using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using KitsuneCafe.Sys;
using MessagePack;
using ObservableCollections;
using UnityEngine;
using Unit = KitsuneCafe.Sys.Unit;

namespace KitsuneCafe.ItemSystem
{
  [MessagePackObject(AllowPrivate = true)]
  [Serializable]
  public partial struct InventoryItem : IEquatable<Item>, ICountable
  {
    [Key(0)]
    public Item Item;

    [Key(1)]
    [SerializeField]
    private int count;

    [IgnoreMember]
    public readonly int Count => count;

    internal InventoryItem(Item item, int count)
    {
      Item = item;
      this.count = count;
    }

    public static int Create(Item item, int count, out InventoryItem? inventoryItem)
    {
      int quantity = Math.Clamp(count, 0, item.MaxStackCount);
      inventoryItem = quantity > 0 ? new InventoryItem(item, quantity) : null;
      return quantity;
    }

    public readonly int IncreaseCount(int count, out InventoryItem? item)
    {
      return Create(Item, Count + count, out item);
    }

    public readonly int ReduceCount(int count, out InventoryItem? item)
    {
      return Create(Item, Count - count, out item);
    }

    public readonly bool Equals(Item other)
    {
      return Item == other;
    }

    public override readonly bool Equals(object obj)
    {
      return obj is InventoryItem other
          && Item == other.Item
          && Count == other.Count;
    }

    public override int GetHashCode()
    {
      return HashCode.Combine(Item, Count);
    }
  }

  public enum InventoryError
  {
    None,
    InventoryFull,
    ItemNotFound,
    NotEnoughQuantity,
    ItemNotStackable,
    InvalidQuantity
  }

  public interface ICountable
  {
    int Count { get; }
  }

  public interface IInventory<T> where T : IEquatable<Item>, ICountable
  {
    int Capacity { get; }
    int Count { get; }

    IResult<Unit, InventoryError> Add(Item item, int count = 1);
    IResult<Unit, InventoryError> Remove(Item item, int count = 1);
    IEnumerable<T> Find(Func<T, bool> predicate);
    bool Has(Item item);
  }

  [MessagePackObject(AllowPrivate = true)]
  [CreateAssetMenu(menuName = KitsuneCafeMenu.Item + "Inventory")]
  public partial class Inventory : ScriptableObject, IList, IInventory<InventoryItem>, IEnumerable<InventoryItem>
  {
    [Key(0)]
    [SerializeField]
    private List<InventoryItem> items = new();
    [IgnoreMember]
    public IReadOnlyList<InventoryItem> Items => items;

    [IgnoreMember]
    [SerializeField]
    private int capacity = 8;

    public event NotifyCollectionChangedEventHandler<InventoryItem> CollectionChanged;

    [IgnoreMember]
    public int Capacity => capacity;

    [IgnoreMember]
    public int Count => items.Count;

    [IgnoreMember]
    public bool IsEmpty => Count == 0;

    [IgnoreMember]
    public bool IsFull => Count == Capacity;

    [IgnoreMember]
    public object SyncRoot => ((IList)items).SyncRoot;

    [IgnoreMember]
    public bool IsFixedSize => ((IList)items).IsFixedSize;

    [IgnoreMember]
    public bool IsReadOnly => ((IList)items).IsReadOnly;

    [IgnoreMember]
    public bool IsSynchronized => ((ICollection)items).IsSynchronized;

    [IgnoreMember]
    object IList.this[int index]
    {
      get => items[index];
      set => items[index] = (InventoryItem)value;
    }

    [IgnoreMember]
    public InventoryItem this[int index]
    {
      get => items[index];
      set => items[index] = value;
    }

    public void Load(Inventory inventory)
    {
      this.items = inventory.items;
    }

    public void Load(IList<InventoryItem> items)
    {
      this.items = items.ToList();
    }

    public bool TryGetValue(int index, out InventoryItem item)
    {
      if (0 <= index && index < Count)
      {
        item = items[index];
        return true;
      }
      else
      {
        item = default;
        return false;
      }
    }

    public IEnumerable<InventoryItem> Find(Func<InventoryItem, bool> predicate)
    {
      for (int i = 0; i < Count; i++)
      {
        var item = items[i];

        if (predicate(item))
        {
          yield return item;
        }
      }
    }

    private IResult<int, InventoryError> AddToExisting(Item item, int count)
    {
      if (count <= 0)
      {
        return Result.Err<int, InventoryError>(InventoryError.InvalidQuantity);
      }

      List<InventoryItem> existing = new();
      List<InventoryItem> updated = new();
      for (int i = 0; i < Count; i++)
      {
        var existingItem = items[i];
        existing.Add(existingItem);

        if (existingItem.Equals(item))
        {
          if (!item.IsStackable)
          {
            return Result.Err<int, InventoryError>(InventoryError.ItemNotStackable);
          }

          var consumedAmount = existingItem.IncreaseCount(count, out var updatedItem);
          updated.Add(updatedItem.Value);
          items[i] = updatedItem.Value;

          count -= consumedAmount;
          if (count <= 0)
          {
            return Result.Ok<int, InventoryError>(0);
          }
        }
      }

      Notify(NotifyCollectionChangedAction.Replace, updated, existing);
      return Result.Ok<int, InventoryError>(count);
    }

    private IResult<Unit, InventoryError> AddNew(Item item, int count)
    {
      List<InventoryItem> added = new();
      while (count > 0)
      {
        if (IsFull)
        {
          return Result.Err<Unit, InventoryError>(InventoryError.InventoryFull);
        }

        count -= InventoryItem.Create(item, count, out var newItem);
        items.Add(newItem.Value);
        added.Add(newItem.Value);
      }

      Notify(NotifyCollectionChangedAction.Add, added);
      return Result.Ok<Unit, InventoryError>(default);
    }

    public IResult<Unit, InventoryError> Add(Item item, int count = 1)
    {
      return AddToExisting(item, count)
          .Where(count => count > 0)
          .SelectMany(count => AddNew(item, count)) switch
      {
        Ok<Unit, InventoryError> ok => ok,
        Err<Unit, InventoryError>(InventoryError.None) => Result.Ok<Unit, InventoryError>(default),
        var err => err
      };
    }

    private void Notify(NotifyCollectionChangedAction action, IList<InventoryItem> newItems = default, IList<InventoryItem> oldItems = default)
    {
      NotifyCollectionChangedEventArgs<InventoryItem> args;

      if (newItems.Count == 1)
      {
        args = new(
          action,
          true,
          newItems[0],
          oldItems != null && oldItems.Count > 0 ? oldItems[0] : default
        );
      }
      else
      {
        args = new(
          action,
          false,
          newItems: newItems.ToArray(),
          oldItems: oldItems.ToArray()
        );
      }

      CollectionChanged?.Invoke(args);
    }

    public IResult<Unit, InventoryError> Remove(Item item, int count = 1)
    {
      if (count <= 0)
      {
        return Result.Err<Unit, InventoryError>(InventoryError.InvalidQuantity);
      }

      List<InventoryItem> removed = new();
      List<InventoryItem> updated = new();
      for (int i = items.Count - 1; i >= 0; i--)
      {
        var existingItem = items[i];

        if (existingItem.Item == item)
        {
          if (existingItem.Count > count)
          {
            existingItem.ReduceCount(count, out var updatedItem);
            items[i] = updatedItem.Value;

            removed.Add(existingItem);
            updated.Add(updatedItem.Value);

            Notify(NotifyCollectionChangedAction.Remove, updated, removed);
            return Result.Ok<Unit, InventoryError>(Unit.Default);
          }
          else
          {
            count -= existingItem.Count;
            items.RemoveAt(i);
            removed.Add(existingItem);

            if (count == 0)
            {
              Notify(NotifyCollectionChangedAction.Remove, updated, removed);
              return Result.Ok<Unit, InventoryError>(Unit.Default);
            }
          }
        }
      }

      if (count > 0)
      {
        return Result.Err<Unit, InventoryError>(InventoryError.NotEnoughQuantity);
      }

      Notify(NotifyCollectionChangedAction.Remove, updated, removed);
      return Result.Ok<Unit, InventoryError>(Unit.Default);
    }

    public bool Has(Item item)
    {
      for (int i = 0; i < Count; i++)
      {
        if (items[i].Equals(item))
        {
          return true;
        }
      }

      return false;
    }

    public IEnumerator<InventoryItem> GetEnumerator()
    {
      return items.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
      return GetEnumerator();
    }

    public int Add(object value)
    {
      return ((IList)items).Add(value);
    }

    public void Clear()
    {
      ((IList)items).Clear();
    }

    public bool Contains(object value)
    {
      return ((IList)items).Contains(value);
    }

    public int IndexOf(object value)
    {
      return ((IList)items).IndexOf(value);
    }

    public void Insert(int index, object value)
    {
      ((IList)items).Insert(index, value);
    }

    public void Remove(object value)
    {
      ((IList)items).Remove(value);
    }

    public void RemoveAt(int index)
    {
      ((IList)items).RemoveAt(index);
    }

    public void CopyTo(Array array, int index)
    {
      ((ICollection)items).CopyTo(array, index);
    }
  }
}