ResourceService.cs

namespace Cook;

using System.Net.Http.Headers;
using System.Text.Json;
using System.Text.Json.Serialization;

public class ResourceService
{
    private readonly IConfiguration configuration;
    private readonly HttpClient httpClient;
    private OAuth2TokenResponse? cachedToken;

    public ResourceService(IConfiguration configuration, HttpClient httpClient)
    {
        this.configuration = configuration;
        this.httpClient = httpClient;
    }

    public async Task<string> GetContentAsync(string name)
    {
        try
        {
            var configServerUri = this.configuration["spring:cloud:config:uri"];

            var appName = this.configuration["spring:application:name"] ?? "application";
            var profile = this.configuration["spring:cloud:config:env"] ?? "default";
            var label = this.configuration["spring:cloud:config:label"] ?? "main";

            var accessToken = await this.GetOrRefreshAccessTokenAsync();

            var request = new HttpRequestMessage(HttpMethod.Get, $"{configServerUri}/{appName}/{profile}/{label}/{name}");
            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);

            var response = await this.httpClient.SendAsync(request);
            if (response.IsSuccessStatusCode)
            {
                return await response.Content.ReadAsStringAsync();
            }
            else
            {
                throw new HttpRequestException($"Failed to fetch resource: {response.StatusCode} - {response.ReasonPhrase}");
            }
        }
        catch (Exception ex)
        {
            throw new InvalidOperationException($"Error fetching resource: {ex.Message}", ex);
        }
    }

    private async Task<string> GetOrRefreshAccessTokenAsync()
    {
        if (this.cachedToken != null && DateTime.UtcNow < this.cachedToken.ExpirationTime)
        {
            return this.cachedToken.AccessToken;
        }

        var clientId = this.configuration["spring:cloud:config:clientId"];
        var clientSecret = this.configuration["spring:cloud:config:clientSecret"];
        var accessTokenUri = this.configuration["spring:cloud:config:accessTokenUri"];

        if (string.IsNullOrEmpty(clientId) || string.IsNullOrEmpty(clientSecret) || string.IsNullOrEmpty(accessTokenUri))
        {
            throw new InvalidOperationException("OAuth2 credentials not configured");
        }

        var tokenRequest = new FormUrlEncodedContent(new[]
        {
            new KeyValuePair<string, string>("grant_type", "client_credentials"),
            new KeyValuePair<string, string>("client_id", clientId),
            new KeyValuePair<string, string>("client_secret", clientSecret),
        });

        var tokenResponse = await this.httpClient.PostAsync(accessTokenUri, tokenRequest);
        if (!tokenResponse.IsSuccessStatusCode)
        {
            throw new HttpRequestException($"Failed to get access token: {tokenResponse.StatusCode} - {tokenResponse.ReasonPhrase}");
        }

        this.cachedToken = this.ExtractTokenData(await tokenResponse.Content.ReadAsStringAsync());

        return this.cachedToken.AccessToken;
    }

    private OAuth2TokenResponse ExtractTokenData(string tokenResponse)
    {
        return JsonSerializer.Deserialize<OAuth2TokenResponse>(tokenResponse) ?? new OAuth2TokenResponse();
    }
}

public class OAuth2TokenResponse
{
    [JsonPropertyName("access_token")]
    public string AccessToken { get; set; } = string.Empty;

    [JsonPropertyName("expires_in")]
    public int ExpiresIn { get; set; } = 3600;

    public DateTime ExpirationTime => DateTime.UtcNow.AddSeconds(this.ExpiresIn - 10); // Subtract 10 seconds for safety
}