add enum ordinal codec

Author: mudkipdev

json/src/main/java/alpine/json/codec/Codec.java

@@ -142,6 +142,26 @@ public <R> R encode(Transcoder<R> transcoder, E value) {
         };
     }
 
+    static <E extends Enum<E>> Codec<E> ordinal(Class<E> enumClass) {
+        return new Codec<>() {
+            @Override
+            public <R> E decode(Transcoder<R> transcoder, R value) {
+                var ordinal = (int) transcoder.decodeNumber(value);
+
+                if (ordinal >= enumClass.getEnumConstants().length) {
+                    throw new DecodingException("Enum ordinal out of bounds: " + ordinal);
+                }
+
+                return enumClass.getEnumConstants()[ordinal];
+            }
+
+            @Override
+            public <R> R encode(Transcoder<R> transcoder, E value) {
+                return transcoder.encodeNumber(value.ordinal());
+            }
+        };
+    }
+
     default FlatCodec<T> flatten() {
         return new FlatCodec<>(this);
     }

json/src/test/java/alpine/json/JsonCodecTest.java

@@ -152,7 +152,7 @@ void testPrimitiveArray() {
     }
 
     @Test
-    void testEnum() {
+    void testEnumName() {
         var codec = Codec.name(Direction.class);
         assertEquals(string("north"), codec.encode(Transcoder.JSON, Direction.NORTH));
         assertEquals(Direction.SOUTH, codec.decode(Transcoder.JSON, string("south")));
@@ -164,6 +164,19 @@ void testEnum() {
         assertThrows(Exception.class, () -> codec.decode(Transcoder.JSON, string("up")));
     }
 
+    @Test
+    void testEnumOrdinal() {
+        var codec = Codec.ordinal(Direction.class);
+        assertEquals(number(0), codec.encode(Transcoder.JSON, Direction.NORTH));
+        assertEquals(Direction.SOUTH, codec.decode(Transcoder.JSON, number(1)));
+
+        for (var direction : Direction.values()) {
+            assertEquals(direction, codec.decode(Transcoder.JSON, codec.encode(Transcoder.JSON, direction)));
+        }
+
+        assertThrows(Exception.class, () -> codec.decode(Transcoder.JSON, number(999)));
+    }
+
     @Test
     void testUuid() {
         var uuid = UUID.fromString("550e8400-e29b-41d4-a716-446655440000");