Generating Windows 95 OEM product keys, using Swift, for the heck of it.

Win95Key.swift

// Inspired by this Hacker News comment:
// https://news.ycombinator.com/item?id=34954579
//
// OEM Windows 95 keys came in the form of XXXXX-OEM-00YYYYY-ZZZZZ. The XXXXX grouping represents when Microsoft issued the key by day-of-year and year, and the operating system would validate any number where the first three numbers range from 001 to 365 (or 366 for year 96), and the last two X digits were 95-99. The YYYYY group must be a multiple to 7, excluding the number 0. The ZZZZZ group is basically noise and anything is permissible in them.
//
// Now you can run a Windows 95 keygen in your head. You're welcome :)
//

import Foundation
import Swift

class Windows95KeyGenerator {
    init() {
    }

    // OEM Windows 95 keys came in the form of XXXXX-OEM-00YYYYY-ZZZZZ
    func generateWindows95Key() -> String {
        let generatedKey: String = (keyX() + "-OEM-" + keyY() + "-" + keyZ()).uppercased()
        return generatedKey
    }

    // The XXXXX grouping represents when Microsoft issued the key by day-of-year and year, and the operating system would validate any number where the first three numbers range from 001 to 365 (or 366 for year 96), and the last two X digits were 95-99
    func keyX() -> String {
        let year: Int = Int.random(in: 95...99)                 // 95 - 99
        let daysInYear: Int = (year == 96) ? 366 : 365          // 365, or 366 for '96
        let yearString: String = String(year)

        let day: Int = Int.random(in: 1...daysInYear)           // 1 - 365/366
        let dayString: String = String(format: "%03d", day)     // String padded with zeroes; "001", "002", "003"...

        return (dayString + yearString)
    }

    // The 00YYYYY group must be a multiple to 7, excluding the number 0
    func keyY() -> String {
        let randomMultipleOf7 = Int.random(in: 1...14285) * 7   // 7 * 14,285 = 99,995, largest 5-character-long multiple of 7
        let randomMultipleString: String = String(format: "%07d", randomMultipleOf7) // Pad out to 7 characters

        return randomMultipleString
    }

    // The ZZZZZ group is basically noise and anything is permissible in them
    func keyZ() -> String {
        let characters: String = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        let randomCharacters: [String] = (0..<5).map { _ in
            String(characters.randomElement() ?? Character("X"))
        }
        let randomString: String = randomCharacters.joined(separator: "")
        return randomString
    }
}


let generator = Windows95KeyGenerator()
generator.generateWindows95Key()

for i in 0..<20 {
    print(generator.generateWindows95Key())
}