fix(library-service): prevent concurrent library scans with a tracking set (#2637)

Signed-off-by: Balázs Szücs <bszucs1209@gmail.com>

booklore-api/src/main/java/org/booklore/service/library/LibraryService.java

@@ -38,6 +38,7 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 
 @Slf4j
@@ -45,6 +46,17 @@ import java.util.stream.Collectors;
 @AllArgsConstructor
 public class LibraryService {
 
+    private static final Set<Long> scanningLibraries = ConcurrentHashMap.newKeySet();
+
+    /**
+     * Checks whether a library is currently being scanned.
+     * Can be used by other components (e.g., file watcher) to avoid processing
+     * files while a full scan is in progress.
+     */
+    public static boolean isLibraryScanning(long libraryId) {
+        return scanningLibraries.contains(libraryId);
+    }
+
     private final LibraryRepository libraryRepository;
     private final LibraryPathRepository libraryPathRepository;
     private final BookRepository bookRepository;
@@ -125,10 +137,16 @@ public class LibraryService {
 
         if (!newPaths.isEmpty()) {
             SecurityContextVirtualThread.runWithSecurityContext(() -> {
+                if (!scanningLibraries.add(libraryId)) {
+                    log.warn("Library {} is already being scanned, skipping duplicate process request", libraryId);
+                    return;
+                }
                 try {
                     libraryProcessingService.processLibrary(libraryId);
                 } catch (InvalidDataAccessApiUsageException e) {
                     log.debug("InvalidDataAccessApiUsageException - Library id: {}", libraryId);
+                } finally {
+                    scanningLibraries.remove(libraryId);
                 }
                 log.info("Parsing task completed!");
             });
@@ -169,10 +187,16 @@ public class LibraryService {
         }
 
         SecurityContextVirtualThread.runWithSecurityContext(() -> {
+            if (!scanningLibraries.add(libraryId)) {
+                log.warn("Library {} is already being scanned, skipping duplicate process request", libraryId);
+                return;
+            }
             try {
                 libraryProcessingService.processLibrary(libraryId);
             } catch (InvalidDataAccessApiUsageException e) {
                 log.debug("InvalidDataAccessApiUsageException - Library id: {}", libraryId);
+            } finally {
+                scanningLibraries.remove(libraryId);
             }
             log.info("Parsing task completed!");
         });
@@ -184,6 +208,10 @@ public class LibraryService {
         libraryRepository.findById(libraryId).orElseThrow(() -> ApiError.LIBRARY_NOT_FOUND.createException(libraryId));
 
         SecurityContextVirtualThread.runWithSecurityContext(() -> {
+            if (!scanningLibraries.add(libraryId)) {
+                log.warn("Library {} is already being scanned, skipping duplicate rescan request", libraryId);
+                return;
+            }
             try {
                 RescanLibraryContext context = RescanLibraryContext.builder()
                         .libraryId(libraryId)
@@ -193,6 +221,8 @@ public class LibraryService {
                 log.debug("InvalidDataAccessApiUsageException - Library id: {}", libraryId);
             } catch (IOException e) {
                 log.error("Error while parsing library books", e);
+            } finally {
+                scanningLibraries.remove(libraryId);
             }
             log.info("Parsing task completed!");
         });