Add support for nested $first/$last in retain() Fix function. (#329)

Author: blackwinter

metafix/src/main/java/org/metafacture/metafix/Value.java

@@ -484,7 +484,18 @@ private Set<Integer> findFields(final String pattern) {
                 indexes().forEach(fieldSet::add);
             }
             else {
-                final int index = Integer.parseInt(pattern) - 1; // TODO: 0-based Catmandu vs. 1-based Metafacture
+                final int index;
+
+                switch (pattern) {
+                    case "$first":
+                        index = 0;
+                        break;
+                    case "$last":
+                        index = size() - 1;
+                        break;
+                    default:
+                        index = Integer.parseInt(pattern) - 1; // TODO: 0-based Catmandu vs. 1-based Metafacture
+                }
 
                 if (index >= 0 && index < size()) {
                     fieldSet.add(index);

metafix/src/test/java/org/metafacture/metafix/MetafixRecordTest.java

@@ -2418,6 +2418,58 @@ public void retainNested() {
         );
     }
 
+    @Test
+    public void retainNestedReservedFields() {
+        MetafixTestHelpers.assertFix(streamReceiver, Arrays.asList(
+                "retain('b[].$first.b','c[].$last')"
+            ),
+            i -> {
+                i.startRecord("1");
+                i.startEntity("b[]");
+                i.startEntity("1");
+                i.literal("a", "1");
+                i.literal("b", "2");
+                i.endEntity();
+                i.startEntity("2");
+                i.literal("a", "1");
+                i.literal("b", "2");
+                i.literal("c", "3");
+                i.endEntity();
+                i.startEntity("3");
+                i.literal("c", "4");
+                i.endEntity();
+                i.endEntity();
+                i.startEntity("c[]");
+                i.startEntity("1");
+                i.literal("a", "1");
+                i.literal("b", "2");
+                i.endEntity();
+                i.startEntity("2");
+                i.literal("a", "1");
+                i.literal("b", "2");
+                i.literal("c", "3");
+                i.endEntity();
+                i.startEntity("3");
+                i.literal("c", "4");
+                i.endEntity();
+                i.endEntity();
+                i.endRecord();
+            },
+            (o, f) -> {
+                o.get().startRecord("1");
+                o.get().startEntity("b[]");
+                o.get().startEntity("1");
+                o.get().literal("b", "2");
+                f.apply(2).endEntity();
+                o.get().startEntity("c[]");
+                o.get().startEntity("1");
+                o.get().literal("c", "4");
+                f.apply(2).endEntity();
+                o.get().endRecord();
+            }
+        );
+    }
+
     @Test
     public void shouldDeleteEmptyArrays() {
         MetafixTestHelpers.assertFix(streamReceiver, Arrays.asList(