AAPT2: Separate out the various steps

An early refactor. Some ideas became clearer as
development continued. Now the various phases are much
clearer and more easily reusable.

Also added a ton of tests!

Change-Id: Ic8f0a70c8222370352e63533b329c40457c0903e
diff --git a/tools/aapt2/ValueVisitor_test.cpp b/tools/aapt2/ValueVisitor_test.cpp
new file mode 100644
index 0000000..1624079
--- /dev/null
+++ b/tools/aapt2/ValueVisitor_test.cpp
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+#include <string>
+
+#include "ResourceValues.h"
+#include "util/Util.h"
+#include "ValueVisitor.h"
+#include "test/Builders.h"
+
+namespace aapt {
+
+struct SingleReferenceVisitor : public ValueVisitor {
+    using ValueVisitor::visit;
+
+    Reference* visited = nullptr;
+
+    void visit(Reference* ref) override {
+        visited = ref;
+    }
+};
+
+struct StyleVisitor : public ValueVisitor {
+    using ValueVisitor::visit;
+
+    std::list<Reference*> visitedRefs;
+    Style* visitedStyle = nullptr;
+
+    void visit(Reference* ref) override {
+        visitedRefs.push_back(ref);
+    }
+
+    void visit(Style* style) override {
+        visitedStyle = style;
+        ValueVisitor::visit(style);
+    }
+};
+
+TEST(ValueVisitorTest, VisitsReference) {
+    Reference ref(ResourceName{u"android", ResourceType::kAttr, u"foo"});
+    SingleReferenceVisitor visitor;
+    ref.accept(&visitor);
+
+    EXPECT_EQ(visitor.visited, &ref);
+}
+
+TEST(ValueVisitorTest, VisitsReferencesInStyle) {
+    std::unique_ptr<Style> style = test::StyleBuilder()
+            .setParent(u"@android:style/foo")
+            .addItem(u"@android:attr/one", test::buildReference(u"@android:id/foo"))
+            .build();
+
+    StyleVisitor visitor;
+    style->accept(&visitor);
+
+    ASSERT_EQ(style.get(), visitor.visitedStyle);
+
+    // Entry attribute references, plus the parent reference, plus one value reference.
+    ASSERT_EQ(style->entries.size() + 2, visitor.visitedRefs.size());
+}
+
+TEST(ValueVisitorTest, ValueCast) {
+    std::unique_ptr<Reference> ref = test::buildReference(u"@android:color/white");
+    EXPECT_NE(valueCast<Reference>(ref.get()), nullptr);
+
+    std::unique_ptr<Style> style = test::StyleBuilder()
+            .addItem(u"@android:attr/foo", test::buildReference(u"@android:color/black"))
+            .build();
+    EXPECT_NE(valueCast<Style>(style.get()), nullptr);
+    EXPECT_EQ(valueCast<Reference>(style.get()), nullptr);
+}
+
+} // namespace aapt