22 files changed, 746 insertions, 5 deletions

diff --git a/.gitignore b/.gitignore
index 27d5402..180afb8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 build
 doxygen
 .cache
+*.db
 
 CMakeLists.txt.user
 CMakeCache.txt
@@ -14,3 +15,4 @@ compile_commands.json
 CTestTestfile.cmake
 _deps
 CMakeUserPresets.json
+
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ab6ecbf..e4922df 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -11,6 +11,7 @@ find_package(SDL2 REQUIRED)
 find_package(SDL2_image REQUIRED)
 find_package(SoLoud REQUIRED)
 find_package(GTest REQUIRED)
+find_library(BERKELEY_DB db)
 
 add_library(crepe SHARED)
 add_executable(test_main EXCLUDE_FROM_ALL)
@@ -23,6 +24,7 @@ target_link_libraries(crepe
 	PRIVATE soloud
 	PUBLIC SDL2
 	PUBLIC SDL2_image
+	PUBLIC ${BERKELEY_DB}
 )
 
 add_subdirectory(crepe)
diff --git a/src/crepe/CMakeLists.txt b/src/crepe/CMakeLists.txt
index 8830e05..fc95bd3 100644
--- a/src/crepe/CMakeLists.txt
+++ b/src/crepe/CMakeLists.txt
@@ -4,6 +4,7 @@ target_sources(crepe PUBLIC
 	ComponentManager.cpp
 	Component.cpp
 	Collider.cpp
+	Exception.cpp
 )
 
 target_sources(crepe PUBLIC FILE_SET HEADERS FILES
@@ -12,6 +13,9 @@ target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	ComponentManager.hpp
 	Component.h
 	Collider.h
+	ValueBroker.h
+	ValueBroker.hpp
+	Exception.h
 )
 
 add_subdirectory(api)
diff --git a/src/crepe/Exception.cpp b/src/crepe/Exception.cpp
new file mode 100644
index 0000000..f27d5a8
--- /dev/null
+++ b/src/crepe/Exception.cpp
@@ -0,0 +1,19 @@
+#include <cstdarg>
+
+#include "Exception.h"
+#include "util/fmt.h"
+
+using namespace std;
+using namespace crepe;
+
+const char * Exception::what() {
+	return error.c_str();
+}
+
+Exception::Exception(const char * fmt, ...) {
+	va_list args;
+	va_start(args, fmt);
+	this->error = va_stringf(args, fmt);
+	va_end(args);
+}
+
diff --git a/src/crepe/Exception.h b/src/crepe/Exception.h
new file mode 100644
index 0000000..e4a7bb8
--- /dev/null
+++ b/src/crepe/Exception.h
@@ -0,0 +1,23 @@
+#pragma once
+
+#include <exception>
+#include <string>
+
+namespace crepe {
+
+//! Exception class with printf-style constructor
+class Exception : public std::exception {
+public:
+	//! printf
+	Exception(const char * fmt, ...);
+	//! Get formatted error message
+	const char * what();
+
+protected:
+	Exception() = default;
+	//! Formatted error message
+	std::string error;
+
+};
+
+}
diff --git a/src/crepe/ValueBroker.h b/src/crepe/ValueBroker.h
new file mode 100644
index 0000000..88988b4
--- /dev/null
+++ b/src/crepe/ValueBroker.h
@@ -0,0 +1,41 @@
+#pragma once
+
+#include <functional>
+
+namespace crepe {
+
+/**
+ * \brief Give reference to value through custom set/get functions
+ *
+ * This class can be used to abstract direct access to any arbitrary value
+ * through a custom get and set function passed to its constructor. Consumers
+ * of this type may want to wrap it in a \c Proxy so it behaves like a regular
+ * variable.
+ *
+ * \tparam T  Type of the underlying variable
+ */
+template <typename T>
+class ValueBroker {
+public:
+	//! Set the value
+	virtual void set(const T &);
+	//! Retrieve the value
+	virtual const T & get();
+
+	typedef std::function<void(const T & target)> setter_t;
+	typedef std::function<const T & ()> getter_t;
+private:
+	setter_t setter;
+	getter_t getter;
+public:
+	/**
+	 * \param setter  Function that sets the variable
+	 * \param getter  Function that retrieves the variable
+	 */
+	ValueBroker(const setter_t & setter, const getter_t & getter);
+};
+
+}
+
+#include "ValueBroker.hpp"
+
diff --git a/src/crepe/ValueBroker.hpp b/src/crepe/ValueBroker.hpp
new file mode 100644
index 0000000..0d08333
--- /dev/null
+++ b/src/crepe/ValueBroker.hpp
@@ -0,0 +1,25 @@
+#pragma once
+
+#include "ValueBroker.h"
+
+namespace crepe {
+
+template <typename T>
+ValueBroker<T>::ValueBroker(const setter_t & setter, const getter_t & getter) :
+	setter(setter),
+	getter(getter)
+	{
+}
+
+template <typename T>
+const T & ValueBroker<T>::get() {
+	return this->getter();
+}
+
+template <typename T>
+void ValueBroker<T>::set(const T & value) {
+	this->setter(value);
+}
+
+}
+
diff --git a/src/crepe/api/CMakeLists.txt b/src/crepe/api/CMakeLists.txt
index 321343a..3b20142 100644
--- a/src/crepe/api/CMakeLists.txt
+++ b/src/crepe/api/CMakeLists.txt
@@ -10,6 +10,8 @@ target_sources(crepe PUBLIC
 	Texture.cpp
 	AssetManager.cpp
 	Sprite.cpp
+	SaveManager.cpp
+	Config.cpp
 	Metadata.cpp
 	Scene.cpp
 	SceneManager.cpp
@@ -31,6 +33,7 @@ target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	Texture.h 
 	AssetManager.h 
 	AssetManager.hpp
+	SaveManager.h
 	Scene.h
 	Metadata.h
 	SceneManager.h
diff --git a/src/crepe/api/Config.cpp b/src/crepe/api/Config.cpp
new file mode 100644
index 0000000..d6206da
--- /dev/null
+++ b/src/crepe/api/Config.cpp
@@ -0,0 +1,9 @@
+#include "Config.h"
+
+using namespace crepe;
+
+Config & Config::get_instance() {
+	static Config instance;
+	return instance;
+}
+
diff --git a/src/crepe/api/Config.h b/src/crepe/api/Config.h
index 88220a7..56e3af5 100644
--- a/src/crepe/api/Config.h
+++ b/src/crepe/api/Config.h
@@ -7,16 +7,17 @@ namespace crepe {
 class Config {
 private:
 	Config() = default;
-
 public:
 	~Config() = default;
 
 public:
 	//! Retrieve handle to global Config instance
-	static Config & get_instance() {
-		static Config instance;
-		return instance;
-	}
+	static Config & get_instance();
+	// singleton
+	Config(const Config &) = delete;
+	Config(Config &&) = delete;
+	Config & operator = (const Config &) = delete;
+	Config & operator = (Config &&) = delete;
 
 public:
 	//! Logging-related settings
@@ -36,6 +37,17 @@ public:
 		bool color = true;
 	} log;
 
+	//! Save manager
+	struct {
+		/**
+		 * \brief Save file location
+		 *
+		 * This location is used by the constructor of SaveManager, and should be
+		 * set before save manager functionality is attempted to be used.
+		 */
+		std::string location = "save.crepe.db";
+	} savemgr;
+
 	//! physics-related settings
 	struct {
 		/**
@@ -48,3 +60,4 @@ public:
 };
 
 } // namespace crepe
+
diff --git a/src/crepe/api/SaveManager.cpp b/src/crepe/api/SaveManager.cpp
new file mode 100644
index 0000000..23587e4
--- /dev/null
+++ b/src/crepe/api/SaveManager.cpp
@@ -0,0 +1,159 @@
+#include "../facade/DB.h"
+#include "../util/log.h"
+
+#include "Config.h"
+#include "ValueBroker.h"
+#include "SaveManager.h"
+
+using namespace std;
+using namespace crepe;
+
+template <>
+string SaveManager::serialize(const string & value) const noexcept {
+	return value;
+}
+template <typename T>
+string SaveManager::serialize(const T & value) const noexcept {
+	return to_string(value);
+}
+template string SaveManager::serialize(const uint8_t &) const noexcept;
+template string SaveManager::serialize(const int8_t &) const noexcept;
+template string SaveManager::serialize(const uint16_t &) const noexcept;
+template string SaveManager::serialize(const int16_t &) const noexcept;
+template string SaveManager::serialize(const uint32_t &) const noexcept;
+template string SaveManager::serialize(const int32_t &) const noexcept;
+template string SaveManager::serialize(const uint64_t &) const noexcept;
+template string SaveManager::serialize(const int64_t &) const noexcept;
+template string SaveManager::serialize(const float &) const noexcept;
+template string SaveManager::serialize(const double &) const noexcept;
+
+template <>
+uint64_t SaveManager::deserialize(const string & value) const noexcept {
+	try {
+		return stoul(value);
+	} catch (std::invalid_argument &) {
+		return 0;
+	}
+}
+template <>
+int64_t SaveManager::deserialize(const string & value) const noexcept {
+	try {
+		return stol(value);
+	} catch (std::invalid_argument &) {
+		return 0;
+	}
+}
+template <>
+float SaveManager::deserialize(const string & value) const noexcept {
+	try {
+		return stof(value);
+	} catch (std::invalid_argument &) {
+		return 0;
+	}
+	return stof(value);
+}
+template <>
+double SaveManager::deserialize(const string & value) const noexcept {
+	try {
+		return stod(value);
+	} catch (std::invalid_argument &) {
+		return 0;
+	}
+}
+template <>
+string SaveManager::deserialize(const string & value) const noexcept {
+	return value;
+}
+
+template <> uint8_t SaveManager::deserialize(const string & value) const noexcept { return deserialize<uint64_t>(value); }
+template <> int8_t SaveManager::deserialize(const string & value) const noexcept { return deserialize<int64_t>(value); }
+template <> uint16_t SaveManager::deserialize(const string & value) const noexcept { return deserialize<uint64_t>(value); }
+template <> int16_t SaveManager::deserialize(const string & value) const noexcept { return deserialize<int64_t>(value); }
+template <> uint32_t SaveManager::deserialize(const string & value) const noexcept { return deserialize<uint64_t>(value); }
+template <> int32_t SaveManager::deserialize(const string & value) const noexcept { return deserialize<int64_t>(value); }
+
+SaveManager::SaveManager() {
+	dbg_trace();
+}
+
+SaveManager & SaveManager::get_instance() {
+	dbg_trace();
+	static SaveManager instance;
+	return instance;
+}
+
+DB & SaveManager::get_db() {
+	Config & cfg = Config::get_instance();
+	// TODO: make this path relative to XDG_DATA_HOME on Linux and whatever the
+	// default equivalent is on Windows using some third party library
+	static DB db(cfg.savemgr.location);
+	return db;
+}
+
+bool SaveManager::has(const string & key) {
+	DB & db = this->get_db();
+	return db.has(key);
+}
+
+template <>
+void SaveManager::set(const string & key, const string & value) {
+	DB & db = this->get_db();
+	db.set(key, value);
+}
+template <typename T>
+void SaveManager::set(const string & key, const T & value) {
+	DB & db = this->get_db();
+	db.set(key, std::to_string(value));
+}
+template void SaveManager::set(const string &, const uint8_t &);
+template void SaveManager::set(const string &, const int8_t &);
+template void SaveManager::set(const string &, const uint16_t &);
+template void SaveManager::set(const string &, const int16_t &);
+template void SaveManager::set(const string &, const uint32_t &);
+template void SaveManager::set(const string &, const int32_t &);
+template void SaveManager::set(const string &, const uint64_t &);
+template void SaveManager::set(const string &, const int64_t &);
+template void SaveManager::set(const string &, const float &);
+template void SaveManager::set(const string &, const double &);
+
+template <typename T>
+ValueBroker<T> SaveManager::get(const string & key, const T & default_value) {
+	if (!this->has(key))
+		this->set<T>(key, default_value);
+	return this->get<T>(key);
+}
+template ValueBroker<uint8_t> SaveManager::get(const string &, const uint8_t &);
+template ValueBroker<int8_t> SaveManager::get(const string &, const int8_t &);
+template ValueBroker<uint16_t> SaveManager::get(const string &, const uint16_t &);
+template ValueBroker<int16_t> SaveManager::get(const string &, const int16_t &);
+template ValueBroker<uint32_t> SaveManager::get(const string &, const uint32_t &);
+template ValueBroker<int32_t> SaveManager::get(const string &, const int32_t &);
+template ValueBroker<uint64_t> SaveManager::get(const string &, const uint64_t &);
+template ValueBroker<int64_t> SaveManager::get(const string &, const int64_t &);
+template ValueBroker<float> SaveManager::get(const string &, const float &);
+template ValueBroker<double> SaveManager::get(const string &, const double &);
+template ValueBroker<string> SaveManager::get(const string &, const string &);
+
+template <typename T>
+ValueBroker<T> SaveManager::get(const string & key) {
+	T value;
+	return {
+		[this, key] (const T & target) { this->set<T>(key, target); },
+		[this, key, value] () mutable -> const T & {
+			value = this->deserialize<T>(this->get_db().get(key));
+			return value;
+		},
+	};
+}
+template ValueBroker<uint8_t> SaveManager::get(const string &);
+template ValueBroker<int8_t> SaveManager::get(const string &);
+template ValueBroker<uint16_t> SaveManager::get(const string &);
+template ValueBroker<int16_t> SaveManager::get(const string &);
+template ValueBroker<uint32_t> SaveManager::get(const string &);
+template ValueBroker<int32_t> SaveManager::get(const string &);
+template ValueBroker<uint64_t> SaveManager::get(const string &);
+template ValueBroker<int64_t> SaveManager::get(const string &);
+template ValueBroker<float> SaveManager::get(const string &);
+template ValueBroker<double> SaveManager::get(const string &);
+template ValueBroker<string> SaveManager::get(const string &);
+
diff --git a/src/crepe/api/SaveManager.h b/src/crepe/api/SaveManager.h
new file mode 100644
index 0000000..3073656
--- /dev/null
+++ b/src/crepe/api/SaveManager.h
@@ -0,0 +1,114 @@
+#pragma once
+
+#include <memory>
+
+#include "../ValueBroker.h"
+
+namespace crepe {
+
+class DB;
+
+/**
+ * \brief Save data manager
+ *
+ * This class provides access to a simple key-value store that stores
+ * - integers (8-64 bit, signed or unsigned)
+ * - real numbers (float or double)
+ * - string (std::string)
+ *
+ * The underlying database is a key-value store.
+ */
+class SaveManager {
+public:
+	/**
+	 * \brief Get a read/write reference to a value and initialize it if it does not yet exist
+	 *
+	 * \param key  The value key
+	 * \param default_value  Value to initialize \c key with if it does not already exist in the database
+	 *
+	 * \return Read/write reference to the value
+	 */
+	template <typename T>
+	ValueBroker<T> get(const std::string & key, const T & default_value);
+
+	/**
+	 * \brief Get a read/write reference to a value
+	 *
+	 * \param key  The value key
+	 *
+	 * \return Read/write reference to the value
+	 *
+	 * \note Attempting to read this value before it is initialized (i.e. set)
+	 * will result in an exception
+	 */
+	template <typename T>
+	ValueBroker<T> get(const std::string & key);
+
+	/**
+	 * \brief Set a value directly
+	 *
+	 * \param key  The value key
+	 * \param value  The value to store
+	 */
+	template <typename T>
+	void set(const std::string & key, const T & value);
+
+	/**
+	 * \brief Check if the save file has a value for this \c key
+	 *
+	 * \param key  The value key
+	 *
+	 * \returns True if the key exists, or false if it does not
+	 */
+	bool has(const std::string & key);
+
+private:
+	SaveManager();
+	virtual ~SaveManager() = default;
+
+private:
+	/**
+	 * \brief Serialize an arbitrary value to STL string
+	 *
+	 * \tparam T  Type of arbitrary value
+	 *
+	 * \returns String representation of value
+	 */
+	template <typename T>
+	std::string serialize(const T &) const noexcept;
+
+	/**
+	 * \brief Deserialize an STL string back to type \c T
+	 *
+	 * \tparam T  Type of value
+	 * \param value  Serialized value
+	 *
+	 * \returns Deserialized value
+	 */
+	template <typename T>
+	T deserialize(const std::string & value) const noexcept;
+
+public:
+	// singleton
+	static SaveManager & get_instance();
+	SaveManager(const SaveManager &) = delete;
+	SaveManager(SaveManager &&) = delete;
+	SaveManager & operator = (const SaveManager &) = delete;
+	SaveManager & operator = (SaveManager &&) = delete;
+
+private:
+	/**
+	 * \brief Create an instance of DB and return its reference
+	 *
+	 * \returns DB instance
+	 *
+	 * This function exists because DB is a facade class, which can't directly be
+	 * used in the API without workarounds
+	 *
+	 * TODO: better solution
+	 */
+	static DB & get_db();
+};
+
+}
+
diff --git a/src/crepe/facade/CMakeLists.txt b/src/crepe/facade/CMakeLists.txt
index c79e16f..4cc53bc 100644
--- a/src/crepe/facade/CMakeLists.txt
+++ b/src/crepe/facade/CMakeLists.txt
@@ -2,11 +2,13 @@ target_sources(crepe PUBLIC
 	Sound.cpp
 	SoundContext.cpp
 	SDLContext.cpp
+	DB.cpp
 )
 
 target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	Sound.h
 	SoundContext.h
 	SDLContext.h
+	DB.h
 )
 
diff --git a/src/crepe/facade/DB.cpp b/src/crepe/facade/DB.cpp
new file mode 100644
index 0000000..c885560
--- /dev/null
+++ b/src/crepe/facade/DB.cpp
@@ -0,0 +1,68 @@
+#include <cstring>
+
+#include "util/log.h"
+#include "Exception.h"
+
+#include "DB.h"
+
+using namespace std;
+using namespace crepe;
+
+DB::DB(const string & path) {
+	dbg_trace();
+	int ret;
+
+	// init database struct
+	libdb::DB * db;
+	if ((ret = libdb::db_create(&db, NULL, 0)) != 0)
+		throw Exception("db_create: %s", libdb::db_strerror(ret));
+	this->db = { db, [] (libdb::DB * db) { db->close(db, 0); } };
+
+	// load or create database file
+	if ((ret = this->db->open(this->db.get(), NULL, path.c_str(), NULL, libdb::DB_BTREE, DB_CREATE, 0)) != 0)
+		throw Exception("db->open: %s", libdb::db_strerror(ret));
+
+	// create cursor
+	libdb::DBC * cursor;
+	if ((ret = this->db->cursor(this->db.get(), NULL, &cursor, 0)) != 0)
+		throw Exception("db->cursor: %s", libdb::db_strerror(ret));
+	this->cursor = { cursor, [] (libdb::DBC * cursor) { cursor->close(cursor); } };
+}
+
+
+libdb::DBT DB::to_thing(const string & thing) const noexcept {
+	libdb::DBT thang;
+	memset(&thang, 0, sizeof(libdb::DBT));
+	thang.data = (void *) thing.data();
+	thang.size = thing.size();
+	return thang;
+}
+
+string DB::get(const string & key) {
+	libdb::DBT db_key = this->to_thing(key);
+	libdb::DBT db_val;
+	memset(&db_val, 0, sizeof(libdb::DBT));
+
+	int ret = this->cursor->get(this->cursor.get(), &db_key, &db_val, DB_FIRST);
+	if (ret != 0)
+		throw Exception("cursor->get: %s", libdb::db_strerror(ret));
+	return { static_cast<char *>(db_val.data), db_val.size };
+}
+
+void DB::set(const string & key, const string & value) {
+	libdb::DBT db_key = this->to_thing(key);
+	libdb::DBT db_val = this->to_thing(value);
+	int ret = this->db->put(this->db.get(), NULL, &db_key, &db_val, 0);
+	if (ret != 0)
+		throw Exception("cursor->get: %s", libdb::db_strerror(ret));
+}
+
+bool DB::has(const std::string & key) noexcept {
+	try {
+		this->get(key);
+	} catch (...) {
+		return false;
+	}
+	return true;
+}
+
diff --git a/src/crepe/facade/DB.h b/src/crepe/facade/DB.h
new file mode 100644
index 0000000..b62a974
--- /dev/null
+++ b/src/crepe/facade/DB.h
@@ -0,0 +1,75 @@
+#pragma once
+
+#include <string>
+#include <functional>
+#include <memory>
+
+namespace libdb {
+extern "C" {
+#include <db.h>
+}
+}
+
+namespace crepe {
+
+/**
+ * \brief Berkeley DB facade
+ *
+ * Berkeley DB is a simple key-value database that stores arbitrary data as
+ * both key and value. This facade uses STL strings as keys/values.
+ */
+class DB {
+public:
+	/**
+	 * \param path  The path of the database (created if nonexistant)
+	 */
+	DB(const std::string & path);
+	virtual ~DB() = default;
+
+public:
+	/**
+	 * \brief Get a value from the database, or throw an exception
+	 *
+	 * \param key  The value key
+	 *
+	 * \return The value
+	 *
+	 * \throws Exception if value is not found in DB or other error occurs
+	 */
+	std::string get(const std::string & key);
+	/**
+	 * \brief Set (create or overwrite) a value in the database
+	 *
+	 * \param key  The value key
+	 * \param value  The value to store
+	 *
+	 * \throws Exception if an error occurs
+	 */
+	void set(const std::string & key, const std::string & value);
+	/**
+	 * \brief Check if a key exists in the database
+	 *
+	 * \param key  The value key
+	 *
+	 * \returns True if the key exists, or false if it does not
+	 */
+	bool has(const std::string & key) noexcept;
+
+private:
+	//! RAII wrapper around \c DB struct
+	std::unique_ptr<libdb::DB, std::function<void(libdb::DB *)>> db;
+	//! RAII wrapper around \c DBC struct
+	std::unique_ptr<libdb::DBC, std::function<void(libdb::DBC *)>> cursor;
+
+private:
+	/**
+	 * \brief Convert an STL string to DBT (data base thang)
+	 *
+	 * \param thing  Input data
+	 * \return \c DBT with the same data as input \c thing
+	 */
+	libdb::DBT to_thing(const std::string & thing) const noexcept;
+};
+
+}
+
diff --git a/src/crepe/util/CMakeLists.txt b/src/crepe/util/CMakeLists.txt
index 3675bee..0fa4343 100644
--- a/src/crepe/util/CMakeLists.txt
+++ b/src/crepe/util/CMakeLists.txt
@@ -8,5 +8,7 @@ target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	LogColor.h
 	log.h
 	fmt.h
+	Proxy.h
+	Proxy.hpp
 )
 
diff --git a/src/crepe/util/Proxy.h b/src/crepe/util/Proxy.h
new file mode 100644
index 0000000..fbfed0c
--- /dev/null
+++ b/src/crepe/util/Proxy.h
@@ -0,0 +1,33 @@
+#pragma once
+
+#include "ValueBroker.h"
+
+namespace crepe {
+
+/**
+ * \brief Utility wrapper for \c ValueBroker
+ *
+ * This class can be used to to wrap a ValueBroker instance so it behaves like
+ * a regular variable.
+ *
+ * \tparam T  Type of the underlying variable
+ */
+template <typename T>
+class Proxy {
+public:
+	//! Set operator
+	Proxy & operator = (const T &);
+	//! Get operator
+	operator const T & ();
+
+public:
+	Proxy(ValueBroker<T>);
+
+private:
+	ValueBroker<T> broker;
+};
+
+}
+
+#include "Proxy.hpp"
+
diff --git a/src/crepe/util/Proxy.hpp b/src/crepe/util/Proxy.hpp
new file mode 100644
index 0000000..4aec9e9
--- /dev/null
+++ b/src/crepe/util/Proxy.hpp
@@ -0,0 +1,22 @@
+#pragma once
+
+#include "Proxy.h"
+
+namespace crepe {
+
+template <typename T>
+Proxy<T>::Proxy(ValueBroker<T> broker) : broker(broker) { }
+
+template <typename T>
+Proxy<T> & Proxy<T>::operator = (const T & val) {
+	this->broker.set(val);
+	return *this;
+}
+
+template <typename T>
+Proxy<T>::operator const T & () {
+	return this->broker.get();
+}
+
+}
+
diff --git a/src/example/CMakeLists.txt b/src/example/CMakeLists.txt
index 782d3ef..36f9d4d 100644
--- a/src/example/CMakeLists.txt
+++ b/src/example/CMakeLists.txt
@@ -23,5 +23,9 @@ add_example(log)
 add_example(rendering)
 add_example(asset_manager)
 add_example(physics)
+add_example(savemgr)
+add_example(proxy)
+add_example(db)
 add_example(ecs)
 add_example(scene_manager)
+
diff --git a/src/example/db.cpp b/src/example/db.cpp
new file mode 100644
index 0000000..c046421
--- /dev/null
+++ b/src/example/db.cpp
@@ -0,0 +1,30 @@
+#include <crepe/facade/DB.h>
+#include <crepe/api/Config.h>
+#include <crepe/util/log.h>
+
+using namespace crepe;
+using namespace std;
+
+// run before main
+static auto _ = [] () {
+	auto & cfg = Config::get_instance();
+	cfg.log.level = LogLevel::TRACE;
+	return 0;
+}();
+
+int main() {
+	dbg_trace();
+
+	DB db("file.db");
+
+	const char * test_key = "test-key";
+	string test_data = "Hello world!";
+
+	dbg_logf("DB has key = %d", db.has(test_key));
+
+	db.set(test_key, test_data);
+
+	dbg_logf("key = \"%s\"", db.get(test_key).c_str());
+
+	return 0;
+}
diff --git a/src/example/proxy.cpp b/src/example/proxy.cpp
new file mode 100644
index 0000000..9f54f96
--- /dev/null
+++ b/src/example/proxy.cpp
@@ -0,0 +1,46 @@
+/** \file
+ * 
+ * Standalone example for usage of the proxy type
+ */
+
+#include <crepe/ValueBroker.h>
+#include <crepe/api/Config.h>
+#include <crepe/util/log.h>
+#include <crepe/util/Proxy.h>
+
+using namespace std;
+using namespace crepe;
+
+void test_ro_ref(const int & val) { }
+void test_rw_ref(int & val) { }
+void test_ro_val(int val) { }
+
+int main() {
+	auto & cfg = Config::get_instance();
+	cfg.log.level = LogLevel::DEBUG;
+
+	int real_value = 0;
+
+	ValueBroker<int> broker {
+		[&real_value] (const int & target) {
+			dbg_logf("set %s to %s", to_string(real_value).c_str(), to_string(target).c_str());
+			real_value = target;
+		},
+		[&real_value] () -> const int & {
+			dbg_logf("get %s", to_string(real_value).c_str());
+			return real_value;
+		},
+	};
+
+	Proxy<int> proxy { broker };
+
+	broker.set(54);
+	proxy = 84;
+
+	test_ro_ref(proxy); // this is allowed
+	// test_rw_ref(proxy); // this should throw a compile error
+	test_ro_val(proxy);
+
+	return 0;
+}
+
diff --git a/src/example/savemgr.cpp b/src/example/savemgr.cpp
new file mode 100644
index 0000000..c8dd2bc
--- /dev/null
+++ b/src/example/savemgr.cpp
@@ -0,0 +1,45 @@
+/** \file
+ * 
+ * Standalone example for usage of the save manager
+ */
+
+#include <cassert>
+#include <crepe/util/log.h>
+#include <crepe/util/Proxy.h>
+#include <crepe/api/SaveManager.h>
+#include <crepe/api/Config.h>
+
+using namespace crepe;
+
+// unrelated setup code
+int _ = [] () {
+	// make sure all log messages get printed
+	auto & cfg = Config::get_instance();
+	cfg.log.level = LogLevel::TRACE;
+
+	return 0; // satisfy compiler
+} ();
+
+int main() {
+	const char * key = "mygame.test";
+
+	SaveManager & mgr = SaveManager::get_instance();
+
+	dbg_logf("has key = %s", mgr.has(key) ? "true" : "false");
+	ValueBroker<int> prop = mgr.get<int>(key, 0);
+	Proxy<int> val        = mgr.get<int>(key, 0);
+
+	dbg_logf("val = %d", mgr.get<int>(key).get());
+	prop.set(1);
+	dbg_logf("val = %d", mgr.get<int>(key).get());
+	val = 2;
+	dbg_logf("val = %d", mgr.get<int>(key).get());
+	mgr.set<int>(key, 3);
+	dbg_logf("val = %d", mgr.get<int>(key).get());
+
+	dbg_logf("has key = %s", mgr.has(key) ? "true" : "false");
+	assert(true == mgr.has(key));
+
+	return 0;
+}
+