Maximum Product Subarray problem

MaxSubarrayProduct.swift

func maxProduct(_ nums: [Int]) -> Int {
    
    guard nums.count > 0 else {
        return 0
    }
    
    guard let first = nums.first, first != 0 else {
        return max(0,maxProduct(Array(nums.dropFirst())))
    }
    
    var productMax = first
    var productAll = first
    var productUntilFirstNegativ: Int? = first < 0 ? Int.min : nil
    
    for (i, num) in Array(nums.dropFirst()).enumerated() {
        if num == 0 {
            return max( maxProduct(Array(nums.dropFirst(i+2))), max(0, productMax))
        } else{
            productAll *= num
            if let t = productUntilFirstNegativ {
                productUntilFirstNegativ = (t == Int.min ? num : t * num)
            } else {
                productUntilFirstNegativ = num < 0 ? Int.min : nil
            }
            
            productMax = max(max(productAll, productUntilFirstNegativ ?? Int.min), productMax)
        }
    }
    return productMax
}