Add Decoder#ofDictionaryEntry.

Change-Id: Ie78096e1a7cfd3bcfa446e3ababe15b910d0c23c

4 files changed, 67 insertions, 2 deletions

diff --git a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java
index fee0407..96e1332 100644
--- a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java
+++ b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java
@@ -8,9 +8,11 @@ import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.charset.Charset;
 import java.text.ParseException;
+import java.util.AbstractMap.SimpleImmutableEntry;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.function.Function;
 import org.apiguardian.api.API;
@@ -155,6 +157,19 @@ public abstract class Decoder<T> {
   }
 
   /**
+   * Creates a {@link Decoder} for a {@code Dictionary Entry} type, decoding into a {@link
+   * Map.Entry}.
+   *
+   * @param keyDecoder a {@link Decoder} for the key component of the dictionary entry.
+   * @param valueDecoder a {@link Decoder} for the value component of the dictionary entry.
+   * @return a new {@link Decoder}.
+   */
+  public static <K, V> Decoder<Map.Entry<K, V>> ofDictionaryEntry(
+      Decoder<K> keyDecoder, Decoder<V> valueDecoder) {
+    return new DictionaryEntryDecoder<>(keyDecoder, valueDecoder);
+  }
+
+  /**
    * Creates a {@link Decoder} for the {@link Variant} type.
    *
    * <p>The contained {@link Object} can be of one of the following types:
@@ -169,6 +184,7 @@ public abstract class Decoder<T> {
    *   <li>{@link Optional} (a GVariant {@code Maybe} type)
    *   <li>{@link List} (a GVariant array)
    *   <li>{@code Object[]} (a GVariant structure)
+   *   <li>{@link java.util.Map.Entry} (a dictionary entry)
    *   <li>{@link Variant} (a nested variant)
    * </ul>
    *
@@ -515,6 +531,32 @@ public abstract class Decoder<T> {
     }
   }
 
+  private static class DictionaryEntryDecoder<K, V> extends Decoder<Map.Entry<K, V>> {
+
+    private final TupleDecoder tupleDecoder;
+
+    DictionaryEntryDecoder(Decoder<K> keyDecoder, Decoder<V> valueDecoder) {
+      this.tupleDecoder = new TupleDecoder(keyDecoder, valueDecoder);
+    }
+
+    @Override
+    public byte alignment() {
+      return tupleDecoder.alignment();
+    }
+
+    @Override
+    public Integer fixedSize() {
+      return tupleDecoder.fixedSize();
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public Map.Entry<K, V> decode(ByteBuffer byteSlice) {
+      Object[] components = tupleDecoder.decode(byteSlice);
+      return new SimpleImmutableEntry<>((K) components[0], (V) components[1]);
+    }
+  }
+
   private static class VariantDecoder extends Decoder<Variant> {
 
     @Override
diff --git a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Signature.java b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Signature.java
index 78e4bdd..6a4d01d 100644
--- a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Signature.java
+++ b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Signature.java
@@ -92,7 +92,17 @@ public final class Signature {
       case 'v' -> Decoder.ofVariant();
       case 'm' -> Decoder.ofMaybe(parseSignature(signature));
       case 'a' -> Decoder.ofArray(parseSignature(signature));
-      case '(', '{' -> Decoder.ofStructure(parseTupleTypes(signature).toArray(new Decoder<?>[0]));
+      case '(' -> Decoder.ofStructure(parseTupleTypes(signature).toArray(new Decoder<?>[0]));
+      case '{' -> {
+        var tupleTypes = parseTupleTypes(signature);
+        if (tupleTypes.size() != 2) {
+          throw new ParseException(
+              String.format(
+                  "dictionary entry type with %d components, expected 2", tupleTypes.size()),
+              signature.position());
+        }
+        yield Decoder.ofDictionaryEntry(tupleTypes.get(0), tupleTypes.get(1));
+      }
       default -> throw new ParseException(
           String.format("encountered unknown signature byte '%c'", c), signature.position());
     };
diff --git a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Variant.java b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Variant.java
index d1c1049..34d3945 100644
--- a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Variant.java
+++ b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Variant.java
@@ -18,6 +18,7 @@ import org.apiguardian.api.API.Status;
  *   <li>{@link java.util.Optional} (a GVariant {@code Maybe} type)
  *   <li>{@link java.util.List} (a GVariant array)
  *   <li>{@code Object[]} (a GVariant structure)
+ *   <li>{@link java.util.Map.Entry} (a dictionary entry)
  *   <li>{@link Variant} (a nested variant)
  * </ul>
  *
diff --git a/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java b/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
index d72a1b6..ab7de44 100644
--- a/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
+++ b/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
@@ -11,6 +11,7 @@ import static org.junit.jupiter.api.Assertions.assertThrows;
 import java.nio.ByteBuffer;
 import java.text.ParseException;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import org.junit.jupiter.api.Test;
 
@@ -271,7 +272,18 @@ class DecoderTest {
   }
 
   @Test
-  void testDictionaryEntry() {
+  void testDictionaryEntryAsMapEntry() {
+    var data =
+        new byte[] {0x61, 0x20, 0x6B, 0x65, 0x79, 0x00, 0x00, 0x00, 0x02, 0x02, 0x00, 0x00, 0x06};
+
+    var decoder =
+        Decoder.ofDictionaryEntry(
+            Decoder.ofString(UTF_8), Decoder.ofInt().withByteOrder(LITTLE_ENDIAN));
+    assertEquals(Map.entry("a key", 514), decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testDictionaryEntryAsRecord() {
     var data =
         new byte[] {0x61, 0x20, 0x6B, 0x65, 0x79, 0x00, 0x00, 0x00, 0x02, 0x02, 0x00, 0x00, 0x06};