using System;
using System.Collections.Generic;

/// <summary>
///This class holds the model of our Shop. It contains an inventory, a price modifier, and an index to select the items.
///In its current setup, view and controller need to get data via polling. Advisable is, to apply observer pattern or
///set up an event system for better integration with View and Controller.
/// </summary>
public abstract class ShopModel : IModelObservable<Item>
{
    public Inventory inventory { get; } // Getter of the inventory, the views might need this to set up the display.
    protected float priceModifier; //Modifies the item's price based on its base price
    protected int selectedItemIndex = 0; //selected item index

    private List<IShopModelObserver<Item>> observers = new List<IShopModelObserver<Item>>();

    //------------------------------------------------------------------------------------------------------------------------
    //                                                  ShopModel()
    //------------------------------------------------------------------------------------------------------------------------        
    public ShopModel(float pPriceModifier, int pItemCount, int pMoney)
    {
        inventory = new Inventory(pItemCount, pMoney); 
    }

    //------------------------------------------------------------------------------------------------------------------------
    //                                                  GetSelectedItem()
    //------------------------------------------------------------------------------------------------------------------------        
    //Returns the selected item
    public Item GetSelectedItem()
    {
        if (selectedItemIndex >= 0 && selectedItemIndex < inventory.GetItemCount())
        {
            return inventory.GetItemByIndex(selectedItemIndex);
        }
        else
        {
            return null;
        }
    }

    //------------------------------------------------------------------------------------------------------------------------
    //                                                  SelectItemByIndex()
    //------------------------------------------------------------------------------------------------------------------------        
    //Attempts to select the item, specified by 'index', fails silently
    public void SelectItemByIndex(int index)
    {
        if (index >= 0 && index < inventory.GetItemCount())
        {
            selectedItemIndex = index;
            OnSelect(GetSelectedItem());
        }
        else
        {
            throw new ArgumentOutOfRangeException();
        }
    }


    //------------------------------------------------------------------------------------------------------------------------
    //                                                  SelectItem(Item item)
    //------------------------------------------------------------------------------------------------------------------------
    //Attempts to select the given item, fails silently
    public void SelectItem(Item item)
    {
        if (item != null)
        {
            int index = inventory.GetItems().IndexOf(item);
            if (index >= 0)
            {
                SelectItemByIndex(index);
            }
        }
    }

    //------------------------------------------------------------------------------------------------------------------------
    //                                                  GetSelectedItemIndex()
    //------------------------------------------------------------------------------------------------------------------------
    //returns the index of the current selected item
    public int GetSelectedItemIndex()
    {
        return selectedItemIndex;
    }

    //------------------------------------------------------------------------------------------------------------------------
    //                                                  Confirm()
    //------------------------------------------------------------------------------------------------------------------------        
    //Concrete classes to implement 
    public abstract void ConfirmSelectedItem();
    
    // Observer pattern. Anything that wants to know what happens regarding item selection subscribes to this. 
    // This could mean all items of this model and its views do it, or all views do it.
    public IDisposable RegisterObserver(IShopModelObserver<Item> observer)
    {
        // Check whether observer is already registered. If not, add it
        if (! observers.Contains(observer)) {
            observers.Add(observer);
            // Provide observer with existing data.
            observer.OnSelected(GetSelectedItem());
        }
        return new Unsubscriber<Item>(observers, observer);
    }

    public void RemoveObserver(IShopModelObserver<Item> observer)
    {
        if (observers.Contains(observer))
            observers.Remove(observer);
    }

    public void OnRemove(Item val)
    {
        // We copy the list so we don't break it while iterating, as it's likely OnRemove will cause an object to unsub
        var observerCopy = observers.ToArray();   
        foreach (var observer in observerCopy)
            observer.OnRemoved(val);
    }

    public void OnSelect(Item val)
    {
        foreach (var observer in observers)
            observer.OnSelected(val);
    }
}