using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;
using DiscordChatExporter.Core.Discord.Data;
using DiscordChatExporter.Core.Exceptions;
using DiscordChatExporter.Core.Utils;
using DiscordChatExporter.Core.Utils.Extensions;
using JsonExtensions.Http;
using JsonExtensions.Reading;

namespace DiscordChatExporter.Core.Discord
{
    public class DiscordClient
    {
        private readonly AuthToken _token;
        private readonly Uri _baseUri = new("https://discord.com/api/v8/", UriKind.Absolute);

        public DiscordClient(AuthToken token) => _token = token;

        private async ValueTask<HttpResponseMessage> GetResponseAsync(string url) =>
            await Http.ResponsePolicy.ExecuteAsync(async () =>
            {
                using var request = new HttpRequestMessage(HttpMethod.Get, new Uri(_baseUri, url));
                request.Headers.Authorization = _token.GetAuthenticationHeader();

                return await Http.Client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
            });

        private async ValueTask<JsonElement> GetJsonResponseAsync(string url)
        {
            using var response = await GetResponseAsync(url);

            if (!response.IsSuccessStatusCode)
            {
                throw response.StatusCode switch
                {
                    HttpStatusCode.Unauthorized => DiscordChatExporterException.Unauthorized(),
                    HttpStatusCode.Forbidden => DiscordChatExporterException.Forbidden(),
                    HttpStatusCode.NotFound => DiscordChatExporterException.NotFound(url),
                    _ => DiscordChatExporterException.FailedHttpRequest(response)
                };
            }

            return await response.Content.ReadAsJsonAsync();
        }

        private async ValueTask<JsonElement?> TryGetJsonResponseAsync(string url)
        {
            using var response = await GetResponseAsync(url);

            return response.IsSuccessStatusCode
                ? await response.Content.ReadAsJsonAsync()
                : null;
        }

        public async IAsyncEnumerable<Guild> GetUserGuildsAsync()
        {
            yield return Guild.DirectMessages;

            var currentAfter = Snowflake.Zero;

            while (true)
            {
                var url = new UrlBuilder()
                    .SetPath("users/@me/guilds")
                    .SetQueryParameter("limit", "100")
                    .SetQueryParameter("after", currentAfter.ToString())
                    .Build();

                var response = await GetJsonResponseAsync(url);

                var isEmpty = true;
                foreach (var guild in response.EnumerateArray().Select(Guild.Parse))
                {
                    yield return guild;

                    currentAfter = guild.Id;
                    isEmpty = false;
                }

                if (isEmpty)
                    yield break;
            }
        }

        public async ValueTask<Guild> GetGuildAsync(Snowflake guildId)
        {
            if (guildId == Guild.DirectMessages.Id)
                return Guild.DirectMessages;

            var response = await GetJsonResponseAsync($"guilds/{guildId}");
            return Guild.Parse(response);
        }

        public async IAsyncEnumerable<Channel> GetGuildChannelsAsync(Snowflake guildId)
        {
            if (guildId == Guild.DirectMessages.Id)
            {
                var response = await GetJsonResponseAsync("users/@me/channels");
                foreach (var channelJson in response.EnumerateArray())
                    yield return Channel.Parse(channelJson);
            }
            else
            {
                var response = await GetJsonResponseAsync($"guilds/{guildId}/channels");

                var responseOrdered = response
                    .EnumerateArray()
                    .OrderBy(j => j.GetProperty("position").GetInt32())
                    .ThenBy(j => Snowflake.Parse(j.GetProperty("id").GetString()))
                    .ToArray();

                var categories = responseOrdered
                    .Where(j => j.GetProperty("type").GetInt32() == (int) ChannelKind.GuildCategory)
                    .Select((j, index) => ChannelCategory.Parse(j, index + 1))
                    .ToDictionary(j => j.Id.ToString(), StringComparer.Ordinal);

                var position = 0;

                foreach (var channelJson in responseOrdered)
                {
                    var parentId = channelJson.GetPropertyOrNull("parent_id")?.GetString();

                    var category = !string.IsNullOrWhiteSpace(parentId)
                        ? categories.GetValueOrDefault(parentId)
                        : null;

                    var channel = Channel.Parse(channelJson, category, position);

                    position++;

                    yield return channel;
                }
            }
        }

        public async IAsyncEnumerable<Role> GetGuildRolesAsync(Snowflake guildId)
        {
            if (guildId == Guild.DirectMessages.Id)
                yield break;

            var response = await GetJsonResponseAsync($"guilds/{guildId}/roles");

            foreach (var roleJson in response.EnumerateArray())
                yield return Role.Parse(roleJson);
        }

        public async ValueTask<Member> GetGuildMemberAsync(Snowflake guildId, User user)
        {
            if (guildId == Guild.DirectMessages.Id)
                return Member.CreateForUser(user);

            var response = await TryGetJsonResponseAsync($"guilds/{guildId}/members/{user.Id}");
            return response?.Pipe(Member.Parse) ?? Member.CreateForUser(user);
        }

        public async ValueTask<ChannelCategory> GetChannelCategoryAsync(Snowflake channelId)
        {
            try
            {
                var response = await GetJsonResponseAsync($"channels/{channelId}");
                return ChannelCategory.Parse(response);
            }
            // In some cases, the Discord API returns an empty body when requesting channel category.
            // Instead, we use an empty channel category as a fallback.
            catch (DiscordChatExporterException)
            {
                return ChannelCategory.Unknown;
            }
        }

        public async ValueTask<Channel> GetChannelAsync(Snowflake channelId)
        {
            var response = await GetJsonResponseAsync($"channels/{channelId}");

            var parentId = response.GetPropertyOrNull("parent_id")?.GetString().Pipe(Snowflake.Parse);

            var category = parentId is not null
                ? await GetChannelCategoryAsync(parentId.Value)
                : null;

            return Channel.Parse(response, category);
        }

        private async ValueTask<Message?> TryGetLastMessageAsync(Snowflake channelId, Snowflake? before = null)
        {
            var url = new UrlBuilder()
                .SetPath($"channels/{channelId}/messages")
                .SetQueryParameter("limit", "1")
                .SetQueryParameter("before", before?.ToString())
                .Build();

            var response = await GetJsonResponseAsync(url);
            return response.EnumerateArray().Select(Message.Parse).LastOrDefault();
        }

        public async IAsyncEnumerable<Message> GetMessagesAsync(
            Snowflake channelId,
            Snowflake? after = null,
            Snowflake? before = null,
            IProgress<double>? progress = null)
        {
            // Get the last message in the specified range.
            // This snapshots the boundaries, which means that messages posted after the export started
            // will not appear in the output.
            // Additionally, it provides the date of the last message, which is used to calculate progress.
            var lastMessage = await TryGetLastMessageAsync(channelId, before);
            if (lastMessage is null || lastMessage.Timestamp < after?.ToDate())
                yield break;

            // Keep track of first message in range in order to calculate progress
            var firstMessage = default(Message);
            var currentAfter = after ?? Snowflake.Zero;

            while (true)
            {
                var url = new UrlBuilder()
                    .SetPath($"channels/{channelId}/messages")
                    .SetQueryParameter("limit", "100")
                    .SetQueryParameter("after", currentAfter.ToString())
                    .Build();

                var response = await GetJsonResponseAsync(url);

                var messages = response
                    .EnumerateArray()
                    .Select(Message.Parse)
                    .Reverse() // reverse because messages appear newest first
                    .ToArray();

                // Break if there are no messages (can happen if messages are deleted during execution)
                if (!messages.Any())
                    yield break;

                foreach (var message in messages)
                {
                    firstMessage ??= message;

                    // Ensure messages are in range (take into account that last message could have been deleted)
                    if (message.Timestamp > lastMessage.Timestamp)
                        yield break;

                    // Report progress based on the duration of exported messages divided by total
                    if (progress is not null)
                    {
                        var exportedDuration = (message.Timestamp - firstMessage.Timestamp).Duration();
                        var totalDuration = (lastMessage.Timestamp - firstMessage.Timestamp).Duration();

                        if (totalDuration > TimeSpan.Zero)
                        {
                            progress.Report(exportedDuration / totalDuration);
                        }
                        // Avoid division by zero if all messages have the exact same timestamp
                        // (which may be the case if there's only one message in the channel)
                        else
                        {
                            progress.Report(1);
                        }
                    }

                    yield return message;
                    currentAfter = message.Id;
                }
            }
        }
    }
}