/* Copyright 2015, Michele Santullo
 * This file is part of DoorKeeper.
 *
 * DoorKeeper is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * DoorKeeper is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with DoorKeeper.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef idBC27D8C2304944D0856C2C2B012AE57B
#define idBC27D8C2304944D0856C2C2B012AE57B

#include "doorkeeper/primitivetypes.hpp"
#include "doorkeeper/implem/saltedid.hpp"
#include <boost/numeric/interval.hpp>
#include <set>
#include <vector>
#include <algorithm>

namespace dk {
	namespace implem {
		template <typename I>
		class IDInterval {
		public:
			IDInterval ( I parFrom, I parTo ) :
				m_interval(parFrom, parTo)
			{
			}

			bool operator< ( const IDInterval& parOther ) const;
			I lower ( void ) const { return m_interval.lower(); }
			I upper ( void ) const { return m_interval.upper(); }

		private:
			boost::numeric::interval<I> m_interval;
		};
	} //namespace implem

	template <unsigned int Salt, unsigned int Indx>
	class IDManager {
	public:
		typedef SaltedID<Salt, Indx> value_type;
		typedef typename value_type::index_type index_type;

		enum {
			bit_count = sizeof(value_type) * CHAR_BIT
		};

		IDManager ( void );

		value_type allocate ( void );
		void free ( value_type parID );
		void reset ( void );

	private:
		typedef typename value_type::salt_type salt_type;
		using id_interval = implem::IDInterval<index_type>;
		using interval_set = std::set<id_interval>;

		interval_set m_free_intervals;
		std::vector<salt_type> m_salts;
	};

	namespace implem {
		template <typename I>
		bool IDInterval<I>::operator< ( const IDInterval& parOther) const {
			return (m_interval.lower() < parOther.m_interval.lower()) and
				(m_interval.upper() < parOther.m_interval.upper());
		}
	} //namespace implem

	template <unsigned int Salt, unsigned int Indx>
	IDManager<Salt, Indx>::IDManager() {
		m_free_intervals.insert(id_interval(1, value_type::max_index));
	}

	template <unsigned int Salt, unsigned int Indx>
	auto IDManager<Salt, Indx>::allocate() -> value_type {
		DK_ASSERT(not m_free_intervals.empty());
		auto first = *m_free_intervals.begin();
		auto free_id = first.lower();
		m_free_intervals.erase(m_free_intervals.begin());
		if (first.lower() + 1 <= first.upper()) {
			m_free_intervals.insert(typename interval_set::value_type(first.lower() + 1, first.upper()));
		}

		if (static_cast<index_type>(m_salts.size()) < free_id) {
			const auto old_size = m_salts.size();
			m_salts.resize(free_id);
			std::fill(m_salts.begin() + old_size, m_salts.end(), 0);
		}

		DK_ASSERT(free_id > 0);
		const auto salt_index = free_id - 1;
		if (m_salts[salt_index] < value_type::max_salt) {
			return value_type(free_id, m_salts[salt_index]++);
		}
		else {
			return value_type(free_id, m_salts[salt_index]);
		}
	}

	template <unsigned int Salt, unsigned int Indx>
	void IDManager<Salt, Indx>::free (value_type parID) {
		if (parID.salt() == value_type::max_salt)
			return;

		const auto id = parID.index();
		DK_ASSERT(id > 0);
		if (m_salts.size() < id or 0 == id)
			return;
		DK_ASSERT(parID.salt() == m_salts[id - 1] - 1);
		if (parID.salt() != m_salts[id - 1] - 1)
			return;

		auto it = m_free_intervals.find(id_interval(id, id));
		if (it != m_free_intervals.end() and it->lower() <= id and it->upper() > id) {
			return;
		}

		it = m_free_intervals.upper_bound(id_interval(id, id));
		if (m_free_intervals.end() == it) {
			return;
		}
		else {
			auto free_interval = *it;

			if (id + 1 != free_interval.lower()) {
				m_free_intervals.insert(id_interval(id, id));
			}
			else {
				if (m_free_intervals.begin() != it) {
					auto it_2 = it;
					--it_2;
					if (it_2->lower() + 1 == id) {
						auto free_interval_2 = *it_2;
						m_free_intervals.erase(it);
						m_free_intervals.erase(it_2);
						m_free_intervals.insert(id_interval(free_interval_2.lower(), free_interval.upper()));
					}
					else {
						m_free_intervals.erase(it);
						m_free_intervals.insert(id_interval(id, free_interval.lower()));
					}
				}
				else {
					m_free_intervals.erase(it);
					m_free_intervals.insert(id_interval(id, free_interval.upper()));
				}
			}
		}
	}

	template <unsigned int Salt, unsigned int Indx>
	void IDManager<Salt, Indx>::reset() {
		m_free_intervals.clear();
		m_free_intervals.insert(id_interval(1, value_type::max_index));
		m_salts.clear();
	}
} //namespace dk

#endif