feat(): 알림 배치화 구현

src/main/java/org/devkor/apu/saerok_server/domain/notification/application/NotificationBatchScheduler.java

@@ -0,0 +1,54 @@
+package org.devkor.apu.saerok_server.domain.notification.application;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.devkor.apu.saerok_server.domain.notification.application.facade.NotificationPublisher;
+import org.devkor.apu.saerok_server.domain.notification.application.model.batch.NotificationBatch;
+import org.devkor.apu.saerok_server.global.core.config.feature.NotificationBatchConfig;
+import org.springframework.scheduling.annotation.Scheduled;
+import org.springframework.stereotype.Component;
+
+import java.util.List;
+
+/**
+ * 알림 배치 스케줄러.
+ * 주기적으로 만료된 배치를 조회하여 전송한다.
+ */
+@Slf4j
+@Component
+@RequiredArgsConstructor
+public class NotificationBatchScheduler {
+
+    private final NotificationBatchService batchService;
+    private final NotificationPublisher publisher;
+    private final NotificationBatchConfig batchConfig;
+
+    /**
+     * 10초마다 만료된 배치를 조회하여 전송.
+     */
+    @Scheduled(fixedDelay = 10000, initialDelay = 10000)
+    public void processExpiredBatches() {
+        if (!batchConfig.isEnabled()) {
+            return;
+        }
+
+        try {
+            List<NotificationBatch> expiredBatches = batchService.findExpiredBatches();
+
+            if (expiredBatches.isEmpty()) {
+                return;
+            }
+
+            for (NotificationBatch batch : expiredBatches) {
+                try {
+                    publisher.pushBatch(batch);
+                } catch (Exception e) {
+                    log.error("만료된 배치 처리에 실패했습니다: key={}", batch.getKey(), e);
+                }
+            }
+
+        } catch (Exception e) {
+            log.error("Error in batch scheduler", e);
+        }
+    }
+}

src/main/java/org/devkor/apu/saerok_server/domain/notification/application/NotificationBatchService.java

@@ -0,0 +1,86 @@
+package org.devkor.apu.saerok_server.domain.notification.application;
+
+import lombok.RequiredArgsConstructor;
+import org.devkor.apu.saerok_server.domain.notification.application.model.batch.*;
+import org.devkor.apu.saerok_server.domain.notification.application.model.payload.ActionNotificationPayload;
+import org.devkor.apu.saerok_server.domain.notification.application.store.NotificationBatchStore;
+import org.devkor.apu.saerok_server.global.core.config.feature.NotificationBatchConfig;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * 알림 배치 관리 서비스.
+ * 배치 생성, 추가, 조회 등의 작업을 담당한다.
+ */
+@Service
+@RequiredArgsConstructor
+public class NotificationBatchService {
+
+    private final NotificationBatchStore batchStore;
+    private final NotificationBatchConfig batchConfig;
+
+    /**
+     * 배치에 알림 추가.
+     * 기존 배치가 있으면 추가하고 최대 시간까지 연장하며, 없으면 새로 생성한다.
+     */
+    public BatchResult addToBatch(ActionNotificationPayload payload) {
+        // 배치 처리가 비활성화되어 있으면 즉시 전송
+        if (!batchConfig.isEnabled()) {
+            return BatchResult.sendImmediately();
+        }
+
+        BatchKey key = new BatchKey(
+                payload.recipientId(),
+                payload.subject(),
+                payload.action(),
+                payload.relatedId()
+        );
+
+        BatchActor actor = BatchActor.of(payload.actorId(), payload.actorName());
+
+        synchronized (this.getLockKey(key)) {
+            Optional<NotificationBatch> existingBatch = batchStore.findBatch(key);
+
+            if (existingBatch.isPresent()) {
+                // 기존 배치에 추가하고 최대 시간까지 연장
+                NotificationBatch updatedBatch = existingBatch.get()
+                        .addActor(actor, payload.extras(), batchConfig.getMaxWindowSeconds());
+
+                batchStore.saveBatch(updatedBatch);
+
+                return BatchResult.added(updatedBatch);
+
+            } else {
+                // 새 배치 생성
+                NotificationBatch newBatch = NotificationBatch.create(
+                        key,
+                        actor,
+                        batchConfig.getInitialWindowSeconds(),
+                        payload.extras()
+                );
+
+                batchStore.saveBatch(newBatch);
+
+                return BatchResult.created(newBatch);
+            }
+        }
+    }
+
+    public List<NotificationBatch> findExpiredBatches() {
+        return batchStore.findExpiredBatches();
+    }
+
+    public void deleteBatch(BatchKey key) {
+        batchStore.deleteBatch(key);
+    }
+
+    /**
+     * 동시성 제어를 위한 락 키 생성.
+     * 같은 배치 키에 대한 동시 접근을 막기 위해 String 인터닝 활용.
+     */
+    private String getLockKey(BatchKey key) {
+        return key.toRedisKey().intern();
+    }
+}

src/main/java/org/devkor/apu/saerok_server/domain/notification/application/assembly/render/BatchedNotificationRenderer.java

@@ -0,0 +1,53 @@
+package org.devkor.apu.saerok_server.domain.notification.application.assembly.render;
+
+import lombok.RequiredArgsConstructor;
+import org.devkor.apu.saerok_server.domain.notification.application.model.payload.BatchedNotificationPayload;
+import org.devkor.apu.saerok_server.domain.notification.application.model.payload.NotificationPayload;
+import org.devkor.apu.saerok_server.global.core.config.feature.NotificationMessagesConfig;
+import org.springframework.stereotype.Component;
+
+import java.util.Map;
+
+/**
+ * 배치 처리된 알림 렌더러.
+ * 액터 수에 따라 단일/집계 메시지를 렌더링한다.
+ */
+@Component
+@RequiredArgsConstructor
+public class BatchedNotificationRenderer implements NotificationRenderer {
+
+    private final NotificationMessagesConfig messages;
+
+    @Override
+    public RenderedMessage render(NotificationPayload p) {
+        if (!(p instanceof BatchedNotificationPayload b)) {
+            throw new IllegalArgumentException("Unsupported payload: " + p.getClass());
+        }
+
+        NotificationMessagesConfig.Template t = messages.forType(b.type());
+
+        // 단일 액터인 경우 기존 메시지 형식 사용
+        if (b.isSingleActor()) {
+            return renderSingle(t, b);
+        }
+
+        return renderBatched(t, b);
+    }
+
+    private RenderedMessage renderSingle(NotificationMessagesConfig.Template t, BatchedNotificationPayload b) {
+        var vars = NotificationTemplateRenderer.toVars(b.extras());
+        vars.put("actorName", NotificationTemplateRenderer.nullToEmpty(b.getFirstActor().name()));
+
+        return NotificationTemplateRenderer.render(t, vars);
+    }
+
+    private RenderedMessage renderBatched(NotificationMessagesConfig.Template t, BatchedNotificationPayload b) {
+        var vars = NotificationTemplateRenderer.toVars(b.extras());
+        vars.put("actorName", NotificationTemplateRenderer.nullToEmpty(b.getFirstActor().name()));
+        vars.put("count", String.valueOf(b.actorCount()));
+        vars.put("othersCount", String.valueOf(b.actorCount() - 1));
+
+        return NotificationTemplateRenderer.renderBatch(t, vars);
+    }
+
+}

src/main/java/org/devkor/apu/saerok_server/domain/notification/application/assembly/render/DelegatingNotificationRenderer.java

@@ -2,6 +2,7 @@
 
 import lombok.RequiredArgsConstructor;
 import org.devkor.apu.saerok_server.domain.notification.application.model.payload.ActionNotificationPayload;
+import org.devkor.apu.saerok_server.domain.notification.application.model.payload.BatchedNotificationPayload;
 import org.devkor.apu.saerok_server.domain.notification.application.model.payload.NotificationPayload;
 import org.devkor.apu.saerok_server.domain.notification.application.model.payload.SystemNotificationPayload;
 import org.springframework.context.annotation.Primary;
@@ -14,6 +15,7 @@ public class DelegatingNotificationRenderer implements NotificationRenderer {
 
     private final ActionNotificationRenderer actionRenderer;
     private final SystemNotificationRenderer systemRenderer;
+    private final BatchedNotificationRenderer batchedRenderer;
 
     @Override
     public RenderedMessage render(NotificationPayload payload) {
@@ -23,6 +25,9 @@ public RenderedMessage render(NotificationPayload payload) {
         if (payload instanceof SystemNotificationPayload) {
             return systemRenderer.render(payload);
         }
+        if (payload instanceof BatchedNotificationPayload) {
+            return batchedRenderer.render(payload);
+        }
         throw new IllegalArgumentException("Unsupported payload: " + payload.getClass());
     }
 }

src/main/java/org/devkor/apu/saerok_server/domain/notification/application/assembly/render/NotificationTemplateRenderer.java

@@ -17,6 +17,12 @@ static RenderedMessage render(NotificationMessagesConfig.Template template, Map<
         return new RenderedMessage(title, body);
     }
 
+    static RenderedMessage renderBatch(NotificationMessagesConfig.Template template, Map<String, String> vars) {
+        String title = renderTemplate(template.getBatchPushTitle(), vars);
+        String body = renderTemplate(template.getBatchPushBody(), vars);
+        return new RenderedMessage(title, body);
+    }
+
     static Map<String, String> toVars(Map<String, Object> extras) {
         Map<String, String> vars = new HashMap<>();
         extras.forEach((k, v) -> vars.put(k, v == null ? "" : String.valueOf(v)));

src/main/java/org/devkor/apu/saerok_server/domain/notification/application/assembly/store/InAppNotificationWriter.java

@@ -1,7 +1,9 @@
 package org.devkor.apu.saerok_server.domain.notification.application.assembly.store;
 
 import lombok.RequiredArgsConstructor;
+import org.devkor.apu.saerok_server.domain.notification.application.model.batch.BatchActor;
 import org.devkor.apu.saerok_server.domain.notification.application.model.payload.ActionNotificationPayload;
+import org.devkor.apu.saerok_server.domain.notification.application.model.payload.BatchedNotificationPayload;
 import org.devkor.apu.saerok_server.domain.notification.application.model.payload.NotificationPayload;
 import org.devkor.apu.saerok_server.domain.notification.core.entity.Notification;
 import org.devkor.apu.saerok_server.domain.notification.core.entity.NotificationType;
@@ -27,13 +29,29 @@ public Long save(NotificationPayload payload) {
         NotificationType type = payload.type();
 
         User actor = null;
+        Map<String, Object> payloadMap = new HashMap<>();
+
+        // 공통 extras 복사
+        if (payload.extras() != null) {
+            payloadMap.putAll(payload.extras());
+        }
+
         if (payload instanceof ActionNotificationPayload a) {
             actor = userRepository.findById(a.actorId())
                     .orElseThrow(() -> new IllegalArgumentException("Actor not found: " + a.actorId()));
         }
 
-        Map<String, Object> payloadMap = new HashMap<>();
-        if (payload.extras() != null) payloadMap.putAll(payload.extras());
+        if (payload instanceof BatchedNotificationPayload b) {
+            // 첫 번째 액터를 대표 액터로 저장
+            BatchActor firstActor = b.getFirstActor();
+            actor = userRepository.findById(firstActor.id())
+                    .orElse(null); // 배치 알림의 경우 액터가 없을 수도 있음 (삭제된 사용자)
+
+            payloadMap.put("actorCount", b.actorCount());
+            payloadMap.put("actors", b.actors().stream()
+                    .map(a -> Map.of("id", a.id(), "name", a.name()))
+                    .toList());
+        }
 
         Notification entity = Notification.builder()
                 .user(recipient)