using System.Net;

namespace Jellyfin.Plugin.Multilang.Services.Providers;

public enum ProviderFailureKind
{
    Retryable,
    Terminal
}

public sealed record ProviderHttpDiagnostics(
    ProviderHttpCount[] Counts,
    ProviderHttpRecent[] Recent);

public sealed record ProviderHttpCount(
    string Provider,
    string Outcome,
    int Count);

public sealed record ProviderHttpRecent(
    string Provider,
    string Url,
    string Outcome,
    int Attempt,
    long At);

public static class ProviderHttp
{
    private static readonly object DiagnosticsLock = new();
    private static readonly Dictionary<string, int> Counts = new(StringComparer.OrdinalIgnoreCase);
    private static readonly Queue<ProviderHttpRecent> Recent = new();

    public static ProviderFailureKind Classify(HttpStatusCode code)
        => code is HttpStatusCode.TooManyRequests or HttpStatusCode.RequestTimeout ||
           (int)code >= 500
            ? ProviderFailureKind.Retryable
            : ProviderFailureKind.Terminal;

    public static async Task<HttpResponseMessage> SendWithRetryAsync(
        HttpClient http,
        HttpRequestMessage request,
        CancellationToken cancellationToken,
        FetchRateLimiter? rateLimiter = null)
    {
        const int maxAttempts = 3;
        for (var attempt = 1; attempt <= maxAttempts; attempt++)
        {
            try
            {
                if (rateLimiter is not null)
                    await rateLimiter.WaitAsync(cancellationToken).ConfigureAwait(false);
                using var attemptRequest = Clone(request);
                var response = await http.SendAsync(attemptRequest, cancellationToken).ConfigureAwait(false);
                Record(request, "HTTP " + (int)response.StatusCode, attempt);
                if (response.IsSuccessStatusCode || Classify(response.StatusCode) == ProviderFailureKind.Terminal || attempt == maxAttempts)
                {
                    return response;
                }

                var delay = GetRetryDelay(response, attempt);
                response.Dispose();
                await Task.Delay(delay < TimeSpan.Zero ? TimeSpan.Zero : delay, cancellationToken).ConfigureAwait(false);
            }
            catch (Exception ex) when (!cancellationToken.IsCancellationRequested && ex is HttpRequestException or OperationCanceledException)
            {
                Record(request, ex.GetType().Name, attempt);
                if (attempt >= maxAttempts)
                {
                    throw;
                }

                await Task.Delay(TimeSpan.FromMilliseconds(250 * attempt), cancellationToken).ConfigureAwait(false);
            }
        }

        throw new HttpRequestException("Provider request failed after retries.");
    }

    public static ProviderHttpDiagnostics GetDiagnostics()
    {
        lock (DiagnosticsLock)
        {
            return new ProviderHttpDiagnostics(
                Counts
                    .Select(kvp =>
                    {
                        var index = kvp.Key.IndexOf('|', StringComparison.Ordinal);
                        var provider = index >= 0 ? kvp.Key[..index] : kvp.Key;
                        var outcome = index >= 0 ? kvp.Key[(index + 1)..] : string.Empty;
                        return new ProviderHttpCount(provider, outcome, kvp.Value);
                    })
                    .OrderBy(c => c.Provider)
                    .ThenBy(c => c.Outcome)
                    .ToArray(),
                Recent.Reverse().ToArray());
        }
    }

    private static TimeSpan GetRetryDelay(HttpResponseMessage response, int attempt)
        => response.Headers.RetryAfter?.Delta ??
           (response.Headers.RetryAfter?.Date is { } date
               ? date - DateTimeOffset.UtcNow
               : TimeSpan.FromMilliseconds(250 * attempt));

    private static void Record(HttpRequestMessage request, string outcome, int attempt)
    {
        var provider = ProviderName(request.RequestUri);
        var key = provider + "|" + outcome;
        var recent = new ProviderHttpRecent(
            provider,
            SafeUrl(request.RequestUri),
            outcome,
            attempt,
            DateTimeOffset.UtcNow.ToUnixTimeSeconds());

        lock (DiagnosticsLock)
        {
            Counts[key] = Counts.TryGetValue(key, out var count) ? count + 1 : 1;
            Recent.Enqueue(recent);
            while (Recent.Count > 50)
                Recent.Dequeue();
        }
    }

    private static string ProviderName(Uri? uri)
    {
        var host = uri?.Host ?? string.Empty;
        if (host.Contains("themoviedb", StringComparison.OrdinalIgnoreCase) || host.Contains("tmdb", StringComparison.OrdinalIgnoreCase))
            return "TMDb";
        if (host.Contains("fanart", StringComparison.OrdinalIgnoreCase))
            return "Fanart.tv";
        return string.IsNullOrWhiteSpace(host) ? "unknown" : host;
    }

    private static string SafeUrl(Uri? uri)
        => uri is null ? string.Empty : uri.GetLeftPart(UriPartial.Path);

    private static HttpRequestMessage Clone(HttpRequestMessage request)
    {
        var clone = new HttpRequestMessage(request.Method, request.RequestUri);
        foreach (var header in request.Headers)
            clone.Headers.TryAddWithoutValidation(header.Key, header.Value);
        return clone;
    }
}