const SCRIPT_PATTERNS = [
  /<script\b/i,
  /javascript:/i,
  /\bon\w+\s*=/i,
  /<iframe\b/i,
  /<object\b/i,
  /<embed\b/i,
];

const MAX_ZIP_COMPRESSION_RATIO = 100;
const MAX_ZIP_LOCAL_HEADERS = 512;

function isZipContainer(mimeType) {
  return (
    mimeType.includes('openxmlformats') ||
    mimeType.includes('msword') ||
    mimeType.includes('ms-excel') ||
    mimeType.includes('ms-powerpoint')
  );
}

function scanTextContent(buffer) {
  const sample = buffer.subarray(0, Math.min(buffer.length, 256 * 1024)).toString('utf8');
  for (const pattern of SCRIPT_PATTERNS) {
    if (pattern.test(sample)) {
      return {
        scanStatus: 'blocked',
        riskLevel: 'high',
        findings: ['text_active_content'],
      };
    }
  }
  return null;
}

function scanZipStructure(buffer) {
  if (buffer.subarray(0, 2).toString('ascii') !== 'PK') {
    return {
      scanStatus: 'blocked',
      riskLevel: 'medium',
      findings: ['zip_signature_mismatch'],
    };
  }

  let offset = 0;
  let headers = 0;
  while (offset + 30 <= buffer.length && headers < MAX_ZIP_LOCAL_HEADERS) {
    if (buffer.subarray(offset, offset + 2).toString('ascii') !== 'PK') break;
    const compressionMethod = buffer.readUInt16LE(offset + 8);
    const compressedSize = buffer.readUInt32LE(offset + 18);
    const uncompressedSize = buffer.readUInt32LE(offset + 22);
    const nameLength = buffer.readUInt16LE(offset + 26);
    const extraLength = buffer.readUInt16LE(offset + 28);
    const headerSize = 30 + nameLength + extraLength;
    if (headerSize <= 0 || offset + headerSize > buffer.length) break;

    if (compressionMethod !== 0 && compressedSize > 0 && uncompressedSize / compressedSize > MAX_ZIP_COMPRESSION_RATIO) {
      return {
        scanStatus: 'blocked',
        riskLevel: 'critical',
        findings: ['zip_bomb_ratio'],
      };
    }

    headers += 1;
    offset += headerSize;
    if (compressedSize > 0) {
      offset += compressedSize;
    }
  }

  return null;
}

export function runBasicFileScan(buffer, { filename, mimeType }) {
  if (!Buffer.isBuffer(buffer) || buffer.length === 0) {
    return {
      scanStatus: 'blocked',
      riskLevel: 'high',
      findings: ['empty_file'],
    };
  }

  if (mimeType.startsWith('text/') || mimeType === 'application/pdf') {
    const textFinding = scanTextContent(buffer);
    if (textFinding) return textFinding;
  }

  if (mimeType === 'application/pdf' && buffer.subarray(0, 5).toString('ascii') !== '%PDF-') {
    return {
      scanStatus: 'blocked',
      riskLevel: 'medium',
      findings: ['pdf_signature_mismatch'],
    };
  }

  if (isZipContainer(mimeType)) {
    const zipFinding = scanZipStructure(buffer);
    if (zipFinding) return zipFinding;
  }

  return {
    scanStatus: 'passed',
    riskLevel: 'none',
    findings: [],
  };
}