AAPT2: Refactor flags into commands

Refactors the flag based command invocation into classes that make using
subcommands easier.

Test: manual tests of printing
Change-Id: Ic8df6af0be30db552e32150afebecbfeec7e1075
diff --git a/tools/aapt2/cmd/Command.h b/tools/aapt2/cmd/Command.h
new file mode 100644
index 0000000..71dc6fe
--- /dev/null
+++ b/tools/aapt2/cmd/Command.h
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2018 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_COMMAND_H
+#define AAPT_COMMAND_H
+
+#include <functional>
+#include <ostream>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+#include "androidfw/StringPiece.h"
+
+#include "util/Maybe.h"
+
+namespace aapt {
+
+class Command {
+ public:
+  explicit Command(const android::StringPiece& name) : name_(name.to_string()),
+                                                       fullname_(name.to_string()) { }
+  explicit Command(const android::StringPiece& name, const android::StringPiece& short_name)
+      : name_(name.to_string()), short_name_(short_name.to_string()), fullname_(name.to_string()) {}
+  virtual ~Command() = default;
+
+  void AddRequiredFlag(const android::StringPiece& name, const android::StringPiece& description,
+      std::string* value);
+  void AddRequiredFlagList(const android::StringPiece& name, const android::StringPiece&
+      description, std::vector<std::string>* value);
+  void AddOptionalFlag(const android::StringPiece& name, const android::StringPiece& description,
+      Maybe<std::string>* value);
+  void AddOptionalFlagList(const android::StringPiece& name,
+      const android::StringPiece& description, std::vector<std::string>* value);
+  void AddOptionalFlagList(const android::StringPiece& name,
+      const android::StringPiece& description, std::unordered_set<std::string>* value);
+  void AddOptionalSwitch(const android::StringPiece& name, const android::StringPiece& description,
+      bool* value);
+  void AddOptionalSubcommand(std::unique_ptr<Command>&& subcommand);
+
+  void SetDescription(const android::StringPiece& name);
+
+  /** Prints the help menu of the command. */
+  void Usage(std::ostream* out);
+
+  /**
+   * Parses the command line arguments, sets the flag variable values, and runs the action of
+   * the command. If the arguments fail to parse to the command and its subcommands, then the action
+   * will not be run and the usage will be printed instead.
+   **/
+  int Execute(const std::vector<android::StringPiece>& args, std::ostream* outError);
+
+  /** The action to preform when the command is executed. */
+  virtual int Action(const std::vector<std::string>& args) = 0;
+
+ private:
+  struct Flag {
+    std::string name;
+    std::string description;
+    std::function<bool(const android::StringPiece& value)> action;
+    bool required;
+    size_t num_args;
+
+    bool parsed;
+  };
+
+  std::string description_;
+  std::string name_;
+  std::string short_name_;
+  std::string fullname_;
+  std::vector<Flag> flags_;
+  std::vector<std::unique_ptr<Command>> subcommands_;
+};
+
+}  // namespace aapt
+
+#endif  // AAPT_COMMAND_H