src/main/java/entgra/mailsender/DAO/MailDAO.java

@@ -8,8 +8,13 @@ import java.util.PriorityQueue;
 
 public interface MailDAO {
      void addMail(MailModel mailModel);
-     PriorityQueue<MailModel> getMailwithHighPriority();
+
+    // List<MailModel> insertInPriorityQueue();
+
      MailModel getMailDetails(Integer mail_id);
+
      void addToSentMail(Integer mail_id);
 
+     List<MailModel> getUnsentMessages();
+
 }

src/main/java/entgra/mailsender/DAO/MailDAOImpl.java

@@ -11,14 +11,14 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.sql.*;
 import java.time.LocalDate;
-import java.util.Comparator;
+import java.util.ArrayList;
 import java.util.List;
-import java.util.PriorityQueue;
 import java.util.logging.Logger;
 
 
 @Service
 public class MailDAOImpl implements MailDAO{
+
 Logger logger = Logger.getLogger(String.valueOf(MailDAOImpl.class));
 
 private Connection getConnection() throws SQLException {
@@ -54,40 +54,62 @@ public void addMail(MailModel mailModel){
     }
 }
 
-@Override
-public PriorityQueue<MailModel> getMailwithHighPriority(){
-    logger.info("came into the function");
-    String sql = "SELECT email_id,priority FROM email WHERE email_id NOT IN (SELECT email_id FROM sentEmail)";
-    PriorityQueue<MailModel> priorityQueue = new PriorityQueue<>(Comparator.comparingInt(MailModel::getPriority));
-
-    try{
-        Connection conn = this.getConnection();
-
-        try (PreparedStatement stmt = conn.prepareStatement(sql);
-             ResultSet rs = stmt.executeQuery()) {
-            while (rs.next()) {
-                int priority = rs.getInt("priority");
-                int mail_id = rs.getInt("email_id");
-                priorityQueue.add(new MailModel(mail_id,null,null,priority,null,null,null,null,null));
-            }
-
-//            MailModel email = priorityQueue.poll();
-            //assert email != null;
-            for (Object element: priorityQueue){
-                System.out.println("element" + element);
-            }
-            return priorityQueue;
+//@Override
+//public List<MailModel> insertInPriorityQueue(){
+//    logger.info("came into the function");
+//
+//
+//    try{
+//        Connection conn = this.getConnection();
+//
+//        try (PreparedStatement stmt = conn.prepareStatement(sql);
+//             ResultSet rs = stmt.executeQuery()) {
+//            while (rs.next()) {
+//                int priority = rs.getInt("priority");
+//                int mail_id = rs.getInt("email_id");
+//                priorityQueue.add(new MailModel(mail_id,null,null,priority,null,null,null,null,null,0));
+//            }
+//
+////            MailModel email = priorityQueue.poll();
+//            //assert email != null;
+//            for (Object element: priorityQueue){
+//                System.out.println("element" + element);
+//            }
+//            return priorityQueue;
+//
+//        } catch (SQLException e) {
+//            logger.info("Error processing result set: " + e.getMessage());
+//            throw new RuntimeException(e);
+//        }
+//
+//
+//    } catch (Exception e) {
+//        logger.info("Error in preparing statement" + e);
+//        throw new RuntimeException(e);
+//    }
+//
+//}
 
-        } catch (SQLException e) {
-            logger.info("Error processing result set: " + e.getMessage());
-            throw new RuntimeException(e);
+@Override
+public List<MailModel> getUnsentMessages(){
+    String sql = "SELECT * FROM email WHERE email_id NOT IN (SELECT email_id FROM sentEmail)";
+
+    List<MailModel> unsentMails = new ArrayList<>();
+
+    try(Connection connection = this.getConnection();
+    PreparedStatement statement = connection.prepareStatement(sql);
+    ResultSet rs = statement.executeQuery()) {
+        while (rs.next()){
+            MailModel mailModel = new MailModel();
+            mailModel.setEmailId(rs.getInt("email_id"));
+            mailModel.setPriority(rs.getInt("priority"));
+            mailModel.setExpiry_at(rs.getDate("expiry_at"));
+            unsentMails.add(mailModel);
         }
-
-
-    } catch (Exception e) {
-        logger.info("Error in preparing statement" + e);
+    } catch (SQLException e) {
         throw new RuntimeException(e);
     }
+    return unsentMails;
 
 }
 
@@ -102,6 +124,7 @@ public MailModel  getMailDetails(Integer mail_id){
                 stmt.setInt(1,mail_id);
                 try(ResultSet rs = stmt.executeQuery()) {
                     while (rs.next()){
+                        logger.info(rs.getString("email_address"));
 
                         mailModel.setEmailId(rs.getInt("email_id"));
                         mailModel.setEmailAddress(rs.getString("email_address"));

src/main/java/entgra/mailsender/DTO/MailModel.java

@@ -26,6 +26,8 @@ public class MailModel {
     private File file;
     private String filename;
     private java.sql.Date expiry_at;
+    private long insertionOrder;
+
 
 
     @Setter

src/main/java/entgra/mailsender/MailsenderApplication.java

@@ -1,13 +1,23 @@
 package entgra.mailsender;
 
+import entgra.mailsender.Service.MailService;
+import entgra.mailsender.Service.MailServiceImpl;
+import jakarta.annotation.PostConstruct;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 
 @SpringBootApplication
 public class MailsenderApplication {
+	@Autowired
+	private MailService mailService;
 
 	public static void main(String[] args) {
 		SpringApplication.run(MailsenderApplication.class, args);
 	}
 
+	@PostConstruct
+	public void init(){
+		mailService.syncMailWithDB();
+	}
 }

src/main/java/entgra/mailsender/Service/MailQueueService.java

@@ -0,0 +1,12 @@
+package entgra.mailsender.Service;
+
+import entgra.mailsender.DTO.MailModel;
+
+import java.util.List;
+
+public interface MailQueueService {
+
+    void enqueMails(List<MailModel> mailModelList);
+    MailModel getHighPriorityMail();
+
+}

src/main/java/entgra/mailsender/Service/MailQueueServiceImpl.java

@@ -0,0 +1,79 @@
+package entgra.mailsender.Service;
+
+import entgra.mailsender.DAO.MailDAO;
+import entgra.mailsender.DTO.MailModel;
+import entgra.mailsender.util.PriorityQueueHolder;
+import lombok.RequiredArgsConstructor;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.logging.Logger;
+
+@Service
+@RequiredArgsConstructor
+public class MailQueueServiceImpl implements MailQueueService{
+    Logger logger = Logger.getLogger(String.valueOf(MailQueueServiceImpl.class));
+
+    @Autowired
+    MailDAO mailDAO;
+
+//    private volatile Thread
+//            processingThread;
+//    private volatile boolean isProcessingMails;
+//    private final MailDAO mailDAO;
+
+    @Override
+    public void enqueMails(List<MailModel> mailModelList){
+        logger.info("came here");
+        BlockingQueue<MailModel> priorityQueue = PriorityQueueHolder.getInstance().getPriorityQueue();
+        AtomicLong insertionOrderCounter = PriorityQueueHolder.getInstance().getInsertionOrderCounter();
+        Set<MailModel> uniqueMails = PriorityQueueHolder.getInstance().getUniqueMails();
+        for (MailModel mailModel : mailModelList){
+            if (!PriorityQueueHolder.getInstance().getUniqueMails().contains(mailModel)){
+                mailModel.setInsertionOrder(insertionOrderCounter.getAndIncrement());
+                priorityQueue.add(mailModel);
+                uniqueMails.add(mailModel);
+            }
+        }
+//        assert priorityQueue.peek() != null;
+//        logger.info(String.valueOf(priorityQueue.peek().getEmailId()));
+//        Integer id = priorityQueue.peek().getEmailId();
+//        logger.info(mailDAO.getMailDetails(id).getEmailAddress());
+//        logger.info((Supplier<String>) uniqueMails);
+    }
+
+    public MailModel getHighPriorityMail(){
+        BlockingQueue<MailModel> priorityQueue = PriorityQueueHolder.getInstance().getPriorityQueue();
+        Set<MailModel> uniqueMails = PriorityQueueHolder.getInstance().getUniqueMails();
+        if (PriorityQueueHolder.getInstance().getPriorityQueue().peek() != null){
+            MailModel mailModel = priorityQueue.poll();
+            uniqueMails.remove(mailModel);
+            //logger.info(String.valueOf(mailModel.getEmailId()));
+            return mailModel;
+        }
+        return null;
+    }
+
+//    public void clearOnServerShutdown(){
+//        BlockingQueue<MailModel> priorityQueue = PriorityQueueHolder.getInstance().getPriorityQueue();
+//        if (processingThread != null){
+//            while (isProcessingMails){
+//                try {
+//                    Thread.sleep(1000);
+//                }catch (InterruptedException e){
+//                    Thread.currentThread().interrupt();
+//                    logger.info("Error waiting for the processing cycle to complete" + e.getMessage());
+//                }
+//                isProcessingMails = priorityQueue.peek() != null;
+//            }
+//            processingThread.interrupt();
+//        }
+//        logger.info("Server shutdown");
+//    }
+
+
+}

src/main/java/entgra/mailsender/Service/MailService.java

@@ -12,6 +12,8 @@ public interface MailService  {
      void sendEmail(MailModel emailModel) throws MessagingException, IOException;
      boolean isValidEmailAddress(String email);
 
+     void syncMailWithDB();
+
 
 }
 

src/main/java/entgra/mailsender/Service/MailServiceImpl.java

@@ -2,13 +2,14 @@ package entgra.mailsender.Service;
 
 import entgra.mailsender.DAO.MailDAO;
 import entgra.mailsender.DTO.MailModel;
+import entgra.mailsender.util.PriorityQueueHolder;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.mail.javamail.JavaMailSender;
 import org.springframework.mail.javamail.MimeMessageHelper;
 import org.springframework.stereotype.Service;
 
-import java.util.List;
-import java.util.PriorityQueue;
+import java.util.*;
+import java.util.function.Supplier;
 import java.util.logging.Logger;
 
 
@@ -21,9 +22,12 @@ public class MailServiceImpl implements MailService {
 
     @Autowired
     private MailDAO mailDAO;
+    @Autowired
+    private MailQueueService mailQueueService;
 
 
     public void sendEmail(MailModel emailModel){
+
         logger.warning("email address : "+emailModel.getEmailAddress());
         if (isValidEmailAddress(emailModel.getEmailAddress())){
             throw new RuntimeException("Invalid Email address 161616161");
@@ -31,53 +35,75 @@ public class MailServiceImpl implements MailService {
 
         mailDAO.addMail(emailModel); // save the mail details in the database
 
+
     //here we need to check the unsent mail details
 
 
-        PriorityQueue<MailModel> mailwithHighPriority = mailDAO.getMailwithHighPriority();
-        MailModel mailModel = mailwithHighPriority.poll();
-        assert mailModel != null;
-        Integer mail_id = mailModel.getEmailId();
+        //PriorityQueue<MailModel> mailwithHighPriority = mailDAO.getMailwithHighPriority();
+//        MailModel mailModel = mailQueueService.getHighPriorityMail();
+//        assert mailModel != null;
+//        Integer mail_id = Integer.valueOf(mailModel.getEmailAddress());
+//        logger.info(mailModel.getEmailAddress());
 
-        MailModel updatedModel = mailDAO.getMailDetails(mail_id);
-        logger.info(updatedModel.getEmailAddress());
+//        MailModel updatedModel = mailDAO.getMailDetails(mail_id);
+//        logger.info("mail id" + updatedModel.getEmailAddress());
 
 
-        javaMailSender.send(mimeMessage -> {
 
-            MimeMessageHelper mimeMessageHelper = new MimeMessageHelper(mimeMessage, true);
-            mimeMessageHelper.setTo(updatedModel.getEmailAddress());
-            logger.info(updatedModel.getEmailAddress());
-            mimeMessageHelper.setSubject("Bill details for March ");
 
-            StringBuilder emailBody = new StringBuilder();
-            emailBody.append(updatedModel.getMsgTemplate()).append("\n");
+    }
+    public boolean isValidEmailAddress(String email){
+        String regex = "^[a-zA-Z0-9_+&*-]+(?:\\.[a-zA-Z0-9_+&*-]+)*@(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,7}$";
+        return !email.matches(regex);
+    }
 
-            // Append parameters to email body
-            List<MailModel.Parameter> parameters = updatedModel.getParameters();
-            for (MailModel.Parameter parameter : parameters) {
-                System.out.println("Parameter name: " + parameter.getKey());
-                System.out.println("Parameter value: " + parameter.getValue());
+    public void syncMailWithDB(){
+        try {
+            List<MailModel> mailModels = mailDAO.getUnsentMessages();
+            if (!mailModels.isEmpty()){
+                mailQueueService.enqueMails(mailModels);
             }
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
 
-            for (MailModel.Parameter parameter : parameters) {
-                emailBody.append("\n").append(parameter.getKey()).append(": ").append(parameter.getValue());
-            }
+        while(PriorityQueueHolder.getInstance().getPriorityQueue().peek() != null) {
+            MailModel prioritizedMail = mailQueueService.getHighPriorityMail();
+            MailModel updatedModel = mailDAO.getMailDetails(prioritizedMail.getEmailId());
+            logger.info("updated mail" + updatedModel.getEmailAddress());
+            javaMailSender.send(mimeMessage -> {
 
-            mimeMessageHelper.setText(emailBody.toString(), false);
-            logger.info(updatedModel.getFilename());
+                        MimeMessageHelper mimeMessageHelper = new MimeMessageHelper(mimeMessage, true);
+                        mimeMessageHelper.setTo(updatedModel.getEmailAddress());
+                        logger.info(updatedModel.getEmailAddress());
+                        mimeMessageHelper.setSubject("Bill details for March ");
 
-            mimeMessageHelper.addAttachment(updatedModel.getFilename() ,updatedModel.getFile());
-            logger.info("Mail sent successfully");
+                        StringBuilder emailBody = new StringBuilder();
+                        emailBody.append(updatedModel.getMsgTemplate()).append("\n");
 
-            mailDAO.addToSentMail(updatedModel.getEmailId());
+                        // Append parameters to email body
+                        List<MailModel.Parameter> parameters = updatedModel.getParameters();
+                        for (MailModel.Parameter parameter : parameters) {
+                            System.out.println("Parameter name: " + parameter.getKey());
+                            System.out.println("Parameter value: " + parameter.getValue());
+                        }
 
+                        for (MailModel.Parameter parameter : parameters) {
+                            emailBody.append("\n").append(parameter.getKey()).append(": ").append(parameter.getValue());
+                        }
 
-        });
-    }
-    public boolean isValidEmailAddress(String email){
-        String regex = "^[a-zA-Z0-9_+&*-]+(?:\\.[a-zA-Z0-9_+&*-]+)*@(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,7}$";
-        return !email.matches(regex);
+                        mimeMessageHelper.setText(emailBody.toString(), false);
+                        logger.info(updatedModel.getFilename());
+
+                        mimeMessageHelper.addAttachment(updatedModel.getFilename(), updatedModel.getFile());
+                        logger.info("Mail sent successfully");
+
+                        mailDAO.addToSentMail(updatedModel.getEmailId());
+
+
+                    }
+            );
+        }
     }
 
 

src/main/java/entgra/mailsender/util/PriorityQueueHolder.java

@@ -0,0 +1,31 @@
+package entgra.mailsender.util;
+
+import entgra.mailsender.DTO.MailModel;
+import lombok.Getter;
+
+import java.util.Comparator;
+import java.util.Set;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.PriorityBlockingQueue;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class PriorityQueueHolder {
+
+    // Singleton instance
+    @Getter
+    private static final PriorityQueueHolder instance = new PriorityQueueHolder();
+    @Getter
+    private final AtomicLong insertionOrderCounter = new AtomicLong(1);
+
+    // PriorityBlockingQueue is thread-safe and supports ordering elements based on their natural order or a custom comparator.
+    @Getter
+    private final BlockingQueue<MailModel> priorityQueue = new PriorityBlockingQueue<>(100, Comparator
+            .comparingLong(MailModel::getPriority)
+            .thenComparing(MailModel::getExpiry_at)
+            .thenComparing(MailModel::getInsertionOrder));
+
+    @Getter
+    private final Set<MailModel> uniqueMails = ConcurrentHashMap.newKeySet();
+
+}