#include "stdafx.h"
#include "ttd.h"
#include "debug.h"
#include "map.h"
#include "tile.h"
#include "command.h"
#include "ai.h"
#include "depot.h"

#define TEST_STATION_NO_DIR 0xFF

// Tests if a station can be build on the given spot
// TODO: make it train compatible
static bool TestCanBuildStationHere(uint tile, byte dir)
{
    Player *p = DEREF_PLAYER(_current_player);
    if (dir == TEST_STATION_NO_DIR) {
        // TODO: currently we only allow spots that can be access from al 4 directions...
        //  should be fixed!!!
        for (dir=0;dir<4;dir++) {
        	int res = AiNew_Build_Station(p, p->ainew.tbt, tile, 1, 1, dir, DC_QUERY_COST);
            if (res != CMD_ERROR)
            	return true;
        }
        return false;
    } else {
       	int res = AiNew_Build_Station(p, p->ainew.tbt, tile, 1, 1, dir, DC_QUERY_COST);
        if (res == CMD_ERROR)
        	return false;
    }
    return true;
}


static bool IsRoad(TileIndex tile)
{
	return
		// MP_STREET, but not a road depot?
		(IsTileType(tile, MP_STREET) && !(IsTileDepotType(tile, TRANSPORT_ROAD))) ||
		(IsTileType(tile, MP_TUNNELBRIDGE) && (
			// road tunnel?
			((_map5[tile] & 0x80) == 0 && (_map5[tile] & 0x4) == 0x4) ||
			// road bridge?
			((_map5[tile] & 0x80) != 0 && (_map5[tile] & 0x2) == 0x2)
		));
}


// Checks if a tile 'a' is between the tiles 'b' and 'c'
#define TILES_BETWEEN(a, b, c) (TileX(a) >= TileX(b) && TileX(a) <= TileX(c) && TileY(a) >= TileY(b) && TileY(a) <= TileY(c))

// Check if the current tile is in our end-area
static int32 AyStar_AiPathFinder_EndNodeCheck(AyStar *aystar, OpenListNode *current)
{
	Ai_PathFinderInfo *PathFinderInfo = (Ai_PathFinderInfo*)aystar->user_target;
	// It is not allowed to have a station on the end of a bridge or tunnel ;)
	if (current->path.node.user_data[0] != 0) return AYSTAR_DONE;
	if (TILES_BETWEEN(current->path.node.tile, PathFinderInfo->end_tile_tl, PathFinderInfo->end_tile_br))
		if (IsTileType(current->path.node.tile, MP_CLEAR) || IsTileType(current->path.node.tile, MP_TREES))
			if (current->path.parent == NULL || TestCanBuildStationHere(current->path.node.tile,AiNew_GetDirection(current->path.parent->node.tile, current->path.node.tile)))
    			return AYSTAR_FOUND_END_NODE;

	return AYSTAR_DONE;
}

// Calculates the hash
//   Currently it is a 10 bit hash, so the hash array has a max depth of 6 bits (so 64)
static uint AiPathFinder_Hash(uint key1, uint key2)
{
	return (TileX(key1) & 0x1F) + ((TileY(key1) & 0x1F) << 5);
}

// Clear the memory of all the things
static void AyStar_AiPathFinder_Free(AyStar *aystar)
{
	AyStarMain_Free(aystar);
	free(aystar);
}

static int32 AyStar_AiPathFinder_CalculateG(AyStar *aystar, AyStarNode *current, OpenListNode *parent);
static int32 AyStar_AiPathFinder_CalculateH(AyStar *aystar, AyStarNode *current, OpenListNode *parent);
static void AyStar_AiPathFinder_FoundEndNode(AyStar *aystar, OpenListNode *current);
static void AyStar_AiPathFinder_GetNeighbours(AyStar *aystar, OpenListNode *current);

// This creates the AiPathFinder
AyStar *new_AyStar_AiPathFinder(int max_tiles_around, Ai_PathFinderInfo *PathFinderInfo) {
	PathNode start_node;
	uint x,y;
	// Create AyStar
	AyStar *result = malloc(sizeof(AyStar));
	init_AyStar(result, AiPathFinder_Hash, 1 << 10);
	// Set the function pointers
	result->CalculateG = AyStar_AiPathFinder_CalculateG;
	result->CalculateH = AyStar_AiPathFinder_CalculateH;
	result->EndNodeCheck = AyStar_AiPathFinder_EndNodeCheck;
	result->FoundEndNode = AyStar_AiPathFinder_FoundEndNode;
	result->GetNeighbours = AyStar_AiPathFinder_GetNeighbours;

	result->free = AyStar_AiPathFinder_Free;

	// Set some information
	result->loops_per_tick = AI_PATHFINDER_LOOPS_PER_TICK;
	result->max_path_cost = 0;
	result->max_search_nodes = AI_PATHFINDER_MAX_SEARCH_NODES;

	// Set the user_data to the PathFinderInfo
	result->user_target = PathFinderInfo;

	// Set the start node
	start_node.parent = NULL;
	start_node.node.direction = 0;
	start_node.node.user_data[0] = 0;

	// Now we add all the starting tiles
	for (x = TileX(PathFinderInfo->start_tile_tl); x <= TileX(PathFinderInfo->start_tile_br); x++) {
		for (y = TileY(PathFinderInfo->start_tile_tl); y <= TileY(PathFinderInfo->start_tile_br); y++) {
			start_node.node.tile = TILE_XY(x,y);
			result->addstart(result, &start_node.node);
		}
	}

	return result;
}

// To reuse AyStar we sometimes have to clean all the memory
void clean_AyStar_AiPathFinder(AyStar *aystar, Ai_PathFinderInfo *PathFinderInfo) {
	PathNode start_node;
	uint x,y;

	aystar->clear(aystar);

	// Set the user_data to the PathFinderInfo
	aystar->user_target = PathFinderInfo;

	// Set the start node
	start_node.parent = NULL;
	start_node.node.direction = 0;
	start_node.node.user_data[0] = 0;
	start_node.node.tile = PathFinderInfo->start_tile_tl;

	// Now we add all the starting tiles
	for (x = TileX(PathFinderInfo->start_tile_tl); x <= TileX(PathFinderInfo->start_tile_br); x++) {
		for (y = TileY(PathFinderInfo->start_tile_tl); y <= TileY(PathFinderInfo->start_tile_br); y++) {
			if (!(IsTileType(TILE_XY(x,y), MP_CLEAR) || IsTileType(TILE_XY(x,y), MP_TREES))) continue;
			if (!TestCanBuildStationHere(TILE_XY(x,y),TEST_STATION_NO_DIR)) continue;
			start_node.node.tile = TILE_XY(x,y);
			aystar->addstart(aystar, &start_node.node);
		}
	}
}

// The h-value, simple calculation
static int32 AyStar_AiPathFinder_CalculateH(AyStar *aystar, AyStarNode *current, OpenListNode *parent) {
	Ai_PathFinderInfo *PathFinderInfo = (Ai_PathFinderInfo*)aystar->user_target;
	int r, r2;
	if (PathFinderInfo->end_direction != AI_PATHFINDER_NO_DIRECTION) {
		// The station is pointing to a direction, add a tile towards that direction, so the H-value is more accurate
		r = DistanceManhattan(current->tile, PathFinderInfo->end_tile_tl + TileOffsByDir(PathFinderInfo->end_direction));
		r2 = DistanceManhattan(current->tile, PathFinderInfo->end_tile_br + TileOffsByDir(PathFinderInfo->end_direction));
	} else {
		// No direction, so just get the fastest route to the station
		r = DistanceManhattan(current->tile, PathFinderInfo->end_tile_tl);
		r2 = DistanceManhattan(current->tile, PathFinderInfo->end_tile_br);
	}
	// See if the bottomright is faster than the topleft..
	if (r2 < r) r = r2;
	return r * AI_PATHFINDER_H_MULTIPLER;
}

// We found the end.. let's get the route back and put it in an array
static void AyStar_AiPathFinder_FoundEndNode(AyStar *aystar, OpenListNode *current) {
	Ai_PathFinderInfo *PathFinderInfo = (Ai_PathFinderInfo*)aystar->user_target;
	uint i = 0;
	PathNode *parent = &current->path;

	do {
     	PathFinderInfo->route_extra[i] = parent->node.user_data[0];
		PathFinderInfo->route[i++] = parent->node.tile;
		if (i > lengthof(PathFinderInfo->route)) {
			// We ran out of space for the PathFinder
			DEBUG(ai,0)("[AiPathFinder] Ran out of spacein the route[] array!!!");
			PathFinderInfo->route_length = -1; // -1 indicates out of space
			return;
		}
		parent = parent->parent;
	} while (parent != NULL);
	PathFinderInfo->route_length = i;
	DEBUG(ai,1)("[Ai-PathFinding] Found route of %d nodes long in %d nodes of searching",i,Hash_Size(&aystar->ClosedListHash));
}

// What tiles are around us.
static void AyStar_AiPathFinder_GetNeighbours(AyStar *aystar, OpenListNode *current) {
		uint i;
		int r;
		int dir;

   	Ai_PathFinderInfo *PathFinderInfo = (Ai_PathFinderInfo*)aystar->user_target;

    aystar->num_neighbours = 0;

  	// Go through all surrounding tiles and check if they are within the limits
   	for (i=0;i<4;i++) {
   		if (TileX(TileOffsByDir(i) + current->path.node.tile) > 1 &&
					TileX(TileOffsByDir(i) + current->path.node.tile) < MapMaxX() - 1 &&
       		TileY(TileOffsByDir(i) + current->path.node.tile) > 1 &&
					TileY(TileOffsByDir(i) + current->path.node.tile) < MapMaxY() - 1) {
       		// We also directly test if the current tile can connect to this tile..
       		//  We do this simply by just building the tile!

       		// If the next step is a bridge, we have to enter it the right way
       		if (!PathFinderInfo->rail_or_road && IsRoad(current->path.node.tile + TileOffsByDir(i))) {
       			if (IsTileType(current->path.node.tile + TileOffsByDir(i), MP_TUNNELBRIDGE)) {
       				// An existing bridge... let's test the direction ;)
       				if ((_map5[current->path.node.tile + TileOffsByDir(i)] & 1U) != (i & 1)) continue;
   					// This problem only is valid for tunnels:
       				// When the last tile was not yet a tunnel, check if we enter from the right side..
       				if ((_map5[current->path.node.tile + TileOffsByDir(i)] & 0x80) == 0) {
       					if (i != (_map5[current->path.node.tile + TileOffsByDir(i)] & 3U)) continue;
       				}
       			}
       		}
       		// But also if we are on a bridge, we can only move a certain direction
       		if (!PathFinderInfo->rail_or_road && IsRoad(current->path.node.tile)) {
       			if (IsTileType(current->path.node.tile, MP_TUNNELBRIDGE)) {
       				// An existing bridge/tunnel... let's test the direction ;)
       				if ((_map5[current->path.node.tile] & 1U) != (i & 1)) continue;
       			}
       		}

       		if ((AI_PATHFINDER_FLAG_BRIDGE & current->path.node.user_data[0]) != 0 ||
       			(AI_PATHFINDER_FLAG_TUNNEL & current->path.node.user_data[0]) != 0) {
       			// We are a bridge/tunnel, how cool!!
       			//  This means we can only point forward.. get the direction from the user_data
       			if (i != (current->path.node.user_data[0] >> 8)) continue;
       		}
       		dir = 0;

       		// First, check if we have a parent
       		if (current->path.parent == NULL && current->path.node.user_data[0] == 0) {
       			// If not, this means we are at the starting station
       			if (PathFinderInfo->start_direction != AI_PATHFINDER_NO_DIRECTION) {
		       		// We do need a direction?
		       		if (AiNew_GetDirection(current->path.node.tile, current->path.node.tile + TileOffsByDir(i)) != PathFinderInfo->start_direction)
		       			// We are not pointing the right way, invalid tile
		       			continue;
		       	}
       		} else if (current->path.node.user_data[0] == 0) {
       			if (PathFinderInfo->rail_or_road) {
       				// Rail check
       				dir = AiNew_GetRailDirection(current->path.parent->node.tile, current->path.node.tile, current->path.node.tile + TileOffsByDir(i));
       				r = DoCommandByTile(current->path.node.tile, 0, dir, DC_AUTO | DC_NO_WATER, CMD_BUILD_SINGLE_RAIL);
       				if (r == CMD_ERROR) continue;
#ifdef AI_PATHFINDER_NO_90DEGREES_TURN
       				if (current->path.parent->parent != NULL) {
       					// Check if we don't make a 90degree curve
       					int dir1 = AiNew_GetRailDirection(current->path.parent->parent->node.tile, current->path.parent->node.tile, current->path.node.tile);
       					if (_illegal_curves[dir1] == dir || _illegal_curves[dir] == dir1) {
       						continue;
       					}
       				}
#endif
       			} else {
       				// Road check
       				dir = AiNew_GetRoadDirection(current->path.parent->node.tile, current->path.node.tile, current->path.node.tile + TileOffsByDir(i));
       				if (IsRoad(current->path.node.tile)) {
       					if (IsTileType(current->path.node.tile, MP_TUNNELBRIDGE)) {
       						// We have a bridge, how nicely! We should mark it...
       						dir = 0;
       					} else {
	       					// It already has road.. check if we miss any bits!
	       					if ((_map5[current->path.node.tile] & dir) != dir) {
	       						// We do miss some pieces :(
	       						dir &= ~_map5[current->path.node.tile];
	       					} else {
	       						dir = 0;
    	   					}
    	   				}
       				}
       				// Only destruct things if it is MP_CLEAR of MP_TREES
       				if (dir != 0) {
       					r = DoCommandByTile(current->path.node.tile, dir, 0, DC_AUTO | DC_NO_WATER, CMD_BUILD_ROAD);
       					if (r == CMD_ERROR) continue;
       				}
       			}

       		}

			// The tile can be connected
   			aystar->neighbours[aystar->num_neighbours].tile = TileOffsByDir(i) + current->path.node.tile;
   			aystar->neighbours[aystar->num_neighbours].user_data[0] = 0;
   			aystar->neighbours[aystar->num_neighbours++].direction = 0;
       	}
    }

    // Next step, check for bridges and tunnels
    if (current->path.parent != NULL && current->path.node.user_data[0] == 0) {

        TileInfo ti;
        // First we get the dir from this tile and his parent
    	int dir = AiNew_GetDirection(current->path.parent->node.tile, current->path.node.tile);
    	// It means we can only walk with the track, so the bridge has to be in the same direction
    	TileIndex tile = current->path.node.tile;
    	TileIndex new_tile = tile;

    	FindLandscapeHeightByTile(&ti, tile);

   		// Bridges can only be build on land that is not flat
   		//  And if there is a road or rail blocking
   		if (ti.tileh != 0 ||
     		(PathFinderInfo->rail_or_road && IsTileType(tile + TileOffsByDir(dir), MP_STREET)) ||
       		(!PathFinderInfo->rail_or_road && IsTileType(tile + TileOffsByDir(dir), MP_RAILWAY))) {

    		for (;;) {
    			new_tile += TileOffsByDir(dir);

    	    	// Precheck, is the length allowed?
    	    	if (!CheckBridge_Stuff(0,GetBridgeLength(tile, new_tile))) break;

    	    	// Check if we hit the station-tile.. we don't like that!
    	    	if (TILES_BETWEEN(new_tile,PathFinderInfo->end_tile_tl,PathFinderInfo->end_tile_br)) break;

    	    	// Try building the bridge..
    	    	r = DoCommandByTile(tile, new_tile, (0<<8) + (MAX_BRIDGES / 2), DC_AUTO, CMD_BUILD_BRIDGE);
	    	   	if (r == CMD_ERROR) continue;
    		   	// We can build a bridge here.. add him to the neighbours
   				aystar->neighbours[aystar->num_neighbours].tile = new_tile;
	   			aystar->neighbours[aystar->num_neighbours].user_data[0] = AI_PATHFINDER_FLAG_BRIDGE + (dir << 8);
	   			aystar->neighbours[aystar->num_neighbours++].direction = 0;
				// We can only have 12 neighbours, and we need 1 left for tunnels
				if (aystar->num_neighbours == 11) break;
			}
    	}

    	// Next, check for tunnels!
    	// Tunnels can only be build with tileh of 3, 6, 9 or 12, depending on the direction
    	//  For now, we check both sides for this tile.. terraforming gives fuzzy result
    	if ((dir == 0 && ti.tileh == 12) ||
    		(dir == 1 && ti.tileh == 6) ||
    		(dir == 2 && ti.tileh == 3) ||
    		(dir == 3 && ti.tileh == 9)) {
    		// Now simply check if a tunnel can be build
    		r = DoCommandByTile(tile, (PathFinderInfo->rail_or_road?0:0x200), 0, DC_AUTO, CMD_BUILD_TUNNEL);
    		FindLandscapeHeightByTile(&ti, _build_tunnel_endtile);
    		if (r != CMD_ERROR && (ti.tileh == 3 || ti.tileh == 6 || ti.tileh == 9 || ti.tileh == 12)) {
    			aystar->neighbours[aystar->num_neighbours].tile = _build_tunnel_endtile;
	   			aystar->neighbours[aystar->num_neighbours].user_data[0] = AI_PATHFINDER_FLAG_TUNNEL + (dir << 8);
	   			aystar->neighbours[aystar->num_neighbours++].direction = 0;
    		}
    	}
  	}
}

extern uint GetRailFoundation(uint tileh, uint bits);
extern uint GetRoadFoundation(uint tileh, uint bits);
extern uint GetBridgeFoundation(uint tileh, byte direction);
enum {
    BRIDGE_NO_FOUNDATION = 1 << 0 | 1 << 3 | 1 << 6 | 1 << 9 | 1 << 12,
};

// The most important function: it calculates the g-value
static int32 AyStar_AiPathFinder_CalculateG(AyStar *aystar, AyStarNode *current, OpenListNode *parent) {
	Ai_PathFinderInfo *PathFinderInfo = (Ai_PathFinderInfo*)aystar->user_target;
	int r, res = 0;
	TileInfo ti, parent_ti;

	// Gather some information about the tile..
	FindLandscapeHeightByTile(&ti, current->tile);
	FindLandscapeHeightByTile(&parent_ti, parent->path.node.tile);

	// Check if we hit the end-tile
	if (TILES_BETWEEN(current->tile,PathFinderInfo->end_tile_tl,PathFinderInfo->end_tile_br)) {
		// We are at the end-tile, check if we had a direction or something...
		if (PathFinderInfo->end_direction != AI_PATHFINDER_NO_DIRECTION && AiNew_GetDirection(current->tile, parent->path.node.tile) != PathFinderInfo->end_direction)
			// We are not pointing the right way, invalid tile
			return AYSTAR_INVALID_NODE;
		// If it was valid, drop out.. we don't build on the endtile
		return 0;
	}

	// Give everything a small penalty
	res += AI_PATHFINDER_PENALTY;

	if (!PathFinderInfo->rail_or_road) {
		// Road has the lovely advantage it can use other road... check if
		//  the current tile is road, and if so, give a good bonus
		if (IsRoad(current->tile)) {
			res -= AI_PATHFINDER_ROAD_ALREADY_EXISTS_BONUS;
		}
	}

	// We should give a penalty when the tile is going up or down.. this is one way to do so!
	//  Too bad we have to count it from the parent.. but that is not so bad.
	// We also dislike long routes on slopes, since they do not look too realistic
	//  when there is a flat land all around, they are more expensive to build, and
	//  especially they essentially block the ability to connect or cross the road
	//  from one side.
	if (parent_ti.tileh != 0 && parent->path.parent != NULL) {
		// Skip if the tile was from a bridge or tunnel
		if (parent->path.node.user_data[0] == 0 && current->user_data[0] == 0) {
			if (PathFinderInfo->rail_or_road) {
				r = GetRailFoundation(parent_ti.tileh, 1 << AiNew_GetRailDirection(parent->path.parent->node.tile, parent->path.node.tile, current->tile));
				// Maybe is BRIDGE_NO_FOUNDATION a bit strange here, but it contains just the right information..
				if (r >= 15 || (r == 0 && (BRIDGE_NO_FOUNDATION & (1 << ti.tileh)))) {
					res += AI_PATHFINDER_TILE_GOES_UP_PENALTY;
				} else {
					res += AI_PATHFINDER_FOUNDATION_PENALTY;
				}
			} else {
				if (!(IsRoad(parent->path.node.tile) && IsTileType(parent->path.node.tile, MP_TUNNELBRIDGE))) {
					r = GetRoadFoundation(parent_ti.tileh, AiNew_GetRoadDirection(parent->path.parent->node.tile, parent->path.node.tile, current->tile));
					if (r >= 15 || r == 0)
						res += AI_PATHFINDER_TILE_GOES_UP_PENALTY;
					else
						res += AI_PATHFINDER_FOUNDATION_PENALTY;
				}
			}
		}
	}

	// Are we part of a tunnel?
	if ((AI_PATHFINDER_FLAG_TUNNEL & current->user_data[0]) != 0) {
		// Tunnels are very expensive when build on long routes..
		// Ironicly, we are using BridgeCode here ;)
		r = AI_PATHFINDER_TUNNEL_PENALTY * GetBridgeLength(current->tile, parent->path.node.tile);
		res += r + (r >> 8);
	}

	// Are we part of a bridge?
	if ((AI_PATHFINDER_FLAG_BRIDGE & current->user_data[0]) != 0) {
		// That means for every length a penalty
		res += AI_PATHFINDER_BRIDGE_PENALTY * GetBridgeLength(current->tile, parent->path.node.tile);
		// Check if we are going up or down, first for the starting point
		// In user_data[0] is at the 8th bit the direction
		if (!(BRIDGE_NO_FOUNDATION & (1 << parent_ti.tileh))) {
			if (GetBridgeFoundation(parent_ti.tileh, (current->user_data[0] >> 8) & 1) < 15)
				res += AI_PATHFINDER_BRIDGE_GOES_UP_PENALTY;
		}
		// Second for the end point
		if (!(BRIDGE_NO_FOUNDATION & (1 << ti.tileh))) {
			if (GetBridgeFoundation(ti.tileh, (current->user_data[0] >> 8) & 1) < 15)
				res += AI_PATHFINDER_BRIDGE_GOES_UP_PENALTY;
		}
		if (parent_ti.tileh == 0)
			res += AI_PATHFINDER_BRIDGE_GOES_UP_PENALTY;
		if (ti.tileh == 0)
			res += AI_PATHFINDER_BRIDGE_GOES_UP_PENALTY;
	}

	//  To prevent the AI from taking the fastest way in tiles, but not the fastest way
	//    in speed, we have to give a good penalty to direction changing
	//  This way, we get almost the fastest way in tiles, and a very good speed on the track
	if (!PathFinderInfo->rail_or_road) {
		if (parent->path.parent != NULL &&
			AiNew_GetDirection(current->tile, parent->path.node.tile) != AiNew_GetDirection(parent->path.node.tile, parent->path.parent->node.tile)) {
			// When road exists, we don't like turning, but its free, so don't be to piggy about it
			if (IsRoad(parent->path.node.tile))
				res += AI_PATHFINDER_DIRECTION_CHANGE_ON_EXISTING_ROAD_PENALTY;
			else
				res += AI_PATHFINDER_DIRECTION_CHANGE_PENALTY;
		}
	} else {
		// For rail we have 1 exeption: diagonal rail..
		// So we fetch 2 raildirection. That of the current one, and of the one before that
		if (parent->path.parent != NULL && parent->path.parent->parent != NULL) {
			int dir1 = AiNew_GetRailDirection(parent->path.parent->node.tile, parent->path.node.tile, current->tile);
			int dir2 = AiNew_GetRailDirection(parent->path.parent->parent->node.tile, parent->path.parent->node.tile, parent->path.node.tile);
			// First, see if we are on diagonal path, that is better than straight path
			if (dir1 > 1) { res -= AI_PATHFINDER_DIAGONAL_BONUS; }

			// First see if they are different
			if (dir1 != dir2) {
				// dir 2 and 3 are 1 diagonal track, and 4 and 5.
				if (!(((dir1 == 2 || dir1 == 3) && (dir2 == 2 || dir2 == 3)) || ((dir1 == 4 || dir1 == 5) && (dir2 == 4 || dir2 == 5)))) {
					// It is not, so we changed of direction
					res += AI_PATHFINDER_DIRECTION_CHANGE_PENALTY;
				}
				if (parent->path.parent->parent->parent != NULL) {
					int dir3 = AiNew_GetRailDirection(parent->path.parent->parent->parent->node.tile, parent->path.parent->parent->node.tile, parent->path.parent->node.tile);
					// Check if we changed 3 tiles of direction in 3 tiles.. bad!!!
					if ((dir1 == 0 || dir1 == 1) && dir2 > 1 && (dir3 == 0 || dir3 == 1)) {
						res += AI_PATHFINDER_CURVE_PENALTY;
					}
				}
			}
		}
	}

	// Res should never be below zero.. if so, make it zero!
	if (res < 0) { res = 0; }

	// Return our value
	return res;
}