Add tax-aware random product combo picker for Sổ Bán Lẻ auto-order

app/libs/productComboPicker.js

+"use strict";
+
+var DEFAULT_TOLERANCE = 50000;
+var DEFAULT_MAX_ATTEMPTS = 20;
+var DEFAULT_MAX_QTY_PER_LINE = 3;
+
+function shuffle(list, random) {
+  var arr = list.slice();
+  for (var i = arr.length - 1; i > 0; i--) {
+    var j = Math.floor(random() * (i + 1));
+    var tmp = arr[i];
+    arr[i] = arr[j];
+    arr[j] = tmp;
+  }
+  return arr;
+}
+
+function computeLineTotal(product, qty) {
+  var rate = product.tax && typeof product.tax.rate === "number" ? product.tax.rate : 0;
+  return Math.round(qty * product.price * (1 + rate / 100));
+}
+
+function pickProductCombo(products, targetAmount, options) {
+  options = options || {};
+  var tolerance = typeof options.tolerance === "number" ? options.tolerance : DEFAULT_TOLERANCE;
+  var maxAttempts = options.maxAttempts || DEFAULT_MAX_ATTEMPTS;
+  var random = options.random || Math.random;
+  var maxQtyPerLine = options.maxQtyPerLine || DEFAULT_MAX_QTY_PER_LINE;
+
+  var candidates = products.filter(function (p) {
+    return p.qty > 0 && p.price > 0;
+  });
+  if (candidates.length === 0) {
+    return null;
+  }
+
+  var minAcceptable = Math.max(1, targetAmount - tolerance);
+
+  for (var attempt = 0; attempt < maxAttempts; attempt++) {
+    var shuffled = shuffle(candidates, random);
+    var total = 0;
+    var lines = [];
+
+    for (var i = 0; i < shuffled.length; i++) {
+      var product = shuffled[i];
+      var maxQty = Math.min(maxQtyPerLine, product.qty);
+      var qty = 1 + Math.floor(random() * maxQty);
+      var lineTotal = computeLineTotal(product, qty);
+
+      if (total + lineTotal > targetAmount) {
+        continue;
+      }
+      total += lineTotal;
+      lines.push({ product_id: product.id, qty: qty });
+      if (total >= minAcceptable) {
+        break;
+      }
+    }
+
+    if (total >= minAcceptable && total <= targetAmount) {
+      return { lines: lines, total: total };
+    }
+  }
+
+  return null;
+}
+
+module.exports = {
+  pickProductCombo: pickProductCombo,
+  computeLineTotal: computeLineTotal,
+};