import pako from 'pako';

// 反混淆：URL安全 Base64 -> 标准 Base64
function deobfuscate(obfStr: string) {
  let base64 = obfStr.replace(/-/g, '+').replace(/_/g, '/');
  while (base64.length % 4) base64 += '=';
  return base64;
}

// Base64 转 Uint8Array
function b642ab(base64: string) {
  const binary = atob(base64);
  const len = binary.length;
  const bytes = new Uint8Array(len);
  for (let i = 0; i < len; i++) {
    bytes[i] = binary.charCodeAt(i);
  }
  return bytes.buffer;
}

// 主函数：反混淆 + 解压成字符串
function deobfuscateAndDecompress(obfStr: string): Uint8Array {
  const b64 = deobfuscate(obfStr);
  const compressedBuf = b642ab(b64);
  const decompressed = pako.inflate(new Uint8Array(compressedBuf));
  return decompressed;
}

export async function decrypt(url: string): Promise<Uint8Array | undefined> {
  const res = await fetch(url).catch((err) => {
    console.error('Error during fetch:', err)
    return undefined
  })
  if (!res) return undefined
  const buffer = await res.text().catch((err) => {
    console.error('Error during get text:', err)
    return undefined
  })
  if (!buffer) return undefined

  return deobfuscateAndDecompress(buffer)
}