feat: Allow Access to ImmutableMetadata Map as unmodifiable Map (#1534)

* feat: Allow Access to ImmutableMetadata Map as unmodifiable Map

Oriented on the AbstractStructure
closes: #1532

Signed-off-by: Carla Köberl <[email protected]>

* fixup: adding back java doc

Signed-off-by: Carla Köberl <[email protected]>

---------

Signed-off-by: Carla Köberl <[email protected]>
Co-authored-by: chrfwow <[email protected]>

Author: carla-was-not-available

src/main/java/dev/openfeature/sdk/ImmutableMetadata.java

@@ -1,5 +1,6 @@
 package dev.openfeature.sdk;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import lombok.EqualsAndHashCode;
@@ -97,6 +98,10 @@ public <T> T getValue(final String key, final Class<T> type) {
         }
     }
 
+    public Map<String, Object> asUnmodifiableMap() {
+        return Collections.unmodifiableMap(metadata);
+    }
+
     public boolean isEmpty() {
         return metadata.isEmpty();
     }

src/test/java/dev/openfeature/sdk/ImmutableMetadataTest.java

@@ -3,6 +3,8 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
 
+import java.util.Map;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
 class ImmutableMetadataTest {
@@ -25,4 +27,15 @@ void equalImmutableMetadataAreEqual() {
 
         assertEquals(i1, i2);
     }
+
+    @Test
+    void retrieveAsUnmodifiableMap() {
+        ImmutableMetadata metadata =
+                ImmutableMetadata.builder().addString("key1", "value1").build();
+
+        Map<String, Object> unmodifiableMap = metadata.asUnmodifiableMap();
+        assertEquals(unmodifiableMap.size(), 1);
+        assertEquals(unmodifiableMap.get("key1"), "value1");
+        Assertions.assertThrows(UnsupportedOperationException.class, () -> unmodifiableMap.put("key3", "value3"));
+    }
 }