using System.Net;
using System.Net.Http.Json;

using collAnon.Client.Services;

using decePubClient.Helpers;
using decePubClient.Models;

namespace decePubClient.Services
{
	/// <summary>
	/// Requests to the PrivaPub API through the "default" HttpClient (AppConfiguration.ApiBaseAddress), at three
	/// authentication levels: Get/Post/Delete need a valid token and sign out on 401, *Anon add the token when there is
	/// one, *TotallyAnon never send it. Nothing throws: a failure comes back as a response carrying an invalid WebResult
	/// (SUtility.ClassifiedFailure, read with ExtensionMethods.ReadWebResult), a cancelled request as HTTP 410.
	/// With retryOnError, 408/429/502/503/504 and transport errors are retried after 1, 2, 4, 8, 16 and 29 seconds, then
	/// every 60, plus jitter, for at most 10 minutes.
	/// </summary>
	public interface IHttpService
	{
		Task<HttpResponseMessage> Get(string uri, string[] queryParams = default, bool retryOnError = false, CancellationToken cancellationToken = default);

		Task<HttpResponseMessage> GetAnon(string uri, string[] queryParams = default, bool retryOnError = false, CancellationToken cancellationToken = default);

		Task<HttpResponseMessage> GetTotallyAnon(string uri, string[] queryParams = default, bool retryOnError = false,
			CancellationToken cancellationToken = default);

		Task<HttpResponseMessage> Post(string uri, object payload = default, bool retryOnError = false, CancellationToken cancellationToken = default);

		Task<HttpResponseMessage> PostAnon(string uri, object payload = default, bool retryOnError = false, CancellationToken cancellationToken = default);

		Task<HttpResponseMessage> PostTotallyAnon(string uri, object payload = default, bool retryOnError = false,
			CancellationToken cancellationToken = default);

		Task<HttpResponseMessage> Delete(string uri, string[] queryParams = default, object payload = default, bool retryOnError = false,
			CancellationToken cancellationToken = default);

		Task<HttpResponseMessage> DeleteTotallyAnon(string uri, string[] queryParams = default, object payload = default, bool retryOnError = false,
			CancellationToken cancellationToken = default);
	}

	public class HttpService(IHttpClientFactory httpClientFactory, TokenAuthStateProvider authStateProvider, AppStatusService statusService,
		ILoggingService logger, CoalescingStringLocalizer localizer) : IHttpService
	{
		static readonly int[] RetryRampUpDelaysMs = [1_000, 2_000, 4_000, 8_000, 16_000, 29_000];
		const int RetryIndefiniteDelayMs = 60_000;
		static readonly TimeSpan RetryDeadline = TimeSpan.FromMinutes(10);
		static readonly int[] RetryableStatusCodes = [408, 429, 502, 503, 504];

		readonly HttpClient httpClient = httpClientFactory.CreateClient("default");

		public Task<HttpResponseMessage> Get(string uri, string[] queryParams = default, bool retryOnError = false, CancellationToken cancellationToken = default) =>
			Send(nameof(Get), () => BuildRequest(HttpMethod.Get, uri, queryParams: queryParams), SendAuthRequest, retryOnError, cancellationToken);

		public Task<HttpResponseMessage> GetAnon(string uri, string[] queryParams = default, bool retryOnError = false, CancellationToken cancellationToken = default) =>
			Send(nameof(GetAnon), () => BuildRequest(HttpMethod.Get, uri, queryParams: queryParams), SendAuthIfAvailableRequest, retryOnError,
				cancellationToken);

		public Task<HttpResponseMessage> GetTotallyAnon(string uri, string[] queryParams = default, bool retryOnError = false,
			CancellationToken cancellationToken = default) =>
			Send(nameof(GetTotallyAnon), () => BuildRequest(HttpMethod.Get, uri, queryParams: queryParams), httpClient.SendAsync, retryOnError,
				cancellationToken);

		public Task<HttpResponseMessage> Post(string uri, object payload = default, bool retryOnError = false, CancellationToken cancellationToken = default) =>
			Send(nameof(Post), () => BuildRequest(HttpMethod.Post, uri, payload, forceContent: true), SendAuthRequest, retryOnError, cancellationToken);

		public Task<HttpResponseMessage> PostAnon(string uri, object payload = default, bool retryOnError = false, CancellationToken cancellationToken = default) =>
			Send(nameof(PostAnon), () => BuildRequest(HttpMethod.Post, uri, payload, forceContent: true), SendAuthIfAvailableRequest, retryOnError,
				cancellationToken);

		public Task<HttpResponseMessage> PostTotallyAnon(string uri, object payload = default, bool retryOnError = false,
			CancellationToken cancellationToken = default) =>
			Send(nameof(PostTotallyAnon), () => BuildRequest(HttpMethod.Post, uri, payload, forceContent: true), httpClient.SendAsync, retryOnError,
				cancellationToken);

		public Task<HttpResponseMessage> Delete(string uri, string[] queryParams = default, object payload = default, bool retryOnError = false,
			CancellationToken cancellationToken = default) =>
			Send(nameof(Delete), () => BuildRequest(HttpMethod.Delete, uri, payload, queryParams), SendAuthRequest, retryOnError, cancellationToken);

		public Task<HttpResponseMessage> DeleteTotallyAnon(string uri, string[] queryParams = default, object payload = default, bool retryOnError = false,
			CancellationToken cancellationToken = default) =>
			Send(nameof(DeleteTotallyAnon), () => BuildRequest(HttpMethod.Delete, uri, payload, queryParams), httpClient.SendAsync, retryOnError,
				cancellationToken);

		async Task<HttpResponseMessage> Send(string caller, Func<HttpRequestMessage> requestFactory,
			Func<HttpRequestMessage, CancellationToken, Task<HttpResponseMessage>> send, bool retryOnError, CancellationToken cancellationToken)
		{
			var deadline = DateTime.UtcNow + RetryDeadline;
			var attempt = 0;
			while (true)
			{
				// A request message can be sent once, so every attempt builds its own.
				var request = requestFactory();
				var where = $"{nameof(HttpService)}.{caller}:{request.RequestUri?.OriginalString}";
				var failure = default(string);
				var transportException = default(Exception);
				try
				{
					var response = await send(request, cancellationToken);
					var status = (int)response.StatusCode;
					if (!retryOnError || !RetryableStatusCodes.Contains(status))
						return status > 499 ? ServerError(response) : response;

					failure = $"HTTP {status}";
					response.Dispose();
				}
				catch (Exception) when (cancellationToken.IsCancellationRequested)
				{
					return SUtility.DefaultTaskCancelled();
				}
				catch (Exception ex) when (ex is HttpRequestException or TaskCanceledException)
				{
					if (!retryOnError)
					{
						await logger.ProcessError(ex, where, cancellationToken);
						return await DescribeUnreachable(ex, 1, cancellationToken);
					}

					failure = ex.Message;
					transportException = ex;
				}
				catch (Exception ex)
				{
					await logger.ProcessError(ex, where, cancellationToken);
					return SUtility.ClassifiedFailure(FailureCodes.ClientError,
						localizer["The request could not be prepared. Reload the page and try again."], HttpStatusCode.ServiceUnavailable);
				}

				var delay = attempt < RetryRampUpDelaysMs.Length ? RetryRampUpDelaysMs[attempt] : RetryIndefiniteDelayMs;
				delay += Random.Shared.Next(0, delay / 4);
				if (deadline - DateTime.UtcNow <= TimeSpan.FromMilliseconds(delay))
				{
					await logger.ProcessError($"Gave up after {attempt + 1} attempts. {failure}", where, cancellationToken);
					if (transportException is not null)
						return await DescribeUnreachable(transportException, attempt + 1, cancellationToken);
					return SUtility.ClassifiedFailure(FailureCodes.RetriesExhausted,
						localizer["The server is still not answering after {0} attempts. Try again later.", attempt + 1], HttpStatusCode.ServiceUnavailable);
				}

				await logger.ProcessWarning($"Attempt {attempt + 1} failed, retrying in {delay}ms. {failure}", where, cancellationToken);
				try
				{
					await Task.Delay(delay, cancellationToken);
				}
				catch (OperationCanceledException)
				{
					return SUtility.DefaultTaskCancelled();
				}

				attempt++;
			}
		}

		HttpResponseMessage ServerError(HttpResponseMessage response)
		{
			var status = response.StatusCode;
			response.Dispose();
			return SUtility.ClassifiedFailure(FailureCodes.ServerError, localizer["The server reported an internal error (HTTP {0}).", (int)status], status);
		}

		/// <summary>Why a request got no answer: the device is offline, it timed out, retries ran out, or the server is unreachable.</summary>
		async Task<HttpResponseMessage> DescribeUnreachable(Exception exception, int attempts, CancellationToken cancellationToken)
		{
			if (!await statusService.IsOnline(cancellationToken))
				return SUtility.ClassifiedFailure(FailureCodes.DeviceOffline,
					localizer["This device is offline. Check the connection and try again."], HttpStatusCode.ServiceUnavailable);

			if (exception is TaskCanceledException { InnerException: TimeoutException })
				return SUtility.ClassifiedFailure(FailureCodes.Timeout,
					localizer["The server took too long to answer. Try again later."], HttpStatusCode.ServiceUnavailable);

			if (attempts > 1)
				return SUtility.ClassifiedFailure(FailureCodes.RetriesExhausted,
					localizer["The server is still not answering after {0} attempts. Try again later.", attempts], HttpStatusCode.ServiceUnavailable);

			return SUtility.ClassifiedFailure(FailureCodes.ApiUnreachable,
				localizer["The server can't be reached. Try again later."], HttpStatusCode.ServiceUnavailable);
		}

		async Task<HttpResponseMessage> SendAuthRequest(HttpRequestMessage request, CancellationToken cancellationToken)
		{
			var token = await authStateProvider.GetToken(cancellationToken);
			if (token is null)
			{
				logger.Process($"NO_TOKEN:{request.RequestUri?.OriginalString}", nameof(SendAuthRequest), LogLevel.Warning);
				return SUtility.DefaultUnauthorized(localizer["Your session has expired. Sign in again."]);
			}

			request.Headers.Authorization = new("Bearer", token);
			var response = await httpClient.SendAsync(request, cancellationToken);
			if (response.StatusCode is not HttpStatusCode.Unauthorized)
				return response;

			response.Dispose();
			await authStateProvider.LogoutAsync(cancellationToken: cancellationToken);
			return SUtility.DefaultUnauthorized(localizer["Your session has expired. Sign in again."]);
		}

		async Task<HttpResponseMessage> SendAuthIfAvailableRequest(HttpRequestMessage request, CancellationToken cancellationToken)
		{
			var token = await authStateProvider.GetToken(cancellationToken);
			if (token is not null)
				request.Headers.Authorization = new("Bearer", token);
			return await httpClient.SendAsync(request, cancellationToken);
		}

		static HttpRequestMessage BuildRequest(HttpMethod method, string uri, object payload = default, string[] queryParams = default,
			bool forceContent = false)
		{
			var target = queryParams is { Length: > 0 } ? $"{uri}?{string.Join('&', queryParams)}" : uri;
			var request = new HttpRequestMessage(method, target);
			if (payload is not null || forceContent)
				request.Content = JsonContent.Create(payload, payload?.GetType() ?? typeof(object), options: SUtility.DefaultSerializer);
			return request;
		}
	}
}