'use strict';

function readPngSize(buf) {
  const sig = Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]);
  if (buf.length < 24 || !buf.subarray(0, 8).equals(sig)) return null;
  if (buf.toString('ascii', 12, 16) !== 'IHDR') return null;
  return { width: buf.readUInt32BE(16), height: buf.readUInt32BE(20) };
}

function readJpegSize(buf) {
  if (buf.length < 4 || buf[0] !== 0xff || buf[1] !== 0xd8) return null;
  let offset = 2;
  const SOF_MARKERS = new Set([
    0xc0, 0xc1, 0xc2, 0xc3, 0xc5, 0xc6, 0xc7,
    0xc9, 0xca, 0xcb, 0xcd, 0xce, 0xcf,
  ]);
  while (offset + 1 < buf.length) {
    if (buf[offset] !== 0xff) { offset++; continue; }
    const marker = buf[offset + 1];
    if (marker === 0xd8 || marker === 0x01 || (marker >= 0xd0 && marker <= 0xd7)) {
      offset += 2;
      continue;
    }
    if (marker === 0xd9 || offset + 3 >= buf.length) break;
    const segmentLength = buf.readUInt16BE(offset + 2);
    if (SOF_MARKERS.has(marker)) {
      const height = buf.readUInt16BE(offset + 5);
      const width = buf.readUInt16BE(offset + 7);
      return { width, height };
    }
    offset += 2 + segmentLength;
  }
  return null;
}

function getImageSize(buffer) {
  try {
    return readPngSize(buffer) || readJpegSize(buffer);
  } catch {
    return null;
  }
}

module.exports = { getImageSize };