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/Diagnostics.h b/tools/aapt2/Diagnostics.h
new file mode 100644
index 0000000..d20ae1b
--- /dev/null
+++ b/tools/aapt2/Diagnostics.h
@@ -0,0 +1,98 @@
+/*
+ * 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.
+ */
+
+#ifndef AAPT_DIAGNOSTICS_H
+#define AAPT_DIAGNOSTICS_H
+
+#include "Source.h"
+
+#include "util/StringPiece.h"
+#include "util/Util.h"
+
+#include <iostream>
+#include <sstream>
+#include <string>
+
+namespace aapt {
+
+struct DiagMessageActual {
+    Source source;
+    std::string message;
+};
+
+struct DiagMessage {
+private:
+    Source mSource;
+    std::stringstream mMessage;
+
+public:
+    DiagMessage() = default;
+
+    DiagMessage(const StringPiece& src) : mSource(src) {
+    }
+
+    DiagMessage(const Source& src) : mSource(src) {
+    }
+
+    template <typename T> DiagMessage& operator<<(const T& value) {
+        mMessage << value;
+        return *this;
+    }
+/*
+    template <typename T> DiagMessage& operator<<(
+            const ::std::function<::std::ostream&(::std::ostream&)>& f) {
+        f(mMessage);
+        return *this;
+    }*/
+
+    DiagMessageActual build() const {
+        return DiagMessageActual{ mSource, mMessage.str() };
+    }
+};
+
+struct IDiagnostics {
+    virtual ~IDiagnostics() = default;
+
+    virtual void error(const DiagMessage& message) = 0;
+    virtual void warn(const DiagMessage& message) = 0;
+    virtual void note(const DiagMessage& message) = 0;
+};
+
+struct StdErrDiagnostics : public IDiagnostics {
+    void emit(const DiagMessage& msg, const char* tag) {
+        DiagMessageActual actual = msg.build();
+        if (!actual.source.path.empty()) {
+            std::cerr << actual.source << ": ";
+        }
+        std::cerr << tag << actual.message << "." << std::endl;
+    }
+
+    void error(const DiagMessage& msg) override {
+        emit(msg, "error: ");
+    }
+
+    void warn(const DiagMessage& msg) override {
+        emit(msg, "warn: ");
+    }
+
+    void note(const DiagMessage& msg) override {
+        emit(msg, "note: ");
+    }
+};
+
+} // namespace aapt
+
+#endif /* AAPT_DIAGNOSTICS_H */