using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using API.Data;
using API.DTOs;
using API.DTOs.Statistics;
using API.Entities.Enums;
using API.Extensions;
using AutoMapper;
using AutoMapper.QueryableExtensions;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

namespace API.Services;

public interface IStatisticService
{
    Task<ServerStatistics> GetServerStatistics();
    Task<UserReadStatistics> GetUserReadStatistics(int userId, IList<int> libraryIds);
    Task<IEnumerable<StatCount<int>>> GetYearCount();
    Task<IEnumerable<StatCount<int>>> GetTopYears();
    Task<IEnumerable<StatCount<PublicationStatus>>> GetPublicationCount();
    Task<IEnumerable<StatCount<MangaFormat>>> GetMangaFormatCount();
    Task<FileExtensionBreakdownDto> GetFileBreakdown();
    Task<IEnumerable<TopReadDto>> GetTopUsers(int days);
    Task<IEnumerable<ReadHistoryEvent>> GetReadingHistory(int userId);
    Task<IEnumerable<ReadHistoryEvent>> GetHistory();
}

/// <summary>
/// Responsible for computing statistics for the server
/// </summary>
/// <remarks>This performs raw queries and does not use a repository</remarks>
public class StatisticService : IStatisticService
{
    private readonly DataContext _context;
    private readonly IMapper _mapper;
    private readonly IUnitOfWork _unitOfWork;

    public StatisticService(DataContext context, IMapper mapper, IUnitOfWork unitOfWork)
    {
        _context = context;
        _mapper = mapper;
        _unitOfWork = unitOfWork;
    }

    public async Task<UserReadStatistics> GetUserReadStatistics(int userId, IList<int> libraryIds)
    {
        if (libraryIds.Count == 0)
            libraryIds = await _context.Library.GetUserLibraries(userId).ToListAsync();


        // Total Pages Read
        var totalPagesRead = await _context.AppUserProgresses
            .Where(p => p.AppUserId == userId)
            .Where(p => libraryIds.Contains(p.LibraryId))
            .SumAsync(p => p.PagesRead);

        var ids = await _context.AppUserProgresses
            .Where(p => p.AppUserId == userId)
            .Where(p => libraryIds.Contains(p.LibraryId))
            .Where(p => p.PagesRead > 0)
            .Select(p => new {p.ChapterId, p.SeriesId})
            .ToListAsync();

        var chapterIds = ids.Select(id => id.ChapterId);

        var timeSpentReading = await _context.Chapter
            .Where(c => chapterIds.Contains(c.Id))
            .SumAsync(c => c.AvgHoursToRead);

        // Maybe make this top 5 genres? But usually there are 3-5 genres that are always common...
        // Maybe use rating to calculate top genres?
        // var genres = await _context.Series
        //     .Where(s => seriesIds.Contains(s.Id))
        //     .Select(s => s.Metadata)
        //     .SelectMany(sm => sm.Genres)
        //     //.DistinctBy(g => g.NormalizedTitle)
        //     .ToListAsync();

        // How many series of each format have you read? (Epub, Archive, etc)

        // Percentage of libraries read. For each library, get the total pages vs read
        //var allLibraryIds = await _context.Library.GetUserLibraries(userId).ToListAsync();

        var chaptersRead = await _context.AppUserProgresses
            .Where(p => p.AppUserId == userId)
            .Where(p => libraryIds.Contains(p.LibraryId))
            .Where(p => p.PagesRead >= _context.Chapter.Single(c => c.Id == p.ChapterId).Pages)
            .CountAsync();

        var lastActive = await _context.AppUserProgresses
            .OrderByDescending(p => p.LastModified)
            .Select(p => p.LastModified)
            .FirstOrDefaultAsync();

        //var

        return new UserReadStatistics()
        {
            TotalPagesRead = totalPagesRead,
            TimeSpentReading = timeSpentReading,
            ChaptersRead = chaptersRead,
            LastActive = lastActive,
        };
    }

    /// <summary>
    /// Returns the Release Years and their count
    /// </summary>
    /// <returns></returns>
    public async Task<IEnumerable<StatCount<int>>> GetYearCount()
    {
        return await _context.SeriesMetadata
            .Where(sm => sm.ReleaseYear != 0)
            .AsSplitQuery()
            .GroupBy(sm => sm.ReleaseYear)
            .Select(sm => new StatCount<int>
            {
                Value = sm.Key,
                Count = _context.SeriesMetadata.Where(sm2 => sm2.ReleaseYear == sm.Key).Distinct().Count()
            })
            .OrderByDescending(d => d.Value)
            .ToListAsync();
    }

    public async Task<IEnumerable<StatCount<int>>> GetTopYears()
    {
        return await _context.SeriesMetadata
            .Where(sm => sm.ReleaseYear != 0)
            .AsSplitQuery()
            .GroupBy(sm => sm.ReleaseYear)
            .Select(sm => new StatCount<int>
            {
                Value = sm.Key,
                Count = _context.SeriesMetadata.Where(sm2 => sm2.ReleaseYear == sm.Key).Distinct().Count()
            })
            .OrderByDescending(d => d.Count)
            .Take(5)
            .ToListAsync();
    }



    public async Task<IEnumerable<StatCount<PublicationStatus>>> GetPublicationCount()
    {
        return await _context.SeriesMetadata
            .AsSplitQuery()
            .GroupBy(sm => sm.PublicationStatus)
            .Select(sm => new StatCount<PublicationStatus>
            {
                Value = sm.Key,
                Count = _context.SeriesMetadata.Where(sm2 => sm2.PublicationStatus == sm.Key).Distinct().Count()
            })
            .ToListAsync();
    }

    public async Task<IEnumerable<StatCount<MangaFormat>>> GetMangaFormatCount()
    {
        return await _context.MangaFile
            .AsSplitQuery()
            .GroupBy(sm => sm.Format)
            .Select(mf => new StatCount<MangaFormat>
            {
                Value = mf.Key,
                Count = _context.MangaFile.Where(mf2 => mf2.Format == mf.Key).Distinct().Count()
            })
            .ToListAsync();
    }


    public async Task<ServerStatistics> GetServerStatistics()
    {
        var mostActiveUsers = _context.AppUserProgresses
            .AsSplitQuery()
            .AsEnumerable()
            .GroupBy(sm => sm.AppUserId)
            .Select(sm => new StatCount<UserDto>
            {
                Value = _context.AppUser.Where(u => u.Id == sm.Key).ProjectTo<UserDto>(_mapper.ConfigurationProvider)
                    .Single(),
                Count = _context.AppUserProgresses.Where(u => u.AppUserId == sm.Key).Distinct().Count()
            })
            .OrderByDescending(d => d.Count)
            .Take(5);

        var mostActiveLibrary = _context.AppUserProgresses
            .AsSplitQuery()
            .AsEnumerable()
            .Where(sm => sm.LibraryId > 0)
            .GroupBy(sm => sm.LibraryId)
            .Select(sm => new StatCount<LibraryDto>
            {
                Value = _context.Library.Where(u => u.Id == sm.Key).ProjectTo<LibraryDto>(_mapper.ConfigurationProvider)
                    .Single(),
                Count = _context.AppUserProgresses.Where(u => u.LibraryId == sm.Key).Distinct().Count()
            })
            .OrderByDescending(d => d.Count)
            .Take(5);

        var mostPopularSeries = _context.AppUserProgresses
            .AsSplitQuery()
            .AsEnumerable()
            .GroupBy(sm => sm.SeriesId)
            .Select(sm => new StatCount<SeriesDto>
            {
                Value = _context.Series.Where(u => u.Id == sm.Key).ProjectTo<SeriesDto>(_mapper.ConfigurationProvider)
                    .Single(),
                Count = _context.AppUserProgresses.Where(u => u.SeriesId == sm.Key).Distinct().Count()
            })
            .OrderByDescending(d => d.Count)
            .Take(5);

        var mostReadSeries = _context.AppUserProgresses
            .AsSplitQuery()
            .AsEnumerable()
            .GroupBy(sm => sm.SeriesId)
            .Select(sm => new StatCount<SeriesDto>
            {
                Value = _context.Series.Where(u => u.Id == sm.Key).ProjectTo<SeriesDto>(_mapper.ConfigurationProvider)
                    .Single(),
                Count = _context.AppUserProgresses.Where(u => u.SeriesId == sm.Key).AsEnumerable().DistinctBy(p => p.AppUserId).Count()
            })
            .OrderByDescending(d => d.Count)
            .Take(5);

        var seriesIds = (await _context.AppUserProgresses
            .AsSplitQuery()
            .OrderByDescending(d => d.LastModified)
            .Select(d => d.SeriesId)
            .ToListAsync())
            .Distinct()
            .Take(5);

        var recentlyRead = _context.Series
            .AsSplitQuery()
            .Where(s => seriesIds.Contains(s.Id))
            .ProjectTo<SeriesDto>(_mapper.ConfigurationProvider)
            .AsEnumerable();

        var distinctPeople = _context.Person
            .AsSplitQuery()
            .AsEnumerable()
            .GroupBy(sm => sm.NormalizedName)
            .Select(sm => sm.Key)
            .Distinct()
            .Count();

        return new ServerStatistics()
        {
            ChapterCount = await _context.Chapter.CountAsync(),
            SeriesCount = await _context.Series.CountAsync(),
            TotalFiles = await _context.MangaFile.CountAsync(),
            TotalGenres = await _context.Genre.CountAsync(),
            TotalPeople = distinctPeople,
            TotalSize = await _context.MangaFile.SumAsync(m => m.Bytes),
            TotalTags = await _context.Tag.CountAsync(),
            VolumeCount = await _context.Volume.Where(v => v.Number != 0).CountAsync(),
            MostActiveUsers = mostActiveUsers,
            MostActiveLibraries = mostActiveLibrary,
            MostPopularSeries = mostPopularSeries,
            MostReadSeries = mostReadSeries,
            RecentlyRead = recentlyRead
        };
    }

    public async Task<FileExtensionBreakdownDto> GetFileBreakdown()
    {
        return new FileExtensionBreakdownDto()
        {
            FileBreakdown = await _context.MangaFile
                .AsSplitQuery()
                .AsNoTracking()
                .GroupBy(sm => sm.Extension)
                .Select(mf => new FileExtensionDto()
                {
                    Extension = mf.Key,
                    Format =_context.MangaFile.Where(mf2 => mf2.Extension == mf.Key).Select(mf2 => mf2.Format).Single(),
                    TotalSize = _context.MangaFile.Where(mf2 => mf2.Extension == mf.Key).Distinct().Sum(mf2 => mf2.Bytes),
                    TotalFiles = _context.MangaFile.Where(mf2 => mf2.Extension == mf.Key).Distinct().Count()
                })
                .ToListAsync(),
            TotalFileSize = await _context.MangaFile
                .AsNoTracking()
                .AsSplitQuery()
                .SumAsync(f => f.Bytes)
        };
    }

    public async Task<IEnumerable<ReadHistoryEvent>> GetReadingHistory(int userId)
    {
        return await _context.AppUserProgresses
            .Where(u => u.AppUserId == userId)
            .AsNoTracking()
            .AsSplitQuery()
            .Select(u => new ReadHistoryEvent
            {
                UserId = u.AppUserId,
                UserName = _context.AppUser.Single(u => u.Id == userId).UserName,
                SeriesName = _context.Series.Single(s => s.Id == u.SeriesId).Name,
                SeriesId = u.SeriesId,
                LibraryId = u.LibraryId,
                ReadDate = u.LastModified,
                ChapterId = u.ChapterId,
                ChapterNumber = _context.Chapter.Single(c => c.Id == u.ChapterId).Number
            })
            .OrderByDescending(d => d.ReadDate)
            .ToListAsync();
    }

    public void ReadCountByDay()
    {
        // _context.AppUserProgresses
        //     .GroupBy(p => p.LastModified.Day)
        //     .Select(g =>
        //     {
        //         Day = g.Key,
        //     })
    }

    public Task<IEnumerable<ReadHistoryEvent>> GetHistory()
    {
        // _context.AppUserProgresses
        //     .AsSplitQuery()
        //     .AsEnumerable()
        //     .GroupBy(sm => sm.LastModified)
        //     .Select(sm => new
        //     {
        //         User = _context.AppUser.Single(u => u.Id == sm.Key),
        //         Chapters = _context.Chapter.Where(c => _context.AppUserProgresses
        //             .Where(u => u.AppUserId == sm.Key)
        //             .Where(p => p.PagesRead > 0)
        //             .Select(p => p.ChapterId)
        //             .Distinct()
        //             .Contains(c.Id))
        //     })
        //     .OrderByDescending(d => d.Chapters.Sum(c => c.AvgHoursToRead))
        //     .Take(5)
        //     .ToList();

        var firstOfWeek = DateTime.Now.StartOfWeek(DayOfWeek.Monday);
        var groupedReadingDays = _context.AppUserProgresses
            .Where(x => x.LastModified >= firstOfWeek)
            .GroupBy(x => x.LastModified.Day)
            .Select(g => new StatCount<int>()
            {
                Value = g.Key,
                Count = _context.AppUserProgresses.Where(p => p.LastModified.Day == g.Key).Select(p => p.ChapterId).Distinct().Count()
            })
            .AsEnumerable();

        // var records = firstOfWeek.Range(7)
        //     .GroupJoin(groupedReadingDays, wd => wd.Day, lg => lg.Key, (_, lg) => lg.Any() ? lg.First().Count() : 0).ToArray();
        return Task.FromResult<IEnumerable<ReadHistoryEvent>>(null);
    }


    public async Task<IEnumerable<TopReadDto>> GetTopUsers(int days)
    {
        var libraries = (await _unitOfWork.LibraryRepository.GetLibrariesAsync()).ToList();
        var users = (await _unitOfWork.UserRepository.GetAllUsersAsync()).ToList();
        var minDate = DateTime.Now.Subtract(TimeSpan.FromDays(days));

        var topUsersAndReadChapters = _context.AppUserProgresses
            .AsSplitQuery()
            .AsEnumerable()
            .GroupBy(sm => sm.AppUserId)
            .Select(sm => new
            {
                User = _context.AppUser.Single(u => u.Id == sm.Key),
                Chapters = _context.Chapter.Where(c => _context.AppUserProgresses
                    .Where(u => u.AppUserId == sm.Key)
                    .Where(p => p.PagesRead > 0)
                    .Where(p => days == 0 || (p.Created >= minDate && p.LastModified >= minDate))
                    .Select(p => p.ChapterId)
                    .Distinct()
                    .Contains(c.Id))
            })
            .OrderByDescending(d => d.Chapters.Sum(c => c.AvgHoursToRead))
            .Take(5)
            .ToList();


        // Need a mapping of Library to chapter ids
        var chapterIdWithLibraryId = topUsersAndReadChapters
            .SelectMany(u => u.Chapters
                .Select(c => c.Id)).Select(d => new
                    {
                        LibraryId = _context.Chapter.Where(c => c.Id == d).AsSplitQuery().Select(c => c.Volume).Select(v => v.Series).Select(s => s.LibraryId).Single(),
                        ChapterId = d
                    })
            .ToList();

        var chapterLibLookup = new Dictionary<int, int>();
        foreach (var cl in chapterIdWithLibraryId)
        {
            if (chapterLibLookup.ContainsKey(cl.ChapterId)) continue;
            chapterLibLookup.Add(cl.ChapterId, cl.LibraryId);
        }

        var user = new Dictionary<int, Dictionary<LibraryType, long>>();
        foreach (var userChapter in topUsersAndReadChapters)
        {
            if (!user.ContainsKey(userChapter.User.Id)) user.Add(userChapter.User.Id, new Dictionary<LibraryType, long>());
            var libraryTimes = user[userChapter.User.Id];

            foreach (var chapter in userChapter.Chapters)
            {
                var library = libraries.First(l => l.Id == chapterLibLookup[chapter.Id]);
                if (!libraryTimes.ContainsKey(library.Type)) libraryTimes.Add(library.Type, 0L);
                var existingHours = libraryTimes[library.Type];
                libraryTimes[library.Type] = existingHours + chapter.AvgHoursToRead;
            }

            user[userChapter.User.Id] = libraryTimes;
        }

        var ret = new List<TopReadDto>();
        foreach (var userId in user.Keys)
        {
            ret.Add(new TopReadDto()
            {
                UserId = userId,
                Username = users.First(u => u.Id == userId).UserName,
                BooksTime = user[userId].ContainsKey(LibraryType.Book) ? user[userId][LibraryType.Book] : 0,
                ComicsTime = user[userId].ContainsKey(LibraryType.Comic) ? user[userId][LibraryType.Comic] : 0,
                MangaTime = user[userId].ContainsKey(LibraryType.Manga) ? user[userId][LibraryType.Manga] : 0,
            });
        }

        return ret;
    }
}