GameScene.swift

class GameScene: SKScene {
    var board = [[CellNode]]()

    let boardSizeX = 46
    let boardSizeY = 25

    override func didMove(to view: SKView) {
        for x in 0...boardSizeX {
            var nodes = [CellNode]()
            for y in 0...boardSizeY {
                let newNode = CellNode.generate()

                if arc4random() % 100 < 13 {
                    newNode.isDead = false
                }

                newNode.position = CGPoint(x: x * 20 - (boardSizeX * 10), y: (y * 20) - (boardSizeY * 10))
                addChild(newNode)
                nodes.append(newNode)
            }
            board.append(nodes)
        }

        // set the neighbors
        for x in 0...boardSizeX {
            let nodes = board[x]
            let beforeNodes = x > 0 ? board[x-1] : []
            let afterNodes = x < (boardSizeX-1) ? board[x+1] : []

            for y in 0...boardSizeY {
                let node = nodes[y]

                if y > 0 {
                    node.neighbors.append(nodes[y-1])
                    if !beforeNodes.isEmpty {
                        node.neighbors.append(beforeNodes[y-1])
                    }
                    if !afterNodes.isEmpty {
                        node.neighbors.append(afterNodes[y-1])
                    }
                }
                if y < (boardSizeY-1) {
                    node.neighbors.append(nodes[y+1])
                    if !beforeNodes.isEmpty {
                        node.neighbors.append(beforeNodes[y+1])
                    }
                    if !afterNodes.isEmpty {
                        node.neighbors.append(afterNodes[y+1])
                    }
                }

                if !beforeNodes.isEmpty {
                    node.neighbors.append(beforeNodes[y])
                }
                if !afterNodes.isEmpty {
                    node.neighbors.append(afterNodes[y])
                }
            }
        }

        // Inject more life when it dies
        let tap = UITapGestureRecognizer(target: self, action: #selector(kick))
        view.addGestureRecognizer(tap)
    }

    func nextGeneration() {
        for row in board {
            for cell in row {
                cell.calculateNextGeneration()
            }
        }
        for row in board {
            for cell in row {
                cell.applyNextGeneration()
            }
        }
    }

    @objc
    func kick() {
        for row in board {
            for cell in row {
                if cell.isDead {
                    cell.isDead = arc4random() % 100 > 13
                }
            }
        }
    }

    override func update(_ currentTime: TimeInterval) {
        nextGeneration()
    }
}

fileprivate extension UIColor {
    static let deadColor = UIColor.blue
    static let aliveColor = UIColor.green
}

class CellNode: SKShapeNode {
    static let baseSize = CGSize(width: 20, height: 20)
    class func generate() -> CellNode {
        let newNode = CellNode(rectOf: baseSize)
        newNode.strokeColor = .black
        return newNode
    }

    var isDead = true {
        didSet {
            self.fillColor = isDead ? .deadColor : .aliveColor
        }
    }

    var neighbors = [CellNode]()

    var willBeDead = true
    func calculateNextGeneration() {
        let livingNeighbors = neighbors.filter { !$0.isDead }
        switch (isDead, livingNeighbors.count) {
            case (true, 3): willBeDead = false
            case (false, 2): willBeDead = false
            case (false, 3): willBeDead = false
            default: willBeDead = true
        }
    }

    func applyNextGeneration() {
        isDead = willBeDead
    }
}