"use strict";

const PNG_SIGNATURE = "89504e470d0a1a0a";

const HEIC_BRANDS = new Set([
  "heic",
  "heix",
  "hevc",
  "hevx",
  "heim",
  "heis",
  "hevm",
  "hevs",
  "mif1",
  "msf1",
  "heif",
]);

/**
 * Определяет тип изображения по сигнатуре первых байтов (magic bytes).
 * @param {Buffer} buffer
 * @returns {'jpeg' | 'png' | 'webp' | 'heic' | null}
 */
function sniffImageType(buffer) {
  if (!Buffer.isBuffer(buffer) || buffer.length < 12) {
    return null;
  }

  // JPEG: FF D8 FF
  if (buffer[0] === 0xff && buffer[1] === 0xd8 && buffer[2] === 0xff) {
    return "jpeg";
  }

  // PNG: 89 50 4E 47 0D 0A 1A 0A
  if (buffer.subarray(0, 8).toString("hex") === PNG_SIGNATURE) {
    return "png";
  }

  // WebP: RIFF....WEBP
  if (
    buffer.toString("ascii", 0, 4) === "RIFF" &&
    buffer.toString("ascii", 8, 12) === "WEBP"
  ) {
    return "webp";
  }

  // HEIC / HEIF: ftyp box
  if (buffer.toString("ascii", 4, 8) === "ftyp") {
    const majorBrand = buffer.toString("ascii", 8, 12).toLowerCase();
    if (HEIC_BRANDS.has(majorBrand)) {
      return "heic";
    }

    // Check compatible brands
    const boxLength = buffer.readUInt32BE(0);
    const limit = Math.min(buffer.length, boxLength > 0 ? boxLength : 64);
    for (let offset = 16; offset + 4 <= limit; offset += 4) {
      const brand = buffer.toString("ascii", offset, offset + 4).toLowerCase();
      if (HEIC_BRANDS.has(brand)) {
        return "heic";
      }
    }
  }

  return null;
}

module.exports = {
  sniffImageType,
  HEIC_BRANDS,
};