Find smallest +ve missing from array in swift

smallestPositiveMissingIntigerInArray.swift

import Foundation

var a = [1, 3, 6, 4, 1, 2]
var b = [1,2,3]
var c = [-1,-2,-3]

func findNearestMissingSmallValue(numberArray:[Int]) -> Int{
    
    var b =  numberArray.sorted()
    var smallestValue:Int?
    for (i,v) in b.enumerated(){
        if i+1 <= b.count{
            if i - i+1 > 0{
                if !(b.contains(v+1)) && v+1 > 0{
                    smallestValue = v+1
                    break
                }
                
            }
        }
        if b[0] > 1{
            smallestValue = b[0] - 1
        }else if b.last! > 0 {
            smallestValue = b.last! + 1
        }
    }
    guard let returnNumber = smallestValue else{
        //no possoble number
        return 1
    }
    return returnNumber
}


print(findNearestMissingSmallValue(numberArray: a))
print(findNearestMissingSmallValue(numberArray: b))
print(findNearestMissingSmallValue(numberArray: c))