"use strict";
/** Verify rendered icons: decode PNG (8-bit RGBA, non-interlaced) and check
 * color composition + whale centering. Usage: node tools/check-icon.js a.png */
const fs = require("node:fs");
const zlib = require("node:zlib");

function decodePng(buf) {
	if (buf.readUInt32BE(0) !== 0x89504e47) throw new Error("not a PNG");
	let pos = 8;
	let width = 0;
	let height = 0;
	let bitDepth = 0;
	let colorType = 0;
	const idat = [];
	while (pos < buf.length) {
		const len = buf.readUInt32BE(pos);
		const type = buf.toString("ascii", pos + 4, pos + 8);
		const data = buf.subarray(pos + 8, pos + 8 + len);
		if (type === "IHDR") {
			width = data.readUInt32BE(0);
			height = data.readUInt32BE(4);
			bitDepth = data[8];
			colorType = data[9];
		} else if (type === "IDAT") idat.push(data);
		else if (type === "IEND") break;
		pos += 12 + len;
	}
	if (bitDepth !== 8 || colorType !== 6) throw new Error(`unsupported PNG: depth=${bitDepth} color=${colorType}`);
	const raw = zlib.inflateSync(Buffer.concat(idat));
	const stride = width * 4;
	const out = Buffer.alloc(width * height * 4);
	const paeth = (a, b, c) => {
		const p = a + b - c;
		const pa = Math.abs(p - a);
		const pb = Math.abs(p - b);
		const pc = Math.abs(p - c);
		return pa <= pb && pa <= pc ? a : pb <= pc ? b : c;
	};
	for (let y = 0; y < height; y++) {
		const filter = raw[y * (stride + 1)];
		const row = raw.subarray(y * (stride + 1) + 1, (y + 1) * (stride + 1));
		const prev = y > 0 ? out.subarray((y - 1) * stride, y * stride) : null;
		for (let x = 0; x < stride; x++) {
			const i = y * stride + x;
			const left = x >= 4 ? out[i - 4] : 0;
			const up = prev ? prev[x] : 0;
			const ul = prev && x >= 4 ? prev[x - 4] : 0;
			let v = row[x];
			if (filter === 1) v = (v + left) & 255;
			else if (filter === 2) v = (v + up) & 255;
			else if (filter === 3) v = (v + ((left + up) >> 1)) & 255;
			else if (filter === 4) v = (v + paeth(left, up, ul)) & 255;
			out[i] = v;
		}
	}
	return { width, height, pixels: out };
}

const file = process.argv[2];
const { width, height, pixels } = decodePng(fs.readFileSync(file));
let transparent = 0;
let white = 0;
let blue = 0;
let black = 0;
let other = 0;
let minX = Infinity;
	let maxX = -Infinity;
	let minY = Infinity;
	let maxY = -Infinity;
for (let y = 0; y < height; y++) {
	for (let x = 0; x < width; x++) {
		const i = (y * width + x) * 4;
		const r = pixels[i];
		const g = pixels[i + 1];
		const b = pixels[i + 2];
		const a = pixels[i + 3];
		if (a < 16) { transparent++; continue; }
		if (r > 220 && g > 220 && b > 220) {
			white++;
			if (x < minX) minX = x;
			if (x > maxX) maxX = x;
			if (y < minY) minY = y;
			if (y > maxY) maxY = y;
		} else if (b > 180 && b > r + 40 && g > r) blue++;
		else if (r < 60 && g < 60 && b < 60) black++;
		else other++;
	}
}
const total = width * height;
const pct = (n) => `${((n / total) * 100).toFixed(1)}%`;
console.log(`${file}: ${width}×${height}`);
console.log(`  transparent=${pct(transparent)} white=${pct(white)} blue=${pct(blue)} black=${pct(black)} other=${pct(other)}`);
if (white > 0) {
	const cx = (minX + maxX) / 2 / width;
	const cy = (minY + maxY) / 2 / height;
	console.log(`  white mass bbox: x ${minX}..${maxX}, y ${minY}..${maxY}; center=(${cx.toFixed(2)}, ${cy.toFixed(2)}) of canvas`);
}