Added backend functionalities for newsletter signup.

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

@@ -0,0 +1,44 @@
+package com.libraryman_api.newsletter;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.Map;
+
+@RestController
+@RequestMapping("/api/newsletter")
+public class NewsletterController {
+
+    @Autowired
+    private NewsletterService newsletterService;
+
+    // Subscribe endpoint
+    @PostMapping("/subscribe")
+    public ResponseEntity<String> subscribe(@RequestBody Map<String, String> requestBody) {
+        String email = requestBody.get("email");
+
+        // Call the service to handle subscription
+        String response = newsletterService.subscribe(email);
+
+        // Return response from the service
+        if (response.equals("Invalid email format.") || response.equals("Email is already subscribed.")) {
+            return ResponseEntity.badRequest().body(response);
+        }
+
+        return ResponseEntity.ok(response);
+    }
+
+    // Unsubscribe endpoint using token
+    @GetMapping("/unsubscribe/{token}")
+    public ResponseEntity<String> unsubscribe(@PathVariable String token) {
+        String response = newsletterService.unsubscribe(token);
+
+        // Check if the response indicates an error
+        if (response.equals("Invalid or expired token.") || response.equals("You are already unsubscribed.")) {
+            return ResponseEntity.badRequest().body(response);
+        }
+
+        return ResponseEntity.ok(response);
+    }
+}

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

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+package com.libraryman_api.newsletter;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import java.util.Optional;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+@Service
+public class NewsletterService {
+
+    @Autowired
+    private NewsletterSubscriberRepository subscriberRepository;
+
+    // Subscribe user after validating email
+    public String subscribe(String email) {
+        if (!isValidEmail(email)) {
+            return "Invalid email format.";
+        }
+
+        // Check if the email already exists
+        Optional<NewsletterSubscriber> optionalSubscriber = subscriberRepository.findByEmail(email);
+
+        if (optionalSubscriber.isPresent()) {
+            NewsletterSubscriber subscriber = optionalSubscriber.get();
+
+            // If the subscriber is inactive, reactivate them
+            if (!subscriber.isActive()) {
+                subscriber.setActive(true); // Reactivate the subscriber
+                subscriber.regenerateToken(); // Generate a new token
+                subscriberRepository.save(subscriber); // Save the updated subscriber
+                return "You have successfully re-subscribed!";
+            } else {
+                return "Email is already subscribed.";
+            }
+        }
+
+        // Save new subscriber if not present
+        NewsletterSubscriber subscriber = new NewsletterSubscriber(email);
+        subscriberRepository.save(subscriber);
+        return "You have successfully subscribed!";
+    }
+
+    // Unsubscribe user using the token
+    public String unsubscribe(String token) {
+        Optional<NewsletterSubscriber> optionalSubscriber = subscriberRepository.findByUnsubscribeToken(token);
+
+        if (optionalSubscriber.isEmpty()) {
+            return "Invalid or expired token.";
+        }
+
+        NewsletterSubscriber subscriber = optionalSubscriber.get();
+
+        if (!subscriber.isActive()) {
+            return "You are already unsubscribed.";
+        }
+
+        subscriber.setActive(false); // Set active to false
+        subscriberRepository.save(subscriber); // Save the updated subscriber
+        return "You have successfully unsubscribed!";
+    }
+
+    // Email validation logic
+    private boolean isValidEmail(String email) {
+        if (email == null || email.trim().isEmpty()) {
+            return false;
+        }
+        String emailRegex = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$";
+        Pattern pattern = Pattern.compile(emailRegex);
+        Matcher matcher = pattern.matcher(email);
+        return matcher.matches();
+    }
+}

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

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+package com.libraryman_api.newsletter;
+
+import jakarta.persistence.*;
+import java.util.UUID;
+
+@Entity
+@Table(name = "newsletter_subscribers")
+public class NewsletterSubscriber {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(nullable = false, unique = true)
+    private String email;
+
+    @Column(nullable = false)
+    private boolean active = true; // Manage subscription status
+
+    @Column(name = "unsubscribe_token", nullable = false, unique = true)
+    private String unsubscribeToken; // Token for unsubscribing
+
+    // Default constructor that initializes the token
+    public NewsletterSubscriber() {
+        this.unsubscribeToken = UUID.randomUUID().toString(); // Generate token by default
+    }
+
+    // Constructor to initialize with email
+    public NewsletterSubscriber(String email) {
+        this();
+        this.email = email;
+    }
+
+    // Getters and setters
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public boolean isActive() {
+        return active;
+    }
+
+    public void setActive(boolean active) {
+        this.active = active;
+    }
+
+    public String getUnsubscribeToken() {
+        return unsubscribeToken;
+    }
+
+    // Method to regenerate a new token
+    public void regenerateToken() {
+        this.unsubscribeToken = UUID.randomUUID().toString();
+    }
+}

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

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+package com.libraryman_api.newsletter;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.Optional;
+
+public interface NewsletterSubscriberRepository extends JpaRepository<NewsletterSubscriber, Long> {
+
+    // Find a subscriber by email
+    Optional<NewsletterSubscriber> findByEmail(String email);
+
+    // Find a subscriber by unsubscribe token
+    Optional<NewsletterSubscriber> findByUnsubscribeToken(String unsubscribeToken);
+}