/*
 * =====================================================================================
 *
 *       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 <atomic>
#include <chrono>
#include <memory>
#include <string.h>
#include <string>
#include <sys/types.h>
#include <unistd.h>

namespace robust
{

using namespace std::chrono;
using namespace std::chrono_literals;
constexpr uint64_t MaskBits(int nbits) { return (uint64_t(1) << nbits) - 1; }

void QuickSleep();

class RobustReqRep
{
	typedef uint32_t State;
	typedef std::string Msg;
	typedef std::chrono::steady_clock::duration Duration;

public:
	enum ErrorCode {
		eSuccess = 0,
		eTimeout = EAGAIN,
		eSizeError = EINVAL,
	};

	explicit RobustReqRep(const uint32_t max_len) :
	    capacity_(max_len), state_(eStateInit), timestamp_(Duration(0)), size_(0) {}

	void PutReady() { state_.store(eStateReady); }
	bool Ready() const { return state_.load() == eStateReady; }
	uint32_t capacity() const { return capacity_; }

	int ClientRequest(const Msg &request, Msg &reply)
	{
		int r = ClientWriteRequest(request);
		if (r == eSuccess) {
			r = ClientReadReply(reply);
		}
		return r;
	}
	int ClientReadReply(Msg &reply);
	int ClientWriteRequest(const Msg &request);
	int ServerReadRequest(Msg &request);
	int ServerWriteReply(const Msg &reply);

private:
	RobustReqRep(const RobustReqRep &);
	RobustReqRep(RobustReqRep &&);
	RobustReqRep &operator=(const RobustReqRep &) = delete;
	RobustReqRep &operator=(RobustReqRep &&) = delete;

	enum {
		eStateInit = 0,
		eStateReady = 0x19833891,
		eClientWriteBegin,
		eClientWriteEnd,
		eServerReadBegin,
		eServerReadEnd,
		eServerWriteBegin,
		eServerWriteEnd,
		eClientReadBegin,
		eClientReadEnd = eStateReady,
	};
	bool StateCas(State exp, State val);
	void Write(const Msg &msg)
	{
		size_.store(msg.size());
		memcpy(buf, msg.data(), msg.size());
	}
	void Read(Msg &msg) { msg.assign(buf, size_.load()); }

	const uint32_t capacity_;
	std::atomic<State> state_;
	static_assert(sizeof(State) == sizeof(state_), "atomic should has no extra data.");
	std::atomic<Duration> timestamp_;
	std::atomic<int32_t> size_;
	char buf[4];
};

class PidLocker
{
public:
	typedef int locker_t;
	static locker_t this_locker()
	{
		static locker_t val = getpid();
		return val;
	}
	static bool is_alive(locker_t locker) { return true; }
};

class RobustPidLocker
{
public:
	typedef int locker_t;
	static locker_t this_locker()
	{
		static locker_t val = getpid();
		return val;
	}
	static bool is_alive(locker_t locker)
	{
		char buf[64] = {0};
		snprintf(buf, sizeof(buf) - 1, "/proc/%d/stat", locker);
		return access(buf, F_OK) == 0;
	}
};

template <class LockerT>
class CasMutex
{
	typedef typename LockerT::locker_t locker_t;
	static inline locker_t this_locker() { return LockerT::this_locker(); }
	static inline bool is_alive(locker_t locker) { return LockerT::is_alive(locker); }

public:
	CasMutex() :
	    meta_(0) {}
	int try_lock()
	{
		const auto t = steady_clock::now().time_since_epoch().count();
		auto old = meta_.load();
		int r = 0;
		if (!Locked(old)) {
			r = MetaCas(old, Meta(1, this_locker()));
		} else if (!is_alive(Locker(old))) {
			r = static_cast<int>(MetaCas(old, Meta(1, this_locker()))) << 1;
			if (r) {
				printf("captured pid %d -> %d, r = %d\n", Locker(old), this_locker(), r);
			}
		}
		return r;
	}
	int lock()
	{
		int r = 0;
		do {
			r = try_lock();
		} while (r == 0);
		return r;
	}
	void unlock()
	{
		auto old = meta_.load();
		if (Locked(old) && Locker(old) == this_locker()) {
			MetaCas(old, Meta(0, this_locker()));
		}
	}

private:
	static_assert(sizeof(locker_t) < sizeof(uint64_t), "locker size must be smaller than 64 bit!");
	std::atomic<uint64_t> meta_;
	bool Locked(uint64_t meta) { return (meta >> 63) != 0; }
	locker_t Locker(uint64_t meta) { return meta & MaskBits(sizeof(locker_t) * 8); }
	uint64_t Meta(uint64_t lk, locker_t lid) { return (lk << 63) | lid; }
	bool MetaCas(uint64_t exp, uint64_t val) { return meta_.compare_exchange_strong(exp, val); }
};

typedef CasMutex<RobustPidLocker> Mutex;

template <class Lock>
class Guard
{
public:
	Guard(Lock &l) :
	    l_(l) { l_.lock(); }
	~Guard() { l_.unlock(); }

private:
	Guard(const Guard &);
	Guard(Guard &&);
	Lock &l_;
};

template <class D, class Alloc = std::allocator<D>>
class CircularBuffer
{
	typedef uint32_t size_type;
	typedef uint32_t count_type;
	typedef uint64_t meta_type;
	static size_type Pos(meta_type meta) { return meta & 0xFFFFFFFF; }
	static count_type Count(meta_type meta) { return meta >> 32; }
	static size_type Meta(meta_type count, size_type pos) { return (count << 32) | pos; }

public:
	typedef D Data;

	CircularBuffer(const size_type cap) :
	    CircularBuffer(cap, Alloc()) {}
	CircularBuffer(const size_type cap, Alloc const &al) :
	    state_(0), capacity_(cap), mhead_(0), mtail_(0), al_(al), buf(al_.allocate(cap))
	{
		if (!buf) {
			throw("robust CircularBuffer allocate error: alloc buffer failed, out of mem!");
		}
	}
	~CircularBuffer() { al_.deallocate(buf, capacity_); }

	size_type size() const { return (capacity_ + tail() - head()) % capacity_; }
	bool full() const { return (capacity_ + tail() + 1 - head()) % capacity_ == 0; }
	bool empty() const { return head() == tail(); }
	bool push_back(Data d)
	{
		Guard<Mutex> guard(mutex_);
		if (!full()) {
			auto old = mtail();
			buf[Pos(old)] = d;
			return mtail_.compare_exchange_strong(old, next(old));
		} else {
			return false;
		}
	}
	bool pop_front(Data &d)
	{
		Guard<Mutex> guard(mutex_);
		if (!empty()) {
			auto old = mhead();
			d = buf[Pos(old)];
			return mhead_.compare_exchange_strong(old, next(old));
		} else {
			return false;
		}
	}
	bool Ready() const { return state_.load() == eStateReady; }
	void PutReady() { state_.store(eStateReady); }

private:
	CircularBuffer(const CircularBuffer &);
	CircularBuffer(CircularBuffer &&);
	CircularBuffer &operator=(const CircularBuffer &) = delete;
	CircularBuffer &operator=(CircularBuffer &&) = delete;

	meta_type next(meta_type meta) const { return Meta(Count(meta) + 1, (Pos(meta) + 1) % capacity_); }
	size_type head() const { return Pos(mhead()); }
	size_type tail() const { return Pos(mtail()); }
	meta_type mhead() const { return mhead_.load(); }
	meta_type mtail() const { return mtail_.load(); }
	// data
	enum { eStateReady = 0x19833891 };
	std::atomic<uint32_t> state_;
	const size_type capacity_;
	Mutex mutex_;
	std::atomic<meta_type> mhead_;
	std::atomic<meta_type> mtail_;
	Alloc al_;
	typename Alloc::pointer buf = nullptr;
};

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