using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Jellyfin.Data.Enums;
using MediaBrowser.Controller.Entities;
using MediaBrowser.Controller.Library;
using Microsoft.Extensions.Logging;

namespace Jellyfin.Plugin.Floatplane.Channel;

/// <summary>
/// Every Jellyfin client lists a channel folder sorted by name by default, and the web
/// client stores a sort choice per folder. To get release order without touching every
/// folder, each video's <c>ForcedSortName</c> is set to its release time reversed
/// (<c>(10^13 - unixMs)</c>, zero-padded), so "Name ascending" = newest first.
/// Runs a few seconds after a listing (the items only exist in the database after
/// Jellyfin has synced them) and during the scheduled refresh.
/// </summary>
public class SortNameUpdater
{
    private const long Epoch = 10_000_000_000_000; // > any unix ms this side of year 2286

    private readonly ILibraryManager _libraryManager;
    private readonly ILogger<SortNameUpdater> _logger;
    private readonly SemaphoreSlim _gate = new(1, 1);
    private int _scheduled;

    public SortNameUpdater(ILibraryManager libraryManager, ILogger<SortNameUpdater> logger)
    {
        _libraryManager = libraryManager;
        _logger = logger;
    }

    /// <summary>Sort name for a release date: newest first under ascending name order.</summary>
    public static string SortNameFor(DateTime? releaseDate)
    {
        var ms = releaseDate.HasValue ? new DateTimeOffset(DateTime.SpecifyKind(releaseDate.Value, DateTimeKind.Utc)).ToUnixTimeMilliseconds() : 0;
        return (Epoch - 1 - Math.Clamp(ms, 0, Epoch - 1)).ToString("D13", CultureInfo.InvariantCulture);
    }

    /// <summary>Schedules one pass shortly after a listing (coalesces bursts of calls).</summary>
    public void ScheduleSoon()
    {
        if (Interlocked.CompareExchange(ref _scheduled, 1, 0) != 0)
        {
            return;
        }

        _ = Task.Run(async () =>
        {
            try
            {
                await Task.Delay(TimeSpan.FromSeconds(10)).ConfigureAwait(false);
                Interlocked.Exchange(ref _scheduled, 0);
                await UpdateAsync(CancellationToken.None).ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                Interlocked.Exchange(ref _scheduled, 0);
                _logger.LogWarning(ex, "Sort-name update failed");
            }
        });
    }

    /// <summary>Sets the forced sort name on every Floatplane video item that lacks the right one.</summary>
    public async Task<int> UpdateAsync(CancellationToken ct)
    {
        await _gate.WaitAsync(ct).ConfigureAwait(false);
        try
        {
            var channelIds = _libraryManager.GetItemList(new InternalItemsQuery
            {
                IncludeItemTypes = [BaseItemKind.Channel],
                Name = "Floatplane"
            }).Select(c => c.Id).ToArray();
            if (channelIds.Length == 0)
            {
                return 0;
            }

            var items = _libraryManager.GetItemList(new InternalItemsQuery
            {
                ChannelIds = channelIds,
                IncludeItemTypes = [BaseItemKind.Video],
                Recursive = true
            });

            var changed = new List<BaseItem>();
            foreach (var item in items)
            {
                if (FloatplaneChannel.PostIdOf(item.ExternalId) is null)
                {
                    continue;
                }

                var wanted = SortNameFor(item.PremiereDate ?? item.DateCreated);
                if (!string.Equals(item.ForcedSortName, wanted, StringComparison.Ordinal))
                {
                    item.ForcedSortName = wanted;
                    changed.Add(item);
                }
            }

            if (changed.Count > 0)
            {
                await _libraryManager.UpdateItemsAsync(changed, changed[0].GetParent(), ItemUpdateType.MetadataEdit, ct).ConfigureAwait(false);
                _logger.LogInformation("Set release-order sort names on {Count} Floatplane videos", changed.Count);
            }

            return changed.Count;
        }
        finally
        {
            _gate.Release();
        }
    }
}