import crypto from "node:crypto";

export const EMAIL_VERIFICATION_PURPOSE_REGISTER = "register";

export type ResendConfig = {
  apiKey: string;
  fromEmail: string;
};

function getVerificationSecret(): string {
  return (
    process.env.EMAIL_VERIFICATION_SECRET ||
    process.env.AUTH_SECRET ||
    "email-verification-secret"
  );
}

export function hashEmailVerificationCode(params: {
  email: string;
  purpose: string;
  code: string;
}): string {
  const payload = `${params.email.toLowerCase()}:${params.purpose}:${params.code}:${getVerificationSecret()}`;
  return crypto.createHash("sha256").update(payload).digest("hex");
}

export function createEmailVerificationCode(): string {
  return String(crypto.randomInt(0, 1000000)).padStart(6, "0");
}

export function isResendConfigured(): boolean {
  return Boolean(process.env.RESEND_API_KEY && process.env.RESEND_FROM_EMAIL);
}

export function resolveResendConfig(config?: {
  apiKey?: string | null;
  fromEmail?: string | null;
}): ResendConfig | null {
  const apiKey = String(config?.apiKey || process.env.RESEND_API_KEY || "").trim();
  const fromEmail = String(config?.fromEmail || process.env.RESEND_FROM_EMAIL || "").trim();
  if (!apiKey || !fromEmail) {
    return null;
  }
  return { apiKey, fromEmail };
}

export async function sendVerificationCodeByResend(params: {
  to: string;
  code: string;
  siteName: string;
  expiresInMinutes: number;
  config?: ResendConfig;
}): Promise<void> {
  const resolvedConfig = params.config || resolveResendConfig();
  if (!resolvedConfig) {
    throw new Error("Resend is not configured");
  }

  const subject = `【${params.siteName}】邮箱验证码`;
  const html = `
    <div style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; padding: 20px; color: #111;">
      <h2 style="margin: 0 0 12px; font-size: 18px;">邮箱验证码</h2>
      <p style="margin: 0 0 12px; font-size: 14px;">你正在注册 ${params.siteName}，验证码如下：</p>
      <div style="font-size: 28px; font-weight: 700; letter-spacing: 6px; margin: 10px 0 16px;">${params.code}</div>
      <p style="margin: 0; font-size: 13px; color: #666;">验证码 ${params.expiresInMinutes} 分钟内有效，请勿泄露给他人。</p>
    </div>
  `;

  const text = `你正在注册 ${params.siteName}，验证码：${params.code}。验证码 ${params.expiresInMinutes} 分钟内有效。`;

  const response = await fetch("https://api.resend.com/emails", {
    method: "POST",
    headers: {
      Authorization: `Bearer ${resolvedConfig.apiKey}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      from: resolvedConfig.fromEmail,
      to: params.to,
      subject,
      html,
      text,
    }),
  });

  if (!response.ok) {
    const detail = await response.text();
    throw new Error(`Resend request failed: ${response.status} ${detail}`);
  }
}