DougDiggem/Assets/Inventory.cs

using System.Collections.Generic;
using UnityEngine;

public class Inventory : MonoBehaviour
{
    public ItemSlot[] itemSlots;

    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {

    }

    // we'll set this up to only try to add one item to the inventory at a time for now
    // there won't be stacked items in the wild for right now
    public bool AddItem(Item item)
    {
        // first try to stack
        for (int i = 0; i < itemSlots.Length; i++)
        {
            if (itemSlots[i] != null)
            {
                if (itemSlots[i].item == item.id && itemSlots[i].quantity < item.maxStack)
                {
                    itemSlots[i].quantity += 1;
                    return true;
                }
            }
        }

        // no stack to add to, try to find an empty slot
        for (int i = 0; i < itemSlots.Length; i++)
        {
            if (itemSlots[i] == null)
            {
                itemSlots[i] = new ItemSlot();

                itemSlots[i].quantity = 1;
                itemSlots[i].item = item.id;
                return true;
            }
        }

        // no open slots, no open stacks, we can't add the item
        return false;
    }

    public bool RemoveItemQuantity(ItemIdEnum itemId, int quantity)
    {
        if (GetItemQuantity(itemId) >= quantity)
        {
            int currentQuantity = quantity;

            for (int i = 0; i < itemSlots.Length; i++)
            {
                if (itemSlots[i] != null && itemSlots[i].item == itemId)
                {
                    // we are trying to remove less items than what exists in the current
                    // stack, so just subtract from the stack 
                    if (currentQuantity < itemSlots[i].quantity)
                    {
                        itemSlots[i].quantity -= currentQuantity;
                        break;
                    }
                    else if (currentQuantity == itemSlots[i].quantity)
                    {
                        // we have exactly enough in the current slot, so nullify it and
                        // exit
                        itemSlots[i] = null;
                        break;
                    }
                    else
                    {
                        // we don't have enough in the stack, but we DO have enough in our
                        // inventory. nullify the stack, subtract that number from the current
                        // count, and move to the next item
                        currentQuantity -= itemSlots[i].quantity;
                        itemSlots[i] = null;
                    }
                }
            }
            
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetItemQuantity(ItemIdEnum itemId)
    {
        int itemCount = 0;

        foreach (ItemSlot slot in itemSlots)
        {
            if (slot != null && slot.item == itemId)
            {
                itemCount += slot.quantity;
            }
        }

        return itemCount;
    }

    #region Inventory Save/Load
    public void SaveInventory(ref InventorySaveData data)
    {
        data.itemSlots = itemSlots;
    }

    public void LoadInventory(InventorySaveData data)
    {
        if (data.itemSlots != null)
        {
            itemSlots = data.itemSlots;
        }
        else
        {
            Debug.Log("new slots");
            itemSlots = new ItemSlot[8];
        }
    }
    #endregion
}

[System.Serializable]
public class ItemSlot
{
    public int quantity;
    public ItemIdEnum item;
}

[System.Serializable]
public struct InventorySaveData
{
    public ItemSlot[] itemSlots;
}