// Minimal PNG encoder (RGBA, 8-bit) using Node's zlib.

import { deflateSync } from "node:zlib";

function crc32(buf: Uint8Array): number {
  let c = ~0;
  for (let k = 0; k < buf.length; k++) {
    c ^= buf[k];
    for (let b = 0; b < 8; b++) c = (c >>> 1) ^ (0xedb88320 & -(c & 1));
  }
  return ~c >>> 0;
}

function chunk(type: string, data: Uint8Array): Uint8Array {
  const out = new Uint8Array(12 + data.length);
  const v = new DataView(out.buffer);
  v.setUint32(0, data.length);
  for (let k = 0; k < 4; k++) out[4 + k] = type.charCodeAt(k);
  out.set(data, 8);
  v.setUint32(8 + data.length, crc32(out.subarray(4, 8 + data.length)));
  return out;
}

export function encodePng(rgba: Uint8ClampedArray, width: number, height: number): Uint8Array {
  const raw = new Uint8Array((width * 4 + 1) * height);
  for (let y = 0; y < height; y++) {
    raw[y * (width * 4 + 1)] = 0;
    raw.set(rgba.subarray(y * width * 4, (y + 1) * width * 4), y * (width * 4 + 1) + 1);
  }
  const ihdr = new Uint8Array(13);
  const v = new DataView(ihdr.buffer);
  v.setUint32(0, width); v.setUint32(4, height);
  ihdr[8] = 8; ihdr[9] = 6; ihdr[10] = 0; ihdr[11] = 0; ihdr[12] = 0;
  const parts = [new Uint8Array([137, 80, 78, 71, 13, 10, 26, 10]), chunk("IHDR", ihdr), chunk("IDAT", new Uint8Array(deflateSync(raw))), chunk("IEND", new Uint8Array(0))];
  const total = parts.reduce((n, p) => n + p.length, 0);
  const out = new Uint8Array(total);
  let o = 0;
  for (const p of parts) { out.set(p, o); o += p.length; }
  return out;
}