import CryptoKit
import Foundation

private let idAlphabet = Array("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")

func newID(_ prefix: String) -> String {
    prefix + String((0..<11).map { _ in idAlphabet.randomElement()! })
}

// IDs from before prefixed IDs were 12 lowercase hex characters; the server renamed each to this same derivation.
func migratedID(_ prefix: String, _ old: String) -> String {
    guard old.count == 12, old.allSatisfy({ "0123456789abcdef".contains($0) }) else {
        return old
    }
    var n = SHA256.hash(data: Data(old.utf8)).prefix(8).reduce(UInt64(0)) { $0 << 8 | UInt64($1) }
    var out = ""
    for _ in 0..<11 {
        out.append(idAlphabet[Int(n % UInt64(idAlphabet.count))])
        n /= UInt64(idAlphabet.count)
    }
    return prefix + out
}