using AsbCloudDb.Model;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using Mapster;
using System.Threading.Tasks;
using Microsoft.Extensions.Configuration;

#nullable enable
namespace AsbCloudInfrastructure.Services.SAUB
{
    public class TelemetryDataCache<TDto>
        where TDto : AsbCloudApp.Data.ITelemetryData
    {
        private const int activeWellCapacity = 12 * 60 * 60;
        private const int doneWellCapacity = 65 * 60;

        private readonly ConcurrentDictionary<int, CyclycArray<TDto>> caches;
        private bool isLoading = false;

        private TelemetryDataCache()
        {
            caches = new();
        }

        private static TelemetryDataCache<TDto>? instance;

        //TODO: Move initialize fromDB to bacground service task 
        public static TelemetryDataCache<TDto> GetInstance<TEntity>(IConfiguration configuration)
            where TEntity : class, ITelemetryData
        {
            if (instance is null)
            {
                instance = new TelemetryDataCache<TDto>();
                _ = Task.Run(() => 
                {
                    using var db = MakeContext(configuration);
                    instance.InitializeCacheFromDB<TEntity>(db);
                    db.Dispose();
                });
            }
            return instance;
        }
        public static TelemetryDataCache<TDto> GetInstance<TEntity>(IAsbCloudDbContext db, out Task initializationTask)
            where TEntity : class, ITelemetryData
        {
            if (instance is null)
            {
                instance = new TelemetryDataCache<TDto>();
                initializationTask = Task.Run(() =>
                {
                    instance.InitializeCacheFromDB<TEntity>(db);
                });
            }
            else
                initializationTask = Task.CompletedTask;
            return instance;
        }

        /// <summary>
        /// Добавить новые элементы в кеш
        /// </summary>
        /// <param name="idTelemetry"></param>
        /// <param name="range"></param>
        public void AddRange(int idTelemetry, IEnumerable<TDto> range)
        {
            CyclycArray<TDto> cacheItem;
            if (isLoading)
            {
                if (caches.TryGetValue(idTelemetry, out CyclycArray<TDto>? localCacheItem))
                    cacheItem = localCacheItem;
                else
                    return;
            }
            else
            {
                cacheItem = caches.GetOrAdd(idTelemetry, _ => new CyclycArray<TDto>(activeWellCapacity));
            }

            var newItems = range
                .OrderBy(i => i.DateTime);
            foreach (var item in newItems)
                item.IdTelemetry = idTelemetry;
            cacheItem.AddRange(newItems);
        }

        /// <summary>
        /// Получить данные из кеша. <br/>
        /// Если dateBegin меньше минимального элемента в кеше, то вернется null.
        /// Даже если intervalSec частично перекрыт данными из кеша.
        /// </summary>
        /// <param name="idTelemetry"></param>
        /// <param name="dateBegin"></param>
        /// <param name="intervalSec"></param>
        /// <param name="approxPointsCount">кол-во элементов до которых эти данные прореживаются</param>
        /// <returns></returns>
        public IEnumerable<TDto>? GetOrDefault(int idTelemetry, DateTime dateBegin, double intervalSec = 600d, int approxPointsCount = 1024)
        {
            if(!caches.TryGetValue(idTelemetry, out CyclycArray<TDto>? cacheItem))
                return null;

            if (cacheItem is null || !cacheItem.Any() || cacheItem[0].DateTime > dateBegin)
                return null;
            
            var dateEnd = dateBegin.AddSeconds(intervalSec);
            var items = cacheItem
                .Where(i => i.DateTime >= dateBegin && i.DateTime <= dateEnd);

            var ratio = items.Count() / approxPointsCount;
            if (ratio > 1)
                items = items
                    .Where((_, index) => index % ratio == 0);

            return items;
        }

        private void InitializeCacheFromDB<TEntity>(IAsbCloudDbContext db)
            where TEntity : class, ITelemetryData
        {
            if (isLoading)
                throw new Exception("Multiple cache loading detected.");

            isLoading = true;
            Well[] wells = Array.Empty<Well>();
                wells = db.Set<Well>()
                    .Include(well => well.Telemetry)
                    .Include(well => well.Cluster)
                    .Where(well => well.IdTelemetry != null)
                    .ToArray();

            foreach (Well well in wells)
            {
                var capacity = well.IdState == 1
                    ? activeWellCapacity
                    : doneWellCapacity;

                var idTelemetry = well.IdTelemetry!.Value;
                var hoursOffset = well.Timezone.Hours;

                IEnumerable<TDto> cacheItemData = GetCacheDataFromDb<TEntity>(db, idTelemetry, capacity, hoursOffset);
                var cacheItem = new CyclycArray<TDto>(capacity);
                cacheItem.AddRange(cacheItemData);
                caches.TryAdd(idTelemetry, cacheItem);
                                
                System.Diagnostics.Trace.TraceInformation($"cache<{typeof(TDto).Name}> for well: {well.Cluster?.Caption}/{well.Caption} loaded");
            }

            System.Diagnostics.Trace.TraceInformation($"cache<{typeof(TDto).Name}> load complete");
            isLoading = false;
        }

        private static IAsbCloudDbContext MakeContext(IConfiguration configuration)
        {
            var connectionString = configuration.GetConnectionString("DefaultConnection");
            var options = new DbContextOptionsBuilder<AsbCloudDbContext>()
                .UseNpgsql(connectionString)
                .Options;
            var db = new AsbCloudDbContext(options);
            return db;
        }

        private static IEnumerable<TDto> GetCacheDataFromDb<TEntity>(IAsbCloudDbContext db, int idTelemetry, int capacity, double hoursOffset)
            where TEntity : class, ITelemetryData
        {
            var entities = db.Set<TEntity>()
                .Where(i => i.IdTelemetry == idTelemetry)
                .OrderByDescending(i => i.DateTime)
                .Take(capacity)
                .ToArray()
                .AsEnumerable()
                .Reverse();

            var dtos = entities.Select(entity => {
                var dto = entity.Adapt<TDto>();
                dto.DateTime = entity.DateTime.ToRemoteDateTime(hoursOffset);
                return dto;
            });

            return dtos;
        }
    }
}
#nullable disable