feat: initial functional release of Stock Pignon

app/src/main/java/com/stock/pignon/CartManager.java

@@ -0,0 +1,60 @@
+// CartManager.java
+package com.stock.pignon;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class CartManager {
+    // Unified and global list for whole application
+    private static final List<CartItem> items = new ArrayList<>();
+
+    // Private constructor: utility class, it should not be instantiated
+    private CartManager() {}
+
+    //  Returns the direct reference to the list to save memory on older devices
+    public static List<CartItem> getItems() {
+        return items;
+    }
+
+    public static CartItem getItemByName(String name) {
+        if (name == null) return null;
+        for (CartItem item : items) {
+            // if item.getName() is null, avoid crash
+            if (item != null && name.equals(item.getName())) return item;
+        }
+        return null;
+    }
+
+    // Logic for adding, updating or removing items based on quantity, prevents duplicate entries
+    public static void addOrUpdateItem(String name, int minPrice, int maxPrice, int quantity, String imageFile) {
+        CartItem current = getItemByName(name);
+
+        if (current != null) {
+            if (quantity <= 0) {
+                items.remove(current);
+            } else {
+                current.setQuantity(quantity);
+            }
+        } else if (quantity > 0) {
+            items.add(new CartItem(name, minPrice, maxPrice, quantity, imageFile));
+        }
+    }
+
+    // Range-based pricing
+
+    public static int getGlobalTotalMin() {
+        int total = 0;
+        for (CartItem item : items) total += item.getTotalMin();
+        return total;
+    }
+
+    public static int getGlobalTotalMax() {
+        int total = 0;
+        for (CartItem item : items) total += item.getTotalMax();
+        return total;
+    }
+
+    public static void clear() {
+        items.clear();
+    }
+}