/* Copyright (C) 2016 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. 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 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. 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 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef INCLUDED_SPATIAL
#define INCLUDED_SPATIAL

#include "simulation2/serialization/SerializeTemplates.h"

/**
 * A very basic subdivision scheme for finding items in ranges.
 * Items are stored in lists in dynamic-sized divisions.
 * Items have a size (min/max values of their axis-aligned bounding box)
 * and are stored in all divisions overlapping that area.
 *
 * It is the caller's responsibility to ensure items are only added
 * once, aren't removed unless they've been added, etc, and that
 * Move/Remove are called with the same coordinates originally passed
 * to Add (since this class doesn't remember which divisions an item
 * occupies).
 */
class SpatialSubdivision
{
	struct SubDivisionGrid
	{
		std::vector<uint32_t> items;

		inline void push_back(uint32_t value)
		{
			items.push_back(value);
		}

		inline void erase(int index)
		{
			// Delete by swapping with the last element then popping
			if ((int)items.size() > 1) // but only if we have more than 1 elements
				items[index] = items.back();
			items.pop_back();
		}

		void copy_items_at_end(std::vector<uint32_t>& out) const
		{
			out.insert(out.end(), items.begin(), items.end());
		}
	};


	entity_pos_t m_DivisionSize;
	SubDivisionGrid* m_Divisions;
	uint32_t m_DivisionsW;
	uint32_t m_DivisionsH;

	friend struct SerializeSpatialSubdivision;

public:
	SpatialSubdivision() : m_Divisions(NULL), m_DivisionsW(0), m_DivisionsH(0)
	{
	}
	~SpatialSubdivision()
	{
		delete[] m_Divisions;
	}
	SpatialSubdivision(const SpatialSubdivision& rhs)
	{
		m_DivisionSize = rhs.m_DivisionSize;
		m_DivisionsW = rhs.m_DivisionsW;
		m_DivisionsH = rhs.m_DivisionsH;
		size_t n = m_DivisionsW * m_DivisionsH;
		m_Divisions = new SubDivisionGrid[n];
		for (size_t i = 0; i < n; ++i)
			m_Divisions[i] = rhs.m_Divisions[i]; // just fall back to piecemeal copy
	}
	SpatialSubdivision& operator=(const SpatialSubdivision& rhs)
	{
		if (this != &rhs)
		{
			m_DivisionSize = rhs.m_DivisionSize;
			size_t n = rhs.m_DivisionsW * rhs.m_DivisionsH;
			if (m_DivisionsW != rhs.m_DivisionsW || m_DivisionsH != rhs.m_DivisionsH)
				Create(n); // size changed, recreate
			
			m_DivisionsW = rhs.m_DivisionsW;
			m_DivisionsH = rhs.m_DivisionsH;
			for (size_t i = 0; i < n; ++i)
				m_Divisions[i] = rhs.m_Divisions[i]; // just fall back to piecemeal copy
		}
		return *this;
	}

	inline entity_pos_t GetDivisionSize() const { return m_DivisionSize; }
	inline uint32_t GetWidth() const { return m_DivisionsW; }
	inline uint32_t GetHeight() const { return m_DivisionsH; }

	void Create(size_t count)
	{
		delete[] m_Divisions;
		m_Divisions = new SubDivisionGrid[count];
	}

	/**
	 * Equivalence test (ignoring order of items within each subdivision)
	 */
	bool operator==(const SpatialSubdivision& rhs) const
	{
		if (m_DivisionSize != rhs.m_DivisionSize || m_DivisionsW != rhs.m_DivisionsW || m_DivisionsH != rhs.m_DivisionsH)
			return false;
		
		uint32_t n = m_DivisionsH * m_DivisionsW;
		for (uint32_t i = 0; i < n; ++i)
		{
			if (m_Divisions[i].items.size() != rhs.m_Divisions[i].items.size())
				return false;

			// don't bother optimizing this, this is only used in the TESTING SUITE
			std::vector<uint32_t> a = m_Divisions[i].items;
			std::vector<uint32_t> b = rhs.m_Divisions[i].items;
			std::sort(a.begin(), a.end());
			std::sort(b.begin(), b.end());
			if (a != b)
				return false;
		}
		return true;
	}

	inline bool operator!=(const SpatialSubdivision& rhs) const
	{
		return !(*this == rhs);
	}

	void Reset(entity_pos_t maxX, entity_pos_t maxZ, entity_pos_t divisionSize)
	{
		m_DivisionSize = divisionSize;
		m_DivisionsW = (maxX / m_DivisionSize).ToInt_RoundToInfinity();
		m_DivisionsH = (maxZ / m_DivisionSize).ToInt_RoundToInfinity();

		Create(m_DivisionsW * m_DivisionsH);
	}


	/**
	 * Add an item with the given 'to' size.
	 * The item must not already be present.
	 */
	void Add(uint32_t item, CFixedVector2D toMin, CFixedVector2D toMax)
	{
		ENSURE(toMin.X <= toMax.X && toMin.Y <= toMax.Y);

		u32 i0 = GetI0(toMin.X);
		u32 j0 = GetJ0(toMin.Y);
		u32 i1 = GetI1(toMax.X);
		u32 j1 = GetJ1(toMax.Y);
		for (u32 j = j0; j <= j1; ++j)
		{
			for (u32 i = i0; i <= i1; ++i)
			{
				m_Divisions[i + j*m_DivisionsW].push_back(item);
			}
		}
	}

	/**
	 * Remove an item with the given 'from' size.
	 * The item should already be present.
	 * The size must match the size that was last used when adding the item.
	 */
	void Remove(uint32_t item, CFixedVector2D fromMin, CFixedVector2D fromMax)
	{
		ENSURE(fromMin.X <= fromMax.X && fromMin.Y <= fromMax.Y);

		u32 i0 = GetI0(fromMin.X);
		u32 j0 = GetJ0(fromMin.Y);
		u32 i1 = GetI1(fromMax.X);
		u32 j1 = GetJ1(fromMax.Y);
		for (u32 j = j0; j <= j1; ++j)
		{
			for (u32 i = i0; i <= i1; ++i)
			{
				SubDivisionGrid& div = m_Divisions[i + j*m_DivisionsW];
				int size = div.items.size();
				for (int n = 0; n < size; ++n)
				{
					if (div.items[n] == item)
					{
						div.erase(n);
						break;
					}
				}
			}
		}
	}

	/**
	 * Equivalent to Remove() then Add(), but potentially faster.
	 */
	void Move(uint32_t item, CFixedVector2D fromMin, CFixedVector2D fromMax, CFixedVector2D toMin, CFixedVector2D toMax)
	{
		// Skip the work if we're staying in the same divisions
		if (GetIndex0(fromMin) == GetIndex0(toMin) && GetIndex1(fromMax) == GetIndex1(toMax))
			return;

		Remove(item, fromMin, fromMax);
		Add(item, toMin, toMax);
	}

	/**
	 * Convenience function for Add() of individual points.
	 * (Note that points on a boundary may occupy multiple divisions.)
	 */
	void Add(uint32_t item, CFixedVector2D to)
	{
		Add(item, to, to);
	}

	/**
	 * Convenience function for Remove() of individual points.
	 */
	void Remove(uint32_t item, CFixedVector2D from)
	{
		Remove(item, from, from);
	}

	/**
	 * Convenience function for Move() of individual points.
	 */
	void Move(uint32_t item, CFixedVector2D from, CFixedVector2D to)
	{
		Move(item, from, from, to, to);
	}

	/**
	 * Returns a sorted list of unique items that includes all items
	 * within the given axis-aligned square range.
	 */
	void GetInRange(std::vector<uint32_t>& out, CFixedVector2D posMin, CFixedVector2D posMax) const
	{
		out.clear();
		ENSURE(posMin.X <= posMax.X && posMin.Y <= posMax.Y);

		u32 i0 = GetI0(posMin.X);
		u32 j0 = GetJ0(posMin.Y);
		u32 i1 = GetI1(posMax.X);
		u32 j1 = GetJ1(posMax.Y);
		for (u32 j = j0; j <= j1; ++j)
		{
			for (u32 i = i0; i <= i1; ++i)
			{
				m_Divisions[i + j*m_DivisionsW].copy_items_at_end(out);
			}
		}
		// some buildings span several tiles, so we need to make it unique
		std::sort(out.begin(), out.end());
		out.erase(std::unique(out.begin(), out.end()), out.end());
	}

	/**
	 * Returns a sorted list of unique items that includes all items
	 * within the given circular distance of the given point.
	 */
	void GetNear(std::vector<uint32_t>& out, CFixedVector2D pos, entity_pos_t range) const
	{
		// TODO: be cleverer and return a circular pattern of divisions,
		// not this square over-approximation
		CFixedVector2D r(range, range);
		GetInRange(out, pos - r, pos + r);
	}

private:
	// Helper functions for translating coordinates into division indexes
	// (avoiding out-of-bounds accesses, and rounding correctly so that
	// points precisely between divisions are counted in both):

	uint32_t GetI0(entity_pos_t x) const
	{
		return Clamp((x / m_DivisionSize).ToInt_RoundToInfinity()-1, 0, (int)m_DivisionsW-1);
	}

	uint32_t GetJ0(entity_pos_t z) const
	{
		return Clamp((z / m_DivisionSize).ToInt_RoundToInfinity()-1, 0, (int)m_DivisionsH-1);
	}

	uint32_t GetI1(entity_pos_t x) const
	{
		return Clamp((x / m_DivisionSize).ToInt_RoundToNegInfinity(), 0, (int)m_DivisionsW-1);
	}

	uint32_t GetJ1(entity_pos_t z) const
	{
		return Clamp((z / m_DivisionSize).ToInt_RoundToNegInfinity(), 0, (int)m_DivisionsH-1);
	}

	uint32_t GetIndex0(CFixedVector2D pos) const
	{
		return GetI0(pos.X) + GetJ0(pos.Y)*m_DivisionsW;
	}

	uint32_t GetIndex1(CFixedVector2D pos) const
	{
		return GetI1(pos.X) + GetJ1(pos.Y)*m_DivisionsW;
	}
};

/**
 * Serialization helper template for SpatialSubdivision
 */
struct SerializeSpatialSubdivision
{
	void operator()(ISerializer& serialize, const char* UNUSED(name), SpatialSubdivision& value)
	{
		serialize.NumberFixed_Unbounded("div size", value.m_DivisionSize);
		serialize.NumberU32_Unbounded("divs w", value.m_DivisionsW);
		serialize.NumberU32_Unbounded("divs h", value.m_DivisionsH);

		size_t count = value.m_DivisionsH * value.m_DivisionsW;
		for (size_t i = 0; i < count; ++i)
			SerializeVector<SerializeU32_Unbounded>()(serialize, "subdiv items", value.m_Divisions[i].items);
	}

	void operator()(IDeserializer& serialize, const char* UNUSED(name), SpatialSubdivision& value)
	{
		serialize.NumberFixed_Unbounded("div size", value.m_DivisionSize);
		serialize.NumberU32_Unbounded("divs w", value.m_DivisionsW);
		serialize.NumberU32_Unbounded("divs h", value.m_DivisionsH);

		size_t count = value.m_DivisionsW * value.m_DivisionsH;
		value.Create(count);
		for (size_t i = 0; i < count; ++i)
			SerializeVector<SerializeU32_Unbounded>()(serialize, "subdiv items", value.m_Divisions[i].items);
	}
};


/**
 * A basic square subdivision scheme for finding entities in range
 * More efficient than SpatialSubdivision, but a bit less precise 
 * (so the querier will get more entities to perform tests on).
 *
 * Items are stored in vectors in fixed-size divisions.
 *
 * Items have a size (min/max values of their axis-aligned bounding box).
 * If that size is higher than a subdivision's size, they're stored in the "general" vector
 * This means that if too many objects have a size that's big, it'll end up being slow
 * We want subdivisions to be as small as possible yet contain as many items as possible.
 *
 * It is the caller's responsibility to ensure items are only added once, aren't removed 
 * unless they've been added, etc, and that Move/Remove are called with the same coordinates
 * originally passed to Add (since this class doesn't remember which divisions an item
 * occupies).
 *
 * TODO: If a unit size were to change, it would need to be updated (that doesn't happen for now)
 */
class FastSpatialSubdivision
{
private:
	static const int SUBDIVISION_SIZE = 20; // bigger than most buildings and entities

	std::vector<entity_id_t> m_OverSizedData;
	std::vector<entity_id_t>* m_SpatialDivisionsData;	// fixed size array of subdivisions
	size_t m_ArrayWidth; // number of columns in m_SpatialDivisionsData

	inline size_t Index(fixed position) const
	{
		return Clamp((position / SUBDIVISION_SIZE).ToInt_RoundToZero(), 0, (int)m_ArrayWidth-1);
	}

	inline size_t SubdivisionIdx(CFixedVector2D position) const
	{
		return Index(position.X) + Index(position.Y)*m_ArrayWidth;
	}

	/**
	 * Efficiently erase from a vector by swapping with the last element and popping it.
	 * Returns true if the element was found and erased, else returns false.
	 */
	bool EraseFrom(std::vector<entity_id_t>& vector, entity_id_t item)
	{
		std::vector<entity_id_t>::iterator it = std::find(vector.begin(), vector.end(), item);
		if (it == vector.end())
			return false;

		*it = vector.back();
		vector.pop_back();
		return true;
	}

public:
	FastSpatialSubdivision() : 
		m_SpatialDivisionsData(NULL), m_ArrayWidth(0) 
	{
	}

	FastSpatialSubdivision(const FastSpatialSubdivision& other) : 
		m_SpatialDivisionsData(NULL), m_ArrayWidth(0)
	{
		Reset(other.m_ArrayWidth);
		std::copy(&other.m_SpatialDivisionsData[0], &other.m_SpatialDivisionsData[m_ArrayWidth*m_ArrayWidth], m_SpatialDivisionsData);
	}

	~FastSpatialSubdivision()
	{
		delete[] m_SpatialDivisionsData;
	}

	void Reset(size_t arrayWidth)
	{
		delete[] m_SpatialDivisionsData;

		m_ArrayWidth = arrayWidth;
		m_SpatialDivisionsData = new std::vector<entity_id_t>[m_ArrayWidth*m_ArrayWidth];
		m_OverSizedData.clear();
	}

	void Reset(fixed w, fixed h)
	{
		ENSURE(w >= fixed::Zero() && h >= fixed::Zero());
		size_t arrayWidth = std::max((w / SUBDIVISION_SIZE).ToInt_RoundToZero(), (h / SUBDIVISION_SIZE).ToInt_RoundToZero()) + 1;
		Reset(arrayWidth);
	}

	FastSpatialSubdivision& operator=(const FastSpatialSubdivision& other)
	{
		if (this != &other)
		{
			Reset(other.m_ArrayWidth);
			std::copy(&other.m_SpatialDivisionsData[0], &other.m_SpatialDivisionsData[m_ArrayWidth*m_ArrayWidth], m_SpatialDivisionsData);
		}
		return *this;
	}

	bool operator==(const FastSpatialSubdivision& other) const
	{
		if (m_ArrayWidth != other.m_ArrayWidth)
			return false;
		if (m_OverSizedData != other.m_OverSizedData)
			return false;
		for (size_t idx = 0; idx < m_ArrayWidth*m_ArrayWidth; ++idx)
			if (m_SpatialDivisionsData[idx] != other.m_SpatialDivisionsData[idx])
				return false;
		return true;
	}

	inline bool operator!=(const FastSpatialSubdivision& rhs) const
	{
		return !(*this == rhs);
	}

	/**
	 * Add an item.
	 */
	void Add(entity_id_t item, CFixedVector2D position, u32 size)
	{
		if (size > SUBDIVISION_SIZE)
		{
			if (std::find(m_OverSizedData.begin(), m_OverSizedData.end(), item) == m_OverSizedData.end())
				m_OverSizedData.push_back(item);
		}
		else 
		{
			std::vector<entity_id_t>& subdivision = m_SpatialDivisionsData[SubdivisionIdx(position)];
			if (std::find(subdivision.begin(), subdivision.end(), item) == subdivision.end())
				subdivision.push_back(item);
		}
	}

	/**
	 * Remove an item.
	 * Position must be where we expect to find it, or we won't find it.
	 */
	void Remove(entity_id_t item, CFixedVector2D position, u32 size)
	{
		if (size > SUBDIVISION_SIZE)
			EraseFrom(m_OverSizedData, item);
		else 
		{
			std::vector<entity_id_t>& subdivision = m_SpatialDivisionsData[SubdivisionIdx(position)];
			EraseFrom(subdivision, item);
		}
	}

	/**
	 * Equivalent to Remove() then Add(), but slightly faster.
	 * In particular for big objects nothing needs to be done.
	 */
	void Move(entity_id_t item, CFixedVector2D oldPosition, CFixedVector2D newPosition, u32 size)
	{		
		if (size > SUBDIVISION_SIZE)
			return;
		if (SubdivisionIdx(newPosition) == SubdivisionIdx(oldPosition))
			return;

		std::vector<entity_id_t>& oldSubdivision = m_SpatialDivisionsData[SubdivisionIdx(oldPosition)];
		if (EraseFrom(oldSubdivision, item))
		{
			std::vector<entity_id_t>& newSubdivision = m_SpatialDivisionsData[SubdivisionIdx(newPosition)];
			newSubdivision.push_back(item);
		}
	}

	/**
	 * Returns a (non sorted) list of items that are either in the square or close to it.
	 * It's the responsibility of the querier to do proper distance checking and entity sorting.
	 */
	void GetInRange(std::vector<entity_id_t>& out, CFixedVector2D posMin, CFixedVector2D posMax) const
	{
		size_t minX = Index(posMin.X);
		size_t minY = Index(posMin.Y);
		size_t maxX = Index(posMax.X) + 1;
		size_t maxY = Index(posMax.Y) + 1;

		// Now expand the subdivisions by one so we make sure we've got all elements potentially in range.
		// Also make sure min >= 0 and max <= width
		minX = minX > 0 ? minX-1 : 0;
		minY = minY > 0 ? minY-1 : 0;
		maxX = maxX < m_ArrayWidth ? maxX+1 : m_ArrayWidth;
		maxY = maxY < m_ArrayWidth ? maxY+1 : m_ArrayWidth;

		ENSURE(out.empty() && "GetInRange: out is not clean");

		// Add oversized items, they can be anywhere
		out.insert(out.end(), m_OverSizedData.begin(), m_OverSizedData.end());

		for (size_t Y = minY; Y < maxY; ++Y)
		{
			for (size_t X = minX; X < maxX; ++X)
			{
				std::vector<entity_id_t>& subdivision = m_SpatialDivisionsData[X + Y*m_ArrayWidth];
				if (!subdivision.empty())
					out.insert(out.end(), subdivision.begin(), subdivision.end());
			}
		}
	}

	/**
	 * Returns a (non sorted) list of items that are either in the circle or close to it.
	 * It's the responsibility of the querier to do proper distance checking and entity sorting.
	 */
	void GetNear(std::vector<entity_id_t>& out, CFixedVector2D pos, entity_pos_t range) const
	{
		// Because the subdivision size is rather big wrt typical ranges, 
		// this square over-approximation is hopefully not too bad.
		CFixedVector2D r(range, range);
		GetInRange(out, pos - r, pos + r);
	}

	size_t GetDivisionSize() const
	{
		return SUBDIVISION_SIZE;
	}

	size_t GetWidth() const 
	{ 
		return m_ArrayWidth; 
	}
};

#endif // INCLUDED_SPATIAL