"use strict";
/**
 * Assemble a Windows multi-resolution .ico from the icon.iconset PNGs.
 *
 * ICO format (PNG-embedded, supported by Windows Vista+):
 *   ICONDIR    (6 bytes):  reserved=0, type=1, count=N
 *   ICONDIRENTRY (16×N):  w,h,colors,reserved,planes,bitcount,size,offset
 *   <PNG bytes concatenated>
 * No native tooling (iconutil/sips) — pure Node, cross-buildable on macOS.
 */
const fs = require("node:fs");
const path = require("node:path");

const ICONSET = path.join(__dirname, "..", "assets", "icon.iconset");
const OUT = path.join(__dirname, "..", "assets", "icon.ico");

const SIZES = [16, 32, 48, 64, 128, 256];
const SOURCES = {
	16: "icon_16x16.png",
	32: "icon_32x32.png",
	64: "icon_32x32@2x.png",
	128: "icon_128x128.png",
	256: "icon_256x256.png",
	// 48 has no direct source; reuse 64 — Windows scales acceptably.
	48: "icon_32x32@2x.png",
};

function pngDims(buf) {
	// PNG IHDR: width (4 bytes BE) at offset 16, height at 20.
	return { width: buf.readUInt32BE(16), height: buf.readUInt32BE(20) };
}

function build() {
	const entries = [];
	for (const size of SIZES) {
		const file = path.join(ICONSET, SOURCES[size]);
		if (!fs.existsSync(file)) { console.warn(`skip ${size}: missing ${SOURCES[size]}`); continue; }
		const buf = fs.readFileSync(file);
		if (buf.slice(0, 8).toString("hex") !== "89504e470d0a1a0a") throw new Error(`${file}: not a PNG`);
		const { width, height } = pngDims(buf);
		entries.push({ size, width, height, buf });
	}
	if (entries.length === 0) throw new Error("no PNG sources found");

	const count = entries.length;
	const headerSize = 6 + 16 * count;
	let offset = headerSize;
	const dir = Buffer.alloc(headerSize);
	dir.writeUInt16LE(0, 0); // reserved
	dir.writeUInt16LE(1, 2); // type = icon
	dir.writeUInt16LE(count, 4);

	entries.forEach((e, i) => {
		const base = 6 + 16 * i;
		dir.writeUInt8(e.size >= 256 ? 0 : e.size, base);       // width (0 = 256)
		dir.writeUInt8(e.size >= 256 ? 0 : e.size, base + 1);   // height
		dir.writeUInt8(0, base + 2);                              // colorCount (0 = ≥8bit)
		dir.writeUInt8(0, base + 3);                              // reserved
		dir.writeUInt16LE(1, base + 4);                           // planes
		dir.writeUInt16LE(32, base + 6);                          // bitCount
		dir.writeUInt32LE(e.buf.length, base + 8);                // bytesInRes
		dir.writeUInt32LE(offset, base + 12);                     // imageOffset
		offset += e.buf.length;
	});

	const out = Buffer.concat([dir, ...entries.map((e) => e.buf)]);
	fs.writeFileSync(OUT, out);
	console.log(`built ${OUT}: ${count} sizes [${entries.map((e) => e.size).join(",")}] (${out.length} bytes)`);
}

build();