Initial backend test for user-based data/customizations (#4144)

Right now only support for colors and no real UX, idea is to test it & allow the idea to grow while figuring out the UX

src/controllers/userdata/UserDataController.hpp

@@ -0,0 +1,60 @@
+#pragma once
+
+#include "common/Singleton.hpp"
+#include "controllers/userdata/UserData.hpp"
+#include "util/QStringHash.hpp"
+#include "util/RapidJsonSerializeQString.hpp"
+#include "util/RapidjsonHelpers.hpp"
+#include "util/serialize/Container.hpp"
+
+#include <QColor>
+#include <QString>
+#include <boost/optional.hpp>
+#include <pajlada/settings.hpp>
+
+#include <shared_mutex>
+#include <unordered_map>
+
+namespace chatterino {
+
+class IUserDataController
+{
+public:
+    virtual ~IUserDataController() = default;
+
+    virtual boost::optional<UserData> getUser(const QString &userID) const = 0;
+
+    virtual void setUserColor(const QString &userID,
+                              const QString &colorString) = 0;
+};
+
+class UserDataController : public IUserDataController, public Singleton
+{
+public:
+    UserDataController();
+
+    // Get extra data about a user
+    // If the user does not have any extra data, return none
+    boost::optional<UserData> getUser(const QString &userID) const override;
+
+    // Update or insert extra data for the user's color override
+    void setUserColor(const QString &userID,
+                      const QString &colorString) override;
+
+protected:
+    void save() override;
+
+private:
+    void update(std::unordered_map<QString, UserData> &&newUsers);
+
+    std::unordered_map<QString, UserData> getUsers() const;
+
+    // Stores a real-time list of users & their customizations
+    std::unordered_map<QString, UserData> users;
+    mutable std::shared_mutex usersMutex;
+
+    std::shared_ptr<pajlada::Settings::SettingManager> sm;
+    pajlada::Settings::Setting<std::unordered_map<QString, UserData>> setting;
+};
+
+}  // namespace chatterino