error("Failed to send notification email", e);
 
             // Update notification status to FAILED
             notification.setNotificationStatus(NotificationStatus.FAILED);
             notificationRepository.save(notification);
 
-            throw new IllegalStateException("Failed to send email", e);
+            throw new IllegalStateException("Failed to send notification email", e);
         }
     }
 }

src/main/java/com/libraryman_api/member/MemberService.java

@@ -225,4 +225,4 @@ public MembersDto EntityToDto(Members members) {
         membersDto.setMembershipDate(members.getMembershipDate());
         return membersDto;
     }
-}
+}

src/main/java/com/libraryman_api/newsletter/NewsletterController.java

@@ -1,26 +1,71 @@
 package com.libraryman_api.newsletter;
 
-import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
 
 @RestController
-@RequestMapping("/newsletter")
+@RequestMapping("/api/newsletter")
 public class NewsletterController {
 
     private final NewsletterService newsletterService;
 
-    @Autowired
     public NewsletterController(NewsletterService newsletterService) {
         this.newsletterService = newsletterService;
     }
 
+    // Subscribe Endpoint
     @PostMapping("/subscribe")
-    public String subscribe(@RequestParam String email) {
-        return newsletterService.subscribe(email);
+    public ResponseEntity<String> subscribe(@RequestParam String email) {
+        try {
+            String result = newsletterService.subscribe(email);
+
+            switch (result) {
+                case "Invalid email format.":
+                    return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(result); // 400 Bad Request
+
+                case "Email is already subscribed.":
+                    return ResponseEntity.status(HttpStatus.CONFLICT).body(result); // 409 Conflict
+
+                case "You have successfully subscribed!":
+                    return ResponseEntity.status(HttpStatus.CREATED).body(result); // 201 Created
+
+                case "You have successfully re-subscribed!":
+                    return ResponseEntity.status(HttpStatus.OK).body(result); // 200 OK
+
+                default:
+                    return ResponseEntity.status(HttpStatus.OK).body(result); // Default 200 OK
+            }
+        } catch (Exception e) {
+            // Handle unexpected errors
+            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
+                    .body("An error occurred while processing your subscription.");
+        }
     }
 
+    // Unsubscribe Endpoint
     @GetMapping("/unsubscribe")
-    public String unsubscribe(@RequestParam String token) {
-        return newsletterService.unsubscribe(token);
+    public ResponseEntity<String> unsubscribe(@RequestParam String token) {
+        try {
+            String result = newsletterService.unsubscribe(token);
+
+            switch (result) {
+                case "Invalid or expired token.":
+                    return ResponseEntity.status(HttpStatus.NOT_FOUND).body(result); // 404 Not Found
+
+                case "You are already unsubscribed.":
+                    return ResponseEntity.status(HttpStatus.CONFLICT).body(result); // 409 Conflict
+
+                case "You have successfully unsubscribed!":
+                    return ResponseEntity.status(HttpStatus.OK).body(result); // 200 OK
+
+                default:
+                    return ResponseEntity.status(HttpStatus.OK).body(result); // Default 200 OK
+            }
+        } catch (Exception e) {
+            // Handle unexpected errors
+            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
+                    .body("An error occurred while processing your unsubscription.");
+        }
     }
 }

src/main/java/com/libraryman_api/newsletter/NewsletterService.java

@@ -60,14 +60,17 @@ private boolean isValidEmail(String email) {
 
     private void sendSubscriptionEmail(String email, String token) {
         String subject = "Welcome to Our Newsletter!";
-        String body = "Thank you for subscribing! To unsubscribe, click the link:\n" +
-                "http://localhost:8080/newsletter/unsubscribe?token=" + token;
-        emailService.send(email, body, subject, null);
+        String body = "Thank you for subscribing! " +
+                "To unsubscribe, click the link:\n" +
+                "http://localhost:8080/api/newsletter/unsubscribe?token=" + token;
+
+        emailService.sendEmail(email, body, subject); // No need to change this line
     }
 
     private void sendUnsubscribeEmail(String email) {
         String subject = "You have been unsubscribed";
         String body = "You have successfully unsubscribed. If this was a mistake, you can re-subscribe.";
-        emailService.send(email, body, subject, null);
+
+        emailService.sendEmail(email, body, subject); // No need to change this line
     }
 }

src/main/java/com/libraryman_api/security/config/WebConfiguration.java

@@ -86,4 +86,4 @@ public CorsFilter corsFilter() {
         return new CorsFilter(corsConfigurationSource());
     }
 
-}
+}

src/main/java/com/libraryman_api/security/services/SignupService.java

@@ -84,4 +84,4 @@ public void signupLibrarian(Members members) {
         new_members.setUsername(members.getUsername());
         memberRepository.save(new_members);
     }
-}
+}

src/main/resources/application-development.properties

@@ -40,4 +40,12 @@ spring.mail.username=Add_Your_Mail_Service_Username
 spring.mail.password=Add_Your_Mail_Service_Password
 spring.mail.properties.mail.smtp.auth=Add_Your_Mail_Service_SMTP
 spring.mail.properties.mail.starttls.enable=Add_Your_Mail_Service_Start_TLS
-spring.mail.properties.domain_name=Add_Your_Mail_Service_Domain_Name
+spring.mail.properties.domain_name=Add_Your_Mail_Service_Domain_Name
+
+
+
+# --- Oauth 2.0 Configurations ---
+spring.security.oauth2.client.registration.google.client-name=google
+spring.security.oauth2.client.registration.google.client-id=ADD_YOUR_CLIENT_ID
+spring.security.oauth2.client.registration.google.client-secret=ADD_YOUR_SECRET_KEY
+spring.security.oauth2.client.registration.google.scope=email,profile