using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Net.Http;
using System.Runtime.CompilerServices;
using System.Text.Json;
using System.Xml.Linq;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using StellaOps.Excititor.Connectors.Abstractions;
using StellaOps.Excititor.Connectors.RedHat.CSAF.Configuration;
using StellaOps.Excititor.Connectors.RedHat.CSAF.Metadata;
using StellaOps.Excititor.Core;
using StellaOps.Excititor.Storage.Mongo;

namespace StellaOps.Excititor.Connectors.RedHat.CSAF;

public sealed class RedHatCsafConnector : VexConnectorBase
{
    private readonly RedHatProviderMetadataLoader _metadataLoader;
    private readonly IHttpClientFactory _httpClientFactory;
    private readonly IVexConnectorStateRepository _stateRepository;
    public RedHatCsafConnector(
        VexConnectorDescriptor descriptor,
        RedHatProviderMetadataLoader metadataLoader,
        IHttpClientFactory httpClientFactory,
        IVexConnectorStateRepository stateRepository,
        ILogger<RedHatCsafConnector> logger,
        TimeProvider timeProvider)
        : base(descriptor, logger, timeProvider)
    {
        _metadataLoader = metadataLoader ?? throw new ArgumentNullException(nameof(metadataLoader));
        _httpClientFactory = httpClientFactory ?? throw new ArgumentNullException(nameof(httpClientFactory));
        _stateRepository = stateRepository ?? throw new ArgumentNullException(nameof(stateRepository));
    }

    public override ValueTask ValidateAsync(VexConnectorSettings settings, CancellationToken cancellationToken)
    {
        // No connector-specific settings yet.
        return ValueTask.CompletedTask;
    }

    public override async IAsyncEnumerable<VexRawDocument> FetchAsync(VexConnectorContext context, [EnumeratorCancellation] CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(context);

        var metadataResult = await _metadataLoader.LoadAsync(cancellationToken).ConfigureAwait(false);
        if (metadataResult.Provider.Discovery.RolIeService is null)
        {
            throw new InvalidOperationException("Red Hat provider metadata did not specify a ROLIE feed.");
        }

        var state = await _stateRepository.GetAsync(Descriptor.Id, cancellationToken).ConfigureAwait(false);

        var sinceTimestamp = context.Since;
        if (state?.LastUpdated is { } persisted && (sinceTimestamp is null || persisted > sinceTimestamp))
        {
            sinceTimestamp = persisted;
        }

        var knownDigests = state?.DocumentDigests ?? ImmutableArray<string>.Empty;
        var digestList = new List<string>(knownDigests);
        var digestSet = new HashSet<string>(knownDigests, StringComparer.OrdinalIgnoreCase);
        var latestUpdated = state?.LastUpdated ?? sinceTimestamp ?? DateTimeOffset.MinValue;
        var stateChanged = false;

        foreach (var entry in await FetchRolieEntriesAsync(metadataResult.Provider.Discovery.RolIeService, cancellationToken).ConfigureAwait(false))
        {
            if (sinceTimestamp is not null && entry.Updated is DateTimeOffset updated && updated <= sinceTimestamp)
            {
                continue;
            }

            if (entry.DocumentUri is null)
            {
                Logger.LogDebug("Skipping ROLIE entry {Id} because no document link was provided.", entry.Id);
                continue;
            }

            var rawDocument = await DownloadCsafDocumentAsync(entry, cancellationToken).ConfigureAwait(false);

            if (!digestSet.Add(rawDocument.Digest))
            {
                Logger.LogDebug("Skipping CSAF document {Uri} because digest {Digest} was already processed.", rawDocument.SourceUri, rawDocument.Digest);
                continue;
            }

            await context.RawSink.StoreAsync(rawDocument, cancellationToken).ConfigureAwait(false);
            digestList.Add(rawDocument.Digest);
            stateChanged = true;

            if (entry.Updated is DateTimeOffset entryUpdated && entryUpdated > latestUpdated)
            {
                latestUpdated = entryUpdated;
            }

            yield return rawDocument;
        }

        if (stateChanged)
        {
            var newLastUpdated = latestUpdated == DateTimeOffset.MinValue ? state?.LastUpdated : latestUpdated;
            var updatedState = new VexConnectorState(
                Descriptor.Id,
                newLastUpdated,
                digestList.ToImmutableArray());

            await _stateRepository.SaveAsync(updatedState, cancellationToken).ConfigureAwait(false);
        }
    }

    public override ValueTask<VexClaimBatch> NormalizeAsync(VexRawDocument document, CancellationToken cancellationToken)
    {
        // This connector relies on format-specific normalizers registered elsewhere.
        throw new NotSupportedException("RedHatCsafConnector does not perform in-line normalization; use the CSAF normalizer component.");
    }

    private async Task<IReadOnlyList<RolieEntry>> FetchRolieEntriesAsync(Uri feedUri, CancellationToken cancellationToken)
    {
        var client = _httpClientFactory.CreateClient(RedHatConnectorOptions.HttpClientName);
        using var response = await client.GetAsync(feedUri, cancellationToken).ConfigureAwait(false);
        response.EnsureSuccessStatusCode();

        await using var stream = await response.Content.ReadAsStreamAsync(cancellationToken).ConfigureAwait(false);
        var document = XDocument.Load(stream);
        var ns = document.Root?.Name.Namespace ?? "http://www.w3.org/2005/Atom";

        var entries = document.Root?
            .Elements(ns + "entry")
            .Select(e => new RolieEntry(
                Id: (string?)e.Element(ns + "id"),
                Updated: ParseUpdated((string?)e.Element(ns + "updated")),
                DocumentUri: ParseDocumentLink(e, ns)))
            .Where(entry => entry.Id is not null && entry.Updated is not null)
            .OrderBy(entry => entry.Updated)
            .ToList() ?? new List<RolieEntry>();

        return entries;
    }

    private static DateTimeOffset? ParseUpdated(string? value)
        => DateTimeOffset.TryParse(value, out var parsed) ? parsed : null;

    private static Uri? ParseDocumentLink(XElement entry, XNamespace ns)
    {
        var linkElements = entry.Elements(ns + "link");
        foreach (var link in linkElements)
        {
            var rel = (string?)link.Attribute("rel");
            var href = (string?)link.Attribute("href");
            if (string.IsNullOrWhiteSpace(href))
            {
                continue;
            }

            if (rel is null || rel.Equals("enclosure", StringComparison.OrdinalIgnoreCase) || rel.Equals("alternate", StringComparison.OrdinalIgnoreCase))
            {
                if (Uri.TryCreate(href, UriKind.Absolute, out var uri))
                {
                    return uri;
                }
            }
        }

        return null;
    }

    private async Task<VexRawDocument> DownloadCsafDocumentAsync(RolieEntry entry, CancellationToken cancellationToken)
    {
        var documentUri = entry.DocumentUri ?? throw new InvalidOperationException("ROLIE entry missing document URI.");

        var client = _httpClientFactory.CreateClient(RedHatConnectorOptions.HttpClientName);
        using var response = await client.GetAsync(documentUri, cancellationToken).ConfigureAwait(false);
        response.EnsureSuccessStatusCode();

        var contentBytes = await response.Content.ReadAsByteArrayAsync(cancellationToken).ConfigureAwait(false);
        var metadata = BuildMetadata(builder => builder
            .Add("redhat.csaf.entryId", entry.Id)
            .Add("redhat.csaf.documentUri", documentUri.ToString())
            .Add("redhat.csaf.updated", entry.Updated?.ToString("O")));

        return CreateRawDocument(VexDocumentFormat.Csaf, documentUri, contentBytes, metadata);
    }

    private sealed record RolieEntry(string? Id, DateTimeOffset? Updated, Uri? DocumentUri);
}