Defines functions for transforming RGBA values.

UIColor+RGBAProtocol.swift

// Created by Nedrow, David E on 2019-04-11.
// Attribution 4.0 International (CC 4.0), see bottom.

import Foundation

// MARK: - UIColor+RGBAProtocol.swift

/// Defines functions for transforming RGBA values.
public protocol RGBAProtocol {
    /// Create a color from the given RGBA value.
    ///
    /// - Parameter rgbValue: The rgb value
    /// - Returns: Color based on the input value.
    static func colorFromRGBA(_ rgbaValue: UInt32) -> UIColor

    /// Create a color using the given RGBA string.
    /// Implementations of this protocol should handle strings containing
    /// a leading pound sign "#".
    ///
    /// - Parameter rgbaString: String description.
    /// - Returns: Color based on the input string.
    static func colorFromRGBAString(_ rgbaString: String) -> UIColor?

    /// Creates an RGBA hex string representation of this color, optionally
    /// decorated with a leading poound (#) sign.
    ///
    /// - Parameter withDecoration: Prefix string with a pound (#) sign.
    /// - Returns: The hex string representation of this color.
    func rgbaString(withDecoration: Bool?) -> String
}

// MARK: - Default implementation of RGBAProtocol static functions.
/// Default implementations of the RGBAProtocol static functions.
public extension RGBAProtocol {
    /// Create a color from the given RGBA value.
    ///
    /// - Parameter rgbValue: The rgb value
    /// - Returns: Color based on the input value.
    static func colorFromRGBA(_ rgbaValue: UInt32) -> UIColor {
        return UIColor(
                red: CGFloat((rgbaValue & 0xFF000000) >> 24) / 255.0,
                green: CGFloat((rgbaValue & 0x00FF0000) >> 16) / 255.0,
                blue: CGFloat((rgbaValue & 0x0000FF00) >> 8) / 255.0,
                alpha: CGFloat(rgbaValue & 0x000000FF) / 255.0
        )
    }

    /// Create a color using the given RGBA string.
    /// Implementations of this protocol should handle strings containing
    /// a leading pound sign "#".
    ///
    /// - Parameter rgbaString: String description.
    /// - Returns: Color based on the input string.
    static func colorFromRGBAString(_ rgbaString: String) -> UIColor? {
        var rgbaStringLength: Int = rgbaString.count

        if rgbaString.firstIndex(of: "#") != nil {
            rgbaStringLength -= 1
        }

        if rgbaStringLength != 8 {
            return nil
        }

        guard let rgbaValue = rgbaString.intFromHexString() /* Ignores "#" prefix else */ else {
            return nil
        }

        return UIColor(
                red: CGFloat((rgbaValue & 0xFF000000) >> 24) / 255.0,
                green: CGFloat((rgbaValue & 0x00FF0000) >> 16) / 255.0,
                blue: CGFloat((rgbaValue & 0x0000FF00) >> 8) / 255.0,
                alpha: CGFloat(rgbaValue & 0x000000FF) / 255.0
        )
    }
}

// MARK: - Default implementation of RGBAProtocol instance functions.
/// Default implementations of the RGBAProtocol instance functions.
extension UIColor: RGBAProtocol {
    /// Creates an RGBA hex string representation of this color, optionally
    /// decorated with a leading poound (#) sign.
    ///
    /// - Parameter withDecoration: Prefix string with a pound (#) sign.
    /// - Returns: The hex string representation of this color.
    public func rgbaString(withDecoration: Bool? = false) -> String {
        var red: CGFloat = 0
        var green: CGFloat = 0
        var blue: CGFloat = 0
        var alpha: CGFloat = 0

        self.getRed(&red, green: &green, blue: &blue, alpha: &alpha)

        let rgba: Int = (Int)(red * 255) << 24 | (Int)(green * 255) << 16 | (Int)(blue * 255) << 8 | (Int)(alpha * 255) << 0

        return String(format: (withDecoration ?? false) ? "#%08x" : "%08x", rgba)
    }
}

// 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/