using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using API.Entities;
using API.Entities.Enums;
using API.Extensions;
using API.Interfaces;
using API.Interfaces.Services;
using API.Parser;
using Hangfire;
using Microsoft.Extensions.Logging;

namespace API.Services.Tasks
{
    public class ScannerService : IScannerService
    {
       private readonly IUnitOfWork _unitOfWork;
       private readonly ILogger<ScannerService> _logger;
       private readonly IArchiveService _archiveService;
       private readonly IMetadataService _metadataService;
       private ConcurrentDictionary<string, List<ParserInfo>> _scannedSeries;
       private bool _forceUpdate;

       public ScannerService(IUnitOfWork unitOfWork, ILogger<ScannerService> logger, IArchiveService archiveService, 
          IMetadataService metadataService)
       {
          _unitOfWork = unitOfWork;
          _logger = logger;
          _archiveService = archiveService;
          _metadataService = metadataService;
       }

       [DisableConcurrentExecution(timeoutInSeconds: 5)] 
       [AutomaticRetry(Attempts = 0, LogEvents = false, OnAttemptsExceeded = AttemptsExceededAction.Delete)]
       public void ScanLibraries()
       {
          var libraries = Task.Run(() => _unitOfWork.LibraryRepository.GetLibrariesAsync()).Result.ToList();
          foreach (var lib in libraries)
          {
             ScanLibrary(lib.Id, false);
          }
       }

       private bool ShouldSkipFolderScan(FolderPath folder, ref int skippedFolders)
       {
          // NOTE: This solution isn't the best, but it has potential. We need to handle a few other cases so it works great. 
          return false;
          
          // if (/*_environment.IsProduction() && */!_forceUpdate && Directory.GetLastWriteTime(folder.Path) < folder.LastScanned)
          // {
          //    _logger.LogDebug($"{folder.Path} hasn't been updated since last scan. Skipping.");
          //    skippedFolders += 1;
          //    return true;
          // }
          //
          // return false;
       }

       private void Cleanup()
       {
          _scannedSeries = null;
       }

       [DisableConcurrentExecution(5)]
       [AutomaticRetry(Attempts = 0, LogEvents = false, OnAttemptsExceeded = AttemptsExceededAction.Delete)]
       public void ScanLibrary(int libraryId, bool forceUpdate)
       {
          _forceUpdate = forceUpdate;
          var sw = Stopwatch.StartNew();
          Cleanup();
           Library library;
           try
           {
              library = Task.Run(() => _unitOfWork.LibraryRepository.GetFullLibraryForIdAsync(libraryId)).Result;
           }
           catch (Exception ex)
           {
              // This usually only fails if user is not authenticated.
              _logger.LogError(ex, "There was an issue fetching Library {LibraryId}", libraryId);
              return;
           }
           
           _scannedSeries = new ConcurrentDictionary<string, List<ParserInfo>>();
           _logger.LogInformation("Beginning scan on {LibraryName}. Forcing metadata update: {ForceUpdate}", library.Name, forceUpdate);

           var totalFiles = 0;
           var skippedFolders = 0;
           foreach (var folderPath in library.Folders)
           {
              if (ShouldSkipFolderScan(folderPath, ref skippedFolders)) continue;

              try {
                 totalFiles += DirectoryService.TraverseTreeParallelForEach(folderPath.Path, (f) =>
                 {
                    try
                    {
                       ProcessFile(f, folderPath.Path);
                    }
                    catch (FileNotFoundException exception)
                    {
                       _logger.LogError(exception, "The file {Filename} could not be found", f);
                    }
                 }, Parser.Parser.MangaFileExtensions);
              }
              catch (ArgumentException ex) {
                 _logger.LogError(ex, "The directory '{FolderPath}' does not exist", folderPath.Path);
              }
              
              folderPath.LastScanned = DateTime.Now;
           }

           var scanElapsedTime = sw.ElapsedMilliseconds;
           _logger.LogInformation("Folders Scanned {TotalFiles} files in {ElapsedScanTime} milliseconds", totalFiles, scanElapsedTime);
           sw.Restart();
           if (skippedFolders == library.Folders.Count)
           {
              _logger.LogInformation("All Folders were skipped due to no modifications to the directories");
              _unitOfWork.LibraryRepository.Update(library);
              _logger.LogInformation("Processed {TotalFiles} files in {ElapsedScanTime} milliseconds for {LibraryName}", totalFiles, sw.ElapsedMilliseconds, library.Name);
              Cleanup();
              return;
           }

           // Remove any series where there were no parsed infos
           var filtered = _scannedSeries.Where(kvp => kvp.Value.Count != 0);
           var series = filtered.ToDictionary(v => v.Key, v => v.Value);
           
           UpdateLibrary(library, series);
           _unitOfWork.LibraryRepository.Update(library);

           if (Task.Run(() => _unitOfWork.Complete()).Result)
           {
              
              _logger.LogInformation("Scan completed on {LibraryName}. Parsed {ParsedSeriesCount} series in {ElapsedScanTime} ms", library.Name, series.Keys.Count, sw.ElapsedMilliseconds);
           }
           else
           {
              _logger.LogError("There was a critical error that resulted in a failed scan. Please check logs and rescan");
           }
           
           _logger.LogInformation("Processed {TotalFiles} files in {ElapsedScanTime} milliseconds for {LibraryName}", totalFiles, sw.ElapsedMilliseconds + scanElapsedTime, library.Name);
       }

       private void UpdateLibrary(Library library, Dictionary<string, List<ParserInfo>> parsedSeries)
       {
          if (parsedSeries == null) throw new ArgumentNullException(nameof(parsedSeries));
          
          // First, remove any series that are not in parsedSeries list
          var foundSeries = parsedSeries.Select(s => Parser.Parser.Normalize(s.Key)).ToList();
          var missingSeries = library.Series.Where(existingSeries =>
             !foundSeries.Contains(existingSeries.NormalizedName) || !parsedSeries.ContainsKey(existingSeries.Name)
              || (existingSeries.LocalizedName != null && !parsedSeries.ContainsKey(existingSeries.LocalizedName))
              || !parsedSeries.ContainsKey(existingSeries.OriginalName));
          var removeCount = 0;
          foreach (var existingSeries in missingSeries)
          {
             library.Series?.Remove(existingSeries);
             removeCount += 1;
          }
          _logger.LogInformation("Removed {RemoveCount} series that are no longer on disk", removeCount);
          
          // Add new series that have parsedInfos
          foreach (var (key, _) in parsedSeries)
          {
             var existingSeries = library.Series.SingleOrDefault(s => s.NormalizedName == Parser.Parser.Normalize(key));
             if (existingSeries == null)
             {
                existingSeries = new Series()
                {
                   Name = key,
                   OriginalName = key,
                   LocalizedName = key,
                   NormalizedName = Parser.Parser.Normalize(key),
                   SortName = key,
                   Summary = "",
                   Volumes = new List<Volume>()
                };
                library.Series.Add(existingSeries);
             } 
             existingSeries.NormalizedName = Parser.Parser.Normalize(key);
             existingSeries.LocalizedName ??= key;
          }
          
          // Now, we only have to deal with series that exist on disk. Let's recalculate the volumes for each series
          var librarySeries = library.Series.ToList();
          Parallel.ForEach(librarySeries, (series) =>
          {
             _logger.LogInformation("Processing series {SeriesName}", series.Name);
             UpdateVolumes(series, parsedSeries[series.Name].ToArray());
             series.Pages = series.Volumes.Sum(v => v.Pages);
             _metadataService.UpdateMetadata(series, _forceUpdate);
          });
          

          foreach (var folder in library.Folders) folder.LastScanned = DateTime.Now;
       }

       private void UpdateVolumes(Series series, ParserInfo[] parsedInfos)
       {
          var startingVolumeCount = series.Volumes.Count;
          // Add new volumes and update chapters per volume
          var distinctVolumes = parsedInfos.Select(p => p.Volumes).Distinct().ToList();
          _logger.LogDebug("Updating {DistinctVolumes} volumes", distinctVolumes.Count);
          foreach (var volumeNumber in distinctVolumes)
          {
             var infos = parsedInfos.Where(p => p.Volumes == volumeNumber).ToArray();
             
             var volume = series.Volumes.SingleOrDefault(s => s.Name == volumeNumber);
             if (volume == null)
             {
                volume = new Volume()
                {
                   Name = volumeNumber,
                   Number = (int) Parser.Parser.MinimumNumberFromRange(volumeNumber),
                   IsSpecial = false,
                   Chapters = new List<Chapter>()
                }; 
                series.Volumes.Add(volume);
             }
             
             volume.IsSpecial = volume.Number == 0 && infos.All(p => p.Chapters == "0");
             _logger.LogDebug("Parsing {SeriesName} - Volume {VolumeNumber}", series.Name, volume.Name);
             UpdateChapters(volume, infos);
             volume.Pages = volume.Chapters.Sum(c => c.Pages);
              _metadataService.UpdateMetadata(volume, _forceUpdate);
          }
          
          

          // Remove existing volumes that aren't in parsedInfos and volumes that have no chapters
          var existingVolumes = series.Volumes.ToList();
          foreach (var volume in existingVolumes)
          {
             // I can't remove based on chapter count as I haven't updated Chapters  || volume.Chapters.Count == 0
             var hasInfo = parsedInfos.Any(v => v.Volumes == volume.Name);
             if (!hasInfo)
             {
                series.Volumes.Remove(volume);
             }
          }

          _logger.LogDebug("Updated {SeriesName} volumes from {StartingVolumeCount} to {VolumeCount}", 
             series.Name, startingVolumeCount, series.Volumes.Count);
       }

       private void UpdateChapters(Volume volume, ParserInfo[] parsedInfos)
       {
          var startingChapters = volume.Chapters.Count;
          // Add new chapters
          foreach (var info in parsedInfos)
          {
             var chapter = volume.Chapters.SingleOrDefault(c => c.Range == info.Chapters);
             if (chapter == null)
             {
                chapter = new Chapter()
                {
                   Number = Parser.Parser.MinimumNumberFromRange(info.Chapters) + "",
                   Range = info.Chapters,
                   Files = new List<MangaFile>()
                };
                volume.Chapters.Add(chapter);
             }

             chapter.Files ??= new List<MangaFile>();
          }
          
          // Add files
          
          foreach (var info in parsedInfos)
          {
             Chapter chapter = null;
             try
             {
                chapter = volume.Chapters.SingleOrDefault(c => c.Range == info.Chapters);
             }
             catch (Exception ex)
             {
                _logger.LogError(ex, "There was an exception parsing chapter. Skipping Vol {VolumeNumber} Chapter {ChapterNumber}", volume.Name, info.Chapters);
             }
             if (chapter == null) continue;
             // I need to reset Files for the first time, hence this work should be done in a separate loop
             AddOrUpdateFileForChapter(chapter, info);
             chapter.Number = Parser.Parser.MinimumNumberFromRange(info.Chapters) + "";
             chapter.Range = info.Chapters;
             chapter.Pages = chapter.Files.Sum(f => f.Pages);
             _metadataService.UpdateMetadata(chapter, _forceUpdate);
          }
          
          
          
          // Remove chapters that aren't in parsedInfos or have no files linked
          var existingChapters = volume.Chapters.ToList();
          foreach (var existingChapter in existingChapters)
          {
             var hasInfo = parsedInfos.Any(v => v.Chapters == existingChapter.Range);
             if (!hasInfo || !existingChapter.Files.Any())
             {
                volume.Chapters.Remove(existingChapter);
             }
          }
          
          _logger.LogDebug("Updated chapters from {StartingChaptersCount} to {ChapterCount}", 
             startingChapters, volume.Chapters.Count);
       }

       /// <summary>
       /// Attempts to either add a new instance of a show mapping to the scannedSeries bag or adds to an existing.
       /// </summary>
       /// <param name="info"></param>
       private void TrackSeries(ParserInfo info)
       {
          if (info.Series == string.Empty) return;
          
          _scannedSeries.AddOrUpdate(info.Series, new List<ParserInfo>() {info}, (_, oldValue) =>
          {
             oldValue ??= new List<ParserInfo>();
             if (!oldValue.Contains(info))
             {
                oldValue.Add(info);
             }

             return oldValue;
          });
       }

       /// <summary>
       /// Processes files found during a library scan.
       /// Populates a collection of <see cref="ParserInfo"/> for DB updates later.
       /// </summary>
       /// <param name="path">Path of a file</param>
       /// <param name="rootPath"></param>
       private void ProcessFile(string path, string rootPath)
       {
          var info = Parser.Parser.Parse(path, rootPath);
          
          if (info == null)
          {
             _logger.LogWarning("Could not parse series from {Path}", path);
             return;
          }
          
          TrackSeries(info);
       }

       private MangaFile CreateMangaFile(ParserInfo info)
       {
          return new MangaFile()
          {
             FilePath = info.FullFilePath,
             Format = info.Format,
             Pages = _archiveService.GetNumberOfPagesFromArchive(info.FullFilePath)
          };
       }
  
       private void AddOrUpdateFileForChapter(Chapter chapter, ParserInfo info)
       {
          chapter.Files ??= new List<MangaFile>();
          var existingFile = chapter.Files.SingleOrDefault(f => f.FilePath == info.FullFilePath);
          if (existingFile != null)
          {
             existingFile.Format = info.Format;
             if (!new FileInfo(existingFile.FilePath).DoesLastWriteMatch(existingFile.LastModified))
             {
                existingFile.Pages = _archiveService.GetNumberOfPagesFromArchive(info.FullFilePath);
             }
          }
          else
          {
             if (info.Format == MangaFormat.Archive)
             {
                chapter.Files.Add(CreateMangaFile(info));
                existingFile = chapter.Files.Last();
             }
             else
             {
                _logger.LogDebug("Ignoring {Filename}. Non-archives are not supported", info.Filename);
             }
          }

          if (existingFile != null)
          {
             existingFile.LastModified = new FileInfo(existingFile.FilePath).LastWriteTime;
          }
       }
    }
}