Multiple Language Support

This is similar to https://gerrit.omnirom.org/#/c/14014

A lot of the features built in the older patch set have been split
out into separate patches, most of which have already been merged.
The remaining functionality here should all be directly related to
language selection and loading. We always load English as a base
before loading other languages over the top of the base. The idea
is that if another language is missing a translation, then we will
still display the English.

Maybe still to do: read the /cache/recovery/last_locale file and
load a language based on that. For me, this file contains just:
en_US
We probably won't bother with region specific translations so we
would have to look at either trimming off the _US or using some
other method like perhaps a symlink or a combination of the two.

Thanks to _that for twmsg.cpp class

Change-Id: I9647a22e47883a3ddd2de1da51f64aab7c328f74
diff --git a/gui/twmsg.cpp b/gui/twmsg.cpp
new file mode 100644
index 0000000..00c6931
--- /dev/null
+++ b/gui/twmsg.cpp
@@ -0,0 +1,129 @@
+/*
+	Copyright 2015 _that/TeamWin
+	This file is part of TWRP/TeamWin Recovery Project.
+
+	TWRP is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	TWRP is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with TWRP.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "../data.hpp"
+#include "pages.hpp"
+#include "resources.hpp"
+
+#include "twmsg.h"
+
+std::string Message::GetFormatString(const std::string& name) const
+{
+	std::string resname;
+	size_t pos = name.find('=');
+	if (pos == std::string::npos)
+		resname = name;
+	else
+		resname = name.substr(0, pos);
+
+	std::string formatstr = resourceLookup(resname);
+	bool notfound = formatstr.empty() || formatstr[0] == '[';  // HACK: TODO: integrate this with resource-not-found logic
+	if (notfound && pos != std::string::npos)
+		// resource not found - use the default format string specified after "="
+		formatstr = name.substr(pos + 1);
+	return formatstr;
+}
+
+// Look up in local replacement vars first, if not found then use outer lookup object
+class LocalLookup : public StringLookup
+{
+	const std::vector<std::string>& vars;
+	const StringLookup& next;
+	public:
+	LocalLookup(const std::vector<std::string>& vars, const StringLookup& next) : vars(vars), next(next) {}
+	virtual std::string operator()(const std::string& name) const
+	{
+		if (!name.empty() && isdigit(name[0])) { // {1}..{9}
+			int i = atoi(name.c_str());
+			if (i > 0 && i <= (int)vars.size())
+				return vars[i - 1];
+		}
+		return next(name);
+	}
+};
+
+// conversion to final string
+Message::operator std::string() const
+{
+	// do resource lookup
+	std::string str = GetFormatString(name);
+
+	LocalLookup lookup(variables, varLookup);
+
+	// now insert stuff into curly braces
+
+	size_t pos = 0;
+	while ((pos = str.find('{', pos)) < std::string::npos) {
+		size_t end = str.find('}', pos);
+		if (end == std::string::npos)
+			break;
+
+		std::string varname = str.substr(pos + 1, end - pos - 1);
+		std::string vartext = lookup(varname);
+
+		str.replace(pos, end - pos + 1, vartext);
+	}
+	// TODO: complain about too many or too few numbered replacement variables
+	return str;
+}
+
+/*
+Resource manager lookup
+*/
+class ResourceLookup : public StringLookup
+{
+public:
+	virtual std::string operator()(const std::string& name) const
+	{
+		const ResourceManager* res = PageManager::GetResources();
+		if (res)
+			return res->FindString(name);
+		return name;
+	}
+};
+ResourceLookup resourceLookup;
+
+
+/*
+DataManager lookup
+*/
+class DataLookup : public StringLookup
+{
+public:
+	virtual std::string operator()(const std::string& name) const
+	{
+		std::string value;
+		if (DataManager::GetValue(name, value) == 0)
+			return value;
+		else
+			return "";
+	}
+};
+DataLookup dataLookup;
+
+
+// Utility functions to create messages. Short names to make usage convenient.
+Message Msg(const char* name)
+{
+	return Message(msg::kNormal, name, resourceLookup, dataLookup);
+}
+
+Message Msg(msg::Kind kind, const char* name)
+{
+	return Message(kind, name, resourceLookup, dataLookup);
+}