Converts UIColor init to a color literal

color-convert.swift

import Foundation

/// Input: 
/// 
/// public static let purple = UIColor(red: 74/255, green: 21/255, blue: 153/255, alpha: 1.0)
///
/// Output:
///
/// #4A1599 (74, 21, 153)
/// public static let purple = #colorLiteral(red: 0.2901960784, green: 0.0823529412, blue: 0.6, alpha: 1)

for argument in CommandLine.arguments.dropFirst() {
    for line in argument.split(separator: "\n") where !line.isEmpty {
        print(try convert(String(line)))
    }
}

func convert(_ input: String) throws -> String {
    let regex = /public static let (\w+) = UIColor\(red: (\d+).*?, green: (\d+).*?, blue: (\d+).*?\)/
    guard let (_, name, red, green, blue) = try regex.firstMatch(in: input)?.output else {
        fatalError("Failed to match input")
    }
    guard let red = Int(red), let green = Int(green), let blue = Int(blue) else {
        fatalError("Failed to parse color")
    }
 
    func render(_ color: Int) -> String {
        (Double(color) / 255).formatted(.number.precision(
            .integerAndFractionLength(integerLimits: 1...1, fractionLimits: 1...10)
        ))
    }

    func hex(from value: Int) -> String {
        String(format: "%02X", value)
    }

    let hex = "#\(hex(from: red))\(hex(from: green))\(hex(from: blue))"

    return """
    /// \(hex) (\(red), \(green), \(blue))
    public static let \(name) = #colorLiteral(red: \(render(red)), green: \(render(green)), blue: \(render(blue)), alpha: 1)
    """
}