using System.Diagnostics;
using System.Net;
using System.Net.Http.Headers;
using System.Net.Http.Json;
using System.Text.Json;
using System.Text.RegularExpressions;

using Myriad.Rest.Exceptions;
using Myriad.Rest.Ratelimit;
using Myriad.Rest.Types;
using Myriad.Serialization;

using Polly;

using Serilog;
using Serilog.Context;

namespace Myriad.Rest;

public class BaseRestClient: IAsyncDisposable
{
    private readonly string _baseUrl;
    private readonly Version _httpVersion = new(2, 0);
    private readonly JsonSerializerOptions _jsonSerializerOptions;
    private readonly ILogger _logger;
    private readonly Ratelimiter _ratelimiter;
    private readonly AsyncPolicy<HttpResponseMessage> _retryPolicy;
    public EventHandler<(string, int, long)> OnResponseEvent;

    public BaseRestClient(string userAgent, string token, ILogger logger, string baseUrl)
    {
        _logger = logger.ForContext<BaseRestClient>();
        _baseUrl = baseUrl;

        if (!token.StartsWith("Bot "))
            token = "Bot " + token;

        Client = new HttpClient();
        Client.DefaultRequestHeaders.TryAddWithoutValidation("User-Agent", userAgent);
        Client.DefaultRequestHeaders.TryAddWithoutValidation("Authorization", token);

        _jsonSerializerOptions = new JsonSerializerOptions().ConfigureForMyriad();

        _ratelimiter = new Ratelimiter(logger);
        var discordPolicy = new DiscordRateLimitPolicy(_ratelimiter);

        // todo: why doesn't the timeout work? o.o
        var timeoutPolicy = Policy.TimeoutAsync<HttpResponseMessage>(TimeSpan.FromSeconds(10));

        var waitPolicy = Policy
            .Handle<RatelimitBucketExhaustedException>()
            .WaitAndRetryAsync(3,
                (_, e, _) => ((RatelimitBucketExhaustedException)e).RetryAfter,
                (_, _, _, _) => Task.CompletedTask)
            .AsAsyncPolicy<HttpResponseMessage>();

        _retryPolicy = Policy.WrapAsync(timeoutPolicy, waitPolicy, discordPolicy);
    }

    public HttpClient Client { get; }

    public ValueTask DisposeAsync()
    {
        _ratelimiter.Dispose();
        Client.Dispose();
        return default;
    }

    public async Task<T?> Get<T>(string path, (string endpointName, ulong major) ratelimitParams) where T : class
    {
        using var response = await Send(() => new HttpRequestMessage(HttpMethod.Get, _baseUrl + path),
            ratelimitParams, true);

        // GET-only special case: 404s are nulls and not exceptions
        if (response.StatusCode == HttpStatusCode.NotFound)
            return null;

        return await ReadResponse<T>(response);
    }

    public async Task<T?> Post<T>(string path, (string endpointName, ulong major) ratelimitParams, object? body)
        where T : class
    {
        using var response = await Send(() =>
        {
            var request = new HttpRequestMessage(HttpMethod.Post, _baseUrl + path);
            SetRequestJsonBody(request, body);
            return request;
        }, ratelimitParams);
        return await ReadResponse<T>(response);
    }

    public async Task<T?> PostMultipart<T>(string path, (string endpointName, ulong major) ratelimitParams,
                                           object? payload, MultipartFile[]? files)
        where T : class
    {
        using var response = await Send(() =>
        {
            var request = new HttpRequestMessage(HttpMethod.Post, _baseUrl + path);
            SetRequestFormDataBody(request, payload, files);
            return request;
        }, ratelimitParams);
        return await ReadResponse<T>(response);
    }

    public async Task<T?> Patch<T>(string path, (string endpointName, ulong major) ratelimitParams, object? body)
        where T : class
    {
        using var response = await Send(() =>
        {
            var request = new HttpRequestMessage(HttpMethod.Patch, _baseUrl + path);
            SetRequestJsonBody(request, body);
            return request;
        }, ratelimitParams);
        return await ReadResponse<T>(response);
    }

    public async Task<T?> Put<T>(string path, (string endpointName, ulong major) ratelimitParams, object? body)
        where T : class
    {
        using var response = await Send(() =>
        {
            var request = new HttpRequestMessage(HttpMethod.Put, _baseUrl + path);
            SetRequestJsonBody(request, body);
            return request;
        }, ratelimitParams);
        return await ReadResponse<T>(response);
    }

    public async Task Delete(string path, (string endpointName, ulong major) ratelimitParams)
    {
        using var _ = await Send(() => new HttpRequestMessage(HttpMethod.Delete, _baseUrl + path), ratelimitParams);
    }

    private void SetRequestJsonBody(HttpRequestMessage request, object? body)
    {
        if (body == null) return;
        request.Content =
            new ReadOnlyMemoryContent(JsonSerializer.SerializeToUtf8Bytes(body, _jsonSerializerOptions));
        request.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
    }

    private void SetRequestFormDataBody(HttpRequestMessage request, object? payload, MultipartFile[]? files)
    {
        var bodyJson = JsonSerializer.SerializeToUtf8Bytes(payload, _jsonSerializerOptions);

        var mfd = new MultipartFormDataContent();
        mfd.Add(new ByteArrayContent(bodyJson), "payload_json");

        if (files != null)
            for (var i = 0; i < files.Length; i++)
            {
                var (filename, stream, _) = files[i];
                mfd.Add(new StreamContent(stream), $"files[{i}]", filename);
            }

        request.Content = mfd;
    }

    private async Task<T?> ReadResponse<T>(HttpResponseMessage response) where T : class
    {
        if (response.StatusCode == HttpStatusCode.NoContent)
            return null;
        return await response.Content.ReadFromJsonAsync<T>(_jsonSerializerOptions);
    }

    private async Task<HttpResponseMessage> Send(Func<HttpRequestMessage> createRequest,
                                                 (string endpointName, ulong major) ratelimitParams,
                                                 bool ignoreNotFound = false)
    {
        return await _retryPolicy.ExecuteAsync(async _ =>
            {
                using var __ = LogContext.PushProperty("EndpointName", ratelimitParams.endpointName);

                var request = createRequest();
                _logger.Debug("Request: {RequestMethod} {RequestPath}",
                    request.Method, CleanForLogging(request.RequestUri!));

                request.Version = _httpVersion;
                request.VersionPolicy = HttpVersionPolicy.RequestVersionOrHigher;

                HttpResponseMessage response;

                var stopwatch = new Stopwatch();
                stopwatch.Start();
                try
                {
                    response = await Client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
                    stopwatch.Stop();
                }
                catch (Exception exc)
                {
                    _logger.Error(exc, "HTTP error: {RequestMethod} {RequestUrl}", request.Method,
                        request.RequestUri);

                    // kill the running thread
                    // in PluralKit.Bot, this error is ignored in "IsOurProblem" (PluralKit.Bot/Utils/MiscUtils.cs)
                    throw;
                }

                _logger.Debug(
                    "Response: {RequestMethod} {RequestPath} -> {StatusCode} {ReasonPhrase} (in {ResponseDurationMs} ms)",
                    request.Method, CleanForLogging(request.RequestUri!), (int)response.StatusCode,
                    response.ReasonPhrase, stopwatch.ElapsedMilliseconds);

                await HandleApiError(response, ignoreNotFound);

                OnResponseEvent?.Invoke(null, (
                    GetEndpointMetricsName(response.RequestMessage!),
                    (int)response.StatusCode,
                    stopwatch.ElapsedTicks
                ));

                return response;
            },
            new Dictionary<string, object>
            {
                {DiscordRateLimitPolicy.EndpointContextKey, ratelimitParams.endpointName},
                {DiscordRateLimitPolicy.MajorContextKey, ratelimitParams.major}
            });
    }

    private async ValueTask HandleApiError(HttpResponseMessage response, bool ignoreNotFound)
    {
        if (response.IsSuccessStatusCode)
            return;

        if (response.StatusCode == HttpStatusCode.NotFound && ignoreNotFound)
            return;

        var body = await response.Content.ReadAsStringAsync();
        var apiError = TryParseApiError(body);
        if (apiError != null)
            _logger.Warning("Discord API error: {DiscordErrorCode} {DiscordErrorMessage}", apiError.Code,
                apiError.Message);

        throw CreateDiscordException(response, body, apiError);
    }

    private DiscordRequestException CreateDiscordException(HttpResponseMessage response, string body,
                                                           DiscordApiError? apiError)
    {
        return response.StatusCode switch
        {
            HttpStatusCode.BadRequest => new BadRequestException(response, body, apiError),
            HttpStatusCode.Forbidden => new ForbiddenException(response, body, apiError),
            HttpStatusCode.Unauthorized => new UnauthorizedException(response, body, apiError),
            HttpStatusCode.NotFound => new NotFoundException(response, body, apiError),
            HttpStatusCode.Conflict => new ConflictException(response, body, apiError),
            HttpStatusCode.TooManyRequests => new TooManyRequestsException(response, body, apiError),
            _ => new UnknownDiscordRequestException(response, body, apiError)
        };
    }

    private DiscordApiError? TryParseApiError(string responseBody)
    {
        if (string.IsNullOrWhiteSpace(responseBody))
            return null;

        try
        {
            return JsonSerializer.Deserialize<DiscordApiError>(responseBody, _jsonSerializerOptions);
        }
        catch (JsonException e)
        {
            _logger.Verbose(e, "Error deserializing API error");
        }

        return null;
    }

    private string NormalizeRoutePath(string url)
    {
        url = Regex.Replace(url, @"/channels/\d+", "/channels/{channel_id}");
        url = Regex.Replace(url, @"/messages/\d+", "/messages/{message_id}");
        url = Regex.Replace(url, @"/members/\d+", "/members/{user_id}");
        url = Regex.Replace(url, @"/webhooks/\d+/[^/]+", "/webhooks/{webhook_id}/{webhook_token}");
        url = Regex.Replace(url, @"/webhooks/\d+", "/webhooks/{webhook_id}");
        url = Regex.Replace(url, @"/users/\d+", "/users/{user_id}");
        url = Regex.Replace(url, @"/bans/\d+", "/bans/{user_id}");
        url = Regex.Replace(url, @"/roles/\d+", "/roles/{role_id}");
        url = Regex.Replace(url, @"/pins/\d+", "/pins/{message_id}");
        url = Regex.Replace(url, @"/emojis/\d+", "/emojis/{emoji_id}");
        url = Regex.Replace(url, @"/guilds/\d+", "/guilds/{guild_id}");
        url = Regex.Replace(url, @"/integrations/\d+", "/integrations/{integration_id}");
        url = Regex.Replace(url, @"/permissions/\d+", "/permissions/{overwrite_id}");
        url = Regex.Replace(url, @"/reactions/[^{/]+/\d+", "/reactions/{emoji}/{user_id}");
        url = Regex.Replace(url, @"/reactions/[^{/]+", "/reactions/{emoji}");
        url = Regex.Replace(url, @"/invites/[^{/]+", "/invites/{invite_code}");
        url = Regex.Replace(url, @"/interactions/\d+/[^{/]+", "/interactions/{interaction_id}/{interaction_token}");
        url = Regex.Replace(url, @"/interactions/\d+", "/interactions/{interaction_id}");

        // catch-all for missed IDs
        url = Regex.Replace(url, @"\d{17,19}", "{snowflake}");

        return url;
    }

    private string GetEndpointMetricsName(HttpRequestMessage req)
    {
        var localPath = Regex.Replace(req.RequestUri!.LocalPath, @"/api/v\d+", "");
        var routePath = NormalizeRoutePath(localPath);
        return $"{req.Method} {routePath}";
    }

    private string CleanForLogging(Uri uri)
    {
        var path = uri.ToString();

        // don't show tokens in logs
        // todo: anything missing here?
        path = Regex.Replace(path, @"/webhooks/(\d+)/[^/]+", "/webhooks/$1/:token");
        path = Regex.Replace(path, @"/interactions/(\d+)/[^{/]+", "/interactions/$1/:token");

        // remove base URL
        path = path.Substring(_baseUrl.Length);

        return path;
    }
}