using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using API.Comparators;
using API.Data.Repositories;
using API.DTOs;
using API.Entities;
using Microsoft.Extensions.Logging;

namespace API.Interfaces.Services
{
    public class ReaderService : IReaderService
    {
        private readonly IUnitOfWork _unitOfWork;
        private readonly ILogger<ReaderService> _logger;
        private readonly ChapterSortComparer _chapterSortComparer = new ChapterSortComparer();
        private readonly ChapterSortComparerZeroFirst _chapterSortComparerForInChapterSorting = new ChapterSortComparerZeroFirst();

        public ReaderService(IUnitOfWork unitOfWork, ILogger<ReaderService> logger)
        {
            _unitOfWork = unitOfWork;
            _logger = logger;
        }

        /// <summary>
        /// Marks all Chapters as Read by creating or updating UserProgress rows. Does not commit.
        /// </summary>
        /// <param name="user"></param>
        /// <param name="seriesId"></param>
        /// <param name="chapters"></param>
        public void MarkChaptersAsRead(AppUser user, int seriesId, IEnumerable<Chapter> chapters)
        {
            foreach (var chapter in chapters)
            {
                var userProgress = GetUserProgressForChapter(user, chapter);

                if (userProgress == null)
                {
                    user.Progresses.Add(new AppUserProgress
                    {
                        PagesRead = chapter.Pages,
                        VolumeId = chapter.VolumeId,
                        SeriesId = seriesId,
                        ChapterId = chapter.Id
                    });
                }
                else
                {
                    userProgress.PagesRead = chapter.Pages;
                    userProgress.SeriesId = seriesId;
                    userProgress.VolumeId = chapter.VolumeId;
                }
            }
        }

        /// <summary>
        /// Marks all Chapters as Unread by creating or updating UserProgress rows. Does not commit.
        /// </summary>
        /// <param name="user"></param>
        /// <param name="seriesId"></param>
        /// <param name="chapters"></param>
        public void MarkChaptersAsUnread(AppUser user, int seriesId, IEnumerable<Chapter> chapters)
        {
            foreach (var chapter in chapters)
            {
                var userProgress = GetUserProgressForChapter(user, chapter);

                if (userProgress == null)
                {
                    user.Progresses.Add(new AppUserProgress
                    {
                        PagesRead = 0,
                        VolumeId = chapter.VolumeId,
                        SeriesId = seriesId,
                        ChapterId = chapter.Id
                    });
                }
                else
                {
                    userProgress.PagesRead = 0;
                    userProgress.SeriesId = seriesId;
                    userProgress.VolumeId = chapter.VolumeId;
                }
            }
        }

        /// <summary>
        /// Gets the User Progress for a given Chapter. This will handle any duplicates that might have occured in past versions and will delete them. Does not commit.
        /// </summary>
        /// <param name="user"></param>
        /// <param name="chapter"></param>
        /// <returns></returns>
        public static AppUserProgress GetUserProgressForChapter(AppUser user, Chapter chapter)
        {
            AppUserProgress userProgress = null;
            try
            {
                userProgress =
                    user.Progresses.SingleOrDefault(x => x.ChapterId == chapter.Id && x.AppUserId == user.Id);
            }
            catch (Exception)
            {
                // There is a very rare chance that user progress will duplicate current row. If that happens delete one with less pages
                var progresses = user.Progresses.Where(x => x.ChapterId == chapter.Id && x.AppUserId == user.Id).ToList();
                if (progresses.Count > 1)
                {
                    user.Progresses = new List<AppUserProgress>()
                    {
                        user.Progresses.First()
                    };
                    userProgress = user.Progresses.First();
                }
            }

            return userProgress;
        }

        /// <summary>
        /// Saves progress to DB
        /// </summary>
        /// <param name="progressDto"></param>
        /// <param name="userId"></param>
        /// <returns></returns>
        public async Task<bool> SaveReadingProgress(ProgressDto progressDto, int userId)
        {
            // Don't let user save past total pages.
            progressDto.PageNum = await CapPageToChapter(progressDto.ChapterId, progressDto.PageNum);

            try
            {
                var userProgress =
                    await _unitOfWork.AppUserProgressRepository.GetUserProgressAsync(progressDto.ChapterId, userId);

                if (userProgress == null)
                {
                    // Create a user object
                    var userWithProgress =
                        await _unitOfWork.UserRepository.GetUserByIdAsync(userId, AppUserIncludes.Progress);
                    userWithProgress.Progresses ??= new List<AppUserProgress>();
                    userWithProgress.Progresses.Add(new AppUserProgress
                    {
                        PagesRead = progressDto.PageNum,
                        VolumeId = progressDto.VolumeId,
                        SeriesId = progressDto.SeriesId,
                        ChapterId = progressDto.ChapterId,
                        BookScrollId = progressDto.BookScrollId,
                        LastModified = DateTime.Now
                    });
                    _unitOfWork.UserRepository.Update(userWithProgress);
                }
                else
                {
                    userProgress.PagesRead = progressDto.PageNum;
                    userProgress.SeriesId = progressDto.SeriesId;
                    userProgress.VolumeId = progressDto.VolumeId;
                    userProgress.BookScrollId = progressDto.BookScrollId;
                    userProgress.LastModified = DateTime.Now;
                    _unitOfWork.AppUserProgressRepository.Update(userProgress);
                }

                if (await _unitOfWork.CommitAsync())
                {
                    return true;
                }
            }
            catch (Exception exception)
            {
                _logger.LogError(exception, "Could not save progress");
                await _unitOfWork.RollbackAsync();
            }

            return false;
        }

        /// <summary>
        /// Ensures that the page is within 0 and total pages for a chapter. Makes one DB call.
        /// </summary>
        /// <param name="chapterId"></param>
        /// <param name="page"></param>
        /// <returns></returns>
        public async Task<int> CapPageToChapter(int chapterId, int page)
        {
            var totalPages = await _unitOfWork.ChapterRepository.GetChapterTotalPagesAsync(chapterId);
            if (page > totalPages)
            {
                page = totalPages;
            }

            if (page < 0)
            {
                page = 0;
            }

            return page;
        }

        /// <summary>
        /// Tries to find the next logical Chapter
        /// </summary>
        /// <example>
        /// V1 → V2 → V3 chapter 0 → V3 chapter 10 → SP 01 → SP 02
        /// </example>
        /// <param name="seriesId"></param>
        /// <param name="volumeId"></param>
        /// <param name="currentChapterId"></param>
        /// <param name="userId"></param>
        /// <returns>-1 if nothing can be found</returns>
        public async Task<int> GetNextChapterIdAsync(int seriesId, int volumeId, int currentChapterId, int userId)
        {
            var volumes = (await _unitOfWork.VolumeRepository.GetVolumesDtoAsync(seriesId, userId)).ToList();
            var currentVolume = volumes.Single(v => v.Id == volumeId);
            var currentChapter = currentVolume.Chapters.Single(c => c.Id == currentChapterId);

            if (currentVolume.Number == 0)
            {
                // Handle specials by sorting on their Filename aka Range
                var chapterId = GetNextChapterId(currentVolume.Chapters.OrderBy(x => x.Range, new NaturalSortComparer()), currentChapter.Number);
                if (chapterId > 0) return chapterId;
            }

            foreach (var volume in volumes)
            {
                if (volume.Number == currentVolume.Number && volume.Chapters.Count > 1)
                {
                    // Handle Chapters within current Volume
                    // In this case, i need 0 first because 0 represents a full volume file.
                    var chapterId = GetNextChapterId(currentVolume.Chapters.OrderBy(x => double.Parse(x.Number), _chapterSortComparerForInChapterSorting), currentChapter.Number);
                    if (chapterId > 0) return chapterId;
                }

                if (volume.Number != currentVolume.Number + 1) continue;

                // Handle Chapters within next Volume
                // ! When selecting the chapter for the next volume, we need to make sure a c0 comes before a c1+
                var chapters = volume.Chapters.OrderBy(x => double.Parse(x.Number), _chapterSortComparer).ToList();
                if (currentChapter.Number.Equals("0") && chapters.Last().Number.Equals("0"))
                {
                    return chapters.Last().Id;
                }

                var firstChapter = chapters.FirstOrDefault();
                if (firstChapter == null) return -1;
                return firstChapter.Id;

            }

            return -1;
        }
        /// <summary>
        /// Tries to find the prev logical Chapter
        /// </summary>
        /// <example>
        /// V1 ← V2 ← V3 chapter 0 ← V3 chapter 10 ← SP 01 ← SP 02
        /// </example>
        /// <param name="seriesId"></param>
        /// <param name="volumeId"></param>
        /// <param name="currentChapterId"></param>
        /// <param name="userId"></param>
        /// <returns>-1 if nothing can be found</returns>
        public async Task<int> GetPrevChapterIdAsync(int seriesId, int volumeId, int currentChapterId, int userId)
        {
            var volumes = (await _unitOfWork.VolumeRepository.GetVolumesDtoAsync(seriesId, userId)).Reverse().ToList();
            var currentVolume = volumes.Single(v => v.Id == volumeId);
            var currentChapter = currentVolume.Chapters.Single(c => c.Id == currentChapterId);

            if (currentVolume.Number == 0)
            {
                var chapterId = GetNextChapterId(currentVolume.Chapters.OrderBy(x => x.Range, new NaturalSortComparer()).Reverse(), currentChapter.Number);
                if (chapterId > 0) return chapterId;
            }

            foreach (var volume in volumes)
            {
                if (volume.Number == currentVolume.Number)
                {
                    var chapterId = GetNextChapterId(currentVolume.Chapters.OrderBy(x => double.Parse(x.Number), _chapterSortComparerForInChapterSorting).Reverse(), currentChapter.Number);
                    if (chapterId > 0) return chapterId;
                }
                if (volume.Number == currentVolume.Number - 1)
                {
                    var lastChapter = volume.Chapters
                        .OrderBy(x => double.Parse(x.Number), _chapterSortComparerForInChapterSorting).LastOrDefault();
                    if (lastChapter == null) return -1;
                    return lastChapter.Id;
                }
            }
            return -1;
        }

        private static int GetNextChapterId(IEnumerable<ChapterDto> chapters, string currentChapterNumber)
        {
            var next = false;
            var chaptersList = chapters.ToList();
            foreach (var chapter in chaptersList)
            {
                if (next)
                {
                    return chapter.Id;
                }
                if (currentChapterNumber.Equals(chapter.Number)) next = true;
            }

            return -1;
        }


    }
}