//========= Copyright © 1996-2005, Valve Corporation, All rights reserved. ============//
//
// Purpose: 
//
// $NoKeywords: $
//
//=============================================================================//
// nav_pathfind.h
// Path-finding mechanisms using the Navigation Mesh
// Author: Michael S. Booth (mike@turtlerockstudios.com), January 2003

#ifndef _NAV_PATHFIND_H_
#define _NAV_PATHFIND_H_

//-------------------------------------------------------------------------------------------------------------------
/**
 * Used when building a path to determine the kind of path to build
 */
enum RouteType
{
	FASTEST_ROUTE,
	SAFEST_ROUTE,
};


//--------------------------------------------------------------------------------------------------------------
/**
 * Functor used with NavAreaBuildPath()
 */
class ShortestPathCost
{
public:
	float operator() ( CNavArea *area, CNavArea *fromArea, const CNavLadder *ladder )
	{
		if (fromArea == NULL)
		{
			// first area in path, no cost
			return 0.0f;
		}
		else
		{
			// compute distance travelled along path so far
			float dist;

			if (ladder)
				dist = ladder->m_length;
			else
				dist = (area->GetCenter() - fromArea->GetCenter()).Length();

			float cost = dist + fromArea->GetCostSoFar();

			// if this is a "crouch" area, add penalty
			if (area->GetAttributes() & NAV_MESH_CROUCH)
			{
				const float crouchPenalty = 20.0f;		// 10
				cost += crouchPenalty * dist;
			}

			// if this is a "jump" area, add penalty
			if (area->GetAttributes() & NAV_MESH_JUMP)
			{
				const float jumpPenalty = 5.0f;
				cost += jumpPenalty * dist;
			}

			return cost;
		}
	}
};

//--------------------------------------------------------------------------------------------------------------
/**
 * Find path from startArea to goalArea via an A* search, using supplied cost heuristic.
 * If cost functor returns -1 for an area, that area is considered a dead end.
 * This doesn't actually build a path, but the path is defined by following parent
 * pointers back from goalArea to startArea.
 * If 'closestArea' is non-NULL, the closest area to the goal is returned (useful if the path fails).
 * If 'goalArea' is NULL, will compute a path as close as possible to 'goalPos'.
 * If 'goalPos' is NULL, will use the center of 'goalArea' as the goal position.
 * Returns true if a path exists.
 */
template< typename CostFunctor >
bool NavAreaBuildPath( CNavArea *startArea, CNavArea *goalArea, const Vector *goalPos, CostFunctor &costFunc, CNavArea **closestArea = NULL )
{
	if (startArea == NULL)
		return false;

	if (goalArea != NULL && goalArea->IsBlocked())
		goalArea = NULL;

	if (goalArea == NULL && goalPos == NULL)
		return false;

	startArea->SetParent( NULL );

	// if we are already in the goal area, build trivial path
	if (startArea == goalArea)
	{
		goalArea->SetParent( NULL );
		return true;
	}

	// determine actual goal position
	Vector actualGoalPos = (goalPos) ? *goalPos : goalArea->GetCenter();

	// start search
	CNavArea::ClearSearchLists();

	// compute estimate of path length
	/// @todo Cost might work as "manhattan distance"
	startArea->SetTotalCost( (startArea->GetCenter() - actualGoalPos).Length() );

	float initCost = costFunc( startArea, NULL, NULL );	
	if (initCost < 0.0f)
		return false;
	startArea->SetCostSoFar( initCost );

	startArea->AddToOpenList();

	// keep track of the area we visit that is closest to the goal
	if (closestArea)
		*closestArea = startArea;
	float closestAreaDist = startArea->GetTotalCost();

	// do A* search
	while( !CNavArea::IsOpenListEmpty() )
	{
		// get next area to check
		CNavArea *area = CNavArea::PopOpenList();

		// don't consider blocked areas
		if ( area->IsBlocked() )
			continue;

		// check if we have found the goal area or position
		if (area == goalArea || (goalArea == NULL && goalPos && area->Contains( *goalPos )))
		{
			if (closestArea)
			{
				*closestArea = area;
			}

			return true;
		}

		// search adjacent areas
		bool searchFloor = true;
		int dir = NORTH;
		const NavConnectList *floorList = area->GetAdjacentList( NORTH );
		int floorIter = floorList->Head();

		bool ladderUp = true;
		const NavLadderConnectList *ladderList = NULL;
		int ladderIter = NavLadderConnectList::InvalidIndex();
		enum { AHEAD = 0, LEFT, RIGHT, BEHIND, NUM_TOP_DIRECTIONS };
		int ladderTopDir = AHEAD;

		while(true)
		{
			CNavArea *newArea;
			NavTraverseType how;
			const CNavLadder *ladder = NULL;

			//
			// Get next adjacent area - either on floor or via ladder
			//
			if (searchFloor)
			{
				// if exhausted adjacent connections in current direction, begin checking next direction
				if (floorIter == floorList->InvalidIndex())
				{
					++dir;

					if (dir == NUM_DIRECTIONS)
					{
						// checked all directions on floor - check ladders next
						searchFloor = false;

						ladderList = area->GetLadderList( CNavLadder::LADDER_UP );
						ladderIter = ladderList->Head();
						ladderTopDir = AHEAD;
					}
					else
					{
						// start next direction
						floorList = area->GetAdjacentList( (NavDirType)dir );
						floorIter = floorList->Head();
					}

					continue;
				}

				newArea = floorList->Element(floorIter).area;
				how = (NavTraverseType)dir;
				floorIter = floorList->Next( floorIter );
			}
			else	// search ladders
			{
				if (ladderIter == ladderList->InvalidIndex())
				{
					if (!ladderUp)
					{
						// checked both ladder directions - done
						break;
					}
					else
					{
						// check down ladders
						ladderUp = false;
						ladderList = area->GetLadderList( CNavLadder::LADDER_DOWN );
						ladderIter = ladderList->Head();
					}
					continue;
				}

				if (ladderUp)
				{
					ladder = ladderList->Element( ladderIter ).ladder;

					// do not use BEHIND connection, as its very hard to get to when going up a ladder
					if (ladderTopDir == AHEAD)
						newArea = ladder->m_topForwardArea;
					else if (ladderTopDir == LEFT)
						newArea = ladder->m_topLeftArea;
					else if (ladderTopDir == RIGHT)
						newArea = ladder->m_topRightArea;
					else
					{
						ladderIter = ladderList->Next( ladderIter );
						ladderTopDir = AHEAD;
						continue;
					}

					how = GO_LADDER_UP;
					++ladderTopDir;
				}
				else
				{
					newArea = ladderList->Element(ladderIter).ladder->m_bottomArea;
					how = GO_LADDER_DOWN;
					ladder = ladderList->Element(ladderIter).ladder;
					ladderIter = ladderList->Next( ladderIter );
				}

				if (newArea == NULL)
					continue;
			}

			// don't backtrack
			if (newArea == area)
				continue;

			// don't consider blocked areas
			if ( newArea->IsBlocked() )
				continue;

			float newCostSoFar = costFunc( newArea, area, ladder );

			// check if cost functor says this area is a dead-end
			if (newCostSoFar < 0.0f)
				continue;

			if ((newArea->IsOpen() || newArea->IsClosed()) && newArea->GetCostSoFar() <= newCostSoFar)
			{
				// this is a worse path - skip it
				continue;
			}
			else
			{
				// compute estimate of distance left to go
				float newCostRemaining = (newArea->GetCenter() - actualGoalPos).Length();

				// track closest area to goal in case path fails
				if (closestArea && newCostRemaining < closestAreaDist)
				{
					*closestArea = newArea;
					closestAreaDist = newCostRemaining;
				}
				
				newArea->SetParent( area, how );
				newArea->SetCostSoFar( newCostSoFar );
				newArea->SetTotalCost( newCostSoFar + newCostRemaining );

				if (newArea->IsClosed())
					newArea->RemoveFromClosedList();

				if (newArea->IsOpen())
				{
					// area already on open list, update the list order to keep costs sorted
					newArea->UpdateOnOpenList();
				}
				else
				{
					newArea->AddToOpenList();
				}
			}
		}

		// we have searched this area
		area->AddToClosedList();
	}

	return false;
}


//--------------------------------------------------------------------------------------------------------------
/**
 * Compute distance between two areas. Return -1 if can't reach 'endArea' from 'startArea'.
 */
template< typename CostFunctor >
float NavAreaTravelDistance( CNavArea *startArea, CNavArea *endArea, CostFunctor &costFunc )
{
	if (startArea == NULL)
		return -1.0f;

	if (endArea == NULL)
		return -1.0f;

	if (startArea == endArea)
		return 0.0f;

	// compute path between areas using given cost heuristic
	if (NavAreaBuildPath( startArea, endArea, NULL, costFunc ) == false)
		return -1.0f;

	// compute distance along path
	float distance = 0.0f;
	for( CNavArea *area = endArea; area->GetParent(); area = area->GetParent() )
	{
		distance += (area->GetCenter() - area->GetParent()->GetCenter()).Length();
	}

	return distance;
}


//--------------------------------------------------------------------------------------------------------------
/**
 * Compute travel distance along shortest path from startPos to goalPos. 
 * Return -1 if can't reach endPos from goalPos.
 */
template< typename CostFunctor >
float NavAreaTravelDistance( const Vector &startPos, const Vector &goalPos, CostFunctor &costFunc )
{
	CNavArea *startArea = TheNavMesh->GetNearestNavArea( startPos );
	if (startArea == NULL)
	{
		return -1.0f;
	}

	// compute path between areas using given cost heuristic
	CNavArea *goalArea = NULL;
	if (NavAreaBuildPath( startArea, NULL, &goalPos, costFunc, &goalArea ) == false)
	{
		return -1.0f;
	}

	// compute distance along path
	if (goalArea->GetParent() == NULL)
	{
		// both points are in the same area - return euclidean distance
		return (goalPos - startPos).Length();
	}
	else
	{
		CNavArea *area;
		float distance;

		// goalPos is assumed to be inside goalArea (or very close to it) - skip to next area
		area = goalArea->GetParent();
		distance = (goalPos - area->GetCenter()).Length();

		for( ; area->GetParent(); area = area->GetParent() )
		{
			distance += (area->GetCenter() - area->GetParent()->GetCenter()).Length();
		}

		// add in distance to startPos
		distance += (startPos - area->GetCenter()).Length();

		return distance;
	}
}


//--------------------------------------------------------------------------------------------------------------
/**
 * Do a breadth-first search, invoking functor on each area.
 * If functor returns 'true', continue searching from this area. 
 * If functor returns 'false', the area's adjacent areas are not explored (dead end).
 * If 'maxRange' is 0 or less, no range check is done (all areas will be examined).
 *
 * NOTE: Returns all areas that overlap range, even partially
 *
 * @todo Use ladder connections
 */

// helper function
inline void AddAreaToOpenList( CNavArea *area, CNavArea *parent, const Vector &startPos, float maxRange )
{
	if (area == NULL)
		return;

	if (!area->IsMarked())
	{
		area->Mark();
		area->SetTotalCost( 0.0f );
		area->SetParent( parent );

		if (maxRange > 0.0f)
		{
			// make sure this area overlaps range
			Vector closePos;
			area->GetClosestPointOnArea( startPos, &closePos );
			if ((closePos - startPos).AsVector2D().IsLengthLessThan( maxRange ))
			{
				// compute approximate distance along path to limit travel range, too
				float distAlong = parent->GetCostSoFar();
				distAlong += (area->GetCenter() - parent->GetCenter()).Length();
				area->SetCostSoFar( distAlong );

				// allow for some fudge due to large size areas
				if (distAlong <= 1.5f * maxRange)
					area->AddToOpenList();
			}
		}
		else
		{
			// infinite range
			area->AddToOpenList();
		}
	}
}


template < typename Functor >
void SearchSurroundingAreas( CNavArea *startArea, const Vector &startPos, Functor &func, float maxRange = -1.0f )
{
	if (startArea == NULL)
		return;

	CNavArea::MakeNewMarker();
	CNavArea::ClearSearchLists();

	startArea->AddToOpenList();
	startArea->SetTotalCost( 0.0f );
	startArea->SetCostSoFar( 0.0f );
	startArea->SetParent( NULL );
	startArea->Mark();

	while( !CNavArea::IsOpenListEmpty() )
	{
		// get next area to check
		CNavArea *area = CNavArea::PopOpenList();

		// don't use blocked areas
		if ( area->IsBlocked() )
			continue;

		// invoke functor on area
		if (func( area ))
		{
			// explore adjacent floor areas
			for( int dir=0; dir<NUM_DIRECTIONS; ++dir )
			{
				int count = area->GetAdjacentCount( (NavDirType)dir );
				for( int i=0; i<count; ++i )
				{
					CNavArea *adjArea = area->GetAdjacentArea( (NavDirType)dir, i );
					
					AddAreaToOpenList( adjArea, area, startPos, maxRange );
				}
			}


			// explore adjacent areas connected by ladders

			// check up ladders
			const NavLadderConnectList *ladderList = area->GetLadderList( CNavLadder::LADDER_UP );
			if (ladderList)
			{
				FOR_EACH_LL( (*ladderList), it )
				{
					const CNavLadder *ladder = (*ladderList)[ it ].ladder;

					// do not use BEHIND connection, as its very hard to get to when going up a ladder
					AddAreaToOpenList( ladder->m_topForwardArea, area, startPos, maxRange );
					AddAreaToOpenList( ladder->m_topLeftArea, area, startPos, maxRange );
					AddAreaToOpenList( ladder->m_topRightArea, area, startPos, maxRange );
				}
			}

			// check down ladders
			ladderList = area->GetLadderList( CNavLadder::LADDER_DOWN );
			if (ladderList)
			{
				FOR_EACH_LL( (*ladderList), it )
				{
					const CNavLadder *ladder = (*ladderList)[ it ].ladder;

					AddAreaToOpenList( ladder->m_bottomArea, area, startPos, maxRange );
				}
			}
		}
	}
}


//--------------------------------------------------------------------------------------------------------------
/**
 * Fuctor that returns lowest cost for farthest away areas
 * For use with FindMinimumCostArea()
 */
class FarAwayFunctor
{
public:
	float operator() ( CNavArea *area, CNavArea *fromArea, const CNavLadder *ladder )
	{
		if (area == fromArea)
			return 9999999.9f;

		return 1.0f/(fromArea->GetCenter() - area->GetCenter()).Length();
	}
};

/**
 * Fuctor that returns lowest cost for areas farthest from given position
 * For use with FindMinimumCostArea()
 */
class FarAwayFromPositionFunctor 
{
public:
	FarAwayFromPositionFunctor( const Vector &pos ) : m_pos( pos )
	{
	}

	float operator() ( CNavArea *area, CNavArea *fromArea, const CNavLadder *ladder )
	{
		return 1.0f/(m_pos - area->GetCenter()).Length();
	}

private:
	const Vector &m_pos;
};


/**
 * Pick a low-cost area of "decent" size
 */
template< typename CostFunctor >
CNavArea *FindMinimumCostArea( CNavArea *startArea, CostFunctor &costFunc )
{
	const float minSize = 150.0f;

	// collect N low-cost areas of a decent size
	enum { NUM_CHEAP_AREAS = 32 };
	struct 
	{
		CNavArea *area;
		float cost;
	}
	cheapAreaSet[ NUM_CHEAP_AREAS ];
	int cheapAreaSetCount = 0;

	FOR_EACH_LL( TheNavAreaList, iter )
	{
		CNavArea *area = TheNavAreaList[iter];

		// skip the small areas
		const Extent &extent = area->GetExtent();
		if (extent.hi.x - extent.lo.x < minSize || extent.hi.y - extent.lo.y < minSize)
			continue;

		// compute cost of this area
		float cost = costFunc( area, startArea, NULL );

		if (cheapAreaSetCount < NUM_CHEAP_AREAS)
		{
			cheapAreaSet[ cheapAreaSetCount ].area = area;
			cheapAreaSet[ cheapAreaSetCount++ ].cost = cost;
		}
		else
		{
			// replace most expensive cost if this is cheaper
			int expensive = 0;
			for( int i=1; i<NUM_CHEAP_AREAS; ++i )
				if (cheapAreaSet[i].cost > cheapAreaSet[expensive].cost)
					expensive = i;

			if (cheapAreaSet[expensive].cost > cost)
			{
				cheapAreaSet[expensive].area = area;
				cheapAreaSet[expensive].cost = cost;
			}
		}
	}

	if (cheapAreaSetCount)
	{
		// pick one of the areas at random
		return cheapAreaSet[ RandomInt( 0, cheapAreaSetCount-1 ) ].area;
	}
	else
	{
		// degenerate case - no decent sized areas - pick a random area
		int numAreas = TheNavAreaList.Count();
		int which = RandomInt( 0, numAreas-1 );

		FOR_EACH_LL( TheNavAreaList, iter )
		{
			if (which-- == 0)
				return TheNavAreaList[iter];
		}

	}
	return cheapAreaSet[ RandomInt( 0, cheapAreaSetCount-1 ) ].area;
}


#endif // _NAV_PATHFIND_H_