Not detecting collision - SpriteKit - Swift - swift

Question

I am trying to detect collision between 2 objects but it works only some times. Most of the time it doesn't work. Maybe you can help me out understanding what i am doing wrong.
static let soldier: UInt32 = 0x1 << 4
static let enemy: UInt32 = 0x1 << 5
function setting the physicsBody for the ground, the soldier and the enemy:
func addPhysicsBody(to sprite: SKSpriteNode, with name: String) {
let centerPoint = CGPoint(x:sprite.size.width / 2 - (sprite.size.width * sprite.anchorPoint.x), y:sprite.size.height / 2 - (sprite.size.height * sprite.anchorPoint.y))
sprite.physicsBody = SKPhysicsBody(rectangleOf: sprite.size, center: centerPoint)
sprite.physicsBody?.allowsRotation = false
sprite.physicsBody?.affectedByGravity = true
sprite.physicsBody?.restitution = 0.0
sprite.physicsBody?.friction = 0
if name.contains(GameConstants.StringConstants.soldierName) {
sprite.physicsBody?.categoryBitMask = GameConstants.PhysicsCategories.soldier
sprite.physicsBody?.contactTestBitMask = GameConstants.PhysicsCategories.enemy
sprite.physicsBody?.collisionBitMask = GameConstants.PhysicsCategories.ground
sprite.physicsBody?.isDynamic = true
} else if name.contains(GameConstants.StringConstants.enemyName) {
sprite.physicsBody?.categoryBitMask = GameConstants.PhysicsCategories.enemy
sprite.physicsBody?.contactTestBitMask = GameConstants.PhysicsCategories.soldier
sprite.physicsBody?.collisionBitMask = GameConstants.PhysicsCategories.ground
sprite.physicsBody?.isDynamic = true
} else if name == GameConstants.StringConstants.groundName {
sprite.physicsBody?.affectedByGravity = false
sprite.physicsBody?.categoryBitMask = GameConstants.PhysicsCategories.ground
sprite.physicsBody?.isDynamic = false
}
}
generating the soldier and the enemy and moving them:
func generateASoldier() {
let soldier = SKSpriteNode(texture: SKTexture(image: UIImage(named: "0\(GameConstants.StringConstants.idlePrefixKey)0")!), color: UIColor.darkGray, size: self.frame.size)
soldier.size = CGSize(width: castle.frame.size.height/4, height: castle.frame.size.height/4)
soldier.name = "\(GameConstants.StringConstants.soldierName)\(soldierCounter)"
soldierCounter+=1
addPhysicsBody(to: soldier, with: soldier.name!)
soldier.position = CGPoint(x: frame.minX-soldier.size.width*2, y: frame.midY/1.1)
soldier.zPosition = GameConstants.ZPositions.playerZ
addChild(soldier)
isMovingSoldier.append(true)
moveSoldier(soldier: soldier, index: isMovingSoldier.count-1)
}
func moveSoldier(soldier: SKSpriteNode, index: Int) {
soldier.physicsBody?.applyImpulse(CGVector(dx: charactersSpeed, dy: 0))
DispatchQueue.main.asyncAfter(deadline: .now() + 1, execute: {
if self.isMovingSoldier[index] {
self.moveSoldier(soldier: soldier, index: index)
}
})
}
func generateAnEnemy() {
let enemy = SKSpriteNode(texture: SKTexture(image: UIImage(named: "1\(GameConstants.StringConstants.idlePrefixKey)0")!), color: UIColor.darkGray, size: self.frame.size)
enemy.size = CGSize(width: -castle.frame.size.height/4, height: castle.frame.size.height/4)
enemy.name = "\(GameConstants.StringConstants.enemyName)\(enemyCounter)"
enemyCounter+=1
addPhysicsBody(to: enemy, with: enemy.name!)
enemy.position = CGPoint(x: frame.maxX-enemy.size.width*2, y: frame.midY/1.1)
enemy.zPosition = GameConstants.ZPositions.playerZ
addChild(enemy)
isMovingEnemy.append(true)
moveEnemy(enemy: enemy, index: isMovingEnemy.count-1)
}
func moveEnemy(enemy: SKSpriteNode, index: Int) {
enemy.physicsBody?.applyImpulse(CGVector(dx: -charactersSpeed, dy: 0))
DispatchQueue.main.asyncAfter(deadline: .now() + 1, execute: {
if self.isMovingEnemy[index] {
self.moveEnemy(enemy: enemy, index: index)
}
})
}
generating the ground:
func generateGround() {
ground = SKSpriteNode(color: .white, size: CGSize(width: frame.maxX*3, height: UIScreen.main.bounds.size.height/2.435))
ground.name = GameConstants.StringConstants.groundName
addPhysicsBody(to: ground, with: ground.name!)
ground.zPosition = GameConstants.ZPositions.playerZ
ground.position = CGPoint(x: frame.midX, y: frame.minY)
self.addChild(ground)
}
Using this code func didBegin(_ contact: SKPhysicsContact) is called a random amount of times and i am trying to make sure it will be called every time the soldier and the enemy collide
Edit:
I found out that the problem is detecting the collision using the applyImpulse function. Using gravity it detects the collision