InventorySystem - Part 6.1

using System.Collections.Generic;
using UnityEngine;

public class InventorySystem : MonoBehaviour
{
    public static InventorySystem Instance { get; private set; }

    public int maxSlots = 15;
    public List<Item> inventory = new List<Item>();
    public Item leftHandItem;
    public Item rightHandItem;
    public Item backpack;

    private Dictionary<Item, List<Item>> storageInventories = new Dictionary<Item, List<Item>>();

    public bool IsBackpackEquipped => backpack != null;

    private void Awake()
    {
        if (Instance == null)
        {
            Instance = this;
            DontDestroyOnLoad(gameObject);
        }
        else
        {
            Destroy(gameObject);
        }
    }

    public bool AddItem(Item item)
    {
        if (inventory.Count < maxSlots)
        {
            inventory.Add(item);
            return true;
        }
        return false;
    }

    public void RemoveItem(Item item)
    {
        inventory.Remove(item);
    }

    public bool HasItem(Item item)
    {
        return inventory.Contains(item);
    }

    public void EquipItem(Item item, bool isLeftHand, bool isTwoHanded)
    {
        if (isTwoHanded)
        {
            leftHandItem = item;
            rightHandItem = item;
        }
        else if (isLeftHand)
        {
            leftHandItem = item;
        }
        else
        {
            rightHandItem = item;
        }
    }

    public void UnequipItem(bool isLeftHand)
    {
        if (leftHandItem != null && leftHandItem.isTwoHanded)
        {
            leftHandItem = null;
            rightHandItem = null;
        }
        else if (isLeftHand)
        {
            leftHandItem = null;
        }
        else
        {
            rightHandItem = null;
        }
    }

    public void EquipBackpack(Item backpackItem)
    {
        if (backpack != null)
        {
            inventory.Add(backpack); // Add the previous backpack back to the inventory
        }

        backpack = backpackItem; // Equip the new backpack
        inventory.Remove(backpackItem); // Remove it from the hand-held items

        StorageSystem.Instance.InitializeStorage(backpack); // Initialize its storage functionality
    }

    public void UnequipBackpack()
    {
        if (backpack != null)
        {
            inventory.Add(backpack);
            backpack = null;
        }
    }

    public void AddItemToStorage(Item storageItem, Item itemToStore)
    {
        if (!storageInventories.ContainsKey(storageItem))
        {
            storageInventories[storageItem] = new List<Item>();
        }
        storageInventories[storageItem].Add(itemToStore);
    }

    public List<Item> GetStorageInventory(Item storageItem)
    {
        if (storageInventories.TryGetValue(storageItem, out List<Item> items))
        {
            return items;
        }
        return new List<Item>();
    }

    public void RemoveItemFromStorage(Item storageItem, Item itemToRemove)
    {
        if (storageInventories.TryGetValue(storageItem, out List<Item> items))
        {
            items.Remove(itemToRemove);
        }
    }

    public bool TryStoreItem(Item storageItem, Item item)
    {
        if (storageInventories[storageItem].Count >= storageItem.storageCapacity)
        {
            UIManager.Instance.ShowError("Storage is full!");
            return false;
        }

        storageInventories[storageItem].Add(item);
        item.transform.SetParent(UIManager.Instance.storageHolder);
        item.gameObject.SetActive(false);
        return true;
    }

    public bool TryWithdrawItem(Item storageItem, Item item)
    {
        if (leftHandItem != null && rightHandItem != null)
        {
            UIManager.Instance.ShowError("Hands are full!");
            return false;
        }

        if (storageInventories[storageItem].Remove(item))
        {
            EquipItem(item, leftHandItem == null, false);
            return true;
        }
        return false;
    }
}