// 逐像素比对两张图（解码成 RGBA 后比），并且区分"差异是否只发生在完全透明的像素下"。
// 这个区分很关键：本项目依赖"A=0 处 RGB 已清零"，因为贴图是 Linear 过滤，
// 透明像素的 RGB 会在线性插值时渗进边缘像素——所以"仅在 A=0 处不同"的转码仍然是不可接受的。
// 用法：node tools/rawdiff.mjs <a> <b>

import { spawn } from "node:child_process";

function decode(file) {
  return new Promise((resolve, reject) => {
    const p = spawn("ffmpeg", ["-v", "error", "-i", file, "-f", "rawvideo", "-pix_fmt", "rgba", "-"], {
      stdio: ["ignore", "pipe", "pipe"],
    });
    const chunks = [];
    let err = "";
    p.stdout.on("data", (d) => chunks.push(d));
    p.stderr.on("data", (d) => (err += d));
    p.on("close", (code) => (code === 0 ? resolve(Buffer.concat(chunks)) : reject(new Error(err || `exit ${code}`))));
  });
}

const [a, b] = process.argv.slice(2);
if (!a || !b) {
  console.error("usage: node tools/rawdiff.mjs <a> <b>");
  process.exit(2);
}

const [da, db] = await Promise.all([decode(a), decode(b)]);
if (da.length !== db.length) {
  console.log(`尺寸/格式不同：${da.length} vs ${db.length} 字节`);
  process.exit(1);
}

const px = da.length / 4;
let diffAny = 0;
let diffHidden = 0; // 仅因为 A=0 而不可见
let diffVisible = 0;
let maxVisible = 0;
let maxHidden = 0;

for (let i = 0; i < da.length; i += 4) {
  const dr = Math.abs(da[i] - db[i]);
  const dg = Math.abs(da[i + 1] - db[i + 1]);
  const db_ = Math.abs(da[i + 2] - db[i + 2]);
  const dA = Math.abs(da[i + 3] - db[i + 3]);
  const m = Math.max(dr, dg, db_, dA);
  if (!m) continue;
  diffAny++;
  if (dA === 0 && da[i + 3] === 0) {
    diffHidden++;
    if (m > maxHidden) maxHidden = m;
  } else {
    diffVisible++;
    if (m > maxVisible) maxVisible = m;
  }
}

const pct = (n) => ((n / px) * 100).toFixed(4) + "%";
console.log(`${a}  vs  ${b}`);
console.log(`  总像素        ${px}`);
console.log(`  有差异像素    ${diffAny} (${pct(diffAny)})`);
console.log(`  可见差异      ${diffVisible} (${pct(diffVisible)})  最大通道差 ${maxVisible}`);
console.log(`  仅透明下差异  ${diffHidden} (${pct(diffHidden)})  最大通道差 ${maxHidden}`);
console.log(
  diffAny === 0
    ? "  结论: 逐像素相同"
    : diffVisible === 0
      ? "  结论: 只在完全透明像素下有差异——渲染仍可能因 Linear 过滤在边缘渗色，不算安全"
      : "  结论: 可见像素被改动",
);
process.exit(diffVisible === 0 && diffAny === 0 ? 0 : 1);