Revert "Simplified genre matcher setup."

This reverts commit e5a5675.

src/main/java/dev/rilling/musicbrainzenricher/core/genre/GenreMatcherService.java

@@ -11,6 +11,7 @@
 import java.util.Locale;
 import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
 @Service
@@ -19,11 +20,22 @@ public class GenreMatcherService {
 
 	private static final Logger LOGGER = LoggerFactory.getLogger(GenreMatcherService.class);
 
-	private final CanonicalStringMatcher canonicalStringMatcher;
+	private static final StringVariantChecker STRING_VARIANT_CHECKER;
+
+	static {
+		Set<String> delimiters = Set.of("-", " ", " and ", " & ");
+		Collator collator = Collator.getInstance(Locale.ROOT);
+		collator.setStrength(Collator.PRIMARY);
+		STRING_VARIANT_CHECKER = new StringVariantChecker(delimiters, collator);
+	}
+
+	private final AtomicReference<CanonicalStringMatcher> canonicalStringMatcherRef = new AtomicReference<>(null);
+
+	private final GenreRepository genreRepository;
 
 
 	GenreMatcherService(GenreRepository genreRepository) {
-		canonicalStringMatcher = createCanonicalStringMatcher(genreRepository.findGenreNames());
+		this.genreRepository = genreRepository;
 	}
 
 	/**
@@ -40,7 +52,7 @@ public Set<String> match(Set<String> unmatchedGenres) {
 		}
 
 		Set<String> matches = unmatchedGenres.stream()
-			.map(canonicalStringMatcher::canonicalize)
+			.map(getCanonicalStringMatcher()::canonicalize)
 			.flatMap(Optional::stream)
 			.collect(Collectors.toUnmodifiableSet());
 
@@ -50,12 +62,17 @@ public Set<String> match(Set<String> unmatchedGenres) {
 	}
 
 
-	private static CanonicalStringMatcher createCanonicalStringMatcher(Set<String> canonicalGenreNames) {
-		Set<String> delimiters = Set.of("-", " ", " and ", " & ");
-		Collator collator = Collator.getInstance(Locale.ROOT);
-		collator.setStrength(Collator.PRIMARY);
-		StringVariantChecker stringVariantChecker = new StringVariantChecker(delimiters, collator);
-
-		return new CanonicalStringMatcher(canonicalGenreNames, stringVariantChecker);
+	private CanonicalStringMatcher getCanonicalStringMatcher() {
+		/*
+		 * It is possible for two threads to concurrently try to initialize the string matcher.
+		 * If that happens, the first one wins, with any further initialization still starting but never being applied.
+		 */
+		if (canonicalStringMatcherRef.get() == null) {
+			Set<String> canonicalGenres = genreRepository.findGenreNames();
+			CanonicalStringMatcher canonicalStringMatcher = new CanonicalStringMatcher(canonicalGenres,
+				STRING_VARIANT_CHECKER);
+			canonicalStringMatcherRef.compareAndSet(null, canonicalStringMatcher);
+		}
+		return canonicalStringMatcherRef.get();
 	}
 }