Address code review comments

Signed-off-by: Andriy Redko <andriy.redko@aiven.io>

Author: reta

src/main/java/org/opensearch/index/codec/customcodecs/CustomCodecPlugin.java

@@ -50,18 +50,10 @@ public Optional<CodecServiceFactory> getCustomCodecServiceFactory(final IndexSet
             || codecName.equals(CustomCodecService.QAT_DEFLATE_CODEC)) {
             return Optional.of(new CustomCodecServiceFactory());
         } else {
-            if (codecName.equals(Lucene99QatCodec.Mode.QAT_LZ4.getCodec())
-                || codecName.equals(Lucene99QatCodec.Mode.QAT_DEFLATE.getCodec())) {
-                if (!QatZipperFactory.isQatAvailable()) {
-                    throw new IllegalArgumentException("QAT codecs are not supported. Please create indices with a different codec.");
-                }
-            }
-
-            if (codecName.equals(Lucene912QatCodec.Mode.QAT_LZ4.getCodec())
-                || codecName.equals(Lucene912QatCodec.Mode.QAT_DEFLATE.getCodec())) {
-                if (!QatZipperFactory.isQatAvailable()) {
-                    throw new IllegalArgumentException("QAT codecs are not supported. Please create indices with a different codec.");
-                }
+            if (!QatZipperFactory.isQatAvailable() && isQatCodec(codecName)) {
+                throw new IllegalArgumentException(
+                    "QAT codecs are not supported (QAT is not available). Please create indices with a different codec."
+                );
             }
         }
         return Optional.empty();
@@ -71,4 +63,11 @@ public Optional<CodecServiceFactory> getCustomCodecServiceFactory(final IndexSet
     public List<Setting<?>> getSettings() {
         return Arrays.asList(Lucene99QatCodec.INDEX_CODEC_QAT_MODE_SETTING);
     }
+
+    private static boolean isQatCodec(String codecName) {
+        return codecName.equals(Lucene99QatCodec.Mode.QAT_LZ4.getCodec())
+            || codecName.equals(Lucene99QatCodec.Mode.QAT_DEFLATE.getCodec())
+            || codecName.equals(Lucene912QatCodec.Mode.QAT_LZ4.getCodec())
+            || codecName.equals(Lucene912QatCodec.Mode.QAT_DEFLATE.getCodec());
+    }
 }

src/main/java/org/opensearch/index/codec/customcodecs/ZstdCompressionMode.java

@@ -45,7 +45,7 @@ protected ZstdCompressionMode() {
      *
      * @param compressionLevel The compression level to use.
      */
-    public ZstdCompressionMode(int compressionLevel) {
+    protected ZstdCompressionMode(int compressionLevel) {
         this.compressionLevel = compressionLevel;
     }
 

src/main/java/org/opensearch/index/codec/customcodecs/ZstdNoDictCompressionMode.java

@@ -40,7 +40,7 @@ protected ZstdNoDictCompressionMode() {
      *
      * @param compressionLevel The compression level.
      */
-    public ZstdNoDictCompressionMode(int compressionLevel) {
+    protected ZstdNoDictCompressionMode(int compressionLevel) {
         this.compressionLevel = compressionLevel;
     }
 

src/main/java/org/opensearch/index/codec/customcodecs/backward_codecs/lucene99/Lucene99CustomStoredFieldsFormat.java

@@ -62,8 +62,10 @@ public Lucene99CustomStoredFieldsFormat(Lucene99CustomCodec.Mode mode) {
     public Lucene99CustomStoredFieldsFormat(Lucene99CustomCodec.Mode mode, int compressionLevel) {
         this.mode = Objects.requireNonNull(mode);
         this.compressionLevel = compressionLevel;
-        zstdCompressionMode = new ZstdCompressionMode(compressionLevel);
-        zstdNoDictCompressionMode = new ZstdNoDictCompressionMode(compressionLevel);
+        zstdCompressionMode = new ZstdCompressionMode(compressionLevel) {
+        };
+        zstdNoDictCompressionMode = new ZstdNoDictCompressionMode(compressionLevel) {
+        };
     }
 
     /**

src/test/java/org/opensearch/index/codec/customcodecs/backward_codecs/Lucene95CustomStoredFieldsFormatTests.java

@@ -6,10 +6,10 @@
  * compatible open source license.
  */
 
-package org.opensearch.index.codec.customcodecs;
+package org.opensearch.index.codec.customcodecs.backward_codecs;
 
-import org.opensearch.index.codec.customcodecs.backward_codecs.Lucene95CustomCodec;
-import org.opensearch.index.codec.customcodecs.backward_codecs.Lucene95CustomStoredFieldsFormat;
+import org.opensearch.index.codec.customcodecs.ZstdCompressionMode;
+import org.opensearch.index.codec.customcodecs.ZstdNoDictCompressionMode;
 import org.opensearch.test.OpenSearchTestCase;
 
 public class Lucene95CustomStoredFieldsFormatTests extends OpenSearchTestCase {