Atoi

class Solution {
    func myAtoi(_ str: String) -> Int {
        var value = 0

        var hasValue = false
        var isNegative = false

        let max = (1 << 31) - 1
        let min = -(1 << 31)

        LOOP: for c in str {
            if let digit = c.wholeNumberValue {
                hasValue = true

                if isNegative {
                    if min + digit > -value * 10 {
                        return min
                    }
                } else {
                    if max - digit < value * 10 {
                        return max
                    }
                }

                value = value * 10 + digit

                continue
            }

            if hasValue {
                break
            }

            switch c {
            case "+":
                hasValue = true
            case "-":
                hasValue = true
                isNegative = true
            case " ":
                continue
            default:
                break LOOP
            }
        }

        return isNegative ? -value : value
    }
}