#pragma once

#include <intrin.h>
#include <windows.h>

class rw_lock {
private:
	volatile long m_requests, m_completions;

	static long atomic_clear_add(volatile long *dest, long clrmask, long val) {
		long cmp, exch, oldval = *dest;

		do {
			cmp = oldval;
			exch = (oldval & ~clrmask) + val;
		} while((oldval = _InterlockedCompareExchange(dest, exch, cmp)) != cmp);

		return oldval;
	}

	static void sleep_heuristic(unsigned int tries) {
		if(tries < 1000) {
#if defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x0400
			SwitchToThread();
#else
			Sleep(0);
#endif
		}
		else Sleep((tries < 2000) ? 100 : 1000);
	}

public:
	rw_lock() : m_requests(0),m_completions(0) {}

	class scoped_read_lock {
	private:
		rw_lock &m_lock;
		bool m_locked;

	public:
		scoped_read_lock(rw_lock &m, bool lock = true) : m_lock(m),m_locked(false) {
			if(lock) this->lock();
		}
		~scoped_read_lock() {
			if(m_locked) this->unlock();
		}

		void lock() {
			if(m_locked) return;

			unsigned int ticket = atomic_clear_add(&m_lock.m_requests, 0x80000000, 0x10000) & 0xffff;

			unsigned int tries = 0;
			while((m_lock.m_completions & 0xffff) != ticket) {
				sleep_heuristic(++tries);
			}

			m_locked = true;
		}

		void unlock() {
			if(!m_locked) return;

			atomic_clear_add(&m_lock.m_completions, 0x80000000, 0x10000);

			m_locked = false;
		}

		bool locked() const { return m_locked; }
	};

	class scoped_write_lock {
	private:
		rw_lock &m_lock;
		bool m_locked;

	public:
		scoped_write_lock(rw_lock &m, bool lock = true) : m_lock(m),m_locked(false) {
			if(lock) this->lock();
		}
		~scoped_write_lock() {
			if(m_locked) this->unlock();
		}

		void lock() {
			if(m_locked) return;

			unsigned int ticket = atomic_clear_add(&m_lock.m_requests, 0x8000, 1);

			unsigned int tries = 0;
			while(m_lock.m_completions != ticket) {
				sleep_heuristic(++tries);
			}

			m_locked = true;
		}

		void unlock() {
			if(!m_locked) return;

			atomic_clear_add(&m_lock.m_completions, 0x8000, 1);

			m_locked = false;
		}

		bool locked() const { return m_locked; }
	};
};