ytLlive/Services/YouTubeAuthService.cs

using System.Net;
using System.Net.Http;
using System.Text;
using System.Text.Json;
using ytLive.Models;

namespace ytLive.Services;

/// <summary>
/// Handles YouTube OAuth2 authentication flow.
/// Uses a local HTTP listener for the redirect callback.
/// </summary>
public class YouTubeAuthService
{
    private const string AuthorizationEndpoint = "https://accounts.google.com/o/oauth2/v2/auth";
    private const string TokenEndpoint = "https://oauth2.googleapis.com/token";
    private const string Scope = "https://www.googleapis.com/auth/youtube https://www.googleapis.com/auth/youtube.force-ssl";

    private readonly string _clientId;
    private readonly string _clientSecret;
    private readonly HttpClient _http = new();

    public YouTubeChannel? CurrentChannel { get; private set; }

    public YouTubeAuthService(string clientId, string clientSecret)
    {
        _clientId = clientId;
        _clientSecret = clientSecret;
    }

    public string GetAuthorizationUrl(string redirectUri)
    {
        var parameters = HttpUtility.ParseQueryString(string.Empty);
        parameters["client_id"] = _clientId;
        parameters["redirect_uri"] = redirectUri;
        parameters["response_type"] = "code";
        parameters["scope"] = Scope;
        parameters["access_type"] = "offline";
        parameters["prompt"] = "consent";

        return $"{AuthorizationEndpoint}?{parameters}";
    }

    public async Task<YouTubeChannel?> ExchangeCodeForToken(string code, string redirectUri)
    {
        var body = new FormUrlEncodedContent(new Dictionary<string, string>
        {
            ["code"] = code,
            ["client_id"] = _clientId,
            ["client_secret"] = _clientSecret,
            ["redirect_uri"] = redirectUri,
            ["grant_type"] = "authorization_code"
        });

        var response = await _http.PostAsync(TokenEndpoint, body);
        if (!response.IsSuccessStatusCode)
            return null;

        var json = await response.Content.ReadAsStringAsync();
        var tokenData = JsonSerializer.Deserialize<JsonElement>(json);

        var accessToken = tokenData.GetProperty("access_token").GetString()!;
        var refreshToken = tokenData.GetProperty("refresh_token").GetString()!;
        var expiresIn = tokenData.GetProperty("expires_in").GetInt32();

        // Fetch channel info
        return await FetchChannelInfo(accessToken, refreshToken, expiresIn);
    }

    public async Task<bool> RefreshToken()
    {
        if (CurrentChannel == null) return false;

        var body = new FormUrlEncodedContent(new Dictionary<string, string>
        {
            ["refresh_token"] = CurrentChannel.RefreshToken,
            ["client_id"] = _clientId,
            ["client_secret"] = _clientSecret,
            ["grant_type"] = "refresh_token"
        });

        var response = await _http.PostAsync(TokenEndpoint, body);
        if (!response.IsSuccessStatusCode) return false;

        var json = await response.Content.ReadAsStringAsync();
        var tokenData = JsonSerializer.Deserialize<JsonElement>(json);

        CurrentChannel.AccessToken = tokenData.GetProperty("access_token").GetString()!;
        CurrentChannel.TokenExpiry = DateTime.UtcNow.AddSeconds(tokenData.GetProperty("expires_in").GetInt32());
        return true;
    }

    private async Task<YouTubeChannel?> FetchChannelInfo(string accessToken, string refreshToken, int expiresIn)
    {
        _http.DefaultRequestHeaders.Authorization = new("Bearer", accessToken);
        var response = await _http.GetAsync("https://www.googleapis.com/youtube/v3/channels?part=snippet&mine=true");
        if (!response.IsSuccessStatusCode) return null;

        var json = await response.Content.ReadAsStringAsync();
        var data = JsonSerializer.Deserialize<JsonElement>(json);
        var items = data.GetProperty("items");

        if (items.GetArrayLength() == 0) return null;

        var snippet = items[0].GetProperty("snippet");
        CurrentChannel = new YouTubeChannel
        {
            ChannelId = items[0].GetProperty("id").GetString()!,
            DisplayName = snippet.GetProperty("title").GetString()!,
            ProfileImageUrl = snippet.GetProperty("thumbnails").GetProperty("default").GetProperty("url").GetString()!,
            AccessToken = accessToken,
            RefreshToken = refreshToken,
            TokenExpiry = DateTime.UtcNow.AddSeconds(expiresIn)
        };

        return CurrentChannel;
    }
}