import { randomBytes } from "crypto";
import { prisma } from "./prisma";

const CODE_ALPHABET = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789";
const CODE_LENGTH = 6;
const CODE_TTL_MINUTES = 60;

export function generateActivationCode(): { code: string; expiresAt: Date } {
  let code = "";
  const bytes = randomBytes(CODE_LENGTH);
  for (let i = 0; i < CODE_LENGTH; i++) {
    code += CODE_ALPHABET[bytes[i] % CODE_ALPHABET.length];
  }
  const expiresAt = new Date(Date.now() + CODE_TTL_MINUTES * 60 * 1000);
  return { code, expiresAt };
}

export async function generateUniqueActivationCode(retries = 5): Promise<{ code: string; expiresAt: Date }> {
  for (let i = 0; i < retries; i++) {
    const { code, expiresAt } = generateActivationCode();
    const existing = await prisma.student.findUnique({ where: { activationCode: code } });
    if (!existing) return { code, expiresAt };
  }
  throw new Error("Failed to generate a unique activation code");
}