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

namespace AsbCloudInfrastructure.Services
{
#nullable enable
    public class JobDto
    {
        public enum JobState { Waiting, Working, Done, Fail };
        public int Id { get; internal set; }
        public JobState State { get; internal set; }
        public object? Result { get; internal set; }
        public Exception? Error { get; internal set; }
    }

    class JobWithProgress: JobDto
    {
        public ReduceSamplingService.OnProgressDelagate OnProgress { get; set; } = null!;
    }

    public class ReduceSamplingService
    {
        public delegate void OnProgressDelagate(JobDto job);
        private static ReduceSamplingService? instance;
        private readonly string connectionString;
        private const int ratio = 5;
        private readonly List<JobWithProgress> jobs = new(5);
        private bool isHandling;
        private CancellationTokenSource? cancellationTokenSource;
        private Task? task;

        private ReduceSamplingService(IConfiguration configuration)
        {
            connectionString = configuration.GetConnectionString("DefaultConnection");
        }

        ~ReduceSamplingService()
        {
            Stop();
        }

        public static ReduceSamplingService GetInstance(IConfiguration configuration)
        {
            if (instance is null)
                instance = new(configuration);
            return instance;
        }

        public int TryEnqueueRediceSamplingJob(int idTelemetry, OnProgressDelagate onProgress)
        {
            var result = 0;
            lock (jobs)
            {
                if (jobs.Any(j => j.Id == idTelemetry))
                    result = - 1;

                var job = new JobWithProgress
                {
                    Id = idTelemetry,
                    State = JobDto.JobState.Waiting,
                    OnProgress = onProgress,
                };

                jobs.Add(job);
                result = jobs.Count;
            }
            EnsureHandleQueueStarted();
            return result;
        }

        public JobDto? GetState(int idTelemetry)
        {
            JobWithProgress? job;
            lock (jobs)
            {
                job = jobs.FirstOrDefault(j=>j.Id == idTelemetry);
            }
            return job;
        }

        public IEnumerable<JobDto> GetJobs()
        {
            return jobs;
        }

        private bool TryTakeWaitingJob(out JobWithProgress? job)
        {
            lock (jobs)
            {
                job = jobs.FirstOrDefault(j => j.State == JobDto.JobState.Waiting);
            }
            return job is not null;
        }

        private void EnsureHandleQueueStarted()
        {
            if(isHandling)
                return;
            isHandling = true;
            cancellationTokenSource = new CancellationTokenSource();
            var token = cancellationTokenSource.Token;
            task = Task.Run(async () => await HandleJobs(token))
                .ContinueWith(_ => isHandling = false);
        }

        private async Task HandleJobs(CancellationToken token)
        {
            while (TryTakeWaitingJob(out JobWithProgress? job))
            {
                job!.State = JobDto.JobState.Working;
                try
                {
                    await RediceSamplingSaubAsync(job, token);
                    await RediceSamplingSpinAsync(job, token);
                    job.State = JobDto.JobState.Done;
                }
                catch (Exception exception)
                {
                    job.State = JobDto.JobState.Fail;
                    job.Error = exception;
                    job.OnProgress.Invoke(job);
                }
                await Task.Delay(100, token);
            }
            await VacuumAsync(token);
            await Task.Delay(1_000, token);
            CleanJobs();
        }

        private void CleanJobs()
        {
            lock (jobs)
            {
                jobs.RemoveAll(j => j.State == JobDto.JobState.Done || j.State == JobDto.JobState.Fail);
            }
        }

        private async Task VacuumAsync(CancellationToken token)
        {
            using var db = MakeContext();
            var sqlVacuum = "vacuum (SKIP_LOCKED);";
            await db.Database.ExecuteSqlRawAsync(sqlVacuum, token);
        }

        private void Stop()
        {
            cancellationTokenSource?.Cancel();
            task?.Wait(1_000);
            task = null;
            cancellationTokenSource = null;
        }

        /// <summary>
        /// Прореживание данных телеметрии САУБ.
        /// Каждая ratio запись будет сохранена, остальные удаляются. Остаются (Row_number % ratio) = 0.
        /// </summary>
        /// <param name="idTelemetry">Id телеметрии</param>
        /// <param name="ratio">желаемое отношение оставшихся записей к исходным</param>
        /// <returns></returns>        
        private Task RediceSamplingSaubAsync(JobWithProgress job, CancellationToken token)
        {
            const int ramLimit = 10 * 1024 * 1024;
            const int dataItemSize = 345; // by profiler
            const int chankSize = ramLimit / dataItemSize; // ~ 90_000
            const double maxWellDepthGap = 0.1;

            var maxDateGapSec = ratio;

            var sqlSelectTemplate =
                "select " +
                "   * " +
                "from " +
                "   (select " +
                "      *, " +
                "      rank() over win1 as row_num, " +
                "      lag(\"date\", 1) over win1 as lag_date, " +
                "      lag(\"mode\", 1) over win1 as lag_mode, " +
                "      lag(mse_state, 1) over win1 as lag_mse_state, " +
                "      lag(well_depth, 1) over win1 as lag_well_depth, " +
                "      lag(id_feed_regulator, 1) over win1 as lag_id_feed_regulator " +
                "   from t_telemetry_data_saub " +
                $"   where id_telemetry = {job.Id} and \"date\" > {{0}}" +
                "   window win1 as (order by \"date\") " +
                "   ) as t_1 " +
                "where " +
                $"   (row_num % {ratio}) = 0 " +
                "   or \"mode\" != lag_mode " +
                $"   or(\"date\" - lag_date) >= interval '{maxDateGapSec} second' " +
                $"   or well_depth - lag_well_depth > {maxWellDepthGap:#0,0#} " +
                "   or mse_state != lag_mse_state " +
                "   or id_feed_regulator != lag_id_feed_regulator " +
                "order by \"date\" ";

            var sqlDeleteTemplate = "delete " +
                "from t_telemetry_data_saub " +
                $"where id_telemetry = {job.Id} and \"date\" between {{0}} and {{1}};";

            return RediceSamplingAsync<TelemetryDataSaub>(
                job,
                chankSize, 
                sqlSelectTemplate, 
                sqlDeleteTemplate,
                token);
        }

        private Task RediceSamplingSpinAsync(JobWithProgress job, CancellationToken token)
        {
            const int ramLimit = 10 * 1024 * 1024;
            const int dataItemSize = 345; // by profiler
            const int chankSize = ramLimit / dataItemSize; // ~ 90_000
            var maxDateGapSec = ratio;

            var sqlSelectTemplate =
                "select " +
                "   * " +
                "from " +
                "   (select " +
                "      *, " +
                "      rank() over win1 as row_num, " +
                "      lag(\"date\", 1) over win1 as lag_date, " +
                "      lag(\"mode\", 1) over win1 as lag_mode, " +
                "      lag(state, 1) over win1 as lag_state " +
                "   from t_telemetry_data_spin " +
                $"   where id_telemetry = {job.Id} and \"date\" > {{0}}" +
                "   window win1 as (order by \"date\") " +
                "   ) as t_1 " +
                "where " +
                $"   (row_num % {ratio}) = 0 " +
                "   or \"mode\" != lag_mode " +
                $"   or(\"date\" - lag_date) >= interval '{maxDateGapSec} second' " +
                "   or state != lag_state " +
                "order by \"date\" ";

            var sqlDeleteTemplate = "delete " +
                "from t_telemetry_data_spin " +
                $"where id_telemetry = {job.Id} and \"date\" between {{0}} and {{1}};";

            return RediceSamplingAsync<TelemetryDataSpin>(
                job,
                chankSize,
                sqlSelectTemplate,
                sqlDeleteTemplate,
                token);
        }

        private async Task RediceSamplingAsync<TEntity>(
            JobWithProgress job,
            int chankSize, 
            string sqlSelectTemplate,
            string sqlDeleteTemplate,
            CancellationToken token)
            where TEntity: class, ITelemetryData
        {
            using var db = MakeContext();
            var dbset = db.Set<TEntity>();

            var deleted = 0;
            var oldCount = await dbset.Where(t => t.IdTelemetry == job.Id).CountAsync(token);

            if (job.Result is Tuple<int, int> tupleResult)
            {
                deleted  += tupleResult.Item1;
                oldCount += tupleResult.Item2;
            }
            job.Result = (deleted, oldCount);
            job.OnProgress?.Invoke(job);
            var startDate = DateTimeOffset.MinValue;

            do
            {
                var query = dbset
                    .FromSqlRaw(sqlSelectTemplate, startDate)
                    .AsNoTracking();

                var data = await query
                    .Take(chankSize)
                    .ToArrayAsync(token);

                var currentDataCount = data.Length;
                if (currentDataCount == 0)
                    break;

                var lastDate = data.Last().DateTime;

                var currentDeleted = await db.Database.ExecuteSqlRawAsync(sqlDeleteTemplate, new object[] { startDate, lastDate }.AsEnumerable(), token);
                if (currentDeleted == 0)
                    break;

                await db.Database.ExecInsertAsync(dbset, data, token);

                startDate = lastDate;
                deleted += currentDeleted;
                job.Result = (deleted, oldCount);
                job.OnProgress?.Invoke(job);
            } while (true);

            return;
        }

        private AsbCloudDbContext MakeContext()
        {
            var options = new DbContextOptionsBuilder<AsbCloudDbContext>()
                .UseNpgsql(connectionString)
                .Options;

            return new AsbCloudDbContext(options);
        }
    }
#nullable disable
}