using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace JiShe.CollectBus.Common.Helpers
{
    /// <summary>
    /// 设备组负载控制
    /// </summary>
    public class DeviceGroupBalanceControl
    {
        /// <summary>
        /// 设备组数量
        /// </summary>
        private const int GroupCount = 50;
        private static List<string>[] _cachedGroups;
        private static Dictionary<string, int> _balancedMapping;

        /// <summary>
        /// 初始化缓存并强制均衡
        /// </summary>
        public static void InitializeCache(List<string> deviceList)
        {
            // 步骤1: 生成均衡映射表
            _balancedMapping = CreateBalancedMapping(deviceList, GroupCount);

            // 步骤2: 根据映射表填充分组
            _cachedGroups = new List<string>[GroupCount];
            for (int i = 0; i < GroupCount; i++)
            {
                _cachedGroups[i] = new List<string>(capacity: deviceList.Count / GroupCount + 1);
            }

            foreach (var deviceId in deviceList)
            {
                int groupId = _balancedMapping[deviceId];
                _cachedGroups[groupId].Add(deviceId);
            }
        }

        /// <summary>
        /// 通过 deviceId 获取分组
        /// </summary>
        public static List<string> GetGroup(string deviceId)
        {
            if (_balancedMapping == null || _cachedGroups == null)
                throw new InvalidOperationException("缓存未初始化");

            int groupId = _balancedMapping[deviceId];
            return _cachedGroups[groupId];
        }


        /// <summary>
        /// 创建均衡映射表
        /// </summary>
        /// <param name="deviceList">数据集合</param>
        /// <param name="groupCount">分组数量</param>
        /// <param name="maxDeviation">允许的最大偏差百分比</param>
        /// <returns></returns>
        public static Dictionary<string, int> CreateBalancedMapping(List<string> deviceList, int groupCount, int maxDeviation = 5)
        {
            var mapping = new Dictionary<string, int>();
            int targetPerGroup = deviceList.Count / groupCount;
            int maxAllowed = (int)(targetPerGroup * (1 + maxDeviation / 100.0));

            // 初始化分组计数器
            int[] groupCounters = new int[groupCount];

            // 随机数生成器用于平衡分配
            Random rand = new Random();

            foreach (var deviceId in deviceList)
            {
                int preferredGroup = GetGroupId(deviceId, groupCount);

                // 如果首选分组未满，直接分配
                if (groupCounters[preferredGroup] < maxAllowed)
                {
                    mapping[deviceId] = preferredGroup;
                    groupCounters[preferredGroup]++;
                }
                else
                {
                    // 寻找当前最空闲的分组
                    int fallbackGroup = Array.IndexOf(groupCounters, groupCounters.Min());
                    mapping[deviceId] = fallbackGroup;
                    groupCounters[fallbackGroup]++;
                }
            }

            return mapping;
        }

        /// <summary>
        /// 分析分组分布
        /// </summary>
        /// <param name="deviceList"></param>
        /// <param name="groupCount"></param>
        /// <returns></returns>
        public static Dictionary<int, int> AnalyzeDistribution(List<string> deviceList, int groupCount)
        {
            Dictionary<int, int> distribution = new Dictionary<int, int>();
            foreach (var deviceId in deviceList)
            {
                int groupId = GetGroupId(deviceId, groupCount);
                distribution[groupId] = distribution.TryGetValue(groupId, out var count) ? count + 1 : 1;
            }
            return distribution;
        }

        /// <summary>
        /// 获取设备ID对应的分组ID
        /// </summary>
        /// <param name="deviceId"></param>
        /// <param name="groupCount"></param>
        /// <returns></returns>
        public static int GetGroupId(string deviceId, int groupCount)
        {
            int hash = Fnv1aHash(deviceId);
            // 双重取模确保分布均匀
            return (hash % groupCount + groupCount) % groupCount;
        }

        /// <summary>
        /// FNV-1a哈希算法
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static int Fnv1aHash(string input)
        {
            const uint fnvPrime = 16777619;
            const uint fnvOffsetBasis = 2166136261;

            uint hash = fnvOffsetBasis;
            foreach (char c in input)
            {
                hash ^= (byte)c;
                hash *= fnvPrime;
            }
            return (int)hash;
        }

        /// <summary>
        /// 打印分组统计数据
        /// </summary>
        public static void PrintDistributionStats()
        {
            var stats = _cachedGroups
                .Select((group, idx) => new { GroupId = idx, Count = group.Count })
                .OrderBy(x => x.GroupId);

            Console.WriteLine("分组数据量统计:");
            foreach (var stat in stats)
            {
                Console.WriteLine($"Group {stat.GroupId}: {stat.Count} 条数据");
            }
        }

    }
}