using System;
using System.Collections.Generic;
using System.Linq;
using Cielonos.MainGame.Inventory;
using Cielonos.MainGame.Inventory.Collections;
using Cielonos.MainGame.Items;
using UnityEngine;

namespace Cielonos.MainGame.Rewards
{
    /// <summary>
    /// RewardProfile 的运行时生成器。它产出 ItemBase：
    /// - prefab 候选适用于商店；
    /// - 临时实例适用于确认后才能交给背包的奖励界面。
    /// </summary>
    public static class RewardGenerator
    {
        public static List<ItemBase> GeneratePrefabOffers(RewardProfile profile, System.Random rng,
            RewardGenerationContext context = null)
        {
            return BuildOffers(profile, rng, context, null, false);
        }

        public static List<ItemBase> GenerateRuntimeOffers(RewardProfile profile, System.Random rng,
            Transform stagingRoot, RewardGenerationContext context = null)
        {
            if (stagingRoot == null)
            {
                Debug.LogError("[RewardGenerator] Runtime offers require a staging root.");
                return new List<ItemBase>();
            }

            return BuildOffers(profile, rng, context, stagingRoot, true);
        }

        private static List<ItemBase> BuildOffers(RewardProfile profile, System.Random rng,
            RewardGenerationContext context, Transform stagingRoot, bool instantiate)
        {
            List<ItemBase> results = new();
            if (profile == null || rng == null)
            {
                return results;
            }

            context ??= new RewardGenerationContext();
            HashSet<RewardEntry> consumedEntries = new();
            HashSet<ItemBase> selectedPrefabs = new();

            List<RewardEntry> profileEntries = profile.entries ?? new List<RewardEntry>();
            for (int slot = 0; slot < profile.offerCount; slot++)
            {
                List<RewardEntry> availableEntries = profileEntries
                    .Where(entry => IsEntryAvailable(entry, context, selectedPrefabs, consumedEntries, instantiate))
                    .ToList();
                RewardEntry selectedEntry = PickEntry(availableEntries, rng);
                if (selectedEntry == null)
                {
                    break;
                }

                if (!TryResolvePrefab(selectedEntry, context, selectedPrefabs, rng, out ItemBase prefab,
                        out ItemBase upgradeTarget))
                {
                    consumedEntries.Add(selectedEntry);
                    continue;
                }

                ItemBase result = prefab;
                if (instantiate)
                {
                    result = UnityEngine.Object.Instantiate(prefab, stagingRoot);
                    result.name = prefab.name;
                    ApplyRuntimeData(result, selectedEntry, upgradeTarget, rng);
                }
                else if (selectedEntry.mode == RewardEntryMode.UpgradeComponent)
                {
                    Debug.LogWarning($"[RewardGenerator] Profile '{profile.name}' uses UpgradeComponent, which cannot be displayed as a prefab offer.");
                    consumedEntries.Add(selectedEntry);
                    continue;
                }

                results.Add(result);
                selectedPrefabs.Add(prefab);
                if (!selectedEntry.allowRepeat)
                {
                    consumedEntries.Add(selectedEntry);
                }
            }

            return results;
        }

        private static bool IsEntryAvailable(RewardEntry entry, RewardGenerationContext context,
            ISet<ItemBase> selectedPrefabs, ISet<RewardEntry> consumedEntries, bool instantiate)
        {
            if (entry == null || entry.weight <= 0 || consumedEntries.Contains(entry))
            {
                return false;
            }

            return entry.mode switch
            {
                RewardEntryMode.FixedItem => CanSelectPrefab(entry.itemPrefab, context, selectedPrefabs,
                    entry.allowRepeat),
                RewardEntryMode.ItemPool => entry.filter != null && ItemPool.HasCandidate(
                    BuildRuntimeFilter(entry, context), selectedPrefabs,
                    entry.filter.GetResourceFolders()),
                RewardEntryMode.UpgradeComponent => instantiate && entry.itemPrefab != null &&
                                                     context.GetUpgradeableItems().Any(),
                _ => false
            };
        }

        private static RewardEntry PickEntry(List<RewardEntry> entries, System.Random rng)
        {
            int totalWeight = entries.Sum(entry => entry.weight);
            if (totalWeight <= 0)
            {
                return null;
            }

            int roll = rng.Next(totalWeight);
            int cumulative = 0;
            foreach (RewardEntry entry in entries)
            {
                cumulative += entry.weight;
                if (roll < cumulative)
                {
                    return entry;
                }
            }

            return entries[^1];
        }

        private static bool TryResolvePrefab(RewardEntry entry, RewardGenerationContext context,
            ISet<ItemBase> selectedPrefabs, System.Random rng, out ItemBase prefab, out ItemBase upgradeTarget)
        {
            prefab = null;
            upgradeTarget = null;

            switch (entry.mode)
            {
                case RewardEntryMode.FixedItem:
                    prefab = entry.itemPrefab;
                    return prefab != null;

                case RewardEntryMode.ItemPool:
                {
                    List<ItemBase> rolled = ItemPool.Roll(1, rng,
                        BuildRuntimeFilter(entry, context), selectedPrefabs,
                        entry.filter.GetResourceFolders());
                    prefab = rolled.Count > 0 ? rolled[0] : null;
                    return prefab != null;
                }

                case RewardEntryMode.UpgradeComponent:
                {
                    List<ItemBase> targets = context.GetUpgradeableItems();
                    if (targets.Count == 0)
                    {
                        return false;
                    }

                    prefab = entry.itemPrefab;
                    upgradeTarget = targets[rng.Next(targets.Count)];
                    return prefab != null;
                }

                default:
                    return false;
            }
        }

        private static bool CanSelectPrefab(ItemBase prefab, RewardGenerationContext context,
            ISet<ItemBase> selectedPrefabs, bool allowRepeat)
        {
            if (prefab == null || context.ShouldExcludeOwnedNonConsumable(prefab))
            {
                return false;
            }

            if (selectedPrefabs == null || !selectedPrefabs.Contains(prefab))
            {
                return true;
            }

            // Consumable 可以按配置重复；主武器、支援装备、被动装备必须保持唯一性。
            return allowRepeat && RewardGenerationContext.IsConsumable(prefab);
        }

        private static ItemFilter BuildRuntimeFilter(RewardEntry entry, RewardGenerationContext context)
        {
            ItemFilter filter = entry.filter.BuildRuntimeFilter(context.forcedRarity);
            if (!context.excludeOwnedNonConsumables)
            {
                return filter;
            }

            return filter.And(new ItemFilter(item => !context.ShouldExcludeOwnedNonConsumable(item)));
        }

        private static void ApplyRuntimeData(ItemBase item, RewardEntry entry, ItemBase upgradeTarget,
            System.Random rng)
        {
            if (item is ConsumableBase consumable)
            {
                int min = Mathf.Max(1, Mathf.Min(entry.quantityRange.x, entry.quantityRange.y));
                int max = Mathf.Max(min, entry.quantityRange.x, entry.quantityRange.y);
                consumable.stackAmount = rng.Next(min, max + 1);
            }

            if (entry.mode == RewardEntryMode.UpgradeComponent && item is PrefabricatedComponent component)
            {
                component.targetEquipment = upgradeTarget;
            }
        }
    }

    public class RewardGenerationContext
    {
        public ItemRarity forcedRarity = ItemRarity.None;
        public List<ItemBase> ownedItems = new();
        public bool excludeOwnedNonConsumables;

        /// <summary>
        /// 开启后，奖励生成会排除玩家已经拥有的主武器、支援装备和被动装备。
        /// Consumable 不参与该排除规则，仍然可以重复出现并堆叠。
        /// </summary>
        public RewardGenerationContext ExcludeOwnedNonConsumables()
        {
            excludeOwnedNonConsumables = true;
            return this;
        }

        public bool ShouldExcludeOwnedNonConsumable(ItemBase item)
        {
            if (!excludeOwnedNonConsumables || item == null || IsConsumable(item))
            {
                return false;
            }

            Type itemIdentity = GetItemIdentity(item);
            return itemIdentity != null && ownedItems.Any(owned => GetItemIdentity(owned) == itemIdentity);
        }

        public List<ItemBase> GetUpgradeableItems()
        {
            return ownedItems.Where(item => item != null && item.IsUpgradable).ToList();
        }

        public static bool IsConsumable(ItemBase item)
        {
            return item is ConsumableBase;
        }

        private static Type GetItemIdentity(ItemBase item)
        {
            if (item == null)
            {
                return null;
            }

            return item.contentData != null && item.contentData.itemClass != null
                ? item.contentData.itemClass
                : item.GetType();
        }

        public static RewardGenerationContext FromPlayer(ItemRarity forcedRarity = ItemRarity.None)
        {
            RewardGenerationContext context = new() { forcedRarity = forcedRarity };
            var backpack = MainGameManager.Player?.inventorySc?.backpackSm;
            if (backpack == null)
            {
                return context;
            }

            context.ownedItems.AddRange(backpack.mainWeapons);
            context.ownedItems.AddRange(backpack.supportEquipments);
            context.ownedItems.AddRange(backpack.passiveEquipments);
            return context;
        }
    }
}