// Trace a flattened pose (from smooth-flatten-for-trace.cjs) with potrace, one colour at a time, plus its shadow.
// potrace fits far smoother curves than vtracer on small art. Colours stack largest first, and each layer's mask
// also covers every layer above it, so a lower colour runs under the upper ones and no hairline gaps can open.
// usage: potrace-pose.cjs <flat.png> <shadow-layer.png (1x, from split-shadow.cjs)> <out.svg>
const sharp = require("module").createRequire("/home/ubuntu/kalki-cli/projects/mybazaar-web/package.json")("sharp");
const { execFileSync } = require("node:child_process");
const fs = require("node:fs"), os = require("node:os"), path = require("node:path");
const [, , flatFile, shadowFile, outFile] = process.argv;
const SHADOW_INK = "#113833", SHADOW_OPACITY = "0.194";
const tmp = fs.mkdtempSync(path.join(os.tmpdir(), "potrace-pose-"));

const trace = (mask, W, H, name) => {
	const rowBytes = Math.ceil(W / 8), bits = Buffer.alloc(rowBytes * H);
	for (let y = 0; y < H; y++) for (let x = 0; x < W; x++) if (mask[y * W + x]) bits[y * rowBytes + (x >> 3)] |= 0x80 >> (x & 7);
	const pbm = path.join(tmp, name + ".pbm"), svg = path.join(tmp, name + ".svg");
	fs.writeFileSync(pbm, Buffer.concat([Buffer.from(`P4\n${W} ${H}\n`), bits]));
	execFileSync("potrace", [pbm, "-s", "-o", svg, "--turdsize", "20", "--alphamax", "1.1", "--opttolerance", "0.2"]);
	const s = fs.readFileSync(svg, "utf8");
	return { transform: /<g transform="([^"]+)"/.exec(s)[1], paths: [...s.matchAll(/<path d="([^"]+)"/g)].map((m) => m[1].replace(/\s+/g, " ")) };
};

(async () => {
	const { data, info } = await sharp(flatFile).ensureAlpha().raw().toBuffer({ resolveWithObject: true });
	const W = info.width, H = info.height, n = W * H;
	const key = (p) => (data[p * 4] << 16) | (data[p * 4 + 1] << 8) | data[p * 4 + 2];
	const area = new Map();
	for (let p = 0; p < n; p++) if (data[p * 4 + 3] > 127) area.set(key(p), (area.get(key(p)) || 0) + 1);
	const order = [...area.keys()].sort((a, b) => area.get(b) - area.get(a));
	const rank = new Map(order.map((c, i) => [c, i]));

	const sm = await sharp(shadowFile).metadata();
	const shadowGrey = await sharp(shadowFile).resize(W, H, { kernel: "lanczos3" }).flatten({ background: "#ffffff" })
		.greyscale().blur(4).extractChannel(0).raw().toBuffer();
	if (sm.width * (W / sm.width) !== W) throw new Error("shadow layer is not the same pose size");

	const out = [`<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 ${W} ${H}" width="${W}" height="${H}">`];
	const shadow = trace(Uint8Array.from(shadowGrey, (v) => (v < 136 ? 1 : 0)), W, H, "shadow");
	if (shadow.paths.length) out.push(`<g transform="${shadow.transform}" fill="${SHADOW_INK}" fill-opacity="${SHADOW_OPACITY}">`, ...shadow.paths.map((d) => `<path d="${d}"/>`), "</g>");
	order.forEach((c, i) => {
		const mask = new Uint8Array(n);
		for (let p = 0; p < n; p++) if (data[p * 4 + 3] > 127 && rank.get(key(p)) >= i) mask[p] = 1;
		const t = trace(mask, W, H, "c" + i);
		const hex = "#" + c.toString(16).padStart(6, "0");
		if (t.paths.length) out.push(`<g transform="${t.transform}" fill="${hex}">`, ...t.paths.map((d) => `<path d="${d}"/>`), "</g>");
		console.log(`  ${hex} ${(100 * area.get(c) / n).toFixed(1)}% -> ${t.paths.length} paths`);
	});
	out.push("</svg>", "");
	fs.writeFileSync(outFile, out.join("\n"));
	fs.rmSync(tmp, { recursive: true });
})();