// <copyright file="NullEvidenceRetrievalService.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under the AGPL-3.0-or-later.
// </copyright>
using System.Security.Cryptography;

namespace StellaOps.AdvisoryAI.Explanation;

public sealed class NullEvidenceRetrievalService : IEvidenceRetrievalService
{
    private static readonly EvidenceContext EmptyContext = new()
    {
        SbomEvidence = Array.Empty<EvidenceNode>(),
        ReachabilityEvidence = Array.Empty<EvidenceNode>(),
        RuntimeEvidence = Array.Empty<EvidenceNode>(),
        VexEvidence = Array.Empty<EvidenceNode>(),
        PatchEvidence = Array.Empty<EvidenceNode>(),
        ContextHash = ComputeEmptyContextHash()
    };

    public Task<EvidenceContext> RetrieveEvidenceAsync(
        string findingId,
        string artifactDigest,
        string vulnerabilityId,
        string? componentPurl = null,
        CancellationToken cancellationToken = default)
        => Task.FromResult(EmptyContext);

    public Task<EvidenceNode?> GetEvidenceNodeAsync(
        string evidenceId,
        CancellationToken cancellationToken = default)
        => Task.FromResult<EvidenceNode?>(null);

    public Task<bool> ValidateEvidenceAsync(
        IEnumerable<string> evidenceIds,
        CancellationToken cancellationToken = default)
        => Task.FromResult(true);

    private static string ComputeEmptyContextHash()
    {
        var bytes = SHA256.HashData(Array.Empty<byte>());
        return Convert.ToHexStringLower(bytes);
    }
}