feat: 이벤트 시간까지 카운트다운 시간을 sse로 전송하는 api 추가

src/main/java/com/softeer/podoarrival/event/controller/ArrivalEventSseController.java

@@ -0,0 +1,25 @@
+package com.softeer.podoarrival.event.controller;
+
+import com.softeer.podoarrival.event.service.ArrivalEventService;
+import io.swagger.v3.oas.annotations.Operation;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.http.MediaType;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import reactor.core.publisher.Flux;
+
+@RestController
+@RequiredArgsConstructor
+@RequestMapping("/arrival")
+@Slf4j
+public class ArrivalEventSseController {
+	private final ArrivalEventService arrivalEventService;
+
+	@GetMapping(value = "/time", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
+	@Operation(summary = "선착순 서버시간 SSE Api")
+	public Flux<Long> streamServerTime() {
+		return arrivalEventService.streamServerTime();
+	}
+}

src/main/java/com/softeer/podoarrival/event/service/ArrivalEventService.java

@@ -5,7 +5,11 @@
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Service;
+import reactor.core.publisher.Flux;
 
+import java.time.Duration;
+import java.time.LocalTime;
+import java.time.format.DateTimeFormatter;
 import java.util.concurrent.CompletableFuture;
 
 @Slf4j
@@ -14,8 +18,24 @@
 public class ArrivalEventService {
 
     private final ArrivalEventReleaseService arrivalEventReleaseServiceRedisImpl;
+    private final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
 
     public CompletableFuture<ArrivalApplicationResponseDto> applyEvent(AuthInfo authInfo) {
         return arrivalEventReleaseServiceRedisImpl.applyEvent(authInfo);
     }
+
+    /**
+     * SSE로 서버시간기준 이벤트 시작 시간까지 남은 시간을 전송
+     * @return Flux<String> sse로 전송하게되는 이벤트까지 남은 시간
+     */
+    public Flux<Long> streamServerTime() {
+        return Flux.concat(
+                Flux.just(0L), // Emit initial value immediately
+                Flux.interval(Duration.ofSeconds(20)))
+                .map(sequence -> {
+                    LocalTime startTime = ArrivalEventReleaseServiceJavaImpl.getStartTime();
+                    long seconds = Duration.between(LocalTime.now(), startTime).getSeconds();
+                    return Math.max(seconds, 0);
+                });
+    }
 }