#!/usr/bin/env node
/**
 * Generate pixel diffs for the side-by-side Angular/React screenshots
 * captured into `comparison-report/visual/screenshots/full/` and emit a
 * JSON file the report.html consumes for the quantitative side of the
 * parity comparison.
 *
 * Pairs are inferred by filename: every `react-{stem}.png` is matched
 * against `angular-{stem}.png` in the same directory. Diffs are written
 * to `comparison-report/visual/diffs-full/{stem}.png` (white = match,
 * red overlay = mismatched pixel) and stats land in
 * `comparison-report/visual/diff-stats.json`.
 *
 * Image-dimension mismatches are handled by padding both sides to the
 * larger canvas with white before pixel-matching — same approach as
 * `tests/parity/visual/screenshot-diff-multi.ts`.
 */

import { readdirSync, readFileSync, writeFileSync, mkdirSync } from "node:fs";
import { resolve, join } from "node:path";
import { PNG } from "pngjs";
import pixelmatch from "pixelmatch";

const ROOT = resolve(process.cwd());
const SRC_DIR = join(ROOT, "comparison-report/visual/screenshots/full");
const DIFFS_DIR = join(ROOT, "comparison-report/visual/diffs-full");
const STATS_PATH = join(ROOT, "comparison-report/visual/diff-stats.json");

mkdirSync(DIFFS_DIR, { recursive: true });

const files = readdirSync(SRC_DIR);
const reactFiles = files.filter((f) => f.startsWith("react-") && f.endsWith(".png"));

const stats = {};
let processed = 0;

for (const reactFile of reactFiles) {
  const stem = reactFile.slice("react-".length); // e.g. "onlineboard-start.png"
  const angularFile = `angular-${stem}`;
  if (!files.includes(angularFile)) {
    console.log(`  skip (no angular pair): ${reactFile}`);
    continue;
  }

  const aBuf = readFileSync(join(SRC_DIR, angularFile));
  const rBuf = readFileSync(join(SRC_DIR, reactFile));
  const aPng = PNG.sync.read(aBuf);
  const rPng = PNG.sync.read(rBuf);

  const width = Math.max(aPng.width, rPng.width);
  const height = Math.max(aPng.height, rPng.height);

  const pad = (src) => {
    const out = new PNG({ width, height });
    for (let i = 0; i < out.data.length; i += 4) {
      out.data[i] = 255; out.data[i + 1] = 255; out.data[i + 2] = 255; out.data[i + 3] = 255;
    }
    for (let y = 0; y < src.height; y++) {
      for (let x = 0; x < src.width; x++) {
        const srcIdx = (y * src.width + x) * 4;
        const dstIdx = (y * width + x) * 4;
        out.data[dstIdx]     = src.data[srcIdx];
        out.data[dstIdx + 1] = src.data[srcIdx + 1];
        out.data[dstIdx + 2] = src.data[srcIdx + 2];
        out.data[dstIdx + 3] = src.data[srcIdx + 3];
      }
    }
    return PNG.sync.read(PNG.sync.write(out));
  };

  const aP = pad(aPng);
  const rP = pad(rPng);
  const diffPng = new PNG({ width, height });

  const mismatchCount = pixelmatch(
    aP.data, rP.data, diffPng.data, width, height,
    { threshold: 0.1, alpha: 0.3 },
  );

  const totalPixels = width * height;
  const mismatchPct = (mismatchCount / totalPixels) * 100;
  const heightDiff = rPng.height - aPng.height;

  const diffName = stem;
  writeFileSync(join(DIFFS_DIR, diffName), PNG.sync.write(diffPng));

  const key = stem.replace(/\.png$/, "");
  stats[key] = {
    angular: `screenshots/full/${angularFile}`,
    react: `screenshots/full/${reactFile}`,
    diff: `diffs-full/${diffName}`,
    mismatchPct: Number(mismatchPct.toFixed(3)),
    mismatchCount,
    totalPixels,
    heightDiff,
    angular_w: aPng.width, angular_h: aPng.height,
    react_w: rPng.width, react_h: rPng.height,
  };

  processed++;
  console.log(`  ${stem}: ${mismatchPct.toFixed(2)}% diff (${mismatchCount.toLocaleString()} / ${totalPixels.toLocaleString()} px)`);
}

writeFileSync(STATS_PATH, JSON.stringify(stats, null, 2));
console.log(`\nDone — ${processed} pairs diffed.`);
console.log(`  Diffs: ${DIFFS_DIR}/`);
console.log(`  Stats: ${STATS_PATH}`);