import { writeFileSync, mkdirSync } from 'fs';

mkdirSync('./public', { recursive: true });

function crc32(buf) {
  const table = new Uint32Array(256);
  for (let n = 0; n < 256; n++) {
    let c = n;
    for (let k = 0; k < 8; k++) c = (c & 1) ? (0xedb88320 ^ (c >>> 1)) : (c >>> 1);
    table[n] = c;
  }
  let crc = 0xffffffff;
  for (const b of buf) crc = (table[(crc ^ b) & 0xff] ^ (crc >>> 8));
  return ((crc ^ 0xffffffff) >>> 0);
}

function chunk(type, data) {
  const t = Buffer.from(type, 'ascii');
  const len = Buffer.allocUnsafe(4);
  len.writeUInt32BE(data.length, 0);
  const crcInput = Buffer.concat([t, data]);
  const crcBuf = Buffer.allocUnsafe(4);
  crcBuf.writeUInt32BE(crc32(crcInput), 0);
  return Buffer.concat([len, t, data, crcBuf]);
}

function deflateStore(raw) {
  // zlib header (deflate, no compression)
  const header = Buffer.from([0x78, 0x01]);
  const blocks = [];
  const SIZE = 32768;
  for (let i = 0; i < raw.length; i += SIZE) {
    const slice = raw.slice(i, i + SIZE);
    const last = (i + SIZE >= raw.length) ? 1 : 0;
    const h = Buffer.allocUnsafe(5);
    h[0] = last;
    h.writeUInt16LE(slice.length, 1);
    h.writeUInt16LE((~slice.length) & 0xffff, 3);
    blocks.push(h, slice);
  }
  // Adler-32
  let s1 = 1, s2 = 0;
  for (const b of raw) {
    s1 = (s1 + b) % 65521;
    s2 = (s2 + s1) % 65521;
  }
  const adler = Buffer.allocUnsafe(4);
  adler.writeUInt32BE(((s2 << 16) | s1) >>> 0, 0);
  return Buffer.concat([header, ...blocks, adler]);
}

function makePNG(size) {
  const cx = size / 2, cy = size / 2;
  const outerR = size * 0.42, innerR = size * 0.30;

  // IHDR
  const ihdr = Buffer.allocUnsafe(13);
  ihdr.writeUInt32BE(size, 0);
  ihdr.writeUInt32BE(size, 4);
  ihdr[8] = 8;  // bit depth
  ihdr[9] = 2;  // RGB
  ihdr[10] = ihdr[11] = ihdr[12] = 0;

  // Raw pixel data (filter byte 0 per row)
  const rows = [];
  for (let y = 0; y < size; y++) {
    const row = Buffer.allocUnsafe(1 + size * 3);
    row[0] = 0; // filter none
    for (let x = 0; x < size; x++) {
      const dx = x - cx, dy = y - cy;
      const d = Math.sqrt(dx * dx + dy * dy);
      let r, g, b;
      if (d < innerR) {
        r = 0x4e; g = 0xcd; b = 0xc4; // teal
      } else if (d < outerR) {
        r = 0x1e; g = 0x6a; b = 0x65; // dark teal ring
      } else {
        r = 0x0d; g = 0x0d; b = 0x0f; // background
      }
      row[1 + x * 3] = r;
      row[2 + x * 3] = g;
      row[3 + x * 3] = b;
    }
    rows.push(row);
  }

  const raw = Buffer.concat(rows);
  const idat = deflateStore(raw);

  const sig = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
  return Buffer.concat([
    sig,
    chunk('IHDR', ihdr),
    chunk('IDAT', idat),
    chunk('IEND', Buffer.alloc(0)),
  ]);
}

writeFileSync('./public/icon-192.png', makePNG(192));
writeFileSync('./public/icon-512.png', makePNG(512));
console.log('✅ Icons generiert: icon-192.png + icon-512.png');