Implementation of user email notification of url expiration

src/main/kotlin/com/zufar/urlshortener/UrlShortenerApplication.kt

@@ -4,6 +4,7 @@ import io.swagger.v3.oas.annotations.OpenAPIDefinition
 import io.swagger.v3.oas.annotations.info.Info
 import org.springframework.boot.autoconfigure.SpringBootApplication
 import org.springframework.boot.runApplication
+import org.springframework.scheduling.annotation.EnableScheduling
 
 @OpenAPIDefinition(
     info = Info(
@@ -13,6 +14,7 @@ import org.springframework.boot.runApplication
     )
 )
 @SpringBootApplication
+@EnableScheduling
 class UrlShortenerApplication
 
 fun main(args: Array<String>) {

src/main/kotlin/com/zufar/urlshortener/auth/service/CustomUserDetailsService.kt

@@ -19,4 +19,10 @@ class CustomUserDetailsService(private val userRepository: UserRepository) : Use
             .authorities(emptyList())
             .build()
     }
+
+    fun getEmailByUserId(userId: String): String {
+        val user = userRepository.findById(userId)
+            .orElseThrow { UsernameNotFoundException("User with ID='$userId' is not found") }
+        return user.email
+    }
 }

src/main/kotlin/com/zufar/urlshortener/shorten/service/EmailNotificationSender.kt

@@ -0,0 +1,32 @@
+package com.zufar.urlshortener.shorten.service
+
+import org.springframework.mail.javamail.JavaMailSender
+import org.springframework.mail.javamail.MimeMessageHelper
+import org.springframework.stereotype.Service
+
+@Service
+class EmailNotificationService(
+    private val mailSender: JavaMailSender
+) {
+    fun sendExpirationNotification(email: String, shortUrl: String, expirationDate: String) {
+        val message = mailSender.createMimeMessage()
+        val helper = MimeMessageHelper(message, true)
+
+        helper.setTo(email)
+        helper.setSubject("Your Short URL is Expiring Soon")
+        helper.setText(
+            """
+            Hello,
+
+            This is a reminder that your short URL ($shortUrl) will expire on $expirationDate.
+            Please consider extending its validity if necessary.
+
+            Best regards,
+            URL Shortener Team
+            """.trimIndent(),
+            false
+        )
+
+        mailSender.send(message)
+    }
+}

src/main/kotlin/com/zufar/urlshortener/shorten/service/UrlExpirationNotificationScheduler.kt

@@ -0,0 +1,44 @@
+package com.zufar.urlshortener.shorten.service
+
+import com.zufar.urlshortener.auth.service.CustomUserDetailsService
+import com.zufar.urlshortener.shorten.repository.UrlRepository
+import org.slf4j.LoggerFactory
+import org.springframework.scheduling.annotation.Scheduled
+import org.springframework.stereotype.Component
+import java.time.LocalDateTime
+
+@Component
+class UrlExpirationNotificationScheduler(
+    private val urlRepository: UrlRepository,
+    private val emailNotificationService: EmailNotificationService,
+    private val userDetailsService: CustomUserDetailsService
+) {
+    private val log = LoggerFactory.getLogger(UrlExpirationNotificationScheduler::class.java)
+
+    @Scheduled(cron = "0 0 0 * * *")
+    fun notifyExpiringUrls() {
+        log.info("Starting expiration notification task")
+        val thresholdDate = LocalDateTime.now().plusDays(7)
+
+        val expiringUrls = urlRepository.findAll().filter { it.expirationDate.isBefore(thresholdDate) }
+
+        if (expiringUrls.isEmpty()) {
+            log.info("No URLs found nearing expiration")
+            return
+        }
+
+        expiringUrls.forEach { url ->
+            val email = userDetailsService.getEmailByUserId(url.userId ?: "")
+            try {
+                emailNotificationService.sendExpirationNotification(
+                    email = email,
+                    shortUrl = url.shortUrl,
+                    expirationDate = url.expirationDate.toString()
+                )
+                log.info("Sent expiration notification for URL: ${url.shortUrl} to user: $email")
+            } catch (e: Exception) {
+                log.error("Failed to send notification for URL: ${url.shortUrl} to user: $email", e)
+            }
+        }
+    }
+}

src/main/resources/application.properties

@@ -1,37 +1,45 @@
 
-# Application Properties
-spring.application.name=URL-Shortener
-app.base-url=${SERVER_BASE_URL}
-server.port=8080
+    # Application Properties
+    spring.application.name=URL-Shortener
+    app.base-url=${SERVER_BASE_URL}
+    server.port=8080
 
-# Springdoc Configuration
-springdoc.swagger-ui.path=/api/v1/swagger-ui
-springdoc.api-docs.path=/api/v1/api-docs
-springdoc.api-docs.enabled=true
-springdoc.show-actuator=true
-springdoc.packages-to-scan=com.zufar.urlshortener
+    # Springdoc Configuration
+    springdoc.swagger-ui.path=/api/v1/swagger-ui
+    springdoc.api-docs.path=/api/v1/api-docs
+    springdoc.api-docs.enabled=true
+    springdoc.show-actuator=true
+    springdoc.packages-to-scan=com.zufar.urlshortener
 
-# JWT Configuration
-jwt.secret=${JWT_SECRET}
-jwt.accessTokenExpiration=3600000
-jwt.refreshTokenExpiration=604800000
+    # JWT Configuration
+    jwt.secret=${JWT_SECRET}
+    jwt.accessTokenExpiration=3600000
+    jwt.refreshTokenExpiration=604800000
 
-# MongoDB Configuration
-spring.data.mongodb.uri=${MONGODB_URI}
-spring.data.mongodb.database=${MONGODB_DATABASE}
+    # MongoDB Configuration
+    spring.data.mongodb.uri=${MONGODB_URI}
+    spring.data.mongodb.database=${MONGODB_DATABASE}
 
-# Actuator
-management.endpoints.web.exposure.include=*
-management.endpoints.web.base-path=/actuator
-management.endpoint.health.show-details=always
+    # Actuator
+    management.endpoints.web.exposure.include=*
+    management.endpoints.web.base-path=/actuator
+    management.endpoint.health.show-details=always
 
-# Logging
-logging.level.root=WARN
-logging.level.org.mongodb.driver=WARN
-logging.level.org.springframework.data.mongodb=WARN
-logging.level.org.springframework.web=WARN
-logging.level.com.zufar.urlshortener=INFO
-logging.file.name=logs/application.log
-logging.logback.rollingpolicy.max-file-size=10MB
-logging.logback.rollingpolicy.max-history=30
-logging.pattern.console="%d{yyyy-MM-dd HH:mm:ss.SSS} - correlationId=%X{correlationId} [%thread] %-5level %logger{36} - %msg%n"
+    # Logging
+    logging.level.root=WARN
+    logging.level.org.mongodb.driver=WARN
+    logging.level.org.springframework.data.mongodb=WARN
+    logging.level.org.springframework.web=WARN
+    logging.level.com.zufar.urlshortener=INFO
+    logging.file.name=logs/application.log
+    logging.logback.rollingpolicy.max-file-size=10MB
+    logging.logback.rollingpolicy.max-history=30
+    logging.pattern.console="%d{yyyy-MM-dd HH:mm:ss.SSS} - correlationId=%X{correlationId} [%thread] %-5level %logger{36} - %msg%n"
+
+    # Mail
+    spring.mail.host=smtp.gmail.com
+    spring.mail.port=587
+    spring.mail.username=${MAIL_USERNAME}
+    spring.mail.password=${MAIL_PASSWORD}
+    spring.mail.properties.mail.smtp.auth=true
+    spring.mail.properties.mail.smtp.starttls.enable=true