UUID Generator — Swift source

// RFC 4122 v4 UUID generator (cryptographically secure).
//
// Language: Swift (5.x, Foundation + Security)
// CosmoDev polyglot showcase port of the `uuid` tool.
// Ported from src/lib/uuid.ts — display source, part of CosmoDev's
// polyglot tool pages.
//
// Produces a random (v4) UUID: 36 characters, lowercase, hyphenated as
// 8-4-4-4-12 hex digits, with the RFC version (4) and variant (10xx)
// bits set. SecRandomCopyBytes is Apple's bridge to the host CSPRNG;
// a non-zero status is the explicit "entropy source unavailable"
// error path.

import Foundation
import Security

/// Return a freshly generated RFC 4122 version-4 UUID string.
func uuidV4() -> String {
    var b = [UInt8](repeating: 0, count: 16)
    let status = SecRandomCopyBytes(kSecRandomDefault, b.count, &b)
    precondition(status == errSecSuccess, "entropy source unavailable")

    b[6] = (b[6] & 0x0f) | 0x40 // version 4: high nibble of byte 6
    b[8] = (b[8] & 0x3f) | 0x80 // variant  : high bits of byte 8

    // Lowercase hex, hyphens at the 8-4-4-4-12 boundaries.
    let hexed = b.map { String(format: "%02x", $0) }.joined()
    return [
        hexed.prefix(8),
        hexed.dropFirst(8).prefix(4),
        hexed.dropFirst(12).prefix(4),
        hexed.dropFirst(16).prefix(4),
        hexed.dropFirst(20),
    ].joined(separator: "-")
}

print(uuidV4())