import fs from "node:fs";
import path from "node:path";
import { fileURLToPath } from "node:url";

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const projectRoot = path.resolve(__dirname, "..");

const sourcePngPath = path.join(projectRoot, "src-tauri", "icons", "128x128@2x.png");
const targetIcoPath = path.join(projectRoot, "src-tauri", "icons", "icon.ico");

const pngBytes = fs.readFileSync(sourcePngPath);

if (pngBytes.length < 24 || pngBytes.toString("ascii", 1, 4) !== "PNG") {
  throw new Error(`Expected a PNG file at ${sourcePngPath}`);
}

const width = pngBytes.readUInt32BE(16);
const height = pngBytes.readUInt32BE(20);

if (width !== 256 || height !== 256) {
  throw new Error(`Expected a 256x256 PNG, received ${width}x${height}`);
}

const headerSize = 6;
const directoryEntrySize = 16;
const imageOffset = headerSize + directoryEntrySize;
const icoBytes = Buffer.alloc(imageOffset + pngBytes.length);

icoBytes.writeUInt16LE(0, 0);
icoBytes.writeUInt16LE(1, 2);
icoBytes.writeUInt16LE(1, 4);

icoBytes.writeUInt8(0, 6);
icoBytes.writeUInt8(0, 7);
icoBytes.writeUInt8(0, 8);
icoBytes.writeUInt8(0, 9);
icoBytes.writeUInt16LE(1, 10);
icoBytes.writeUInt16LE(32, 12);
icoBytes.writeUInt32LE(pngBytes.length, 14);
icoBytes.writeUInt32LE(imageOffset, 18);

pngBytes.copy(icoBytes, imageOffset);

fs.writeFileSync(targetIcoPath, icoBytes);
console.log(`Generated ${path.relative(projectRoot, targetIcoPath)} from ${path.relative(projectRoot, sourcePngPath)}`);