feat: extract minimal assignment cache map (#55)

* minimal map
* comments and version (minor bump for a new api)

Author: typotter

build.gradle

@@ -6,7 +6,7 @@ plugins {
 }
 
 group = 'cloud.eppo'
-version = '3.4.2-SNAPSHOT'
+version = '3.5.0-SNAPSHOT'
 ext.isReleaseVersion = !version.endsWith("SNAPSHOT")
 
 java {
@@ -51,18 +51,14 @@ spotless {
   ratchetFrom 'origin/main'
 
   format 'misc', {
-    // define the files to apply `misc` to
     target '*.gradle', '.gitattributes', '.gitignore'
 
-    // define the steps to apply to those files
     trimTrailingWhitespace()
-    indentWithSpaces(2) // or spaces. Takes an integer argument if you don't like 4
+    indentWithSpaces(2)
     endWithNewline()
   }
   java {
-    // apply a specific flavor of google-java-format
     googleJavaFormat('1.7')
-    // fix formatting of type annotations
     formatAnnotations()
   }
 }

src/main/java/cloud/eppo/api/AbstractAssignmentCache.java

@@ -3,18 +3,44 @@
 import cloud.eppo.cache.AssignmentCacheEntry;
 import cloud.eppo.cache.AssignmentCacheKey;
 import java.util.Map;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * {@link IAssignmentCache} implementation which takes a map to use as the underlying storage
  * mechanism.
  */
 public abstract class AbstractAssignmentCache implements IAssignmentCache {
-  protected final Map<String, String> delegate;
 
-  protected AbstractAssignmentCache(final Map<String, String> delegate) {
+  /** Minimal "map" implementation required to store cached assignment data. */
+  public interface CacheDelegate {
+    void put(String cacheKey, @NotNull String serializedEntry);
+
+    @Nullable String get(String cacheKey);
+  }
+
+  protected final CacheDelegate delegate;
+
+  protected AbstractAssignmentCache(final CacheDelegate delegate) {
     this.delegate = delegate;
   }
 
+  protected AbstractAssignmentCache(final Map<String, String> delegate) {
+    this(
+        new CacheDelegate() {
+
+          @Override
+          public void put(String cacheKey, @NotNull String serializedEntry) {
+            delegate.put(cacheKey, serializedEntry);
+          }
+
+          @Nullable @Override
+          public String get(String cacheKey) {
+            return delegate.get(cacheKey);
+          }
+        });
+  }
+
   @Override
   public boolean hasEntry(AssignmentCacheEntry entry) {
     String serializedEntry = get(entry.getKey());