using System.Collections.Generic;
using System.Linq;
using UnityEngine;

namespace Entity
{
    public class Inventory
    {
        public Entity From { get; private set; }
        private readonly List<InventorySlot> _slots;
        public int Capacity { get; private set; }

        public event System.Action<Item.ItemResource, int> OnItemAdded;
        public event System.Action<Item.ItemResource, int> OnItemRemoved;
        public event System.Action OnInventoryChanged;

        public Inventory(Entity owner, int capacity = 20)
        {
            From = owner;
            Capacity = Mathf.Max(1, capacity);
            _slots = new List<InventorySlot>(Capacity);
        }

        public int AddItem(Item.ItemResource itemResource, int quantity)
        {
            if (itemResource == null || quantity <= 0)
            {
                Debug.LogWarning(
                    $"Inventory for {From?.ToString() ?? "Unknown"}: Attempted to add null item or zero/negative quantity.");
                return quantity;
            }

            var remainingQuantity = quantity;
            var addedTotal = 0;

            // 1. 尝试堆叠到现有槽位 (使用 DefName 进行比较)
            if (itemResource.MaxStack > 1)
            {
                foreach (var slot in _slots.Where(s =>
                             s.Item != null && s.Item.DefName == itemResource.DefName && !s.IsFull))
                {
                    var addedToSlot = slot.AddQuantity(remainingQuantity);
                    remainingQuantity -= addedToSlot;
                    addedTotal += addedToSlot;
                    if (remainingQuantity <= 0) break;
                }
            }

            // 2. 如果还有剩余，尝试添加到新槽位
            while (remainingQuantity > 0 && _slots.Count < Capacity)
            {
                var quantityToAdd = Mathf.Min(remainingQuantity, itemResource.MaxStack);
                var newSlot = new InventorySlot(itemResource, quantityToAdd);
                _slots.Add(newSlot);
                remainingQuantity -= quantityToAdd;
                addedTotal += quantityToAdd;
            }

            if (addedTotal > 0)
            {
                OnItemAdded?.Invoke(itemResource, addedTotal);
                OnInventoryChanged?.Invoke();
            }

            if (remainingQuantity > 0)
            {
                Debug.LogWarning(
                    $"Inventory for {From?.ToString() ?? "Unknown"} is full or cannot stack. {remainingQuantity} of {itemResource.Name} (DefName: {itemResource.DefName}) could not be added.");
            }

            return remainingQuantity;
        }

        public int RemoveItem(Item.ItemResource itemResource, int quantity)
        {
            if (itemResource == null || quantity <= 0)
            {
                Debug.LogWarning(
                    $"Inventory for {From?.ToString() ?? "Unknown"}: Attempted to remove null item or zero/negative quantity.");
                return quantity;
            }

            var remainingQuantity = quantity;
            var removedTotal = 0;
            var slotsToClean = new List<InventorySlot>();

            // 从后往前遍历，以便安全地移除空槽位 (使用 DefName 进行比较)
            for (var i = _slots.Count - 1; i >= 0; i--)
            {
                var slot = _slots[i];
                if (slot.Item != null && slot.Item.DefName == itemResource.DefName)
                {
                    var removedFromSlot = slot.RemoveQuantity(remainingQuantity);
                    remainingQuantity -= removedFromSlot;
                    removedTotal += removedFromSlot;

                    if (slot.IsEmpty)
                    {
                        slotsToClean.Add(slot);
                    }

                    if (remainingQuantity <= 0) break;
                }
            }

            foreach (var slot in slotsToClean)
            {
                _slots.Remove(slot);
            }

            if (removedTotal > 0)
            {
                OnItemRemoved?.Invoke(itemResource, removedTotal);
                OnInventoryChanged?.Invoke();
            }

            if (remainingQuantity > 0)
            {
                Debug.LogWarning(
                    $"Inventory for {From?.ToString() ?? "Unknown"}: Not enough {itemResource.Name} (DefName: {itemResource.DefName}). {remainingQuantity} could not be removed.");
            }

            return remainingQuantity;
        }

        public bool HasItem(Item.ItemResource itemResource, int quantity = 1)
        {
            if (itemResource == null || quantity <= 0) return false;
            return GetItemCount(itemResource) >= quantity;
        }

        public int GetItemCount(Item.ItemResource itemResource)
        {
            if (itemResource == null) return 0;
            // 使用 DefName 进行计数
            return _slots.Where(s => s.Item != null && s.Item.DefName == itemResource.DefName)
                .Sum(s => s.Quantity);
        }

        public IReadOnlyList<InventorySlot> GetSlots()
        {
            return _slots.AsReadOnly();
        }
        public InventorySlot GetSlot(Item.ItemResource itemResource)
        {
            if (itemResource == null) return null;

            foreach (var slot in _slots)
            {
                if (slot.Item != null && slot.Item.DefName == itemResource.DefName)
                {
                    return slot;
                }
            }

            return null;
        }
        public InventorySlot GetSlot(int i)
        {
            if (i < 0 || i >= OccupiedSlotsCount)
                return null;
            return _slots[i];
        }

        public int OccupiedSlotsCount => _slots.Count;
        public int AvailableSlotsCount => Capacity - _slots.Count;
    }
}