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/Flags.cpp b/tools/aapt2/Flags.cpp
new file mode 100644
index 0000000..6ae5af7
--- /dev/null
+++ b/tools/aapt2/Flags.cpp
@@ -0,0 +1,158 @@
+/*
+ * 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 "Flags.h"
+#include "util/StringPiece.h"
+
+#include <iomanip>
+#include <iostream>
+#include <string>
+#include <vector>
+
+namespace aapt {
+
+Flags& Flags::requiredFlag(const StringPiece& name, const StringPiece& description,
+                         std::string* value) {
+    auto func = [value](const StringPiece& arg) -> bool {
+        *value = arg.toString();
+        return true;
+    };
+
+    mFlags.push_back(Flag{ name.toString(), description.toString(), func, true, 1, false});
+    return *this;
+}
+
+Flags& Flags::requiredFlagList(const StringPiece& name, const StringPiece& description,
+                               std::vector<std::string>* value) {
+    auto func = [value](const StringPiece& arg) -> bool {
+        value->push_back(arg.toString());
+        return true;
+    };
+
+    mFlags.push_back(Flag{ name.toString(), description.toString(), func, true, 1, false });
+    return *this;
+}
+
+Flags& Flags::optionalFlag(const StringPiece& name, const StringPiece& description,
+                           Maybe<std::string>* value) {
+    auto func = [value](const StringPiece& arg) -> bool {
+        *value = arg.toString();
+        return true;
+    };
+
+    mFlags.push_back(Flag{ name.toString(), description.toString(), func, false, 1, false });
+    return *this;
+}
+
+Flags& Flags::optionalFlagList(const StringPiece& name, const StringPiece& description,
+                               std::vector<std::string>* value) {
+    auto func = [value](const StringPiece& arg) -> bool {
+        value->push_back(arg.toString());
+        return true;
+    };
+
+    mFlags.push_back(Flag{ name.toString(), description.toString(), func, false, 1, false });
+    return *this;
+}
+
+Flags& Flags::optionalSwitch(const StringPiece& name, const StringPiece& description,
+                             bool* value) {
+    auto func = [value](const StringPiece& arg) -> bool {
+        *value = true;
+        return true;
+    };
+
+    mFlags.push_back(Flag{ name.toString(), description.toString(), func, false, 0, false });
+    return *this;
+}
+
+void Flags::usage(const StringPiece& command, std::ostream* out) {
+    *out << command << " [options]";
+    for (const Flag& flag : mFlags) {
+        if (flag.required) {
+            *out << " " << flag.name << " arg";
+        }
+    }
+
+    *out << " files...\n\nOptions:\n";
+
+    for (const Flag& flag : mFlags) {
+        std::string argLine = flag.name;
+        if (flag.numArgs > 0) {
+            argLine += " arg";
+        }
+        *out << " " << std::setw(30) << std::left << argLine << flag.description << "\n";
+    }
+    *out << " " << std::setw(30) << std::left << "-h" << "Displays this help menu\n";
+    out->flush();
+}
+
+bool Flags::parse(const StringPiece& command, const std::vector<StringPiece>& args,
+                  std::ostream* outError) {
+    for (size_t i = 0; i < args.size(); i++) {
+        StringPiece arg = args[i];
+        if (*(arg.data()) != '-') {
+            mArgs.push_back(arg.toString());
+            continue;
+        }
+
+        if (arg == "-h" || arg == "--help") {
+            usage(command, outError);
+            return false;
+        }
+
+        bool match = false;
+        for (Flag& flag : mFlags) {
+            if (arg == flag.name) {
+                if (flag.numArgs > 0) {
+                    i++;
+                    if (i >= args.size()) {
+                        *outError << flag.name << " missing argument.\n\n";
+                        usage(command, outError);
+                        return false;
+                    }
+                    flag.action(args[i]);
+                } else {
+                    flag.action({});
+                }
+                flag.parsed = true;
+                match = true;
+                break;
+            }
+        }
+
+        if (!match) {
+            *outError << "unknown option '" << arg << "'.\n\n";
+            usage(command, outError);
+            return false;
+        }
+    }
+
+    for (const Flag& flag : mFlags) {
+        if (flag.required && !flag.parsed) {
+            *outError << "missing required flag " << flag.name << "\n\n";
+            usage(command, outError);
+            return false;
+        }
+    }
+    return true;
+}
+
+const std::vector<std::string>& Flags::getArgs() {
+    return mArgs;
+}
+
+} // namespace aapt