using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml;
using MediaBrowser.Common;
using MediaBrowser.Common.Net;
using MediaBrowser.Controller.Entities.Audio;
using MediaBrowser.Controller.Providers;
using MediaBrowser.Model.Entities;
using MediaBrowser.Model.Providers;
using MediaBrowser.Providers.Plugins.MusicBrainz;
using Microsoft.Extensions.Logging;

namespace MediaBrowser.Providers.Music
{
    public class MusicBrainzAlbumProvider : IRemoteMetadataProvider<MusicAlbum, AlbumInfo>, IHasOrder
    {
        /// <summary>
        /// The Jellyfin user-agent is unrestricted but source IP must not exceed
        /// one request per second, therefore we rate limit to avoid throttling.
        /// Be prudent, use a value slightly above the minimun required.
        /// https://musicbrainz.org/doc/XML_Web_Service/Rate_Limiting
        /// </summary>
        private readonly long _musicBrainzQueryIntervalMs;

        /// <summary>
        /// For each single MB lookup/search, this is the maximum number of
        /// attempts that shall be made whilst receiving a 503 Server
        /// Unavailable (indicating throttled) response.
        /// </summary>
        private const uint MusicBrainzQueryAttempts = 5u;

        internal static MusicBrainzAlbumProvider Current;

        private readonly IHttpClient _httpClient;
        private readonly IApplicationHost _appHost;
        private readonly ILogger _logger;

        private readonly string _musicBrainzBaseUrl;

        private Stopwatch _stopWatchMusicBrainz = new Stopwatch();

        public MusicBrainzAlbumProvider(
            IHttpClient httpClient,
            IApplicationHost appHost,
            ILogger logger)
        {
            _httpClient = httpClient;
            _appHost = appHost;
            _logger = logger;

            _musicBrainzBaseUrl = Plugin.Instance.Configuration.Server;
            _musicBrainzQueryIntervalMs = Plugin.Instance.Configuration.RateLimit;

            // Use a stopwatch to ensure we don't exceed the MusicBrainz rate limit
            _stopWatchMusicBrainz.Start();

            Current = this;
        }

        /// <inheritdoc />
        public string Name => "MusicBrainz";

        /// <inheritdoc />
        public int Order => 0;

        /// <inheritdoc />
        public async Task<IEnumerable<RemoteSearchResult>> GetSearchResults(AlbumInfo searchInfo, CancellationToken cancellationToken)
        {
            // TODO maybe remove when artist metadata can be disabled
            if (!Plugin.Instance.Configuration.Enable)
            {
                return Enumerable.Empty<RemoteSearchResult>();
            }

            var releaseId = searchInfo.GetReleaseId();
            var releaseGroupId = searchInfo.GetReleaseGroupId();

            string url;

            if (!string.IsNullOrEmpty(releaseId))
            {
                url = "/ws/2/release/?query=reid:" + releaseId.ToString(CultureInfo.InvariantCulture);
            }
            else if (!string.IsNullOrEmpty(releaseGroupId))
            {
                url = "/ws/2/release?release-group=" + releaseGroupId.ToString(CultureInfo.InvariantCulture);
            }
            else
            {
                var artistMusicBrainzId = searchInfo.GetMusicBrainzArtistId();

                if (!string.IsNullOrWhiteSpace(artistMusicBrainzId))
                {
                    url = string.Format(
                        CultureInfo.InvariantCulture,
                        "/ws/2/release/?query=\"{0}\" AND arid:{1}",
                        WebUtility.UrlEncode(searchInfo.Name),
                        artistMusicBrainzId);
                }
                else
                {
                    // I'm sure there is a better way but for now it resolves search for 12" Mixes
                    var queryName = searchInfo.Name.Replace("\"", string.Empty);

                    url = string.Format(
                        CultureInfo.InvariantCulture,
                        "/ws/2/release/?query=\"{0}\" AND artist:\"{1}\"",
                        WebUtility.UrlEncode(queryName),
                        WebUtility.UrlEncode(searchInfo.GetAlbumArtist()));
                }
            }

            if (!string.IsNullOrWhiteSpace(url))
            {
                using (var response = await GetMusicBrainzResponse(url, cancellationToken).ConfigureAwait(false))
                using (var stream = response.Content)
                {
                    return GetResultsFromResponse(stream);
                }
            }

            return Enumerable.Empty<RemoteSearchResult>();
        }

        private IEnumerable<RemoteSearchResult> GetResultsFromResponse(Stream stream)
        {
            using (var oReader = new StreamReader(stream, Encoding.UTF8))
            {
                var settings = new XmlReaderSettings()
                {
                    ValidationType = ValidationType.None,
                    CheckCharacters = false,
                    IgnoreProcessingInstructions = true,
                    IgnoreComments = true
                };

                using (var reader = XmlReader.Create(oReader, settings))
                {
                    var results = ReleaseResult.Parse(reader);

                    return results.Select(i =>
                    {
                        var result = new RemoteSearchResult
                        {
                            Name = i.Title,
                            ProductionYear = i.Year
                        };

                        if (i.Artists.Count > 0)
                        {
                            result.AlbumArtist = new RemoteSearchResult
                            {
                                SearchProviderName = Name,
                                Name = i.Artists[0].Item1
                            };

                            result.AlbumArtist.SetProviderId(MetadataProviders.MusicBrainzArtist, i.Artists[0].Item2);
                        }

                        if (!string.IsNullOrWhiteSpace(i.ReleaseId))
                        {
                            result.SetProviderId(MetadataProviders.MusicBrainzAlbum, i.ReleaseId);
                        }

                        if (!string.IsNullOrWhiteSpace(i.ReleaseGroupId))
                        {
                            result.SetProviderId(MetadataProviders.MusicBrainzReleaseGroup, i.ReleaseGroupId);
                        }

                        return result;
                    });
                }
            }
        }

        /// <inheritdoc />
        public async Task<MetadataResult<MusicAlbum>> GetMetadata(AlbumInfo id, CancellationToken cancellationToken)
        {
            var releaseId = id.GetReleaseId();
            var releaseGroupId = id.GetReleaseGroupId();

            var result = new MetadataResult<MusicAlbum>
            {
                Item = new MusicAlbum()
            };

            // TODO maybe remove when artist metadata can be disabled
            if (!Plugin.Instance.Configuration.Enable)
            {
                return result;
            }

            // If we have a release group Id but not a release Id...
            if (string.IsNullOrWhiteSpace(releaseId) && !string.IsNullOrWhiteSpace(releaseGroupId))
            {
                releaseId = await GetReleaseIdFromReleaseGroupId(releaseGroupId, cancellationToken).ConfigureAwait(false);
                result.HasMetadata = true;
            }

            if (string.IsNullOrWhiteSpace(releaseId))
            {
                var artistMusicBrainzId = id.GetMusicBrainzArtistId();

                var releaseResult = await GetReleaseResult(artistMusicBrainzId, id.GetAlbumArtist(), id.Name, cancellationToken).ConfigureAwait(false);

                if (releaseResult != null)
                {
                    if (!string.IsNullOrWhiteSpace(releaseResult.ReleaseId))
                    {
                        releaseId = releaseResult.ReleaseId;
                        result.HasMetadata = true;
                    }

                    if (!string.IsNullOrWhiteSpace(releaseResult.ReleaseGroupId))
                    {
                        releaseGroupId = releaseResult.ReleaseGroupId;
                        result.HasMetadata = true;
                    }

                    result.Item.ProductionYear = releaseResult.Year;
                    result.Item.Overview = releaseResult.Overview;
                }
            }

            // If we have a release Id but not a release group Id...
            if (!string.IsNullOrWhiteSpace(releaseId) && string.IsNullOrWhiteSpace(releaseGroupId))
            {
                releaseGroupId = await GetReleaseGroupFromReleaseId(releaseId, cancellationToken).ConfigureAwait(false);
                result.HasMetadata = true;
            }

            if (!string.IsNullOrWhiteSpace(releaseId) || !string.IsNullOrWhiteSpace(releaseGroupId))
            {
                result.HasMetadata = true;
            }

            if (result.HasMetadata)
            {
                if (!string.IsNullOrEmpty(releaseId))
                {
                    result.Item.SetProviderId(MetadataProviders.MusicBrainzAlbum, releaseId);
                }

                if (!string.IsNullOrEmpty(releaseGroupId))
                {
                    result.Item.SetProviderId(MetadataProviders.MusicBrainzReleaseGroup, releaseGroupId);
                }
            }

            return result;
        }

        private Task<ReleaseResult> GetReleaseResult(string artistMusicBrainId, string artistName, string albumName, CancellationToken cancellationToken)
        {
            if (!string.IsNullOrEmpty(artistMusicBrainId))
            {
                return GetReleaseResult(albumName, artistMusicBrainId, cancellationToken);
            }

            if (string.IsNullOrWhiteSpace(artistName))
            {
                return Task.FromResult(new ReleaseResult());
            }

            return GetReleaseResultByArtistName(albumName, artistName, cancellationToken);
        }

        private async Task<ReleaseResult> GetReleaseResult(string albumName, string artistId, CancellationToken cancellationToken)
        {
            var url = string.Format("/ws/2/release/?query=\"{0}\" AND arid:{1}",
                WebUtility.UrlEncode(albumName),
                artistId);

            using (var response = await GetMusicBrainzResponse(url, cancellationToken).ConfigureAwait(false))
            using (var stream = response.Content)
            using (var oReader = new StreamReader(stream, Encoding.UTF8))
            {
                var settings = new XmlReaderSettings()
                {
                    ValidationType = ValidationType.None,
                    CheckCharacters = false,
                    IgnoreProcessingInstructions = true,
                    IgnoreComments = true
                };

                using (var reader = XmlReader.Create(oReader, settings))
                {
                    return ReleaseResult.Parse(reader).FirstOrDefault();
                }
            }
        }

        private async Task<ReleaseResult> GetReleaseResultByArtistName(string albumName, string artistName, CancellationToken cancellationToken)
        {
            var url = string.Format(
                CultureInfo.InvariantCulture,
                "/ws/2/release/?query=\"{0}\" AND artist:\"{1}\"",
                WebUtility.UrlEncode(albumName),
                WebUtility.UrlEncode(artistName));

            using (var response = await GetMusicBrainzResponse(url, cancellationToken).ConfigureAwait(false))
            using (var stream = response.Content)
            using (var oReader = new StreamReader(stream, Encoding.UTF8))
            {
                var settings = new XmlReaderSettings()
                {
                    ValidationType = ValidationType.None,
                    CheckCharacters = false,
                    IgnoreProcessingInstructions = true,
                    IgnoreComments = true
                };

                using (var reader = XmlReader.Create(oReader, settings))
                {
                    return ReleaseResult.Parse(reader).FirstOrDefault();
                }
            }
        }

        private class ReleaseResult
        {
            public string ReleaseId;
            public string ReleaseGroupId;
            public string Title;
            public string Overview;
            public int? Year;

            public List<ValueTuple<string, string>> Artists = new List<ValueTuple<string, string>>();

            public static IEnumerable<ReleaseResult> Parse(XmlReader reader)
            {
                reader.MoveToContent();
                reader.Read();

                // Loop through each element
                while (!reader.EOF && reader.ReadState == ReadState.Interactive)
                {
                    if (reader.NodeType == XmlNodeType.Element)
                    {
                        switch (reader.Name)
                        {
                            case "release-list":
                                {
                                    if (reader.IsEmptyElement)
                                    {
                                        reader.Read();
                                        continue;
                                    }

                                    using (var subReader = reader.ReadSubtree())
                                    {
                                        return ParseReleaseList(subReader).ToList();
                                    }
                                }
                            default:
                                {
                                    reader.Skip();
                                    break;
                                }
                        }
                    }
                    else
                    {
                        reader.Read();
                    }
                }

                return Enumerable.Empty<ReleaseResult>();
            }

            private static IEnumerable<ReleaseResult> ParseReleaseList(XmlReader reader)
            {
                reader.MoveToContent();
                reader.Read();

                // Loop through each element
                while (!reader.EOF && reader.ReadState == ReadState.Interactive)
                {
                    if (reader.NodeType == XmlNodeType.Element)
                    {
                        switch (reader.Name)
                        {
                            case "release":
                                {
                                    if (reader.IsEmptyElement)
                                    {
                                        reader.Read();
                                        continue;
                                    }
                                    var releaseId = reader.GetAttribute("id");

                                    using (var subReader = reader.ReadSubtree())
                                    {
                                        var release = ParseRelease(subReader, releaseId);
                                        if (release != null)
                                        {
                                            yield return release;
                                        }
                                    }
                                    break;
                                }
                            default:
                                {
                                    reader.Skip();
                                    break;
                                }
                        }
                    }
                    else
                    {
                        reader.Read();
                    }
                }
            }

            private static ReleaseResult ParseRelease(XmlReader reader, string releaseId)
            {
                var result = new ReleaseResult
                {
                    ReleaseId = releaseId
                };

                reader.MoveToContent();
                reader.Read();

                // http://stackoverflow.com/questions/2299632/why-does-xmlreader-skip-every-other-element-if-there-is-no-whitespace-separator

                // Loop through each element
                while (!reader.EOF && reader.ReadState == ReadState.Interactive)
                {
                    if (reader.NodeType == XmlNodeType.Element)
                    {
                        switch (reader.Name)
                        {
                            case "title":
                                {
                                    result.Title = reader.ReadElementContentAsString();
                                    break;
                                }
                            case "date":
                                {
                                    var val = reader.ReadElementContentAsString();
                                    if (DateTime.TryParse(val, out var date))
                                    {
                                        result.Year = date.Year;
                                    }
                                    break;
                                }
                            case "annotation":
                                {
                                    result.Overview = reader.ReadElementContentAsString();
                                    break;
                                }
                            case "release-group":
                                {
                                    result.ReleaseGroupId = reader.GetAttribute("id");
                                    reader.Skip();
                                    break;
                                }
                            case "artist-credit":
                                {
                                    using (var subReader = reader.ReadSubtree())
                                    {
                                        var artist = ParseArtistCredit(subReader);

                                        if (!string.IsNullOrEmpty(artist.Item1))
                                        {
                                            result.Artists.Add(artist);
                                        }
                                    }

                                    break;
                                }
                            default:
                                {
                                    reader.Skip();
                                    break;
                                }
                        }
                    }
                    else
                    {
                        reader.Read();
                    }
                }

                return result;
            }
        }

        private static ValueTuple<string, string> ParseArtistCredit(XmlReader reader)
        {
            reader.MoveToContent();
            reader.Read();

            // http://stackoverflow.com/questions/2299632/why-does-xmlreader-skip-every-other-element-if-there-is-no-whitespace-separator

            // Loop through each element
            while (!reader.EOF && reader.ReadState == ReadState.Interactive)
            {
                if (reader.NodeType == XmlNodeType.Element)
                {
                    switch (reader.Name)
                    {
                        case "name-credit":
                            {
                                using (var subReader = reader.ReadSubtree())
                                {
                                    return ParseArtistNameCredit(subReader);
                                }
                            }
                        default:
                            {
                                reader.Skip();
                                break;
                            }
                    }
                }
                else
                {
                    reader.Read();
                }
            }

            return new ValueTuple<string, string>();
        }

        private static (string, string) ParseArtistNameCredit(XmlReader reader)
        {
            reader.MoveToContent();
            reader.Read();

            // http://stackoverflow.com/questions/2299632/why-does-xmlreader-skip-every-other-element-if-there-is-no-whitespace-separator

            // Loop through each element
            while (!reader.EOF && reader.ReadState == ReadState.Interactive)
            {
                if (reader.NodeType == XmlNodeType.Element)
                {
                    switch (reader.Name)
                    {
                        case "artist":
                            {
                                var id = reader.GetAttribute("id");
                                using (var subReader = reader.ReadSubtree())
                                {
                                    return ParseArtistArtistCredit(subReader, id);
                                }
                            }
                        default:
                            {
                                reader.Skip();
                                break;
                            }
                    }
                }
                else
                {
                    reader.Read();
                }
            }

            return (null, null);
        }

        private static (string name, string id) ParseArtistArtistCredit(XmlReader reader, string artistId)
        {
            reader.MoveToContent();
            reader.Read();

            string name = null;

            // http://stackoverflow.com/questions/2299632/why-does-xmlreader-skip-every-other-element-if-there-is-no-whitespace-separator

            // Loop through each element
            while (!reader.EOF && reader.ReadState == ReadState.Interactive)
            {
                if (reader.NodeType == XmlNodeType.Element)
                {
                    switch (reader.Name)
                    {
                        case "name":
                            {
                                name = reader.ReadElementContentAsString();
                                break;
                            }
                        default:
                            {
                                reader.Skip();
                                break;
                            }
                    }
                }
                else
                {
                    reader.Read();
                }
            }

            return (name, artistId);
        }

        private async Task<string> GetReleaseIdFromReleaseGroupId(string releaseGroupId, CancellationToken cancellationToken)
        {
            var url = "/ws/2/release?release-group=" + releaseGroupId.ToString(CultureInfo.InvariantCulture);

            using (var response = await GetMusicBrainzResponse(url, cancellationToken).ConfigureAwait(false))
            using (var stream = response.Content)
            using (var oReader = new StreamReader(stream, Encoding.UTF8))
            {
                var settings = new XmlReaderSettings()
                {
                    ValidationType = ValidationType.None,
                    CheckCharacters = false,
                    IgnoreProcessingInstructions = true,
                    IgnoreComments = true
                };

                using (var reader = XmlReader.Create(oReader, settings))
                {
                    var result = ReleaseResult.Parse(reader).FirstOrDefault();

                    if (result != null)
                    {
                        return result.ReleaseId;
                    }
                }
            }

            return null;
        }

        /// <summary>
        /// Gets the release group id internal.
        /// </summary>
        /// <param name="releaseEntryId">The release entry id.</param>
        /// <param name="cancellationToken">The cancellation token.</param>
        /// <returns>Task{System.String}.</returns>
        private async Task<string> GetReleaseGroupFromReleaseId(string releaseEntryId, CancellationToken cancellationToken)
        {
            var url = "/ws/2/release-group/?query=reid:" + releaseEntryId.ToString(CultureInfo.InvariantCulture);

            using (var response = await GetMusicBrainzResponse(url, cancellationToken).ConfigureAwait(false))
            using (var stream = response.Content)
            using (var oReader = new StreamReader(stream, Encoding.UTF8))
            {
                var settings = new XmlReaderSettings()
                {
                    ValidationType = ValidationType.None,
                    CheckCharacters = false,
                    IgnoreProcessingInstructions = true,
                    IgnoreComments = true
                };

                using (var reader = XmlReader.Create(oReader, settings))
                {
                    reader.MoveToContent();
                    reader.Read();

                    // Loop through each element
                    while (!reader.EOF && reader.ReadState == ReadState.Interactive)
                    {
                        if (reader.NodeType == XmlNodeType.Element)
                        {
                            switch (reader.Name)
                            {
                                case "release-group-list":
                                    {
                                        if (reader.IsEmptyElement)
                                        {
                                            reader.Read();
                                            continue;
                                        }
                                        using (var subReader = reader.ReadSubtree())
                                        {
                                            return GetFirstReleaseGroupId(subReader);
                                        }
                                    }
                                default:
                                    {
                                        reader.Skip();
                                        break;
                                    }
                            }
                        }
                        else
                        {
                            reader.Read();
                        }
                    }

                    return null;
                }
            }
        }

        private string GetFirstReleaseGroupId(XmlReader reader)
        {
            reader.MoveToContent();
            reader.Read();

            // Loop through each element
            while (!reader.EOF && reader.ReadState == ReadState.Interactive)
            {
                if (reader.NodeType == XmlNodeType.Element)
                {
                    switch (reader.Name)
                    {
                        case "release-group":
                            {
                                return reader.GetAttribute("id");
                            }
                        default:
                            {
                                reader.Skip();
                                break;
                            }
                    }
                }
                else
                {
                    reader.Read();
                }
            }

            return null;
        }

        /// <summary>
        /// Makes request to MusicBrainz server and awaits a response.
        /// A 503 Service Unavailable response indicates throttling to maintain a rate limit.
        /// A number of retries shall be made in order to try and satisfy the request before
        /// giving up and returning null.
        /// </summary>
        internal async Task<HttpResponseInfo> GetMusicBrainzResponse(string url, CancellationToken cancellationToken)
        {
            var options = new HttpRequestOptions
            {
                Url = _musicBrainzBaseUrl.TrimEnd('/') + url,
                CancellationToken = cancellationToken,
                // MusicBrainz request a contact email address is supplied, as comment, in user agent field:
                // https://musicbrainz.org/doc/XML_Web_Service/Rate_Limiting#User-Agent
                UserAgent = string.Format(
                    CultureInfo.InvariantCulture,
                    "{0} ( {1} )",
                    _appHost.ApplicationUserAgent,
                    _appHost.ApplicationUserAgentAddress),
                BufferContent = false
            };

            HttpResponseInfo response;
            var attempts = 0u;

            do
            {
                attempts++;

                if (_stopWatchMusicBrainz.ElapsedMilliseconds < _musicBrainzQueryIntervalMs)
                {
                    // MusicBrainz is extremely adamant about limiting to one request per second
                    var delayMs = _musicBrainzQueryIntervalMs - _stopWatchMusicBrainz.ElapsedMilliseconds;
                    await Task.Delay((int)delayMs, cancellationToken).ConfigureAwait(false);
                }

                // Write time since last request to debug log as evidence we're meeting rate limit
                // requirement, before resetting stopwatch back to zero.
                _logger.LogDebug("GetMusicBrainzResponse: Time since previous request: {0} ms", _stopWatchMusicBrainz.ElapsedMilliseconds);
                _stopWatchMusicBrainz.Restart();

                response = await _httpClient.SendAsync(options, "GET").ConfigureAwait(false);

                // We retry a finite number of times, and only whilst MB is indicating 503 (throttling)
            }
            while (attempts < MusicBrainzQueryAttempts && response.StatusCode == HttpStatusCode.ServiceUnavailable);

            // Log error if unable to query MB database due to throttling
            if (attempts == MusicBrainzQueryAttempts && response.StatusCode == HttpStatusCode.ServiceUnavailable)
            {
                _logger.LogError("GetMusicBrainzResponse: 503 Service Unavailable (throttled) response received {0} times whilst requesting {1}", attempts, options.Url);
            }

            return response;
        }

        /// <inheritdoc />
        public Task<HttpResponseInfo> GetImageResponse(string url, CancellationToken cancellationToken)
        {
            throw new NotImplementedException();
        }
    }
}