BansheeEngine/BansheeUtility/Include/BsBinarySerializer.h

#pragma once

#include <unordered_map>

#include "BsPrerequisitesUtil.h"
#include "BsSerializedObject.h"
#include "BsRTTIField.h"

namespace BansheeEngine
{
	class IReflectable;
	struct RTTIReflectableFieldBase;
	struct RTTIReflectablePtrFieldBase;

	// TODO - Low priority. I will probably want to extract a generalized Serializer class so we can re-use the code
	// in text or other serializers
	// TODO - Low priority. Encode does a chunk-based encode so that we don't need to know the buffer size in advance,
	// and don't have to use a lot of memory for the buffer. Consider doing something similar for decode.
	// TODO - Low priority. Add a simple encode method that doesn't require a callback, instead it calls the callback internally
	// and creates the buffer internally.
	/**
	 * @brief	Encodes all the fields of the provided object into a binary format. Fields are
	 * 			encoded using their unique IDs. Encoded data will remain compatible for decoding even
	 * 			if you modify the encoded class, as long as you assign new unique field IDs to
	 * 			added/modified fields.
	 * 			
	 *			Like for any serializable class, fields are defined in RTTIType that each
	 *			IReflectable class must be able to return.
	 *
	 * 			Any data the object or its children are pointing to will also be serialized 
	 *			(unless the pointer isn't registered in RTTIType). Upon decoding the pointer 
	 *			addresses will be set to proper values.
	 * 			
	 * @note	Child elements are guaranteed to be fully deserialized before their parents, except for fields
	 *			marked with WeakRef flag.
	 */
	class BS_UTILITY_EXPORT BinarySerializer
	{
	public:
		BinarySerializer();

		/**
		 * @brief	Encodes all serializable fields provided by "object" into a binary format. Data is written in chunks.
		 * 			Whenever a chunk is filled a callback is triggered that gives the user opportunity to expand or 
		 * 			empty the buffer (for example write the chunk to disk)
		 *
		 * @param		object				Object to encode into binary format.
		 * @param [out]	buffer				Preallocated buffer where the data will be stored.
		 * @param	bufferLength			Length of the buffer, in bytes.
		 * @param [out]	bytesWritten		Length of the data that was actually written to the buffer,
		 * 									in bytes.
		 * @param	flushBufferCallback 	This callback will get called whenever the buffer gets full (Be careful to check the provided
		 * 									"bytesRead" variable, as buffer might not be full completely). User must then
		 * 									either create a new buffer or empty the existing one, and then return it by the callback.
		 * 									If the returned buffer address is NULL, encoding is aborted.
		 * @param	shallow					Determines how to handle referenced objects. If true then references will not be encoded
		 *									and will be set to null. If false then references will be encoded as well and restored
		 *									upon decoding.
		 */
		void encode(IReflectable* object, UINT8* buffer, UINT32 bufferLength, UINT32* bytesWritten,
			std::function<UINT8*(UINT8* buffer, UINT32 bytesWritten, UINT32& newBufferSize)> flushBufferCallback,
			bool shallow = false);

		/**
		 * @brief	Decodes an object from binary data.
		 *
		 * @param 	data  	Binary data to decode.
		 * @param	dataLength	Length of the data in bytes.
		 */
		SPtr<IReflectable> decode(UINT8* data, UINT32 dataLength);

		/**
		 * @brief	Encodes an object into an intermediate representation.
		 *
		 * @param	object		Object to encode.
		 * @param	shallow		Determines how to handle referenced objects. If true then references will not be encoded
		 *						and will be set to null. If false then references will be encoded as well and restored
		 *						upon decoding.
		 */
		SPtr<SerializedObject> _encodeIntermediate(IReflectable* object, bool shallow = false);

		/**
		 * @brief	Decodes an object in memory into an intermediate representation for easier parsing.
		 *			
		 * @param 	data  		Binary data to decode.
		 * @param	dataLength	Length of the data in bytes.
		 * @param	copyData	Determines should the data be copied or just referenced. If referenced
		 *						then the returned serialized object will be invalid as soon as the original
		 *						data buffer is destroyed. Referencing is faster than copying.
		 *
		 * @note	Internal method.
		 *			References to field data will point to the original buffer and will become invalid 
		 *			when it is destroyed.
		 */
		SPtr<SerializedObject> _decodeIntermediate(UINT8* data, UINT32 dataLength, bool copyData = false);

		/**
		 * @brief	Decodes an intermediate representation of a serialized object into the actual object.
		 *			
		 * @note	Internal method.
		 */
		SPtr<IReflectable> _decodeIntermediate(const SPtr<SerializedObject>& serializedObject);

	private:
		struct ObjectMetaData
		{
			UINT32 objectMeta;
			UINT32 typeId;
		};

		struct ObjectToEncode
		{
			ObjectToEncode(UINT32 _objectId, std::shared_ptr<IReflectable> _object)
				:objectId(_objectId), object(_object)
			{ }

			UINT32 objectId;
			std::shared_ptr<IReflectable> object;
		};

		struct ObjectToDecode
		{
			ObjectToDecode(const SPtr<IReflectable>& _object, const SPtr<SerializedObject>& serializedObject)
				:object(_object), serializedObject(serializedObject), isDecoded(false)
			{ }

			SPtr<IReflectable> object;
			SPtr<SerializedObject> serializedObject;
			bool isDecoded;
		};

		/**
		 * @brief	Parses the entire object and calculates total size required for
		 *			saving the object and all the objects it contains.
		 */
		UINT32 getObjectSize(IReflectable* object);

		/**
		 * @brief	Encodes a single IReflectable object. 
		 */
		UINT8* encodeInternal(IReflectable* object, UINT32 objectId, UINT8* buffer, UINT32& bufferLength, UINT32* bytesWritten,
			std::function<UINT8*(UINT8* buffer, UINT32 bytesWritten, UINT32& newBufferSize)> flushBufferCallback, bool shallow);

		/**
		 * @brief	Decodes a single IReflectable object.
		 */
		void decodeInternal(const SPtr<IReflectable>& object, const SPtr<SerializedObject>& serializableObject);

		/**
		 * @brief	Decodes an object in memory into an intermediate representation for easier parsing.
		 */
		bool decodeIntermediateInternal(UINT8* data, UINT32 dataLength, UINT32& bytesRead, SPtr<SerializedObject>& output, bool copyData);

		/**
		 * @brief	Helper method for encoding a complex object and copying its data to a buffer.
		 */
		UINT8* complexTypeToBuffer(IReflectable* object, UINT8* buffer, UINT32& bufferLength, UINT32* bytesWritten,
			std::function<UINT8*(UINT8* buffer, UINT32 bytesWritten, UINT32& newBufferSize)> flushBufferCallback, bool shallow);

		/**
		 * @brief	Helper method for encoding a data block to a buffer.
		 */
		UINT8* dataBlockToBuffer(UINT8* data, UINT32 size, UINT8* buffer, UINT32& bufferLength, UINT32* bytesWritten,
			std::function<UINT8*(UINT8* buffer, UINT32 bytesWritten, UINT32& newBufferSize)> flushBufferCallback);

		/**
		 * @brief	Finds an existing, or creates a unique unique identifier for the specified object. 
		 */
		UINT32 findOrCreatePersistentId(IReflectable* object);

		/**
		 * @brief	Finds or creates an id for the provided object and returns it.
		 * 			And it adds the object to a list of objects that need to be encoded,
		 * 			if it's not already there.
		 */
		UINT32 registerObjectPtr(std::shared_ptr<IReflectable> object);

		/**
		 * @brief	Encodes data required for representing a serialized field, into 4 bytes.
		 */
		static UINT32 encodeFieldMetaData(UINT16 id, UINT8 size, bool array, SerializableFieldType type, bool hasDynamicSize);

		/**
		 * @brief	Decode meta field that was encoded using encodeFieldMetaData.
		 */
		static void decodeFieldMetaData(UINT32 encodedData, UINT16& id, UINT8& size, bool& array, SerializableFieldType& type, bool& hasDynamicSize);

		/**
		 * @brief	Encodes data required for representing an object identifier, into 8 bytes.
		 * 			
		 * 			@note		Id can be a maximum of 30 bits, as two bits are reserved.
		 *
		 * @param	objId	   	Unique ID of the object instance.
		 * @param	objTypeId  	Unique ID of the object type.
		 * @param	isBaseClass	true if this object is base class (i.e. just a part of a larger object).
		 */
		static ObjectMetaData encodeObjectMetaData(UINT32 objId, UINT32 objTypeId, bool isBaseClass);

		/**
		* @brief	Decode meta field that was encoded using encodeObjectMetaData.
		*/
		static void decodeObjectMetaData(ObjectMetaData encodedData, UINT32& objId, UINT32& objTypeId, bool& isBaseClass);

		/**
		 * @brief	Returns true if the provided encoded meta data represents object meta data.
		 */
		static bool isObjectMetaData(UINT32 encodedData);

		UnorderedMap<void*, UINT32> mObjectAddrToId;
		UINT32 mLastUsedObjectId;
		Vector<ObjectToEncode> mObjectsToEncode;
		UINT32 mTotalBytesWritten;

		UnorderedMap<SPtr<SerializedObject>, ObjectToDecode> mObjectMap;
		UnorderedMap<UINT32, SPtr<SerializedObject>> mInterimObjectMap;

		static const int META_SIZE = 4; // Meta field size
		static const int NUM_ELEM_FIELD_SIZE = 4; // Size of the field storing number of array elements
		static const int COMPLEX_TYPE_FIELD_SIZE = 4; // Size of the field storing the size of a child complex type
		static const int DATA_BLOCK_TYPE_FIELD_SIZE = 4;
	};
}