decePubClient/Extensions/ExtensionMethods.cs

using Blazored.LocalStorage;

using decePubClient.Helpers;
using decePubClient.Models;
using decePubClient.Models.Mastodon;
using decePubClient.Services;

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Components.WebAssembly.Hosting;

using PrivaPub.ClientModels;

using System.Globalization;
using System.Net;
using System.Net.Http.Json;
using System.Text.Json;
using System.Text.RegularExpressions;
using System.Web;

namespace decePubClient.Extensions
{
	public static partial class ExtensionMethods
	{
		#region Setups

		/// <summary>The languages with resources (Resources/AllStrings.*.resx); any other browser language gets English.</summary>
		public static readonly string[] SupportedLanguages = ["en", "it"];

		public static async Task SetDefaultCulture(this WebAssemblyHost host, CancellationToken cancellationToken = default)
		{
			var culture = ToCulture(default);
			try
			{
				var storage = host.Services.GetRequiredService<ILocalStorageService>();
				var publicCache = await storage.GetItemAsync<PublicCacheData>(nameof(PublicCacheData), cancellationToken);
				if (publicCache is null)
				{
					var browserLanguage = host.Services.GetRequiredService<AppStatusService>().Language();
					publicCache = new();
					publicCache.PageSettings.CurrentLanguageCode =
						SupportedLanguages.FirstOrDefault(language => browserLanguage?.StartsWith(language) ?? false) ?? "en";
					await storage.SetItemAsync(nameof(PublicCacheData), publicCache, cancellationToken);
				}

				culture = ToCulture(publicCache.PageSettings.CurrentLanguageCode);
			}
			catch (Exception ex)
			{
				Console.WriteLine(ex);
			}

			CultureInfo.DefaultThreadCurrentCulture = culture;
			CultureInfo.DefaultThreadCurrentUICulture = culture;
		}

		static CultureInfo ToCulture(string languageCode) => languageCode is "it" ? new("it-IT") : new("en-GB");

		#endregion Setups

		#region Models

		public static string ToString(this WebResult webResult, CoalescingStringLocalizer localizer) =>
				localizer["{0} - {1}", webResult.StatusCode, webResult.ErrorMessage];

		/// <summary>
		/// Reads a failed response as a WebResult: a failure HttpService made up (FailureHeader) as is, 401/403 and 5xx
		/// as a generic message, validation ProblemDetails as their errors, anything else as the server's WebResult.
		/// A cancelled request (410) becomes SUtility.DefaultTaskCancelledResult.
		/// </summary>
		public static async Task<WebResult> ReadWebResult(this HttpContent content, HttpStatusCode statusCode,
			CoalescingStringLocalizer localizer, CancellationToken cancellationToken = default)
		{
			if (statusCode is HttpStatusCode.Gone)
				return SUtility.DefaultTaskCancelledResult;

			var result = new WebResult();
			try
			{
				var json = await content.ReadAsStringAsync(cancellationToken);
				if (content.Headers.Contains(SUtility.FailureHeader))
					return JsonSerializer.Deserialize<WebResult>(json, SUtility.DefaultSerializer);

				if (statusCode is HttpStatusCode.Unauthorized or HttpStatusCode.Forbidden)
					return result.Invalidate(localizer["You are not authorized to do this."], (int)statusCode, FailureCodes.Unauthorized);

				if ((int)statusCode > 499)
					return result.Invalidate(localizer["The server reported an internal error (HTTP {0}).", (int)statusCode], (int)statusCode,
						FailureCodes.ServerError);

				if (TryReadMastodonError(json) is { } mastodonError)
					return result.Invalidate(mastodonError, (int)statusCode);

				if (json.Contains("\"title\""))
				{
					var validationErrors = JsonSerializer.Deserialize<ValidationErrors>(json, SUtility.DefaultSerializer);
					var lines = validationErrors.Errors.Select(error => $"{error.Key}: {string.Join(", ", error.Value)}").Prepend(validationErrors.Title);
					return result.Invalidate(string.Join('\n', lines), validationErrors.Status);
				}

				return JsonSerializer.Deserialize<WebResult>(json, SUtility.DefaultSerializer) ??
					result.Invalidate(localizer["The server sent an invalid response."], (int)statusCode);
			}
			catch (OperationCanceledException)
			{
				return SUtility.DefaultTaskCancelledResult;
			}
			catch (Exception ex)
			{
				return result.Invalidate(localizer["The server sent an invalid response."], (int)HttpStatusCode.BadRequest, exception: ex);
			}
		}

		/// <summary>The message of a Mastodon API or /oauth error ({"error": ..., "error_description": ...}), or null.</summary>
		static string TryReadMastodonError(string json)
		{
			if (!json.Contains("\"error\"") || json.Contains("\"errorMessage\""))
				return null;
			try
			{
				var error = JsonSerializer.Deserialize<MastodonError>(json, SUtility.MastodonSerializer);
				return error?.ErrorDescription ?? error?.Error;
			}
			catch (JsonException)
			{
				return null;
			}
		}

		/// <summary>
		/// Reads a successful Mastodon API body (snake_case); a cancelled read, or a body that does not fit T (written to the
		/// browser console), returns SUtility.CancellationDefault.
		/// </summary>
		public static async Task<T> MastodonReadFromJsonAsync<T>(this HttpResponseMessage response, CancellationToken cancellationToken = default)
		{
			try
			{
				return await response.Content.ReadFromJsonAsync<T>(SUtility.MastodonSerializer, cancellationToken);
			}
			catch (OperationCanceledException)
			{
				return SUtility.CancellationDefault<T>();
			}
			catch (JsonException ex)
			{
				Console.Error.WriteLine($"{nameof(MastodonReadFromJsonAsync)}<{typeof(T).Name}> {response.RequestMessage?.RequestUri}: {ex.Message}");
				return SUtility.CancellationDefault<T>();
			}
		}

		/// <summary>
		/// The paging cursors of a Mastodon list: max_id from the Link header's next (older items), min_id from its prev
		/// (newer items). Either is null when the header does not name it.
		/// </summary>
		public static (string MaxId, string MinId) PageCursors(this HttpResponseMessage response)
		{
			if (!response.Headers.TryGetValues("Link", out var values))
				return (null, null);
			string maxId = null, minId = null;
			foreach (Match link in LinkHeader().Matches(string.Join(',', values)))
			{
				var query = HttpUtility.ParseQueryString(new Uri(link.Groups[1].Value, UriKind.Absolute).Query);
				if (link.Groups[2].Value == "next")
					maxId = query["max_id"];
				else if (link.Groups[2].Value == "prev")
					minId = query["min_id"] ?? query["since_id"];
			}
			return (maxId, minId);
		}

		[GeneratedRegex("<([^>]+)>\\s*;\\s*rel=\"([a-z]+)\"")]
		private static partial Regex LinkHeader();

		/// <summary>
		/// Reads a successful /clientapi body; a cancelled read, or a body that does not fit T (written to the browser
		/// console), returns SUtility.CancellationDefault.
		/// </summary>
		public static async Task<T> DefaultReadFromJsonAsync<T>(this HttpResponseMessage response, CancellationToken cancellationToken = default)
		{
			try
			{
				return await response.Content.ReadFromJsonAsync<T>(SUtility.DefaultSerializer, cancellationToken);
			}
			catch (OperationCanceledException)
			{
				return SUtility.CancellationDefault<T>();
			}
			catch (JsonException ex)
			{
				Console.Error.WriteLine($"{nameof(DefaultReadFromJsonAsync)}<{typeof(T).Name}> {response.RequestMessage?.RequestUri}: {ex.Message}");
				return SUtility.CancellationDefault<T>();
			}
		}

		public static AuthorizationPolicy IsAdminPolicy() =>
				new AuthorizationPolicyBuilder().RequireAuthenticatedUser()
						.RequireClaim(Policies.IsAdmin, "true")
						.RequireClaim(Policies.IsUser, "true")
						.RequireClaim(Policies.IsModerator, "true")
						.Build();

		public static AuthorizationPolicy IsUserPolicy() =>
				new AuthorizationPolicyBuilder().RequireAuthenticatedUser()
						.RequireClaim(Policies.IsUser, "true")
						.Build();

		public static AuthorizationPolicy IsUserModeratorPolicy() =>
				new AuthorizationPolicyBuilder().RequireAuthenticatedUser()
						.RequireClaim(Policies.IsModerator, "true")
						.Build();

		#endregion
	}
}