libki/include/ki/pclass/StaticProperty.h

#pragma once
#include "ki/pclass/Property.h"
#include "ki/util/exception.h"

namespace ki
{
namespace pclass
{
	// Forward declare StaticProperty<ValueT> for our helpers
	template <typename ValueT>
	class StaticProperty;

	/// @cond DOXYGEN_SKIP
	/**
	 * A helper utility that provides the right implementation of construct(),
	 * copy(), get_object() and set_object(), based on characteristics of type: ValueT.
	 */
	template <
		typename ValueT,
		typename IsPointerEnable = void,
		typename IsBaseEnable = void
	>
	struct value_object_helper
	{
		static ValueT construct(const Type &type)
		{
			// In cases where ValueT is not a pointer, and does not derive from PropertyClass,
			// just call the default constructor.
			return ValueT();
		}

		static ValueT copy(const StaticProperty<ValueT> &prop)
		{
			// In cases where ValueT is not a pointer, and does not derive from PropertyClass,
			// just call the copy constructor.
			return ValueT(prop.m_value);
		}

		static const PropertyClass *get_object(const StaticProperty<ValueT> &prop)
		{
			// ValueT does not derive from PropertyClass, and so, this property is not
			// storing an object.
			throw runtime_error(
				"Tried calling get_object() on a property that does not store an object."
			);
		}

		static void set_object(StaticProperty<ValueT> &prop, PropertyClass *object)
		{
			// ValueT does not derive from PropertyClass, and so, this property is not
			// storing an object.
			throw runtime_error(
				"Tried calling set_object() on a property that does not store an object."
			);
		}
	};

	/**
	 * Specialization for when ValueT is:
	 * - A pointer; but
	 * - does not derive from PropertyClass
	 * 
	 * This should:
	 * - Construct to a nullptr;
	 * - Copy construct to the same pointer as the original; and
	 * - Throw an exception when get_object() or set_object() is called.
	 */
	template <typename ValueT>
	struct value_object_helper<
		ValueT,
		typename std::enable_if<
			std::is_pointer<ValueT>::value
		>::type,
		typename std::enable_if<
			!std::is_base_of<
				PropertyClass,
				typename std::remove_pointer<ValueT>::type
			>::value
		>::type
	>
	{
		static ValueT construct(const Type &type)
		{
			// The default value of pointers is null
			return nullptr;
		}

		static ValueT copy(const StaticProperty<ValueT> &prop)
		{
			// The copy constructor for all pointers is to copy the pointer
			// without creating a new copy of the object it's pointing to.
			return prop.m_value;
		}

		static const PropertyClass *get_object(const StaticProperty<ValueT> &prop)
		{
			// ValueT does not derive from PropertyClass, and so, this property is not
			// storing an object.
			throw runtime_error(
				"Tried calling get_object() on a property that does not store an object."
			);
		}

		static void set_object(StaticProperty<ValueT> &prop, PropertyClass *object)
		{
			// ValueT does not derive from PropertyClass, and so, this property is not
			// storing an object.
			throw runtime_error(
				"Tried calling set_object() on a property that does not store an object."
			);
		}
	};

	/**
	 * Specialization for when ValueT is:
	 * - A pointer; and
	 * - does derive from PropertyClass
	 * 
	 * This should:
	 * - Construct to a nullptr;
	 * - Copy construct to the same pointer as the original;
	 * - Return a pointer to a ValueT instance (as a PropertyClass *)
	 *   when get_object() is called; and
	 * - Throw an exception when the object supplied to set_object()
	 *   does not inherit from the property's type, but set m_value otherwise.
	 */
	template <typename ValueT>
	struct value_object_helper<
		ValueT,
		typename std::enable_if<
			std::is_pointer<ValueT>::value
		>::type,
		typename std::enable_if<
			std::is_base_of<
				PropertyClass,
				typename std::remove_pointer<ValueT>::type
			>::value
		>::type
	>
	{
		static ValueT construct(const Type &type)
		{
			// The default value of pointers is null
			return nullptr;
		}

		static ValueT copy(const StaticProperty<ValueT> &prop)
		{
			// The copy constructor for all pointers is to copy the pointer
			// without creating a new copy of the object it's pointing to.
			return prop.m_value;
		}

		static const PropertyClass *get_object(const StaticProperty<ValueT> &prop)
		{
			// ValueT does derive from PropertyClass, and we have a pointer to an instance
			// of ValueT, so we can cast down to a PropertyClass pointer.
			return dynamic_cast<const PropertyClass *>(prop.m_value);
		}

		static void set_object(StaticProperty<ValueT> &prop, PropertyClass *object)
		{
			// Ensure that object inherits the type of the property
			if (object)
				assert_type_match(prop.get_type(), object->get_type(), true);

			// ValueT does derive from PropertyClass, and we have a pointer to an instance
			// of PropertyClass, so cast the pointer up to a ValueT.
			prop.m_value = dynamic_cast<ValueT>(object);
		}
	};

	/**
	 * Specialization for when ValueT is:
	 * - Not a pointer; and
	 * - does derive from PropertyClass
	 * 
	 * This should:
	 * - Construct an instance of ValueT by passing the property
	 *   type and the type's type system; and
	 * - Return a pointer to a ValueT instance (as a PropertyClass *)
	 *   when get_object() is called.
	 */
	template <typename ValueT>
	struct value_object_helper<
		ValueT,
		typename std::enable_if<
			!std::is_pointer<ValueT>::value
		>::type,
		typename std::enable_if<
			std::is_base_of<
				PropertyClass,
				typename std::remove_pointer<ValueT>::type
			>::value
		>::type
	>
	{
		static ValueT construct(const Type &type)
		{
			// Derivitives of PropertyClass cannot have a default constructor since
			// they require their Type and TypeSystem, so we need to pass these
			// along from what the StaticProperty constructor has been given.
			return ValueT(type, type.get_type_system());
		}

		static ValueT copy(const StaticProperty<ValueT> &prop)
		{
			// Derivitives of PropertyClass implement a clone method that returns
			// a pointer to a copy.
			ValueT *value_ptr = dynamic_cast<ValueT *>(prop.m_value.clone());
			ValueT value = *value_ptr;
			delete value_ptr;
			return value;
		}

		static const PropertyClass *get_object(const StaticProperty<ValueT> &prop)
		{
			// ValueT does derive from PropertyClass, and we have an instance of ValueT,
			// so we can cast down to a PropertyClass pointer.
			return dynamic_cast<const PropertyClass *>(&prop.m_value);
		}

		static void set_object(StaticProperty<ValueT> &prop, PropertyClass *object)
		{
			// Ensure that object is not nullptr
			if (!object)
				throw runtime_error("Value cannot be null.");

			// Ensure that object is exactly the type of the property.
			assert_type_match(prop.get_type(), object->get_type());

			// ValueT does derive from PropertyClass, but we don't store a pointer,
			// so we need to copy the value in.
			prop.m_value = *dynamic_cast<ValueT *>(object);
			delete object;
		}
	};
	
	/**
	 * A helper utility that provides the right implementation of write() and read()
	 * based on whether ValueT is a pointer.
	 */
	template <
		typename ValueT,
		typename IsPointerEnable = void
	>
	struct value_rw_helper
	{
		static void write(const StaticProperty<ValueT> &prop, BitStream &stream)
		{
			prop.get_type().write_to(
				stream,
				Value::make_reference<ValueT>(prop.m_value)
			);
		}

		static void read(StaticProperty<ValueT> &prop, BitStream &stream)
		{
			Value value = prop.get_type().read_from(stream);
			prop.m_value = value.get<ValueT>();
		}
	};

	/**
	 * Specialization for when ValueT is a pointer.
	 * 
	 * Dereference the pointer before creating Value instances.
	 * This is so that the Value stores a pointer to a ValueT instance,
	 * rather than storing a pointer to a pointer.
	 */
	template <typename ValueT>
	struct value_rw_helper<
		ValueT,
		typename std::enable_if<
			std::is_pointer<ValueT>::value
		>::type
	>
	{
		using type = typename std::remove_pointer<ValueT>::type;

		static void write(const StaticProperty<ValueT> &prop, BitStream &stream)
		{
			prop.get_type().write_to(
				stream,
				Value::make_reference<type>(*prop.m_value)
			);
		}

		static void read(StaticProperty<ValueT> &prop, BitStream &stream)
		{
			Value value = prop.get_type().read_from(stream);
			prop.m_value = value.take<type>();
		}
	};

	/**
	 * A helper utility that combines functions provided by value_object_helper
	 * and value_rw_helper into a single type.
	 */
	template <typename ValueT>
	struct value_helper
	{
		static ValueT construct(const Type &type)
		{
			return value_object_helper<ValueT>::construct(type);
		}

		static ValueT copy(const StaticProperty<ValueT> &prop)
		{
			return value_object_helper<ValueT>::copy(prop);
		}

		static const PropertyClass *get_object(const StaticProperty<ValueT> &prop)
		{
			return value_object_helper<ValueT>::get_object(prop);
		}

		static void set_object(StaticProperty<ValueT> &prop, PropertyClass *object)
		{
			value_object_helper<ValueT>::set_object(prop, object);
		}

		static void write(const StaticProperty<ValueT> &prop, BitStream &stream)
		{
			value_rw_helper<ValueT>::write(prop, stream);
		}

		static void read(StaticProperty<ValueT> &prop, BitStream &stream)
		{
			value_rw_helper<ValueT>::read(prop, stream);
		}
	};
	/// @endcond

	/**
	 * TODO: Documentation
	 */
	template <typename ValueT>
	class StaticProperty : public IProperty
	{
		// Allow helper utilities access to m_value
		friend value_object_helper<ValueT>;
		friend value_rw_helper<ValueT>;

	public:
		// Do not allow copy assignment. Once a property has been constructed,
		// it shouldn't be able to change.
		StaticProperty<ValueT> &operator=(const StaticProperty<ValueT> &that) = delete;

		StaticProperty(PropertyClass &object,
			const std::string &name, const Type &type)
			: IProperty(object, name, type)
			, m_value(value_helper<ValueT>::construct(type))
		{}

		StaticProperty(PropertyClass &object,
			const std::string &name, const Type &type, ValueT value)
			: IProperty(object, name, type)
		{
			m_value = value;
		}

		StaticProperty(PropertyClass &object, const StaticProperty<ValueT> &that)
			: IProperty(object, that)
			, m_value(value_helper<ValueT>::copy(that))
		{}

		constexpr bool is_pointer() const override
		{
			return std::is_pointer<ValueT>::value;
		}

		constexpr bool is_dynamic() const override
		{
			return false;
		}

		Value get_value() const override
		{
			return Value::make_reference(m_value);
		}

		const PropertyClass *get_object() const override
		{
			return value_helper<ValueT>::get_object(*this);
		}

		void set_object(PropertyClass *object) override
		{
			return value_helper<ValueT>::set_object(*this, object);
		}

		void write_value_to(BitStream &stream) const override
		{
			value_helper<ValueT>::write(*this, stream);
		}

		void read_value_from(BitStream &stream) override
		{
			value_helper<ValueT>::read(*this, stream);
		}

		ValueT &get()
		{
			return m_value;
		}

		const ValueT &get() const
		{
			return m_value;
		}

		operator ValueT &()
		{
			return m_value;
		}

		operator const ValueT &() const
		{
			return m_value;
		}

		ValueT *operator&()
		{
			return &m_value;
		}

		const ValueT *operator&() const
		{
			return &m_value;
		}

		void operator=(const ValueT &value)
		{
			m_value = value;
		}

	protected:
		ValueT m_value;
	};
}
}