"use server";

import { createHash, timingSafeEqual } from "node:crypto";
import { env } from "@/env";
import { sendMail } from "@/lib/services/email";
import { siteSettings } from "@/lib/services/site-settings";

// Stateless email verification, AtomCMS-faithful but DB-table-free.
//
// Instead of persisting a row (password_resets style), the token is a keyed
// digest of the email address: sha256(email + APP_KEY). Because APP_KEY is a
// server-only secret, an attacker who only knows the email cannot forge a
// matching token, and /verify can recompute + compare it without any storage.
// The token is therefore deterministic per (email, secret) pair and stays valid
// until the account's mail_verified flips to '1' (after which /verify no-ops).

/** Secret mixed into the digest. Requires at least one of APP_KEY or AUTH_SECRET. */
function verifySecret(): string {
	const secret = env.APP_KEY || env.AUTH_SECRET;
	if (!secret)
		throw new Error(
			"APP_KEY or AUTH_SECRET must be set for email verification",
		);
	return secret;
}

/** Compute the verification token for an email (lowercased + trimmed). */
export async function verificationToken(email: string): Promise<string> {
	const normalised = email.trim().toLowerCase();
	return createHash("sha256")
		.update(`${normalised}|${verifySecret()}`)
		.digest("hex");
}

/**
 * Constant-time check that `token` matches the expected digest for `email`.
 * Returns false on any length/format mismatch rather than throwing.
 */
export async function isValidVerificationToken(
	email: string,
	token: string,
): Promise<boolean> {
	if (!email || !token || !/^[a-f0-9]{64}$/i.test(token)) return false;
	const expected = await verificationToken(email);
	const a = Buffer.from(expected, "utf8");
	const b = Buffer.from(token.toLowerCase(), "utf8");
	if (a.length !== b.length) return false;
	return timingSafeEqual(a, b);
}

/**
 * Build the verification link + email and send it. No-ops gracefully when SMTP
 * is unconfigured (sendMail returns false).
 */
export async function sendVerification(email: string): Promise<boolean> {
	const normalised = email.trim().toLowerCase();
	if (!normalised) return false;

	const token = await verificationToken(normalised);
	const base = env.APP_URL.replace(/\/+$/, "");
	const link = `${base}/verify?token=${encodeURIComponent(token)}&email=${encodeURIComponent(normalised)}`;

	const hotelName =
		(await siteSettings.get("hotel_name", env.HOTEL_NAME)) ?? env.HOTEL_NAME;

	const html = `
    <div style="font-family:sans-serif;line-height:1.5;color:#0f172a">
      <h2 style="margin:0 0 0.5rem">Verify your email</h2>
      <p>Welcome to ${escapeHtml(hotelName)}! Confirm this email address to finish setting up your account.</p>
      <p style="margin:1.25rem 0">
        <a href="${link}"
           style="display:inline-block;padding:0.6rem 1.2rem;border-radius:8px;background:#eeb425;color:#1a1a2e;font-weight:700;text-decoration:none">
          Verify email
        </a>
      </p>
      <p style="color:#64748b;font-size:0.875rem">If the button doesn't work, paste this link into your browser:</p>
      <p style="color:#64748b;font-size:0.875rem;word-break:break-all">${link}</p>
    </div>
  `.trim();

	return sendMail(normalised, `Verify your email · ${hotelName}`, html);
}

function escapeHtml(s: string): string {
	return s
		.replace(/&/g, "&amp;")
		.replace(/</g, "&lt;")
		.replace(/>/g, "&gt;")
		.replace(/"/g, "&quot;");
}