/*
 * =====================================================================================
 *
 *       Filename:  robust.h
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  2021年04月27日 10时04分29秒
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Li Chao (), lichao@aiotlink.com
 *   Organization:  
 *
 * =====================================================================================
 */

#ifndef ROBUST_Q31RCWYU
#define ROBUST_Q31RCWYU

#include "bh_util.h"
#include "log.h"
#include <atomic>
#include <chrono>
#include <unistd.h>

namespace robust
{

// atomic queue, length is 1.
// lowest bit is used for data flag, 63 bit for data.
class AtomicQ63
{
public:
	typedef int64_t Data;
	AtomicQ63() { memset(this, 0, sizeof(*this)); }
	bool push(const Data d, bool try_more = false)
	{
		auto cur = buf.load();
		return Empty(cur) && buf.compare_exchange_strong(cur, Enc(d));
	}
	bool pop(Data &d, bool try_more = false)
	{
		Data cur = buf.load();
		bool r = !Empty(cur) && buf.compare_exchange_strong(cur, 0);
		if (r) { d = Dec(cur); }
		return r;
	}

private:
	static inline bool Empty(const Data d) { return (d & 1) == 0; } // lowest bit 1 means data ok.
	static inline Data Enc(const Data d) { return (d << 1) | 1; }   // lowest bit 1 means data ok.
	static inline Data Dec(const Data d) { return d >> 1; }         // lowest bit 1 means data ok.

	typedef std::atomic<Data> AData;
	static_assert(sizeof(Data) == sizeof(AData));

	AData buf;
};

// atomic request-reply process, one cycle a time.
class AtomicReqRep
{
public:
	typedef int64_t Data;
	typedef std::function<Data(const Data)> Handler;
	bool ClientRequest(const Data request, Data &reply);
	bool ServerProcess(Handler onReq);
	AtomicReqRep() :
	    data_(0), timestamp_(now()) {}

private:
	enum State {
		eStateFree,
		eStateRequest,
		eStateReply
	};
	static int GetState(Data d) { return d & MaskBits(3); }
	static Data Encode(Data d, State st) { return (d << 3) | st; }
	static Data Decode(Data d) { return d >> 3; }
	typedef std::chrono::steady_clock steady_clock;
	typedef steady_clock::duration Duration;
	static Duration now() { return steady_clock::now().time_since_epoch(); }

	bool DataCas(Data expected, Data val) { return data_.compare_exchange_strong(expected, val); }
	std::atomic<Data> data_;
	std::atomic<Duration> timestamp_;
};

} // namespace robust
#endif // end of include guard: ROBUST_Q31RCWYU