//
// Created by Vlad Zamskoi on 8/19/17.
// Copyright (c) 2017 MobileAppSoft. All rights reserved.
//

class HexColorToRGBConverter {
    static func convert(_ hex: String) -> (r: CGFloat, g: CGFloat, b: CGFloat, a: CGFloat)? {
        guard isValidColorHexString(hex) else { return nil }
        let hexWithoutPrefix = hex.replacingOccurrences(of: "#", with: "")
        return convertValidHexColorToRGB(hexWithoutPrefix)
    }

    private static func convertValidHexColorToRGB(_ hexColor: String) -> (r: CGFloat, g: CGFloat, b: CGFloat, a: CGFloat)? {
        var rgb: UInt32 = 0
        guard Scanner(string: hexColor).scanHexInt32(&rgb) else { return nil }

        var bitsPerColorComponent, redComponentOffset, shortToLongFormMultiplier: UInt32
        var alphaSpecified: Bool
        switch hexColor.characters.count {
        case 8:
            bitsPerColorComponent = 8
            redComponentOffset = 3
            shortToLongFormMultiplier = 1
            alphaSpecified = true
        case 6:
            bitsPerColorComponent = 8
            redComponentOffset = 2
            shortToLongFormMultiplier = 1
            alphaSpecified = false
        case 4:
            bitsPerColorComponent = 4
            redComponentOffset = 3
            shortToLongFormMultiplier = 0x11
            alphaSpecified = true
        case 3:
            bitsPerColorComponent = 4
            redComponentOffset = 2
            shortToLongFormMultiplier = 0x11
            alphaSpecified = false
        default:
            return nil
        }

        let mask = 0xFF / shortToLongFormMultiplier
        let normalizer = CGFloat(255.0)
        let redOffsetInBits = UInt32(redComponentOffset * bitsPerColorComponent)
        let greenOffsetInBits = UInt32((redComponentOffset - 1) * bitsPerColorComponent)
        let blueOffsetInBits = UInt32((redComponentOffset - 2) * bitsPerColorComponent)
        let r = CGFloat(((rgb & (mask << redOffsetInBits)) >> redOffsetInBits)
                * shortToLongFormMultiplier) / normalizer
        let g = CGFloat(((rgb & (mask << greenOffsetInBits)) >> greenOffsetInBits)
                * shortToLongFormMultiplier) / normalizer
        let b = CGFloat(((rgb & (mask << blueOffsetInBits)) >> blueOffsetInBits)
                * shortToLongFormMultiplier) / normalizer
        let a = alphaSpecified ? CGFloat((rgb & mask) * shortToLongFormMultiplier) / normalizer
                : 1.0
        return (r, g, b, a)
    }

    private static func isValidColorHexString(_ hexStr: String) -> Bool {
        let uppercasedHex = hexStr.uppercased()
        let hexDigitRegex = "[0-9A-F]"
        let hexColorRegex: String = "#?(\(hexDigitRegex){3,4}"
                + "|\(hexDigitRegex){6}"
                + "|\(hexDigitRegex){8})"
        let test = NSPredicate(format: "SELF MATCHES %@", hexColorRegex)
        return test.evaluate(with: uppercasedHex)
    }
}