vknet_vk/VkNet/Infrastructure/Authorization/ImplicitFlow/AuthorizationFormHtmlParser.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using HtmlAgilityPack;
using JetBrains.Annotations;
using VkNet.Abstractions.Utils;
using VkNet.Exception;
using VkNet.Model;
using VkNet.Utils;

namespace VkNet.Infrastructure.Authorization.ImplicitFlow;

/// <inheritdoc cref="IAuthorizationFormHtmlParser" />
[UsedImplicitly]
public sealed class AuthorizationFormHtmlParser : IAuthorizationFormHtmlParser
{
	private readonly IRestClient _restClient;

	/// <summary>
	/// Инициализирует новый экземпляр класса <see cref="AuthorizationFormHtmlParser" />
	/// </summary>
	public AuthorizationFormHtmlParser(IRestClient restClient) => _restClient = restClient;

	/// <inheritdoc />
	public async Task<VkHtmlFormResult> GetFormAsync(Uri url, CancellationToken token = default)
	{
		var response = await _restClient
			.PostAsync(url, [], Encoding.GetEncoding(1251), token: token)
			.ConfigureAwait(false);

		if (!response.IsSuccess)
		{
			throw new VkAuthorizationException(response.Message);
		}

		if (Utilities.TryDeserializeObject<VkAuthError>(response.Value, out var authError))
		{
			throw new VkAuthorizationException(authError.ErrorDescription);
		}

		var doc = new HtmlDocument();
		doc.LoadHtml(response.Value);
		var formNode = GetFormNode(doc);
		var inputs = ParseInputs(formNode);

		var actionUrl = GetActionUrl(formNode, url);
		var urlToCaptcha = GetUrlToCaptcha(doc);
		var method = GetMethod(formNode);

		return new()
		{
			Fields = inputs,
			Action = actionUrl,
			UrlToCaptcha = urlToCaptcha,
			Method = method
		};
	}

	/// <summary>
	/// Получить из HTML элемента.
	/// </summary>
	/// <param name="html">Исходный HTML элемент</param>
	/// <returns> HTML элемент </returns>
	/// <exception cref="VkApiException"> Элемент не найден на форме. </exception>
	private static HtmlNode GetFormNode(HtmlDocument html)
	{
		HtmlNode.ElementsFlags.Remove("form");
		var form = html.DocumentNode.SelectSingleNode("//form");

		if (form is null)
		{
			throw new VkApiException("Form element not found.");
		}

		return form;
	}

	/// <summary>
	/// Разобрать поля ввода.
	/// </summary>
	/// <param name="formNode">HTML элемент</param>
	/// <returns> Коллекция полей ввода </returns>
	private static Dictionary<string, string> ParseInputs(HtmlNode formNode)
	{
		var inputs = new Dictionary<string, string>();

		foreach (var nodeAttributes in formNode.SelectNodes("//input")
					.Select(x => x.Attributes))
		{
			var nameAttribute = nodeAttributes["name"];
			var valueAttribute = nodeAttributes["value"];

			var name = nameAttribute is not null
				? nameAttribute.Value
				: string.Empty;

			var value = valueAttribute is not null
				? valueAttribute.Value
				: string.Empty;

			if (string.IsNullOrEmpty(name))
			{
				continue;
			}

			inputs.Add(name, Uri.EscapeDataString(value));
		}

		return inputs;
	}

	/// <summary>
	/// URL действия.
	/// </summary>
	/// <param name="formNode">HTML элемент</param>
	/// <param name="url">Url</param>
	private static string GetActionUrl(HtmlNode formNode, Uri url)
	{
		var action = formNode.Attributes["action"];

		if (action is null)
		{
			return null;
		}

		var link = action.Value;

		if (!string.IsNullOrWhiteSpace(link) && !link.StartsWith("http", StringComparison.Ordinal)) // относительный URL
		{
			link = Url.Combine(GetResponseBaseUrl(url), link);
		}

		return string.IsNullOrWhiteSpace(link)
			? url.ToString()
			: link; // абсолютный путь
	}

	/// <summary>
	/// URL действия.
	/// </summary>
	/// <param name="formNode">Html элемент</param>
	private static string GetMethod(HtmlNode formNode)
	{
		var method = formNode.Attributes["method"];

		return method?.Value;
	}

	private static string GetResponseBaseUrl(Uri uri) => uri.Scheme + "://" + uri.Host + ":" + uri.Port;

	/// <summary>
	/// Возвращает URL для получения капчи
	/// </summary>
	/// <param name="document">HTML документ</param>
	private static string GetUrlToCaptcha(HtmlDocument document)
	{
		var element = document.GetElementbyId("captcha");

		var urlToCaptcha = element?.Attributes["src"];

		return urlToCaptcha?.Value;
	}
}