AuthorBuddy/Services/FactCheckService.cs

using AuthorBuddy.Web.Models;
using System.Text;

namespace AuthorBuddy.Web.Services;

public class FactCheckService : IFactCheckService
{
    private readonly IDuckDuckGoService _duckDuckGo;
    private readonly IOllamaService _ollama;
    private readonly OllamaSettings _settings;

    public FactCheckService(IDuckDuckGoService duckDuckGo, IOllamaService ollama, OllamaSettings settings)
    {
        _duckDuckGo = duckDuckGo;
        _ollama = ollama;
        _settings = settings;
    }

    public async Task<List<FactCheckResult>> VerifyAsync(string answer, string? backendName = null, int maxClaims = 3)
    {
        var results = new List<FactCheckResult>();
        var claims = ExtractClaims(answer);

        foreach (var claim in claims.Take(maxClaims))
        {
            var searchResults = await _duckDuckGo.SearchAsync(claim);
            if (searchResults.Count == 0)
            {
                results.Add(new FactCheckResult
                {
                    Claim = claim,
                    Verdict = FactCheckVerdict.NoInformation,
                    Reasoning = "Keine Quellen gefunden."
                });
                continue;
            }

            var verdict = await GetVerdictAsync(claim, searchResults, backendName);
            results.Add(verdict);
        }

        return results;
    }

    private async Task<FactCheckResult> GetVerdictAsync(string claim, List<DuckDuckGoResult> searchResults, string? backendName)
    {
        var sourcesText = new StringBuilder();
        var sources = new List<string>();

        foreach (var r in searchResults)
        {
            if (!string.IsNullOrWhiteSpace(r.AbstractText))
                sourcesText.AppendLine($"- {r.AbstractText}");
            if (!string.IsNullOrWhiteSpace(r.Answer))
                sourcesText.AppendLine($"- {r.Answer}");
            foreach (var related in r.RelatedTexts)
                sourcesText.AppendLine($"- {related}");
            if (!string.IsNullOrWhiteSpace(r.AbstractUrl))
                sources.Add(r.AbstractUrl);
        }

        if (sourcesText.Length == 0)
        {
            return new FactCheckResult
            {
                Claim = claim,
                Verdict = FactCheckVerdict.NoInformation,
                Reasoning = "Keine verwertbaren Quellen gefunden.",
                Sources = sources
            };
        }

        var prompt = $@"Du bist ein Faktenprüfer. Vergleiche die folgende Behauptung mit den DuckDuckGo-Suchergebnissen.

BEHAUPTUNG: {claim}

SUCHERGEBNISSE:
{sourcesText}

Bewerte, ob die Behauptung durch die Suchergebnisse bestätigt oder widerlegt wird.

Antworte NUR in diesem Format:
URTEIL: BESTAETIGT oder WIDERSPROCHEN oder TEILWEISE oder KEINE_INFORMATION
BEGRUENDUNG: Maximal 2 Sätze.";

        var raw = await _ollama.Chat(_settings.StyleModel, prompt, temperature: 0.1, backendName: backendName ?? _settings.StyleBackend);

        return new FactCheckResult
        {
            Claim = claim,
            Verdict = ParseVerdict(raw),
            Reasoning = ExtractReasoning(raw),
            Sources = sources
        };
    }

    private static List<string> ExtractClaims(string text)
    {
        var claims = new List<string>();
        if (string.IsNullOrWhiteSpace(text)) return claims;

        var sentences = System.Text.RegularExpressions.Regex.Split(text, @"(?<=[.!?])\s+");

        foreach (var sentence in sentences)
        {
            var trimmed = sentence.Trim().Trim('"');
            if (trimmed.Length < 25) continue;
            if (trimmed.EndsWith("?")) continue;
            if (trimmed.StartsWith("```") || trimmed.StartsWith("#")) continue;

            claims.Add(trimmed.Length > 200 ? trimmed[..200] + "..." : trimmed);
            if (claims.Count >= 5) break;
        }

        return claims;
    }

    private static FactCheckVerdict ParseVerdict(string raw)
    {
        var upper = raw.ToUpperInvariant();
        if (upper.Contains("BESTAETIGT") || upper.Contains("CONFIRMED") || upper.Contains("BESTÄTIGT"))
            return FactCheckVerdict.Confirmed;
        if (upper.Contains("WIDERSPROCHEN") || upper.Contains("CONTRADICT") || upper.Contains("REFUTED"))
            return FactCheckVerdict.Contradicted;
        if (upper.Contains("TEILWEISE") || upper.Contains("PARTIAL"))
            return FactCheckVerdict.Partial;
        return FactCheckVerdict.NoInformation;
    }

    private static string ExtractReasoning(string raw)
    {
        var idx = raw.IndexOf("BEGRUENDUNG:", StringComparison.OrdinalIgnoreCase);
        if (idx < 0)
            idx = raw.IndexOf("BEGRÜNDUNG:", StringComparison.OrdinalIgnoreCase);
        if (idx < 0)
            idx = raw.IndexOf("REASONING:", StringComparison.OrdinalIgnoreCase);
        if (idx >= 0)
        {
            var reasoning = raw[(idx + 1)..];
            if (reasoning.Contains(':'))
                reasoning = reasoning[(reasoning.IndexOf(':') + 1)..];
            return reasoning.Trim();
        }
        return raw.Trim();
    }
}