/**
 * Generates placeholder PNG icons for the famapp PWA.
 *
 * Usage: node scripts/generate-icons.mjs
 *
 * Produces:
 *   public/icon-192.png
 *   public/icon-384.png
 *   public/icon-512.png
 *   public/icon-512-maskable.png  (same image; OS applies its own mask)
 *   public/icon-180.png           (apple-touch-icon)
 *
 * All images are solid indigo (#4F46E5) squares — replace with a real
 * branded export from icon.svg when assets are finalised.
 */

import { deflateSync } from "zlib";
import { writeFileSync } from "fs";
import { resolve, dirname } from "path";
import { fileURLToPath } from "url";

const __dir = dirname(fileURLToPath(import.meta.url));
const publicDir = resolve(__dir, "../public");

// Build CRC-32 lookup table once.
const CRC_TABLE = new Uint32Array(256);
for (let i = 0; i < 256; i++) {
  let c = i;
  for (let k = 0; k < 8; k++) c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
  CRC_TABLE[i] = c;
}

function crc32(buf) {
  let crc = 0xffffffff;
  for (let i = 0; i < buf.length; i++) crc = CRC_TABLE[(crc ^ buf[i]) & 0xff] ^ (crc >>> 8);
  return (crc ^ 0xffffffff) >>> 0;
}

function u32(n) {
  const b = Buffer.alloc(4);
  b.writeUInt32BE(n, 0);
  return b;
}

function pngChunk(type, data) {
  const typeBytes = Buffer.from(type, "ascii");
  const crc = u32(crc32(Buffer.concat([typeBytes, data])));
  return Buffer.concat([u32(data.length), typeBytes, data, crc]);
}

/**
 * Returns a Buffer containing a valid PNG of size×size filled with (r, g, b).
 */
function solidPNG(size, r, g, b) {
  const PNG_SIG = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);

  const ihdr = pngChunk(
    "IHDR",
    Buffer.concat([
      u32(size),
      u32(size),
      Buffer.from([8, 2, 0, 0, 0]), // 8-bit RGB, no interlace
    ]),
  );

  // One filter byte (0 = None) followed by size×3 RGB bytes per row.
  const rowLen = 1 + size * 3;
  const raw = Buffer.alloc(size * rowLen);
  for (let y = 0; y < size; y++) {
    const base = y * rowLen;
    raw[base] = 0;
    for (let x = 0; x < size; x++) {
      raw[base + 1 + x * 3] = r;
      raw[base + 2 + x * 3] = g;
      raw[base + 3 + x * 3] = b;
    }
  }

  const idat = pngChunk("IDAT", deflateSync(raw));
  const iend = pngChunk("IEND", Buffer.alloc(0));

  return Buffer.concat([PNG_SIG, ihdr, idat, iend]);
}

// Indigo-600 (#4F46E5)
const [R, G, B] = [0x4f, 0x46, 0xe5];

const icons = [
  { name: "icon-192.png", size: 192 },
  { name: "icon-384.png", size: 384 },
  { name: "icon-512.png", size: 512 },
  { name: "icon-512-maskable.png", size: 512 },
  { name: "icon-180.png", size: 180 },
];

for (const { name, size } of icons) {
  const out = resolve(publicDir, name);
  writeFileSync(out, solidPNG(size, R, G, B));
  console.log(`  ✓  public/${name}  (${size}×${size})`);
}