Introduce pluggable email and image upload

src/main/java/com/openisle/service/CosImageUploader.java

@@ -0,0 +1,24 @@
+package com.openisle.service;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+
+/**
+ * ImageUploader implementation using Tencent Cloud COS.
+ * For simplicity this demo just returns a URL composed of the base URL and file name.
+ */
+@Service
+public class CosImageUploader extends ImageUploader {
+
+    private final String baseUrl;
+
+    public CosImageUploader(@Value("${cos.base-url:https://example.com}") String baseUrl) {
+        this.baseUrl = baseUrl;
+    }
+
+    @Override
+    public String upload(byte[] data, String filename) {
+        // In a real implementation you would call COS SDK here
+        return baseUrl + "/" + filename;
+    }
+}

src/main/java/com/openisle/service/EmailSender.java

@@ -0,0 +1,14 @@
+package com.openisle.service;
+
+/**
+ * Abstract email sender used to deliver emails.
+ */
+public abstract class EmailSender {
+    /**
+     * Send an email to a recipient.
+     * @param to recipient email address
+     * @param subject email subject
+     * @param text email body
+     */
+    public abstract void sendEmail(String to, String subject, String text);
+}

src/main/java/com/openisle/service/ImageUploader.java

@@ -0,0 +1,14 @@
+package com.openisle.service;
+
+/**
+ * Abstract service for uploading images.
+ */
+public abstract class ImageUploader {
+    /**
+     * Upload an image and return its accessible URL.
+     * @param data image binary data
+     * @param filename name of the file
+     * @return accessible URL of the uploaded file
+     */
+    public abstract String upload(byte[] data, String filename);
+}

src/main/java/com/openisle/service/ResendEmailSender.java

@@ -12,13 +12,14 @@ import java.util.HashMap;
 import java.util.Map;
 
 @Service
-public class EmailService {
+public class ResendEmailSender extends EmailSender {
 
     @Value("${resend.api.key}")
     private String apiKey;
 
     private final RestTemplate restTemplate = new RestTemplate();
 
+    @Override
     public void sendEmail(String to, String subject, String text) {
         String url = "https://api.resend.com/emails"; // hypothetical endpoint
 

src/main/java/com/openisle/service/UserService.java

@@ -78,4 +78,15 @@ public class UserService {
                 .filter(User::isVerified)
                 .filter(user -> passwordEncoder.matches(password, user.getPassword()));
     }
+
+    public Optional<User> findByUsername(String username) {
+        return userRepository.findByUsername(username);
+    }
+
+    public User updateAvatar(String username, String avatarUrl) {
+        User user = userRepository.findByUsername(username)
+                .orElseThrow(() -> new IllegalArgumentException("User not found"));
+        user.setAvatar(avatarUrl);
+        return userRepository.save(user);
+    }
 }