import { createCipheriv, createHmac } from "node:crypto";

// ── Key derivation ────────────────────────────────────────────────────────────
// Redsys HMAC_SHA256_V1: derive a per-order signature key by 3DES-CBC encrypting
// the padded order ID with the merchant secret key.

function deriveKey(secretKeyBase64: string, orderId: string): Buffer {
  const rawKey = Buffer.from(secretKeyBase64, "base64");
  // 3DES-CBC requires exactly 24 bytes
  const key24 = Buffer.alloc(24);
  rawKey.copy(key24, 0, 0, Math.min(rawKey.length, 24));

  // Pad order ID to a multiple of 8 bytes with zeros
  const orderBuf = Buffer.from(orderId, "ascii");
  const remainder = orderBuf.length % 8;
  const paddedOrder =
    remainder === 0 ? orderBuf : Buffer.concat([orderBuf, Buffer.alloc(8 - remainder)]);

  // 3DES-CBC with 8-byte zero IV, no auto-padding
  const iv = Buffer.alloc(8, 0);
  const cipher = createCipheriv("des-ede3-cbc", key24, iv);
  cipher.setAutoPadding(false);
  return Buffer.concat([cipher.update(paddedOrder), cipher.final()]);
}

function normalizeBase64(s: string): string {
  return s.replace(/-/g, "+").replace(/_/g, "/").replace(/=/g, "");
}

// ── Public API ────────────────────────────────────────────────────────────────

export function encodeParams(params: Record<string, string>): string {
  return Buffer.from(JSON.stringify(params)).toString("base64");
}

export function decodeParams(merchantParams: string): Record<string, string> {
  // Redsys sends back URL-safe Base64; normalize before decoding
  const normalized = merchantParams.replace(/-/g, "+").replace(/_/g, "/");
  return JSON.parse(Buffer.from(normalized, "base64").toString("utf8"));
}

export function sign(secretKeyBase64: string, orderId: string, data: string): string {
  const derivedKey = deriveKey(secretKeyBase64, orderId);
  return createHmac("sha256", derivedKey).update(data).digest("base64");
}

export function isPaymentApproved(decodedParams: Record<string, string>): boolean {
  const code = parseInt(decodedParams["Ds_Response"] ?? "9999", 10);
  return Number.isFinite(code) && code >= 0 && code <= 99;
}

export type RedsysConfig = {
  secretKey: string;
  merchantCode: string;
  terminal: string;
  isTest: boolean;
  orderId: string;
  amount: number; // in cents
  urlOk: string;
  urlKo: string;
  merchantUrl: string;
  productDescription?: string;
};

export function buildPaymentForm(config: RedsysConfig): {
  tpvUrl: string;
  merchantParams: string;
  signature: string;
  signatureVersion: string;
} {
  const tpvUrl = config.isTest
    ? "https://sis-t.redsys.es:25443/sis/realizarPago"
    : "https://sis.redsys.es/sis/realizarPago";

  const params: Record<string, string> = {
    DS_MERCHANT_AMOUNT: String(config.amount),
    DS_MERCHANT_ORDER: config.orderId,
    DS_MERCHANT_MERCHANTCODE: config.merchantCode,
    DS_MERCHANT_CURRENCY: "978",
    DS_MERCHANT_TRANSACTIONTYPE: "0",
    DS_MERCHANT_TERMINAL: config.terminal,
    DS_MERCHANT_URLOK: config.urlOk,
    DS_MERCHANT_URLKO: config.urlKo,
    DS_MERCHANT_MERCHANTURL: config.merchantUrl,
    DS_MERCHANT_CONSUMERLANGUAGE: "001",
  };
  if (config.productDescription) {
    params["DS_MERCHANT_PRODUCTDESCRIPTION"] = config.productDescription;
  }

  const merchantParams = encodeParams(params);
  const signature = sign(config.secretKey, config.orderId, merchantParams);
  return { tpvUrl, merchantParams, signature, signatureVersion: "HMAC_SHA256_V1" };
}

export function verifyNotification(
  secretKeyBase64: string,
  merchantParams: string,
  receivedSignature: string,
): boolean {
  try {
    const decoded = decodeParams(merchantParams);
    const orderId = decoded["Ds_Order"] ?? decoded["DS_MERCHANT_ORDER"] ?? "";
    if (!orderId) return false;
    const expectedSig = sign(secretKeyBase64, orderId, merchantParams);
    return normalizeBase64(expectedSig) === normalizeBase64(receivedSignature);
  } catch {
    return false;
  }
}