import fs from 'fs/promises';
import UPNG from 'upng-js';

const countUniqueColors = (data) => {
  const uniqueColors = new Set();
  for (let i = 0; i < data.length; i += 4) {
    uniqueColors.add(`${data[i]},${data[i + 1]},${data[i + 2]},${data[i + 3]}`);
    if (uniqueColors.size > 256) {
      return uniqueColors.size;
    }
  }
  return uniqueColors.size;
};

export async function compressPng (filePath) {
  const buffer = await fs.readFile(filePath);
  const arrayBuffer = buffer.buffer.slice(buffer.byteOffset, buffer.byteOffset + buffer.byteLength);
  const img = UPNG.decode(arrayBuffer);
  const rgba = new Uint8Array(img.data);
  const frameData = new Uint8Array(img.width * img.height * 4);
  frameData.set(rgba.subarray(0, frameData.length));
  const cnum = countUniqueColors(rgba) <= 256 ? 256 : 0;
  const optimizedArrayBuffer = UPNG.encode([frameData.buffer], img.width, img.height, cnum, img.depth);
  const optimizedBuffer = Buffer.from(optimizedArrayBuffer);
  await fs.writeFile(filePath, optimizedBuffer);
  return filePath;
};