// 把两张图的差异降采样成 ASCII 热力图，好在纯文本里看出"差异落在画面哪里"。
// 用法：node tools/heatmap.mjs <a.png> <b.png> [cols] [rows]

import { spawn } from "node:child_process";

const [a, b, cols = "48", rows = "20"] = process.argv.slice(2);
if (!a || !b) {
  console.error("usage: node tools/heatmap.mjs <a.png> <b.png> [cols] [rows]");
  process.exit(2);
}

const W = Number(cols);
const H = Number(rows);
const RAMP = " .:-=+*#%@";

const buf = await new Promise((resolve) => {
  const p = spawn(
    "ffmpeg",
    [
      "-hide_banner", "-loglevel", "error",
      "-i", a, "-i", b,
      "-lavfi", `blend=all_mode=difference,format=gray,scale=${W}:${H}:flags=area`,
      "-f", "rawvideo", "-pix_fmt", "gray", "-",
    ],
    { stdio: ["ignore", "pipe", "pipe"] },
  );
  const chunks = [];
  p.stdout.on("data", (d) => chunks.push(d));
  p.on("close", () => resolve(Buffer.concat(chunks)));
});

if (buf.length < W * H) {
  console.error(`ffmpeg 只返回 ${buf.length} 字节，期望 ${W * H}`);
  process.exit(1);
}

console.log(`${a}  vs  ${b}   (${W}x${H} 降采样，越亮=差异越大)`);
console.log("    +" + "-".repeat(W) + "+");
for (let y = 0; y < H; y++) {
  let line = "";
  for (let x = 0; x < W; x++) {
    const v = buf[y * W + x];
    line += RAMP[Math.min(RAMP.length - 1, Math.round((v / 255) * (RAMP.length - 1) * 2))];
  }
  console.log(String(y).padStart(3) + " |" + line + "|");
}
console.log("    +" + "-".repeat(W) + "+");