using System.Collections.Generic;
using System.Globalization;
using System.Net;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Threading;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using MongoDB.Bson;
using StellaOps.Feedser.Models;
using StellaOps.Feedser.Source.CertCc.Configuration;
using StellaOps.Feedser.Source.CertCc.Internal;
using StellaOps.Feedser.Source.Common;
using StellaOps.Feedser.Source.Common.Fetch;
using StellaOps.Feedser.Storage.Mongo;
using StellaOps.Feedser.Storage.Mongo.Advisories;
using StellaOps.Feedser.Storage.Mongo.Documents;
using StellaOps.Feedser.Storage.Mongo.Dtos;
using StellaOps.Plugin;

namespace StellaOps.Feedser.Source.CertCc;

public sealed class CertCcConnector : IFeedConnector
{
    private static readonly JsonSerializerOptions DtoSerializerOptions = new(JsonSerializerDefaults.Web)
    {
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        WriteIndented = false,
    };

    private static readonly byte[] EmptyArrayPayload = Encoding.UTF8.GetBytes("[]");
    private static readonly string[] DetailEndpoints = { "note", "vendors", "vuls", "vendors-vuls" };

    private readonly CertCcSummaryPlanner _summaryPlanner;
    private readonly SourceFetchService _fetchService;
    private readonly RawDocumentStorage _rawDocumentStorage;
    private readonly IDocumentStore _documentStore;
    private readonly IDtoStore _dtoStore;
    private readonly IAdvisoryStore _advisoryStore;
    private readonly ISourceStateRepository _stateRepository;
    private readonly CertCcOptions _options;
    private readonly TimeProvider _timeProvider;
    private readonly ILogger<CertCcConnector> _logger;
    private readonly CertCcDiagnostics _diagnostics;

    public CertCcConnector(
        CertCcSummaryPlanner summaryPlanner,
        SourceFetchService fetchService,
        RawDocumentStorage rawDocumentStorage,
        IDocumentStore documentStore,
        IDtoStore dtoStore,
        IAdvisoryStore advisoryStore,
        ISourceStateRepository stateRepository,
        IOptions<CertCcOptions> options,
        CertCcDiagnostics diagnostics,
        TimeProvider? timeProvider,
        ILogger<CertCcConnector> logger)
    {
        _summaryPlanner = summaryPlanner ?? throw new ArgumentNullException(nameof(summaryPlanner));
        _fetchService = fetchService ?? throw new ArgumentNullException(nameof(fetchService));
        _rawDocumentStorage = rawDocumentStorage ?? throw new ArgumentNullException(nameof(rawDocumentStorage));
        _documentStore = documentStore ?? throw new ArgumentNullException(nameof(documentStore));
        _dtoStore = dtoStore ?? throw new ArgumentNullException(nameof(dtoStore));
        _advisoryStore = advisoryStore ?? throw new ArgumentNullException(nameof(advisoryStore));
        _stateRepository = stateRepository ?? throw new ArgumentNullException(nameof(stateRepository));
        _options = (options ?? throw new ArgumentNullException(nameof(options))).Value ?? throw new ArgumentNullException(nameof(options));
        _options.Validate();
        _diagnostics = diagnostics ?? throw new ArgumentNullException(nameof(diagnostics));
        _timeProvider = timeProvider ?? TimeProvider.System;
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public string SourceName => CertCcConnectorPlugin.SourceName;

    public async Task FetchAsync(IServiceProvider services, CancellationToken cancellationToken)
    {
        var cursor = await GetCursorAsync(cancellationToken).ConfigureAwait(false);

        var pendingDocuments = cursor.PendingDocuments.ToHashSet();
        var pendingMappings = cursor.PendingMappings.ToHashSet();
        var pendingNotes = new HashSet<string>(cursor.PendingNotes, StringComparer.OrdinalIgnoreCase);
        var processedNotes = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        var now = _timeProvider.GetUtcNow();
        var remainingBudget = _options.MaxNotesPerFetch;

        // Resume notes that previously failed before fetching new summaries.
        if (pendingNotes.Count > 0 && remainingBudget > 0)
        {
            var replay = pendingNotes.ToArray();
            foreach (var noteId in replay)
            {
                if (remainingBudget <= 0)
                {
                    break;
                }

                try
                {
                    if (!processedNotes.Add(noteId))
                    {
                        continue;
                    }

                    if (await HasPendingDocumentBundleAsync(noteId, pendingDocuments, cancellationToken).ConfigureAwait(false))
                    {
                        pendingNotes.Remove(noteId);
                        continue;
                    }

                    await FetchNoteBundleAsync(noteId, null, pendingDocuments, pendingNotes, cancellationToken).ConfigureAwait(false);
                    if (!pendingNotes.Contains(noteId))
                    {
                        remainingBudget--;
                    }
                }
                catch (Exception ex)
                {
                    await _stateRepository.MarkFailureAsync(SourceName, now, TimeSpan.FromMinutes(5), ex.Message, cancellationToken).ConfigureAwait(false);
                    throw;
                }
            }
        }

        var plan = _summaryPlanner.CreatePlan(cursor.SummaryState);
        _diagnostics.PlanEvaluated(plan.Window, plan.Requests.Count);

        try
        {
            foreach (var request in plan.Requests)
            {
                cancellationToken.ThrowIfCancellationRequested();
                var shouldProcessNotes = remainingBudget > 0;

                try
                {
                    _diagnostics.SummaryFetchAttempt(request.Scope);
                    var metadata = BuildSummaryMetadata(request);
                    var existingSummary = await _documentStore.FindBySourceAndUriAsync(SourceName, request.Uri.ToString(), cancellationToken).ConfigureAwait(false);
                    var fetchRequest = new SourceFetchRequest(
                        CertCcOptions.HttpClientName,
                        SourceName,
                        HttpMethod.Get,
                        request.Uri,
                        metadata,
                        existingSummary?.Etag,
                        existingSummary?.LastModified,
                        null,
                        new[] { "application/json" });

                    var result = await _fetchService.FetchAsync(fetchRequest, cancellationToken).ConfigureAwait(false);
                    if (result.IsNotModified)
                    {
                        _diagnostics.SummaryFetchUnchanged(request.Scope);
                        continue;
                    }

                    if (!result.IsSuccess || result.Document is null)
                    {
                        _diagnostics.SummaryFetchFailure(request.Scope);
                        continue;
                    }

                    _diagnostics.SummaryFetchSuccess(request.Scope);

                    if (!shouldProcessNotes)
                    {
                        continue;
                    }

                    var noteTokens = await ReadSummaryNotesAsync(result.Document, cancellationToken).ConfigureAwait(false);
                    foreach (var token in noteTokens)
                    {
                        if (remainingBudget <= 0)
                        {
                            break;
                        }

                        var noteId = TryNormalizeNoteToken(token, out var vuIdentifier);
                        if (string.IsNullOrEmpty(noteId))
                        {
                            continue;
                        }

                        if (!processedNotes.Add(noteId))
                        {
                            continue;
                        }

                        await FetchNoteBundleAsync(noteId, vuIdentifier, pendingDocuments, pendingNotes, cancellationToken).ConfigureAwait(false);
                        if (!pendingNotes.Contains(noteId))
                        {
                            remainingBudget--;
                        }
                    }
                }
                catch
                {
                    _diagnostics.SummaryFetchFailure(request.Scope);
                    throw;
                }
            }
        }
        catch (Exception ex)
        {
            var failureCursor = cursor
                .WithPendingSummaries(Array.Empty<Guid>())
                .WithPendingNotes(pendingNotes)
                .WithPendingDocuments(pendingDocuments)
                .WithPendingMappings(pendingMappings)
                .WithLastRun(now);

            await UpdateCursorAsync(failureCursor, cancellationToken).ConfigureAwait(false);
            await _stateRepository.MarkFailureAsync(SourceName, now, TimeSpan.FromMinutes(5), ex.Message, cancellationToken).ConfigureAwait(false);
            throw;
        }

        var updatedCursor = cursor
            .WithSummaryState(plan.NextState)
            .WithPendingSummaries(Array.Empty<Guid>())
            .WithPendingNotes(pendingNotes)
            .WithPendingDocuments(pendingDocuments)
            .WithPendingMappings(pendingMappings)
            .WithLastRun(now);

        await UpdateCursorAsync(updatedCursor, cancellationToken).ConfigureAwait(false);
    }

    private async Task<bool> HasPendingDocumentBundleAsync(string noteId, HashSet<Guid> pendingDocuments, CancellationToken cancellationToken)
    {
        if (pendingDocuments.Count == 0)
        {
            return false;
        }

        var required = new HashSet<string>(DetailEndpoints, StringComparer.OrdinalIgnoreCase);

        foreach (var documentId in pendingDocuments)
        {
            var document = await _documentStore.FindAsync(documentId, cancellationToken).ConfigureAwait(false);
            if (document?.Metadata is null)
            {
                continue;
            }

            if (!document.Metadata.TryGetValue("certcc.noteId", out var metadataNoteId) ||
                !string.Equals(metadataNoteId, noteId, StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }

            var endpoint = document.Metadata.TryGetValue("certcc.endpoint", out var endpointValue)
                ? endpointValue
                : "note";

            required.Remove(endpoint);
            if (required.Count == 0)
            {
                return true;
            }
        }

        return false;
    }

    public async Task ParseAsync(IServiceProvider services, CancellationToken cancellationToken)
    {
        if (!_options.EnableDetailMapping)
        {
            return;
        }

        var cursor = await GetCursorAsync(cancellationToken).ConfigureAwait(false);
        if (cursor.PendingDocuments.Count == 0)
        {
            return;
        }

        var pendingDocuments = cursor.PendingDocuments.ToHashSet();
        var pendingMappings = cursor.PendingMappings.ToHashSet();

        var groups = new Dictionary<string, NoteDocumentGroup>(StringComparer.OrdinalIgnoreCase);

        foreach (var documentId in cursor.PendingDocuments)
        {
            cancellationToken.ThrowIfCancellationRequested();

            var document = await _documentStore.FindAsync(documentId, cancellationToken).ConfigureAwait(false);
            if (document is null)
            {
                pendingDocuments.Remove(documentId);
                continue;
            }

            if (!TryGetMetadata(document, "certcc.noteId", out var noteId) || string.IsNullOrWhiteSpace(noteId))
            {
                await _documentStore.UpdateStatusAsync(document.Id, DocumentStatuses.Failed, cancellationToken).ConfigureAwait(false);
                pendingDocuments.Remove(documentId);
                continue;
            }

            var endpoint = TryGetMetadata(document, "certcc.endpoint", out var endpointValue)
                ? endpointValue
                : "note";

            var group = groups.TryGetValue(noteId, out var existing)
                ? existing
                : (groups[noteId] = new NoteDocumentGroup(noteId));

            group.Add(endpoint, document);
        }

        foreach (var group in groups.Values)
        {
            cancellationToken.ThrowIfCancellationRequested();

            if (group.Note is null)
            {
                continue;
            }

            try
            {
                var noteBytes = await DownloadDocumentAsync(group.Note, cancellationToken).ConfigureAwait(false);
                var vendorsBytes = group.Vendors is null
                    ? EmptyArrayPayload
                    : await DownloadDocumentAsync(group.Vendors, cancellationToken).ConfigureAwait(false);
                var vulsBytes = group.Vuls is null
                    ? EmptyArrayPayload
                    : await DownloadDocumentAsync(group.Vuls, cancellationToken).ConfigureAwait(false);
                var vendorStatusesBytes = group.VendorStatuses is null
                    ? EmptyArrayPayload
                    : await DownloadDocumentAsync(group.VendorStatuses, cancellationToken).ConfigureAwait(false);

                var dto = CertCcNoteParser.Parse(noteBytes, vendorsBytes, vulsBytes, vendorStatusesBytes);
                var json = JsonSerializer.Serialize(dto, DtoSerializerOptions);
                var payload = MongoDB.Bson.BsonDocument.Parse(json);

                _diagnostics.ParseSuccess(
                    dto.Vendors.Count,
                    dto.VendorStatuses.Count,
                    dto.Vulnerabilities.Count);

                var dtoRecord = new DtoRecord(
                    Guid.NewGuid(),
                    group.Note.Id,
                    SourceName,
                    "certcc.vince.note.v1",
                    payload,
                    _timeProvider.GetUtcNow());

                await _dtoStore.UpsertAsync(dtoRecord, cancellationToken).ConfigureAwait(false);
                await _documentStore.UpdateStatusAsync(group.Note.Id, DocumentStatuses.PendingMap, cancellationToken).ConfigureAwait(false);
                pendingMappings.Add(group.Note.Id);
                pendingDocuments.Remove(group.Note.Id);

                if (group.Vendors is not null)
                {
                    await _documentStore.UpdateStatusAsync(group.Vendors.Id, DocumentStatuses.Mapped, cancellationToken).ConfigureAwait(false);
                    pendingDocuments.Remove(group.Vendors.Id);
                }

                if (group.Vuls is not null)
                {
                    await _documentStore.UpdateStatusAsync(group.Vuls.Id, DocumentStatuses.Mapped, cancellationToken).ConfigureAwait(false);
                    pendingDocuments.Remove(group.Vuls.Id);
                }

                if (group.VendorStatuses is not null)
                {
                    await _documentStore.UpdateStatusAsync(group.VendorStatuses.Id, DocumentStatuses.Mapped, cancellationToken).ConfigureAwait(false);
                    pendingDocuments.Remove(group.VendorStatuses.Id);
                }
            }
            catch (Exception ex)
            {
                _diagnostics.ParseFailure();
                _logger.LogError(ex, "CERT/CC parse failed for note {NoteId}", group.NoteId);
                if (group.Note is not null)
                {
                    await _documentStore.UpdateStatusAsync(group.Note.Id, DocumentStatuses.Failed, cancellationToken).ConfigureAwait(false);
                    pendingDocuments.Remove(group.Note.Id);
                }
            }
        }

        var updatedCursor = cursor
            .WithPendingDocuments(pendingDocuments)
            .WithPendingMappings(pendingMappings);

        await UpdateCursorAsync(updatedCursor, cancellationToken).ConfigureAwait(false);
    }

    public async Task MapAsync(IServiceProvider services, CancellationToken cancellationToken)
    {
        if (!_options.EnableDetailMapping)
        {
            return;
        }

        var cursor = await GetCursorAsync(cancellationToken).ConfigureAwait(false);
        if (cursor.PendingMappings.Count == 0)
        {
            return;
        }

        var pendingMappings = cursor.PendingMappings.ToHashSet();

        foreach (var documentId in cursor.PendingMappings)
        {
            cancellationToken.ThrowIfCancellationRequested();

            var dtoRecord = await _dtoStore.FindByDocumentIdAsync(documentId, cancellationToken).ConfigureAwait(false);
            var document = await _documentStore.FindAsync(documentId, cancellationToken).ConfigureAwait(false);

            if (dtoRecord is null || document is null)
            {
                pendingMappings.Remove(documentId);
                continue;
            }

            try
            {
                var json = dtoRecord.Payload.ToJson();
                var dto = JsonSerializer.Deserialize<CertCcNoteDto>(json, DtoSerializerOptions);
                if (dto is null)
                {
                    throw new InvalidOperationException($"CERT/CC DTO payload deserialized as null for document {documentId}.");
                }

                var advisory = CertCcMapper.Map(dto, document, dtoRecord, SourceName);
                var affectedCount = advisory.AffectedPackages.Length;
                var normalizedRuleCount = advisory.AffectedPackages.Sum(static package => package.NormalizedVersions.Length);
                await _advisoryStore.UpsertAsync(advisory, cancellationToken).ConfigureAwait(false);
                await _documentStore.UpdateStatusAsync(document.Id, DocumentStatuses.Mapped, cancellationToken).ConfigureAwait(false);
                _diagnostics.MapSuccess(affectedCount, normalizedRuleCount);
            }
            catch (Exception ex)
            {
                _diagnostics.MapFailure();
                _logger.LogError(ex, "CERT/CC mapping failed for document {DocumentId}", documentId);
                await _documentStore.UpdateStatusAsync(documentId, DocumentStatuses.Failed, cancellationToken).ConfigureAwait(false);
            }

            pendingMappings.Remove(documentId);
        }

        var updatedCursor = cursor.WithPendingMappings(pendingMappings);
        await UpdateCursorAsync(updatedCursor, cancellationToken).ConfigureAwait(false);
    }

    private async Task FetchNoteBundleAsync(
        string noteId,
        string? vuIdentifier,
        HashSet<Guid> pendingDocuments,
        HashSet<string> pendingNotes,
        CancellationToken cancellationToken)
    {
        var missingEndpoints = new List<(string Endpoint, HttpStatusCode? Status)>();

        try
        {
            foreach (var endpoint in DetailEndpoints)
            {
                cancellationToken.ThrowIfCancellationRequested();

                var uri = BuildDetailUri(noteId, endpoint);
                var metadata = BuildDetailMetadata(noteId, vuIdentifier, endpoint);
                var existing = await _documentStore.FindBySourceAndUriAsync(SourceName, uri.ToString(), cancellationToken).ConfigureAwait(false);

                var request = new SourceFetchRequest(CertCcOptions.HttpClientName, SourceName, uri)
                {
                    Metadata = metadata,
                    ETag = existing?.Etag,
                    LastModified = existing?.LastModified,
                    AcceptHeaders = new[] { "application/json" },
                };

                SourceFetchResult result;
                _diagnostics.DetailFetchAttempt(endpoint);
                try
                {
                    result = await _fetchService.FetchAsync(request, cancellationToken).ConfigureAwait(false);
                }
                catch (HttpRequestException httpEx)
                {
                    var status = httpEx.StatusCode ?? TryParseStatusCodeFromMessage(httpEx.Message);
                    if (ShouldTreatAsMissing(status, endpoint))
                    {
                        _diagnostics.DetailFetchMissing(endpoint);
                        missingEndpoints.Add((endpoint, status));
                        continue;
                    }

                    _diagnostics.DetailFetchFailure(endpoint);
                    throw;
                }
                Guid documentId;
                if (result.IsSuccess && result.Document is not null)
                {
                    _diagnostics.DetailFetchSuccess(endpoint);
                    documentId = result.Document.Id;
                }
                else if (result.IsNotModified)
                {
                    _diagnostics.DetailFetchUnchanged(endpoint);
                    if (existing is null)
                    {
                        continue;
                    }

                    documentId = existing.Id;
                }
                else
                {
                    _diagnostics.DetailFetchFailure(endpoint);
                    _logger.LogWarning(
                        "CERT/CC detail endpoint {Endpoint} returned {StatusCode} for note {NoteId}; will retry.",
                        endpoint,
                        (int)result.StatusCode,
                        noteId);

                    throw new HttpRequestException(
                        $"CERT/CC endpoint '{endpoint}' returned {(int)result.StatusCode} ({result.StatusCode}) for note {noteId}.",
                        null,
                        result.StatusCode);
                }

                pendingDocuments.Add(documentId);

                if (_options.DetailRequestDelay > TimeSpan.Zero)
                {
                    await Task.Delay(_options.DetailRequestDelay, cancellationToken).ConfigureAwait(false);
                }
            }

            if (missingEndpoints.Count > 0)
            {
                var formatted = string.Join(
                    ", ",
                    missingEndpoints.Select(item =>
                        item.Status.HasValue
                            ? $"{item.Endpoint} ({(int)item.Status.Value})"
                            : item.Endpoint));

                _logger.LogWarning(
                    "CERT/CC detail fetch completed with missing endpoints for note {NoteId}: {Endpoints}",
                    noteId,
                    formatted);
            }

            pendingNotes.Remove(noteId);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "CERT/CC detail fetch failed for note {NoteId}", noteId);
            pendingNotes.Add(noteId);
            throw;
        }
    }

    private static Dictionary<string, string> BuildSummaryMetadata(CertCcSummaryRequest request)
    {
        var metadata = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
        {
            ["certcc.scope"] = request.Scope.ToString().ToLowerInvariant(),
            ["certcc.year"] = request.Year.ToString("D4", CultureInfo.InvariantCulture),
        };

        if (request.Month.HasValue)
        {
            metadata["certcc.month"] = request.Month.Value.ToString("D2", CultureInfo.InvariantCulture);
        }

        return metadata;
    }

    private static Dictionary<string, string> BuildDetailMetadata(string noteId, string? vuIdentifier, string endpoint)
    {
        var metadata = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
        {
            ["certcc.endpoint"] = endpoint,
            ["certcc.noteId"] = noteId,
        };

        if (!string.IsNullOrWhiteSpace(vuIdentifier))
        {
            metadata["certcc.vuid"] = vuIdentifier;
        }

        return metadata;
    }

    private async Task<IReadOnlyList<string>> ReadSummaryNotesAsync(DocumentRecord document, CancellationToken cancellationToken)
    {
        if (!document.GridFsId.HasValue)
        {
            return Array.Empty<string>();
        }

        var payload = await _rawDocumentStorage.DownloadAsync(document.GridFsId.Value, cancellationToken).ConfigureAwait(false);
        return CertCcSummaryParser.ParseNotes(payload);
    }

    private async Task<byte[]> DownloadDocumentAsync(DocumentRecord document, CancellationToken cancellationToken)
    {
        if (!document.GridFsId.HasValue)
        {
            throw new InvalidOperationException($"Document {document.Id} has no GridFS payload.");
        }

        return await _rawDocumentStorage.DownloadAsync(document.GridFsId.Value, cancellationToken).ConfigureAwait(false);
    }

    private Uri BuildDetailUri(string noteId, string endpoint)
    {
        var suffix = endpoint switch
        {
            "note" => $"{noteId}/",
            "vendors" => $"{noteId}/vendors/",
            "vuls" => $"{noteId}/vuls/",
            "vendors-vuls" => $"{noteId}/vendors/vuls/",
            _ => $"{noteId}/",
        };

        return new Uri(_options.BaseApiUri, suffix);
    }

    private static string? TryNormalizeNoteToken(string token, out string? vuIdentifier)
    {
        vuIdentifier = null;
        if (string.IsNullOrWhiteSpace(token))
        {
            return null;
        }

        var trimmed = token.Trim();
        var digits = new string(trimmed.Where(char.IsDigit).ToArray());
        if (digits.Length == 0)
        {
            return null;
        }

        vuIdentifier = trimmed.StartsWith("vu", StringComparison.OrdinalIgnoreCase)
            ? trimmed.Replace(" ", string.Empty, StringComparison.Ordinal)
            : $"VU#{digits}";

        return digits;
    }

    private static bool TryGetMetadata(DocumentRecord document, string key, out string value)
    {
        value = string.Empty;
        if (document.Metadata is null)
        {
            return false;
        }

        if (!document.Metadata.TryGetValue(key, out var metadataValue))
        {
            return false;
        }

        value = metadataValue;
        return true;
    }

    private async Task<CertCcCursor> GetCursorAsync(CancellationToken cancellationToken)
    {
        var record = await _stateRepository.TryGetAsync(SourceName, cancellationToken).ConfigureAwait(false);
        return CertCcCursor.FromBson(record?.Cursor);
    }

    private async Task UpdateCursorAsync(CertCcCursor cursor, CancellationToken cancellationToken)
    {
        var completedAt = _timeProvider.GetUtcNow();
        await _stateRepository.UpdateCursorAsync(SourceName, cursor.ToBsonDocument(), completedAt, cancellationToken).ConfigureAwait(false);
    }

    private sealed class NoteDocumentGroup
    {
        public NoteDocumentGroup(string noteId)
        {
            NoteId = noteId;
        }

        public string NoteId { get; }

        public DocumentRecord? Note { get; private set; }

        public DocumentRecord? Vendors { get; private set; }

        public DocumentRecord? Vuls { get; private set; }

        public DocumentRecord? VendorStatuses { get; private set; }

        public void Add(string endpoint, DocumentRecord document)
        {
            switch (endpoint)
            {
                case "note":
                    Note = document;
                    break;
                case "vendors":
                    Vendors = document;
                    break;
                case "vuls":
                    Vuls = document;
                    break;
                case "vendors-vuls":
                    VendorStatuses = document;
                    break;
                default:
                    Note ??= document;
                    break;
            }
        }
    }

    private static bool ShouldTreatAsMissing(HttpStatusCode? statusCode, string endpoint)
    {
        if (statusCode is null)
        {
            return false;
        }

        if (statusCode is HttpStatusCode.NotFound or HttpStatusCode.Gone)
        {
            return !string.Equals(endpoint, "note", StringComparison.OrdinalIgnoreCase);
        }

        // Treat vendors/vendors-vuls/vuls 403 as optional air-gapped responses.
        if (statusCode == HttpStatusCode.Forbidden && !string.Equals(endpoint, "note", StringComparison.OrdinalIgnoreCase))
        {
            return true;
        }

        return false;
    }

    private static HttpStatusCode? TryParseStatusCodeFromMessage(string? message)
    {
        if (string.IsNullOrWhiteSpace(message))
        {
            return null;
        }

        const string marker = "status ";
        var index = message.IndexOf(marker, StringComparison.OrdinalIgnoreCase);
        if (index < 0)
        {
            return null;
        }

        index += marker.Length;
        var end = index;
        while (end < message.Length && char.IsDigit(message[end]))
        {
            end++;
        }

        if (end == index)
        {
            return null;
        }

        if (int.TryParse(message[index..end], NumberStyles.Integer, CultureInfo.InvariantCulture, out var code) &&
            Enum.IsDefined(typeof(HttpStatusCode), code))
        {
            return (HttpStatusCode)code;
        }

        return null;
    }
}