/*
 * This file is a part of Winix
 * and is distributed under the 2-Clause BSD licence.
 * Author: Tomasz Sowa <t.sowa@ttmath.org>
 */

/*
 * Copyright (c) 2014-2018, Tomasz Sowa
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 */

#ifndef headerfile_winix_core_sessionidmanager
#define headerfile_winix_core_sessionidmanager

#include <string>
#include <vector>
#include <ctime>
#include <fstream>
#include "base64.h"
#include "space/space.h"
#include "aes.h"
#include "winixbase.h"



namespace Winix
{


/*
 * this class is used to encode/decode the session cookie
 * in which there is a session id and a session's index
 *
 * session index is incremented each time a request comes to this session
 *
 * format of the encoded token:
 *  1 byte    - algorithm type, currently only one algorithm: 'a'
 *  1 byte    - an AES keys pair index
 *  ---- below everything is encoded by AES (two 128 bits blocks, first block
 *       is encoded by the first key and the second block is encoded by the second key) ------
 *  1 byte    - top padding value
 *  1 byte    - bottom padding value
 *  1 byte    - top padding size
 *  1 byte    - bottom padding size
 *  5-9 bytes - top padding
 *  8 bytes   - the session id
 *  4 bytes   - the session index
 *  5-9 bytes - bottom padding (bottom_padding_size = 14 - top_padding_size)
 *  1 byte    - the sum of all previous bytes
 *  1 byte    - the xor of all previous bytes (with the previous sum too)
 *
 * and at the end everyting is base64 encoded
 *
 *
 */
class SessionIdManager : public WinixBase
{
public:

	SessionIdManager();

	/*
	 * initialization
	 * this method takes about 1MB memory more (for AES key expansions)
	 * if you do not need the session cookie to be enrypted then don't call this method
	 *
	 */
	void Init(const std::wstring & keys_file);

	/*
	 * how often a new AES key pairs should be generated
	 */
	void SetKeyRenewTime(time_t renew_time);

	/*
	 * encode/decode the session cookie
	 * make sure the Init() method is called first
	 */
	bool EncodeToken(size_t id, unsigned int index, time_t cur_utc_time, std::wstring & token);
	bool DecodeToken(const std::wstring & token, size_t & id, unsigned int & index);


private:

	bool was_inited;
	char algorithm_type;
	std::string string_token, string_token_base64;
	std::vector<std::string> key_tab1, key_tab2;
	size_t key_index;
	time_t last_key_generated;
	time_t key_renew_time;
	Tito::Base64 base64;
	size_t key_tab_size;
	std::ofstream out_file;
	std::string tmp_key_base64_encoded;
	std::wstring key_file_name;
	std::string file_name_ascii;
	std::vector<Tito::AES> aes1, aes2;

	bool ReadKeysFromFile(const wchar_t * file);
	bool ReadKeysFromFile(const std::wstring & file);
	bool SaveKeysToFile(const wchar_t * file);
	bool SaveKeysToFile(const std::wstring & file);
	void ReadKey(const wchar_t * name, pt::Space & space, std::vector<std::string> & dest_key);
	bool AreKeysCorrect(size_t index);
	void GenerateKeys(size_t index, time_t cur_utc_time);
	void CheckKeys(time_t cur_utc_time);
	void GenerateKey(std::string & key, time_t cur_utc_time);
	void SaveKeysToFile(std::vector<std::string> & keys);
	void InitializeAesKeys();
	void RandPadding(size_t & pad_top_size, char & pad_top_value, size_t & pad_bottom_size, char & pad_bottom_value);
	void AppendSum(std::string & str);
	void AppendXor(std::string & str);
	void CopyString(const std::string & in, std::wstring & out);
	void CopyString(const std::wstring & in, std::string & out);
	bool Encode(std::string & str);
	bool DecodeTokenA(size_t & id, unsigned int & index);
	bool IsPaddingCorrect(const char * str, size_t len, char val);
	bool CheckControlSums(const char * str);
	void InitializeAesKeys(size_t index);
	bool DecodeAES(const char * str, size_t key);

	template<typename Value>
	void Append(std::string & str, Value val);

	template<typename Value>
	void Read(const char * str, Value & val);

};



template<typename Value>
void SessionIdManager::Append(std::string & str, Value val)
{
	int move = sizeof(Value) * 8 - 8;
	int v;

	do
	{
		if( move > 0 )
			v = ((val >> move) & 0xff);
		else
			v = val & 0xff;

		str  += (unsigned char)v;
		move -= 8;
	}
	while( move >= 0 );
}



template<typename Value>
void SessionIdManager::Read(const char * str, Value & val)
{
	val = 0;

	for(size_t i=0 ; i<sizeof(Value) ; ++i)
	{
		val = val << 8;
		val = val | (unsigned char)str[i];
	}
}


} // namespace Winix


#endif