// AUTOGENERATED COPYRIGHT HEADER START
// Copyright (C) 2023 Michael Fabian 'Xaymar' Dirks <info@xaymar.com>
// AUTOGENERATED COPYRIGHT HEADER END

#pragma once
#include "util/util-singleton.hpp"

#include "warning-disable.hpp"
#include <functional>
#include <list>
#include <map>
#include <memory>
#include <mutex>
#include "warning-enable.hpp"

namespace streamfx::util {
	class poolbase {
		public:
		virtual ~poolbase(){};

		protected:
		virtual void reset(void* ptr){};
	};

	/** Simple pool for objects of a single type.
	 * 
	 */
	template<class _self, class _type, uint64_t _lifetime>
	class pool : public poolbase, public streamfx::util::singleton<_self> {
		typedef std::chrono::high_resolution_clock::time_point _time;
		typedef _type*                                         _ptr;
		typedef std::shared_ptr<_type>                         _tracked;

		friend _tracked;
		friend streamfx::util::singleton<_self>;

		std::list<std::pair<_time, _ptr>> _pool;
		std::mutex                        _lock;

		public:
		~pool()
		{
			std::unique_lock<decltype(_lock)> lock(_lock);
			for (auto kv : _pool) {
				delete kv.second;
			}
		}

		protected:
		pool(void) {}

		void release(_ptr ptr)
		{
			std::unique_lock<decltype(_lock)> lock(_lock);

			_time now = std::chrono::high_resolution_clock::now();

			// Insert the released object into the pool.
			_pool.emplace_front(std::pair<_time, _ptr>{now, ptr});
			reset(ptr);

			// Clean up any stragglers that exceeded their time limit.
			for (auto pit = _pool.begin(); pit != _pool.end();) {
				if ((pit->first - now) >= std::chrono::milliseconds(_lifetime)) {
					delete pit->second; // Internal object is untracked.
					pit = _pool.erase(pit);
				} else {
					pit++;
				}
			}
		}

		public:
		template<class... _valuetypes>
		_tracked acquire(_valuetypes&&... _values)
		{
			std::unique_lock<decltype(_lock)> lock(_lock);

			// Try and find a free object.
			_ptr ptr = nullptr;
			if (_pool.size() > 0) {
				ptr = _pool.front().second;
				_pool.pop_front();
			}

			// If there was no usable object, create a new one.
			if (!ptr) {
				ptr = new _type(std::forward<_valuetypes>(_values)...);
			}

			// Generate a shared pointer which automatically releases the object back to the pool after the end of use.
			auto self = this->shared_from_this();
			return std::shared_ptr<_type>(ptr, [self](_type* v) { self->release(v); });
		}
	};

	/** Generic template for resource pooling with lifetimes.
	 *
	 * Declaration / Definition:
	 *     class example {
	 *       ...
	 *       public:
	 *       class pool;
	 *       typedef example_type_t _pool_key_t;
	 *       typedef streamfx::util::pool<example::pool, example, 1000, _pool_key_t> _pool_t;
	 *       class pool : public _pool_t {
	 *         friend streamfx::util::singleton<example::pool>;
	 *         protected:
	 *         pool() : _pool_t() {}
	 *
	 *         static _pool_key_t as_key(example*) {...}
	 *         static _pool_key_t as_key(example_type_t) {...}
	 *       };
	 *     };
	 *
	 * Usage:
	 *     auto inst = example::pool::instance()->acquire(...);
	 *
	 * The returned pointer will keep a reference to the pool, and automatically release back into it when needed.
	 */
	template<class _self, class _type, uint64_t _lifetime, typename _key>
	class multipool : public poolbase, public streamfx::util::singleton<_self> {
		typedef std::chrono::high_resolution_clock::time_point _time;
		typedef _type*                                         _ptr;
		typedef std::shared_ptr<_type>                         _tracked;

		friend _tracked;
		friend streamfx::util::singleton<_self>;

		std::map<_key, std::list<std::pair<_time, _ptr>>> _pool;
		std::mutex                                        _lock;

		public:
		~multipool()
		{
			std::unique_lock<decltype(_lock)> lock(_lock);
			for (auto kv : _pool) {
				for (auto lv : kv.second) {
					delete lv.second;
				}
			}
		}

		protected:
		multipool(void) : _pool(), _lock() {}

		void release(_ptr ptr)
		{
			std::unique_lock<decltype(_lock)> lock(_lock);

			_time now = std::chrono::high_resolution_clock::now();

			// Re-insert the released object into the pool(s).
			auto hash = _self::as_key(ptr);
			if (auto kv = _pool.find(hash); kv != _pool.end()) {
				kv->second.emplace_front(now, ptr);
			} else {
				_pool.emplace(hash, std::list<std::pair<_time, _ptr>>{{now, ptr}});
			}
			reset(ptr);

			// Clean up any stragglers that exceeded their time limit.
			for (auto pit = _pool.begin(); pit != _pool.end();) {
				for (auto lit = pit->second.begin(); lit != pit->second.end();) {
					if ((lit->first - now) >= std::chrono::milliseconds(_lifetime)) {
						delete lit->second; // Internal object is untracked.
						lit = pit->second.erase(lit);
					} else {
						lit++;
					}
				}

				// Delete any empty lists from memory.
				if (pit->second.empty()) {
					pit = _pool.erase(pit);
				} else {
					pit++;
				}
			}
		}

		public:
		template<class... _valuetypes>
		_tracked acquire(_valuetypes&&... _values)
		{
			std::unique_lock<decltype(_lock)> lock(_lock);

			// Try and find an existing pool, and a free object.
			_ptr ptr  = nullptr;
			auto hash = _self::as_key(std::forward<_valuetypes>(_values)...);
			if (auto kv = _pool.find(hash); kv != _pool.cend()) {
				if (kv->second.size() > 0) {
					ptr = kv->second.front().second;
					kv->second.pop_front();
				}
			}

			// If there was no usable object, create a new one.
			if (!ptr) {
				ptr = new _type(std::forward<_valuetypes>(_values)...);
			}

			// Generate a shared pointer which automatically releases the object back to the pool after the end of use.
			auto self = this->shared_from_this();
			return std::shared_ptr<_type>(ptr, [self](_type* v) { self->release(v); });
		}
	};
} // namespace streamfx::util