using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml;
using System.Xml.Linq;
using Jellyfin.Plugin.Jellypod.Api.Models;
using Jellyfin.Plugin.Jellypod.Models;
using Microsoft.Extensions.Logging;

namespace Jellyfin.Plugin.Jellypod.Services;

/// <summary>
/// Service for handling OPML import and export operations.
/// </summary>
public class OpmlService : IOpmlService
{
    private readonly ILogger<OpmlService> _logger;
    private readonly IRssFeedService _rssFeedService;
    private readonly IPodcastStorageService _storageService;

    /// <summary>
    /// Initializes a new instance of the <see cref="OpmlService"/> class.
    /// </summary>
    /// <param name="logger">Logger instance.</param>
    /// <param name="rssFeedService">RSS feed service.</param>
    /// <param name="storageService">Storage service.</param>
    public OpmlService(
        ILogger<OpmlService> logger,
        IRssFeedService rssFeedService,
        IPodcastStorageService storageService)
    {
        _logger = logger;
        _rssFeedService = rssFeedService;
        _storageService = storageService;
    }

    /// <inheritdoc />
    public IReadOnlyList<OpmlOutline> ParseOpml(string opmlContent)
    {
        using var reader = new StringReader(opmlContent);
        var doc = XDocument.Load(reader);
        return ParseOpmlDocument(doc);
    }

    /// <inheritdoc />
    public IReadOnlyList<OpmlOutline> ParseOpml(Stream stream)
    {
        var doc = XDocument.Load(stream);
        return ParseOpmlDocument(doc);
    }

    private List<OpmlOutline> ParseOpmlDocument(XDocument doc)
    {
        var outlines = new List<OpmlOutline>();
        var body = doc.Root?.Element("body");

        if (body == null)
        {
            _logger.LogWarning("OPML document has no body element");
            return outlines;
        }

        // Recursively find all outline elements with xmlUrl (podcast feeds)
        ParseOutlines(body.Elements("outline"), outlines, null);

        _logger.LogInformation("Parsed {Count} podcast feeds from OPML", outlines.Count);
        return outlines;
    }

    private void ParseOutlines(
        IEnumerable<XElement> elements,
        List<OpmlOutline> outlines,
        string? parentCategory)
    {
        foreach (var element in elements)
        {
            var xmlUrl = element.Attribute("xmlUrl")?.Value;
            var text = element.Attribute("text")?.Value;

            if (!string.IsNullOrEmpty(xmlUrl))
            {
                // This is a feed outline
                outlines.Add(new OpmlOutline
                {
                    Text = text,
                    Title = element.Attribute("title")?.Value,
                    XmlUrl = xmlUrl,
                    HtmlUrl = element.Attribute("htmlUrl")?.Value,
                    Description = element.Attribute("description")?.Value,
                    Category = parentCategory ?? element.Attribute("category")?.Value
                });
            }
            else if (element.HasElements)
            {
                // This might be a category/folder - use text as category for children
                var category = parentCategory ?? text;
                ParseOutlines(element.Elements("outline"), outlines, category);
            }
        }
    }

    /// <inheritdoc />
    public async Task<OpmlImportResult> ImportPodcastsAsync(
        IReadOnlyList<OpmlOutline> outlines,
        CancellationToken cancellationToken = default)
    {
        var result = new OpmlImportResult { TotalFeeds = outlines.Count };

        // Get existing feeds to check for duplicates
        var existingPodcasts = await _storageService.GetAllPodcastsAsync().ConfigureAwait(false);
        var existingUrls = existingPodcasts
            .Select(p => p.FeedUrl)
            .ToHashSet(StringComparer.OrdinalIgnoreCase);

        foreach (var outline in outlines)
        {
            if (cancellationToken.IsCancellationRequested)
            {
                break;
            }

            if (string.IsNullOrWhiteSpace(outline.XmlUrl))
            {
                continue;
            }

            // Check if already subscribed
            if (existingUrls.Contains(outline.XmlUrl))
            {
                result.SkippedCount++;
                result.SkippedFeeds.Add(outline.XmlUrl);
                _logger.LogDebug("Skipping already subscribed feed: {Url}", outline.XmlUrl);
                continue;
            }

            try
            {
                var podcast = await _rssFeedService.FetchPodcastAsync(
                    outline.XmlUrl,
                    cancellationToken).ConfigureAwait(false);

                if (podcast == null)
                {
                    result.FailedCount++;
                    result.Errors.Add(new OpmlImportError
                    {
                        FeedUrl = outline.XmlUrl,
                        Title = outline.DisplayTitle,
                        Error = "Failed to fetch or parse RSS feed"
                    });
                    continue;
                }

                // Preserve category from OPML if the feed doesn't have one
                if (string.IsNullOrEmpty(podcast.Category) && !string.IsNullOrEmpty(outline.Category))
                {
                    podcast.Category = outline.Category;
                }

                await _storageService.AddPodcastAsync(podcast).ConfigureAwait(false);

                result.ImportedCount++;
                result.ImportedPodcasts.Add(podcast.Title);
                existingUrls.Add(outline.XmlUrl); // Prevent duplicate adds within same import

                _logger.LogInformation("Imported podcast: {Title} ({Url})", podcast.Title, podcast.FeedUrl);
            }
            catch (Exception ex)
            {
                result.FailedCount++;
                result.Errors.Add(new OpmlImportError
                {
                    FeedUrl = outline.XmlUrl,
                    Title = outline.DisplayTitle,
                    Error = ex.Message
                });
                _logger.LogWarning(ex, "Failed to import feed: {Url}", outline.XmlUrl);
            }
        }

        _logger.LogInformation(
            "OPML import complete: {Imported} imported, {Skipped} skipped, {Failed} failed out of {Total}",
            result.ImportedCount,
            result.SkippedCount,
            result.FailedCount,
            result.TotalFeeds);

        return result;
    }

    /// <inheritdoc />
    public async Task<string> ExportToOpmlAsync()
    {
        var podcasts = await _storageService.GetAllPodcastsAsync().ConfigureAwait(false);

        var doc = new XDocument(
            new XDeclaration("1.0", "utf-8", null),
            new XElement(
                "opml",
                new XAttribute("version", "2.0"),
                new XElement(
                    "head",
                    new XElement("title", "Jellypod Podcast Subscriptions"),
                    new XElement("dateCreated", DateTime.UtcNow.ToString("r", CultureInfo.InvariantCulture)),
                    new XElement("docs", "http://opml.org/spec2.opml")),
                new XElement(
                    "body",
                    podcasts.Select(p => CreateOutlineElement(p)))));

        var settings = new XmlWriterSettings
        {
            Indent = true,
            Encoding = new UTF8Encoding(false),
            OmitXmlDeclaration = false
        };

        using var stringWriter = new StringWriter();
        using (var xmlWriter = XmlWriter.Create(stringWriter, settings))
        {
            doc.Save(xmlWriter);
        }

        _logger.LogInformation("Exported {Count} podcasts to OPML", podcasts.Count);
        return stringWriter.ToString();
    }

    private static XElement CreateOutlineElement(Podcast podcast)
    {
        var element = new XElement(
            "outline",
            new XAttribute("type", "rss"),
            new XAttribute("text", podcast.Title),
            new XAttribute("title", podcast.Title),
            new XAttribute("xmlUrl", podcast.FeedUrl));

        if (!string.IsNullOrEmpty(podcast.Description))
        {
            element.Add(new XAttribute("description", TruncateDescription(podcast.Description)));
        }

        if (!string.IsNullOrEmpty(podcast.Category))
        {
            element.Add(new XAttribute("category", podcast.Category));
        }

        return element;
    }

    private static string TruncateDescription(string description, int maxLength = 200)
    {
        if (string.IsNullOrEmpty(description) || description.Length <= maxLength)
        {
            return description;
        }

        return string.Concat(description.AsSpan(0, maxLength), "...");
    }
}