(Feat) Add build cost

Assets/GAME/Script/Building/BuildableData.cs

@@ -1,4 +1,5 @@
 using UnityEngine;
+using Ashwild.Inventory;
 
 namespace Ashwild.Building
 {
@@ -30,6 +31,10 @@ namespace Ashwild.Building
         [Tooltip("The real structure spawned once the placement is confirmed.")]
         [SerializeField] private GameObject builtPrefab;
 
+        [Header("Cost")]
+        [Tooltip("Resources consumed from the builder's inventory on each placement. Leave empty for a free build.")]
+        [SerializeField] private BuildCost[] cost;
+
         #endregion
 
         #region Public API
@@ -39,6 +44,24 @@ namespace Ashwild.Building
         public string Description => description;
         public GameObject GhostPrefab => ghostPrefab;
         public GameObject BuiltPrefab => builtPrefab;
+        public BuildCost[] Cost => cost;
+
+        /// <summary>
+        /// Whether the given inventory holds enough of every cost line to place this structure once.
+        /// A null inventory or an empty cost list counts as affordable (free build).
+        /// </summary>
+        public bool CanAfford(PlayerInventory inventory)
+        {
+            if (cost == null || cost.Length == 0) return true;
+            if (inventory == null) return false;
+
+            for (int i = 0; i < cost.Length; i++)
+            {
+                if (cost[i].item == null) continue;
+                if (!inventory.HasItem(cost[i].item, cost[i].quantity)) return false;
+            }
+            return true;
+        }
 
         #endregion
     }