Swift 3 SpriteKit Detecting Contacts

I'm new to swift and I have been trying to figure out how to use bitmasks and didBegin(_ contact: SKPhysicsContact) to detect when two spaceships touch each other. I can't seem to figure out how.

Here is what I have so far:

import SpriteKit
import GameplayKit

class GameScene: SKScene, SKPhysicsContactDelegate {

let pufferCategory: UInt32 = 1 << 0;

let enemyCategory: UInt32 = 1 << 1;

var spaceship1: SKSpriteNode!
var spaceship2: SKSpriteNode!

override func didMove(to view: SKView) {
    spaceship1 = SKSpriteNode(imageNamed: "Spaceship");
    spaceship1.setScale(CGFloat(0.1))
    spaceship1.position = CGPoint(x: self.frame.width / 2, y: (self.frame.height / 2));
    spaceship1.name = "spaceship1";


    spaceship1.physicsBody = SKPhysicsBody(circleOfRadius: spaceship1.size.width / 2);
    spaceship1.physicsBody?.isDynamic = true // apply gravity, friction, and collision
    spaceship1.physicsBody?.affectedByGravity = false;
    spaceship1.physicsBody?.allowsRotation = false
    spaceship1.physicsBody = SKPhysicsBody(circleOfRadius: spaceship1.size.width / 2);
    spaceship1.physicsBody?.categoryBitMask = pufferCategory
    spaceship1.physicsBody?.contactTestBitMask = enemyCategory

    spaceship2 = SKSpriteNode(imageNamed: "Spaceship");
    spaceship2.setScale(CGFloat(0.1))
    spaceship2.position = CGPoint(x: self.frame.width / 2, y: (spaceship1.position.y + 300));
    spaceship2.name = "puffer2";

    spaceship2.physicsBody = SKPhysicsBody(circleOfRadius: spaceship2.size.width / 2);
    spaceship2.physicsBody?.isDynamic = true // apply gravity, friction, and collision
    spaceship2.physicsBody?.affectedByGravity = false;
    spaceship2.physicsBody?.allowsRotation = false
    spaceship2.physicsBody = SKPhysicsBody(circleOfRadius: spaceship2.size.width / 2);
    spaceship2.physicsBody?.categoryBitMask = enemyCategory
    spaceship2.physicsBody?.contactTestBitMask = pufferCategory

    addChild(spaceship1)
    addChild(spaceship2)
}

func didBegin(_ contact: SKPhysicsContact) {
    print("contact")
}

    override func update(_ currentTime: TimeInterval) {
        spaceship1.physicsBody?.affectedByGravity = false;
  }
}

Thanks in advance!

I figured it out!

Here's my code :)

import SpriteKit
import GameplayKit

class GameScene: SKScene, SKPhysicsContactDelegate {

let enemy2Category: UInt32 = 1

let enemyCategory: UInt32 = 2

var spaceship1: SKSpriteNode!
var spaceship2: SKSpriteNode!

override func didMove(to view: SKView) {
    self.physicsWorld.contactDelegate = self
    spaceship1 = SKSpriteNode(imageNamed: "Spaceship");
    spaceship1.setScale(CGFloat(0.1))
    spaceship1.position = CGPoint(x: self.frame.width / 2, y: (self.frame.height / 2));
    spaceship1.name = "spaceship1";


    spaceship1.physicsBody = SKPhysicsBody(circleOfRadius: spaceship1.size.width / 2);
    spaceship1.physicsBody?.isDynamic = true // apply gravity, friction, and collision
    spaceship1.physicsBody?.affectedByGravity = false;
    spaceship1.physicsBody?.allowsRotation = false
    spaceship1.physicsBody = SKPhysicsBody(circleOfRadius: spaceship1.size.width / 2);
    spaceship1.physicsBody?.categoryBitMask = enemy2Category
    spaceship1.physicsBody?.collisionBitMask = enemyCategory
    spaceship1.physicsBody?.contactTestBitMask = enemyCategory

    spaceship2 = SKSpriteNode(imageNamed: "Spaceship");
    spaceship2.setScale(CGFloat(0.1))
    spaceship2.position = CGPoint(x: self.frame.width / 2, y: (spaceship1.position.y + 300));
    spaceship2.name = "spaceship2";

    spaceship2.physicsBody = SKPhysicsBody(circleOfRadius: spaceship2.size.width / 2);
    spaceship2.physicsBody?.isDynamic = true // apply gravity, friction, and collision
    spaceship2.physicsBody?.affectedByGravity = false;
    spaceship2.physicsBody?.allowsRotation = false
    spaceship2.physicsBody = SKPhysicsBody(circleOfRadius: spaceship2.size.width / 2);
    spaceship2.physicsBody?.categoryBitMask = enemyCategory
    spaceship2.physicsBody?.collisionBitMask = enemy2Category
    spaceship2.physicsBody?.contactTestBitMask = enemy2Category

    addChild(spaceship1)
    addChild(spaceship2)
}

 func didBegin(_ contact: SKPhysicsContact) {
    print("contact")
}

    override func update(_ currentTime: TimeInterval) {
        spaceship1.physicsBody?.affectedByGravity = false;
   }
}

I used this video to help: https://www.youtube.com/watch?v=43hzb4NmQfw