TouchesMoved Lag with Pathfinding - swift

Question

I'm making a game where the player follows a touch. The game has obstacles and pathfinding, and I'm experiencing extreme lag with touches moved. Upon loading the game, everything works, but after a few seconds of dragging my finger around (especially around obstacles) the game freezes to the point where moving a touch will freeze all physics (0 fps) until the touch is ended.
I'm assuming the culprit is my function makeGraph(), which finds a path for the player from player.position:CGPoint() to player.destination:CGPoint(), storing a path in player.goto:[CGPoint()], the update function then takes care of moving to the next goto point.
This function is called every cycle of touchesmoved, so the player can switch directions if the finger moves over an obstacle
My question is: 1) what in this code is causing the unbearable lag, 2) how can I make this code more efficient?
My code:
initializing vars:
var obstacles = [GKPolygonObstacle(points: [float2()])]
var navgraph = GKObstacleGraph()
setting up a graph (called at start of level):
func setupGraph(){
var wallnodes :[SKSpriteNode] = [SKSpriteNode]()
self.enumerateChildNodes(withName: "wall") {
node, stop in
wallnodes.append(node as! SKSpriteNode)
}
self.enumerateChildNodes(withName: "crate") {
node, stop in
wallnodes.append(node as! SKSpriteNode)
}
obstacles = SKNode.obstacles(fromNodeBounds: wallnodes)
navgraph = GKObstacleGraph(obstacles: obstacles, bufferRadius: Float(gridSize/2))
}
touchesmoved: I keep track of multiple touches using strings. only one finger may act as the "MoveFinger." this string is created at touchesbegan and emptied at touchesended
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
touchloop: for touch in touches {
if MoveFinger == String(format: "%p", touch) {
let location = touch.location(in: self)
player.destination = location
makeGraph()
player.moving = true
player.UpdateMoveMode()
continue touchloop
}
// .... more if statements ....
}
}
and graph function (called every touchesmoved cycle):
func makeGraph(){
let startNode = GKGraphNode2D(point: float2(Float(player.position.x), Float(player.position.y)))
let endNode = GKGraphNode2D(point: float2(Float(player.destination.x), Float(player.destination.y)))
let graphcopy = navgraph
graphcopy.connectUsingObstacles(node: startNode)
graphcopy.connectUsingObstacles(node: endNode)
let path = graphcopy.findPath(from: startNode, to: endNode)
player.goto = []
for node:GKGraphNode in path {
if let point2d = node as? GKGraphNode2D {
let point = CGPoint(x: CGFloat(point2d.position.x), y: CGFloat(point2d.position.y))
player.goto.append(point)
}
}
if player.goto.count == 0 {
//if path is empty, go straight to destination
player.goto = [player.destination]
} else {
//if path is not empty, remove first point (start point)
player.goto.remove(at: 0)
}
}
any ideas?