using MongoDB.Entities;

using PrivaPub.Federation.Rendering;
using PrivaPub.Models.Post;

using System.Text.Json.Nodes;
using System.Text.RegularExpressions;

namespace PrivaPub.Domain.Content
{
	// This server's own custom emoji (completion program R7), in memory: the ones offered now (neither disabled nor deleted),
	// for the places that read them one text at a time (a post published or edited, a profile saved, a Note or an actor
	// rendered, a reaction, the Mastodon API's lists). Read at start, again after every change an administrator makes
	// (EmojiAdminController) and when five minutes old; a process that never loaded it starts with none and loads it on
	// first use.
	//
	// A local post or profile keeps the emoji its text named when it was written (Post.Emojis, Avatar.Emojis); what is
	// rendered of them is what they are now: one disabled or deleted since is left out, and one whose picture changed is
	// shown with the new one, its `updated` telling the servers that hold the old one to fetch it again.
	public static class LocalEmojis
	{
		/// <summary>Where each emoji is served as an ActivityPub `Emoji` object: /emojis/{shortcode}, its id on other servers.
		/// The plan's name, waiting for the owner's confirmation; it is frozen once it has federated (CLAUDE.md, routes).</summary>
		public const string Path = "emojis";
		public const int MaxShortcodeLength = 64;
		public const int MaxPerObject = 64;//what ObjectShapes reads of anyone's object
		const string ServerUsePrefix = "emoji:";

		static readonly TimeSpan Staleness = TimeSpan.FromMinutes(5);
		static readonly Regex Shortcode = new("^[a-zA-Z0-9_]{2,64}$", RegexOptions.CultureInvariant);
		// `:name:` with no letter or digit right before or after it, as Mastodon scans texts (`:a::b:` is two)
		static readonly Regex Named = new(@"(?<![a-zA-Z0-9]):([a-zA-Z0-9_]{2,64}):(?![a-zA-Z0-9])", RegexOptions.CultureInvariant);

		public sealed record Live(string Id, string Shortcode, string Url, string StaticUrl, string ContentType, DateTime ImageUpdatedAt, string Category,
			bool VisibleInPicker);

		static volatile IReadOnlyDictionary<string, Live> _current = new Dictionary<string, Live>(StringComparer.Ordinal);
		static DateTime _loadedAt = DateTime.MinValue;
		static int _reloading;

		/// <summary>The emoji offered now, by their exact shortcode.</summary>
		public static IReadOnlyDictionary<string, Live> Current
		{
			get
			{
				RefreshIfStale();
				return _current;
			}
		}

		public static bool IsShortcode(string text) => !string.IsNullOrEmpty(text) && Shortcode.IsMatch(text);

		/// <summary>The id an emoji federates under: {base}/emojis/{shortcode}.</summary>
		public static string Uri(string baseAddress, string shortcode) => $"{baseAddress}/{Path}/{shortcode}";

		/// <summary>What holds its picture (MediaAttachment.ServerUse): the janitor and the media audit leave such rows alone.</summary>
		public static string ServerUse(string shortcode) => ServerUsePrefix + shortcode;

		public static bool IsEmojiUse(string serverUse) => serverUse?.StartsWith(ServerUsePrefix, StringComparison.Ordinal) == true;

		public static Live Find(string shortcode) =>
			shortcode != default && Current.TryGetValue(shortcode, out var emoji) ? emoji : default;

		public static async Task Reload(CancellationToken token = default)
		{
			var offered = await DB.Default.Find<LocalEmoji>().Match(e => e.DeletedAt == null && !e.Disabled).ExecuteAsync(token);
			_current = offered.Where(e => IsShortcode(e.Shortcode) && !string.IsNullOrEmpty(e.Url))
				.GroupBy(e => e.Shortcode, StringComparer.Ordinal)
				.ToDictionary(g => g.Key, g => g.Select(e => new Live(e.ID, e.Shortcode, e.Url, e.StaticUrl ?? e.Url, e.ContentType ?? "image/png", e.ImageUpdatedAt,
					e.Category, e.VisibleInPicker)).First(), StringComparer.Ordinal);
			_loadedAt = DateTime.UtcNow;
		}

		static void RefreshIfStale()
		{
			if (DateTime.UtcNow - _loadedAt < Staleness || Interlocked.Exchange(ref _reloading, 1) == 1)
				return;
			_ = Task.Run(async () =>
			{
				try
				{
					await Reload(CancellationToken.None);
				}
				catch (Exception ex)
				{
					Serilog.Log.ForContext(typeof(LocalEmojis)).Warning(ex, "The custom emoji could not be reloaded");
				}
				finally
				{
					Interlocked.Exchange(ref _reloading, 0);
				}
			});
		}

		/// <summary>The emoji offered now that the texts name as `:shortcode:`, as a post or a profile keeps them; remote
		/// shortcodes are not ours and are never taken.</summary>
		public static List<CustomEmoji> In(IEnumerable<string> texts)
		{
			var current = Current;
			if (current.Count == 0)
				return new List<CustomEmoji>();
			return texts.Where(t => !string.IsNullOrEmpty(t))
				.SelectMany(t => Named.Matches(t).Select(m => m.Groups[1].Value))
				.Distinct(StringComparer.Ordinal)
				.Select(code => current.GetValueOrDefault(code))
				.Where(e => e != default)
				.Take(MaxPerObject)
				.Select(e => new CustomEmoji { Shortcode = e.Shortcode, URL = e.Url, Updated = e.ImageUpdatedAt })
				.ToList();
		}

		public static List<CustomEmoji> In(params string[] texts) => In((IEnumerable<string>)texts);

		/// <summary>A persona's emoji: those its name, its bio and its fields name.</summary>
		public static List<CustomEmoji> OfProfile(Models.User.Avatar avatar) =>
			In(new[] { avatar.Name, avatar.Biography }.Concat((avatar.Fields ?? new()).SelectMany(f => new[] { f.Key, f.Value })));

		/// <summary>What a local post's or persona's kept emoji are now: those still offered, as they are now.</summary>
		public static List<Live> Of(IEnumerable<CustomEmoji> kept)
		{
			var current = Current;
			if (kept == default || current.Count == 0)
				return new List<Live>();
			return kept.Where(e => e?.Shortcode != default).Select(e => current.GetValueOrDefault(e.Shortcode)).Where(e => e != default)
				.DistinctBy(e => e.Shortcode).Take(MaxPerObject).ToList();
		}

		/// <summary>The local emoji a reaction names: `:shortcode:`, `:shortcode@this-host:` or the bare shortcode (Mastodon's
		/// announcements, Pleroma's clients); none for a unicode emoji or another server's.</summary>
		public static Live ForReaction(string content, string domain)
		{
			var text = content?.Trim();
			if (string.IsNullOrEmpty(text) || text.Length > 300)
				return default;
			if (text.Length > 2 && text.StartsWith(':') && text.EndsWith(':'))
				text = text[1..^1];
			var at = text.IndexOf('@');
			if (at >= 0)
			{
				if (!string.Equals(text[(at + 1)..], domain, StringComparison.OrdinalIgnoreCase))
					return default;
				text = text[..at];
			}
			return IsShortcode(text) ? Find(text) : default;
		}

		/// <summary>An emoji as a tag of a Note, Question, actor or EmojiReact, in Mastodon's shape (GoToSocial needs its id).</summary>
		public static JsonObject Tag(Live emoji, string baseAddress) => Build(emoji, baseAddress, new JsonObject());

		/// <summary>The document served at the emoji's id: the same object, with the context.</summary>
		public static JsonObject Document(Live emoji, string baseAddress) =>
			Build(emoji, baseAddress, new JsonObject { ["@context"] = ActivityPubRenderer.Context() });

		static JsonObject Build(Live emoji, string baseAddress, JsonObject into)
		{
			into["id"] = Uri(baseAddress, emoji.Shortcode);
			into["type"] = "Emoji";
			into["name"] = $":{emoji.Shortcode}:";
			into["updated"] = ActivityPubRenderer.Timestamp(emoji.ImageUpdatedAt);
			into["icon"] = new JsonObject { ["type"] = "Image", ["mediaType"] = emoji.ContentType, ["url"] = emoji.Url };
			return into;
		}
	}
}