using System.Collections.Concurrent;
using System.Threading.Channels;
using Microsoft.Extensions.Options;
using VocaluxeSongServer.Contracts;
using VocaluxeSongServer.Library;

namespace VocaluxeSongServer.Sources
{
    /// <summary>Searches all enabled sources at once.</summary>
    public sealed class CSongSearch
    {
        private readonly IReadOnlyList<ISongSource> _Sources;
        private readonly CLibraryIndex _Index;
        private readonly ILogger<CSongSearch> _Logger;

        public CSongSearch(IEnumerable<ISongSource> sources, CLibraryIndex index, ILogger<CSongSearch> logger)
        {
            _Sources = sources.ToList();
            _Index = index;
            _Logger = logger;
        }

        public IReadOnlyList<ISongSource> Sources => _Sources;

        public ISongSource? GetSource(string id)
        {
            return _Sources.FirstOrDefault(s => s.Id == id);
        }

        public static string SongKey(string artist, string title)
        {
            return CSourceHelper.Normalize(artist) + "|" + CSourceHelper.Normalize(title);
        }

        public async Task<SearchResponse> SearchAsync(string query, CancellationToken ct)
        {
            var response = new SearchResponse();
            if (CSourceHelper.Normalize(query).Length < 2)
            {
                return response;
            }

            var inLibrary = new HashSet<string>((_Index.Current?.Dto.Songs ?? new List<SongDto>()).Select(s => SongKey(s.Artist, s.Title)));
            var tasks = _Sources.Where(s => s.Enabled).Select(async source =>
            {
                using var timeout = CancellationTokenSource.CreateLinkedTokenSource(ct);
                timeout.CancelAfter(TimeSpan.FromSeconds(20));
                try
                {
                    return (source, results: await source.SearchAsync(query, timeout.Token), error: (string?)null);
                }
                catch (Exception e) when (!ct.IsCancellationRequested)
                {
                    _Logger.LogWarning("Search in {Source} failed: {Message}", source.Id, e.Message);
                    return (source, results: new List<SearchResultDto>(), error: e is OperationCanceledException ? "timeout" : e.Message);
                }
            }).ToList();

            foreach (var (source, results, error) in await Task.WhenAll(tasks))
            {
                if (error != null)
                {
                    response.Errors[source.Id] = error;
                }

                foreach (var r in results)
                {
                    r.InLibrary = inLibrary.Contains(SongKey(r.Artist, r.Title));
                    response.Results.Add(r);
                }
            }

            // Best matches first: artist/title starting with the query, then alphabetically.
            var q = CSourceHelper.Normalize(query);
            response.Results = response.Results
                                       .OrderByDescending(r => CSourceHelper.Normalize(r.Artist + " " + r.Title).StartsWith(q) || CSourceHelper.Normalize(r.Title).StartsWith(q))
                                       .ThenBy(r => r.Artist, StringComparer.OrdinalIgnoreCase)
                                       .ThenBy(r => r.Title, StringComparer.OrdinalIgnoreCase)
                                       .ToList();
            return response;
        }
    }

    /// <summary>
    ///     Runs downloads one after another in the background. A song is downloaded into a temporary folder and moved to
    ///     "&lt;library&gt;/&lt;DownloadFolder&gt;/&lt;source&gt;/&lt;Artist - Title&gt;" when complete; then the library is rescanned.
    /// </summary>
    public sealed class CDownloadQueue : BackgroundService
    {
        private sealed class CJob
        {
            public required DownloadJobDto Dto;
            public required ISongSource Source;
        }

        private readonly Channel<CJob> _Queue = Channel.CreateUnbounded<CJob>();
        private readonly ConcurrentDictionary<string, CJob> _Jobs = new();
        private readonly CLibraryIndex _Index;
        private readonly CSongSearch _Search;
        private readonly CLibraryOptions _Options;
        private readonly ILogger<CDownloadQueue> _Logger;

        public CDownloadQueue(CLibraryIndex index, CSongSearch search, IOptions<CLibraryOptions> options, ILogger<CDownloadQueue> logger)
        {
            _Index = index;
            _Search = search;
            _Options = options.Value;
            _Logger = logger;
        }

        public IEnumerable<DownloadJobDto> Jobs => _Jobs.Values.Select(j => j.Dto).OrderByDescending(j => j.Created);

        /// <summary>Queues a download. Returns the existing job if the same song is already queued or running.</summary>
        public DownloadJobDto Enqueue(DownloadRequest request)
        {
            var source = _Search.GetSource(request.Source);
            if (source == null || !source.Enabled)
            {
                throw new ArgumentException("Unknown or disabled source: " + request.Source);
            }

            var existing = _Jobs.Values.FirstOrDefault(j => j.Dto.Source == request.Source && j.Dto.SourceId == request.SourceId && j.Dto.State is "queued" or "running");
            if (existing != null)
            {
                return existing.Dto;
            }

            var job = new CJob
            {
                Source = source,
                Dto = new DownloadJobDto
                {
                    Id = Guid.NewGuid().ToString("N")[..12],
                    Source = request.Source,
                    SourceId = request.SourceId,
                    Artist = request.Artist,
                    Title = request.Title,
                    State = "queued",
                    Created = DateTimeOffset.UtcNow.ToString("O")
                }
            };
            _Jobs[job.Dto.Id] = job;
            _Queue.Writer.TryWrite(job);

            // Keep the list short: forget old finished jobs.
            foreach (var old in _Jobs.Values.Where(j => j.Dto.State is "done" or "failed").OrderByDescending(j => j.Dto.Created).Skip(50).ToList())
            {
                _Jobs.TryRemove(old.Dto.Id, out _);
            }

            return job.Dto;
        }

        public string DownloadRoot => Path.Combine(_Index.Root, _Options.DownloadFolder);

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            await foreach (var job in _Queue.Reader.ReadAllAsync(stoppingToken))
            {
                await _RunAsync(job, stoppingToken);
            }
        }

        private async Task _RunAsync(CJob job, CancellationToken ct)
        {
            var dto = job.Dto;
            dto.State = "running";
            var name = CSourceHelper.SafeName(dto.Artist.Length > 0 ? dto.Artist + " - " + dto.Title : dto.Title);
            if (name.Length == 0)
            {
                name = dto.Source + "-" + CSourceHelper.SafeName(dto.SourceId);
            }

            var target = Path.Combine(DownloadRoot, dto.Source, name);
            var temp = Path.Combine(DownloadRoot, ".incoming", dto.Id);
            try
            {
                if (Directory.Exists(target))
                {
                    dto.State = "done";
                    dto.Progress = 1;
                    dto.Message = "Already downloaded";
                    return;
                }

                Directory.CreateDirectory(temp);
                await job.Source.DownloadAsync(dto.SourceId, temp, new Progress<double>(p => dto.Progress = Math.Clamp(p, 0, 1)), ct);
                if (!Directory.EnumerateFiles(temp, "*.txt").Any(f => !Path.GetFileName(f).Equals("license.txt", StringComparison.OrdinalIgnoreCase)))
                {
                    throw new InvalidOperationException("The download contains no song file");
                }

                Directory.CreateDirectory(Path.GetDirectoryName(target)!);
                Directory.Move(temp, target);
                dto.State = "done";
                dto.Progress = 1;
                dto.Message = "";
                _Logger.LogInformation("Downloaded {Artist} - {Title} from {Source}", dto.Artist, dto.Title, dto.Source);
                _Index.RequestRescan();
            }
            catch (Exception e)
            {
                dto.State = "failed";
                dto.Message = e is OperationCanceledException ? "cancelled" : e.Message;
                _Logger.LogWarning("Download of {Artist} - {Title} from {Source} failed: {Message}", dto.Artist, dto.Title, dto.Source, e.Message);
            }
            finally
            {
                try
                {
                    if (Directory.Exists(temp))
                    {
                        Directory.Delete(temp, true);
                    }
                }
                catch (IOException)
                {
                    // left for the next start
                }
            }
        }
    }
}