using System.Collections.Generic;
using System.Collections.Immutable;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Net;
using System.Text.Json;
using System.Threading.Tasks;
using DHT.Server.Data;
using DHT.Server.Data.Filters;
using DHT.Server.Database;
using DHT.Server.Service;
using DHT.Utils.Collections;
using DHT.Utils.Http;
using Microsoft.AspNetCore.Http;

namespace DHT.Server.Endpoints {
	sealed class TrackMessagesEndpoint : BaseEndpoint {
		public TrackMessagesEndpoint(IDatabaseFile db, ServerParameters parameters) : base(db, parameters) {}

		protected override async Task<(HttpStatusCode, object?)> Respond(HttpContext ctx) {
			var root = await ReadJson(ctx);

			if (root.ValueKind != JsonValueKind.Array) {
				throw new HttpException(HttpStatusCode.BadRequest, "Expected root element to be an array.");
			}

			var addedMessageIds = new HashSet<ulong>();
			var messages = new Message[root.GetArrayLength()];

			int i = 0;
			foreach (JsonElement ele in root.EnumerateArray()) {
				var message = ReadMessage(ele, "message");
				messages[i++] = message;
				addedMessageIds.Add(message.Id);
			}

			var addedMessageFilter = new MessageFilter { MessageIds = addedMessageIds };
			bool anyNewMessages = Db.CountMessages(addedMessageFilter) < messages.Length;

			Db.AddMessages(messages);

			return (HttpStatusCode.OK, anyNewMessages ? 1 : 0);
		}

		private static Message ReadMessage(JsonElement json, string path) => new() {
			Id = json.RequireSnowflake("id", path),
			Sender = json.RequireSnowflake("sender", path),
			Channel = json.RequireSnowflake("channel", path),
			Text = json.RequireString("text", path),
			Timestamp = json.RequireLong("timestamp", path),
			EditTimestamp = json.HasKey("editTimestamp") ? json.RequireLong("editTimestamp", path) : null,
			RepliedToId = json.HasKey("repliedToId") ? json.RequireSnowflake("repliedToId", path) : null,
			Attachments = json.HasKey("attachments") ? ReadAttachments(json.RequireArray("attachments", path + ".attachments"), path + ".attachments[]").ToImmutableArray() : ImmutableArray<Attachment>.Empty,
			Embeds = json.HasKey("embeds") ? ReadEmbeds(json.RequireArray("embeds", path + ".embeds"), path + ".embeds[]").ToImmutableArray() : ImmutableArray<Embed>.Empty,
			Reactions = json.HasKey("reactions") ? ReadReactions(json.RequireArray("reactions", path + ".reactions"), path + ".reactions[]").ToImmutableArray() : ImmutableArray<Reaction>.Empty
		};

		[SuppressMessage("ReSharper", "ConvertToLambdaExpression")]
		private static IEnumerable<Attachment> ReadAttachments(JsonElement.ArrayEnumerator array, string path) => array.Select(ele => new Attachment {
			Id = ele.RequireSnowflake("id", path),
			Name = ele.RequireString("name", path),
			Type = ele.HasKey("type") ? ele.RequireString("type", path) : null,
			Url = ele.RequireString("url", path),
			Size = (ulong) ele.RequireLong("size", path)
		}).DistinctByKeyStable(static attachment => {
			// Some Discord messages have duplicate attachments with the same id for unknown reasons.
			return attachment.Id;
		});

		private static IEnumerable<Embed> ReadEmbeds(JsonElement.ArrayEnumerator array, string path) => array.Select(ele => new Embed {
			Json = ele.ValueKind == JsonValueKind.String ? ele.ToString()! : throw new HttpException(HttpStatusCode.BadRequest, "Expected key '" + path + "' to be a string.")
		});

		private static IEnumerable<Reaction> ReadReactions(JsonElement.ArrayEnumerator array, string path) => array.Select(ele => {
			var reaction = new Reaction {
				EmojiId = ele.HasKey("id") ? ele.RequireSnowflake("id", path) : null,
				EmojiName = ele.HasKey("name") ? ele.RequireString("name", path) : null,
				EmojiFlags = ReadEmojiFlag(ele, "isAnimated", path, EmojiFlags.Animated),
				Count = ele.RequireInt("count", path)
			};

			if (reaction.EmojiId == null && reaction.EmojiName == null) {
				throw new HttpException(HttpStatusCode.BadRequest, "Expected key '" + path + ".id' and/or '" + path + ".name' to be present.");
			}

			return reaction;
		});

		private static EmojiFlags ReadEmojiFlag(JsonElement ele, string key, string path, EmojiFlags flag) {
			return ele.HasKey(key) && ele.RequireBool(key, path) ? flag : EmojiFlags.None;
		}
	}
}