This protocol defines functions related to hex string conversion.

String+IntFromHex.swift

//  Created by Nedrow, David E on 3/25/19.
// This work is licensed under Attribution 4.0 International (CC 4.0)

import UIKit

// MARK: - String+IntFromHex.swift

/// This protocol defines functions related to hex string conversion.
public protocol HexStringProtocol {
    /// Create an int from a given hex value string.
    ///
    /// - Parameter hexStr: String in the form "[#]XXXXXX"
    /// - Returns: The int value for the hex string. `nil` is returned for inputs that can not be converted.
    func intFromHexString() -> UInt32?
}

extension String: HexStringProtocol {
    public func intFromHexString() -> UInt32? {
        var hexInt: UInt32 = 0

        // Make sure we only have strings that look like a normal [A]RGB hex value
        let regex = try? NSRegularExpression(pattern: "^[#]?([A-Fa-f0-9]{6}|[A-Fa-f0-9]{8})$", options: .caseInsensitive)
        if (regex?.matches(in: self, options: [], range: NSRange(location: 0, length: self.count)))?.count ?? 0 == 0 {
            return nil
        }

        let scanner: Scanner = Scanner(string: self.uppercased())
        scanner.charactersToBeSkipped = CharacterSet(charactersIn: "#")
        scanner.scanHexInt32(&hexInt)

        return hexInt != UInt.max ? hexInt : nil
    }
}

// This work is licensed under Attribution 4.0 International (CC 4.0)
// You are free to:
// Share — copy and redistribute the material in any medium or format
// Adapt — remix, transform, and build upon the material
// for any purpose, even commercially.
//
// This license is acceptable for Free Cultural Works.
// The licensor cannot revoke these freedoms as long as you follow the license terms.
// See https://creativecommons.org/licenses/by/4.0/