Chestny Znak scanner: bundle offline ZXing decoder, ЧЗ badge, session auto-push

- Native BarcodeDetector needs Google Play Services (fails "Barcode detection
  service unavailable" on de-Googled ROMs). Replace it with a bundled, fully
  offline ZXing decoder (frontend/lib/zxing.js, @zxing/library UMD): scanner uses
  BrowserDatamatrixCodeReader (TRY_HARDER) for live camera and decodeFromImageUrl
  for the photo fallback. No Google, codes never leave the device.
- Source badge "ЧЗ" (src-chzn) for products added via the scanner.
- tools/chzn_export.sh: adb push the exported session to the device Downloads so
  BalDav's file picker can import it directly.

frontend/css/styles.css

@@ -1649,6 +1649,7 @@ select {
 .src-kdv { background: rgba(255, 167, 38, 0.25); color: #ffb74d; }
 .src-ion { background: rgba(158, 158, 158, 0.2); color: #9e9e9e; }
 .src-manual { background: rgba(255, 235, 59, 0.2); color: #fff176; }
+.src-chzn { background: rgba(66, 165, 245, 0.22); color: #64b5f6; }
 
 .food-nutrients {
   font-size: 11px;

frontend/index.html

@@ -18,6 +18,7 @@
   <script src="lib/chart.min.js"></script>
   <script src="lib/chartjs-plugin-zoom.min.js"></script>
   <script src="lib/jszip.min.js"></script>
+  <script src="lib/zxing.js"></script>
   <script src="js/db.js"></script>
   <script src="js/bmr.js"></script>
   <script src="js/tilecache.js"></script>

frontend/js/main.js

@@ -1844,15 +1844,16 @@ function showAddProductModal(onSaved, prefill) {
   });
 }
 
-// Честный знак scanner: camera (BarcodeDetector) with photo/manual fallbacks.
-// On a decoded DataMatrix -> ChZ.resolve -> prefill the new-product modal.
+// Честный знак scanner: camera + photo/manual, decoded by bundled ZXing
+// (frontend/lib/zxing.js) — fully offline, no Google Play Services (the native
+// BarcodeDetector needs GMS and is absent on de-Googled ROMs). On a decoded
+// DataMatrix -> ChZ.resolve -> prefill the new-product modal.
 function showChznScanModal(onSaved) {
   if (!ChZ.hasSession()) {
     appAlert("Сессия Честного знака не импортирована.\nНастройки → Честный знак → Импорт сессии (файл chzn_session.json из tools/chzn_export.sh).");
     return;
   }
-  let hasBD = ("BarcodeDetector" in window);
-  let detector = hasBD ? new BarcodeDetector({ formats: ["data_matrix", "qr_code"] }) : null;
+  let hasZX = (typeof ZXing !== "undefined" && ZXing.BrowserDatamatrixCodeReader);
 
   let ov = document.createElement("div");
   ov.className = "modal-overlay";
@@ -1874,16 +1875,28 @@ function showChznScanModal(onSaved) {
     </div>`;
   document.body.appendChild(ov);
 
-  let stream = null, scanning = false, busy = false;
+  let controls = null, busy = false;
   let base = winStack.length;
   let statusEl = ov.querySelector("#cz-status");
   let video = ov.querySelector("#cz-video");
 
-  function cleanup() {
-    scanning = false;
-    if (stream) { stream.getTracks().forEach(t => t.stop()); stream = null; }
+  let reader = null;
+  if (hasZX) {
+    let hints = new Map();
+    hints.set(ZXing.DecodeHintType.TRY_HARDER, true); // better on curved/low-contrast codes
+    reader = new ZXing.BrowserDatamatrixCodeReader(hints, { delayBetweenScanAttempts: 120 });
   }
-  winPush("chzn-scan", () => { cleanup(); ov.remove(); });
+
+  function stopCamera() {
+    try { if (controls) controls.stop(); } catch {}
+    controls = null;
+    try {
+      let s = video && video.srcObject;
+      if (s && s.getTracks) s.getTracks().forEach(t => t.stop());
+      if (video) video.srcObject = null;
+    } catch {}
+  }
+  winPush("chzn-scan", () => { stopCamera(); ov.remove(); });
   function close() {
     let count = winStack.length - base;
     for (let i = 0; i < count; i++) winStack.pop().close();
@@ -1893,38 +1906,31 @@ function showChznScanModal(onSaved) {
 
   async function onDecoded(rawVal) {
     if (busy) return;
-    busy = true; scanning = false;
+    busy = true;
+    try { if (controls) controls.stop(); } catch {}
     statusEl.textContent = "Код распознан, запрашиваю КБЖУ...";
     try {
       let prefill = await ChZ.resolve(rawVal);
-      cleanup();
+      stopCamera();
       close();
       showAddProductModal(onSaved, prefill);
     } catch (e) {
       busy = false;
       statusEl.textContent = (e.notFound ? "Код не найден в Честном знаке. " : "Ошибка: " + e.message + ". ") + "Наведите ещё раз.";
-      if (detector && stream) { scanning = true; requestAnimationFrame(loop); }
+      if (reader) startCamera(); // resume continuous scan
     }
   }
 
-  async function loop() {
-    if (busy || !scanning) return;
-    try {
-      let codes = await detector.detect(video);
-      if (codes && codes.length) { scanning = false; onDecoded(codes[0].rawValue); return; }
-    } catch (e) { /* transient decode error, keep scanning */ }
-    requestAnimationFrame(loop);
-  }
-
   async function startCamera() {
-    if (!detector) { statusEl.textContent = "Сканер недоступен в этом WebView. Выберите фото кода или введите вручную."; return; }
+    if (!reader) { statusEl.textContent = "Декодер ZXing не загрузился — пересобери приложение."; return; }
     try {
-      stream = await navigator.mediaDevices.getUserMedia({ video: { facingMode: { ideal: "environment" } } });
-      video.srcObject = stream;
-      await video.play();
-      scanning = true;
       statusEl.textContent = "Наведите на код Честного знака...";
-      loop();
+      controls = await reader.decodeFromConstraints(
+        { video: { facingMode: { ideal: "environment" } } },
+        video,
+        (result) => { if (result && !busy) onDecoded(result.getText()); }
+        // per-frame NotFoundException is normal — ignored
+      );
     } catch (e) {
       statusEl.textContent = "Камера недоступна (" + (e.name || e.message) + "). Выберите фото или введите код.";
     }
@@ -1932,13 +1938,16 @@ function showChznScanModal(onSaved) {
 
   ov.querySelector("#cz-photo").onclick = () => {
     pickFile("image/*", async (buf) => {
-      if (!detector) { statusEl.textContent = "Сканер недоступен — введите код вручную."; return; }
+      if (!reader) { statusEl.textContent = "Декодер ZXing не загрузился."; return; }
+      let url = URL.createObjectURL(new Blob([buf]));
       try {
-        let bmp = await createImageBitmap(new Blob([buf]));
-        let codes = await detector.detect(bmp);
-        if (codes && codes.length) onDecoded(codes[0].rawValue);
-        else statusEl.textContent = "Код на фото не распознан. Попробуйте более резкое фото.";
-      } catch (e) { statusEl.textContent = "Ошибка распознавания: " + e.message; }
+        let result = await reader.decodeFromImageUrl(url);
+        onDecoded(result.getText());
+      } catch (e) {
+        statusEl.textContent = (e && e.name === "NotFoundException")
+          ? "Код на фото не распознан. Попробуйте более резкое фото."
+          : "Ошибка распознавания: " + (e.message || e);
+      } finally { URL.revokeObjectURL(url); }
     }, true);
   };
   ov.querySelector("#cz-manual").onclick = async () => {
@@ -7434,6 +7443,7 @@ function sourceBadge(source) {
     "5ka": ["5ка", "src-5ka"],
     kdv: ["KDV", "src-kdv"],
     ion: ["ИОН", "src-ion"],
+    chzn: ["ЧЗ", "src-chzn"],
     manual: ["Свой", "src-manual"],
     recipe_import: ["Импорт", "src-manual"],
   };