// <copyright file="NullExplanationInferenceClient.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under the BUSL-1.1.
// </copyright>
using System.Security.Cryptography;
using System.Text;

namespace StellaOps.AdvisoryAI.Explanation;

public sealed class NullExplanationInferenceClient : IExplanationInferenceClient
{
    public Task<ExplanationInferenceResult> GenerateAsync(
        ExplanationPrompt prompt,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(prompt);

        var promptHash = ComputeHash(prompt.Content ?? string.Empty);
        var content = $"Placeholder explanation (no model). prompt_hash=sha256:{promptHash}";

        return Task.FromResult(new ExplanationInferenceResult
        {
            Content = content,
            Confidence = 0.0,
            ModelId = "stub-explainer:v0"
        });
    }

    private static string ComputeHash(string content)
    {
        var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(content));
        return Convert.ToHexStringLower(bytes);
    }
}