Finlytic/FinlyticNews/Services/N8nService.cs

using System.Text.Json;
using System.Text.Json.Serialization;
using FinlyticCore.Util;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

namespace FinlyticNews.Services;

using FinlyticCore.Dtos.News;

/// <summary>
/// Defines integration operations with the external n8n AI workflow webhook.
/// </summary>
public interface IN8nService
{
    /// <summary>
    /// Submits raw article content and pre-filtered assets to n8n, returning the parsed response metadata.
    /// </summary>
    Task<N8nResponsePayload?> AnalyzeArticleAsync(string content, List<FilteredAssetPayload> filteredAssets, CancellationToken ct = default);
}

/// <inheritdoc />
public class N8nService : IN8nService
{
    private readonly HttpClient _httpClient;
    private readonly IServiceScopeFactory _scopeFactory;
    private readonly IConfiguration _configuration;
    private readonly ILogger<N8nService> _logger;

    /// <summary>
    /// Initializes a new instance of the <see cref="N8nService"/> class.
    /// </summary>
    public N8nService(
        HttpClient httpClient,
        IServiceScopeFactory scopeFactory,
        IConfiguration configuration,
        ILogger<N8nService> logger)
    {
        _httpClient = httpClient;
        _scopeFactory = scopeFactory;
        _configuration = configuration;
        _logger = logger;
    }

    /// <inheritdoc />
    public async Task<N8nResponsePayload?> AnalyzeArticleAsync(string content, List<FilteredAssetPayload> filteredAssets, CancellationToken ct = default)
    {
        string? targetUrl = null;

        // 1. Dynamic Settings Resolution (DB Scope -> AppSettings Fallback)
        using (var scope = _scopeFactory.CreateScope())
        {
            var settingsDb = scope.ServiceProvider.GetService<ISettingsDbService>();
            if (settingsDb != null)
            {
                var settings = await settingsDb.GetSettingsAsync();
                targetUrl = settings?.N8nWebhookUrl;
            }
        }

        if (string.IsNullOrWhiteSpace(targetUrl))
        {
            targetUrl = _configuration["N8N__WebhookUrl"] 
                        ?? _configuration["N8N:WebhookUrl"];
        }

        if (string.IsNullOrWhiteSpace(targetUrl))
        {
            _logger.LogError("[{Channel}] N8nWebhookUrl is not configured in DB or application settings.", "NewsChannel");
            return null;
        }

        _logger.LogInformation("[{Channel}] Posting article to n8n webhook pipeline at: {Url}", "NewsChannel", targetUrl);

        var payload = new N8nRequestPayload(content, filteredAssets ?? []);

        try
        {
            // Zero-Allocation / Source-Generated Request Serialization
            var jsonContent = JsonSerializer.Serialize(payload, FinlyticJsonSerializerContext.Default.N8nRequestPayload);
            using var requestContent = new StringContent(jsonContent, System.Text.Encoding.UTF8, "application/json");

            using var response = await _httpClient.PostAsync(targetUrl, requestContent, ct);

            if (!response.IsSuccessStatusCode)
            {
                var errorMsg = await response.Content.ReadAsStringAsync(ct);
                _logger.LogError("[{Channel}] n8n webhook returned status code {StatusCode}. Error payload: {Error}", "NewsChannel", response.StatusCode, errorMsg);
                return null;
            }

            using var responseStream = await response.Content.ReadAsStreamAsync(ct);
            using var doc = await JsonDocument.ParseAsync(responseStream, cancellationToken: ct);
            
            var root = doc.RootElement;

            // 2. Robust n8n Array-Unwrapping (Handles [{ "json": { ... } }])
            if (root.ValueKind == JsonValueKind.Array)
            {
                if (root.GetArrayLength() == 0)
                {
                    _logger.LogWarning("[{Channel}] n8n webhook returned an empty array.", "NewsChannel");
                    return null;
                }
                root = root[0];
            }

            // 3. Dynamic Node Wrapper Unwrapping ("json", "output", "data", "body")
            if (root.ValueKind == JsonValueKind.Object)
            {
                if (root.TryGetProperty("json", out var jsonChild) && jsonChild.ValueKind == JsonValueKind.Object)
                    root = jsonChild;
                else if (root.TryGetProperty("output", out var outChild) && outChild.ValueKind == JsonValueKind.Object)
                    root = outChild;
                else if (root.TryGetProperty("data", out var dataChild) && dataChild.ValueKind == JsonValueKind.Object)
                    root = dataChild;
                else if (root.TryGetProperty("body", out var bodyChild) && bodyChild.ValueKind == JsonValueKind.Object)
                    root = bodyChild;
            }

            // 4. Source-Generated Deserialization directly from JsonElement
            var result = root.Deserialize(FinlyticJsonSerializerContext.Default.N8nResponsePayload);
            return result;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "[{Channel}] Failed to communicate with or parse response from n8n webhook workflow.", "NewsChannel");
            return null;
        }
    }
}