using StellaOps.Graph.Api.Contracts;

namespace StellaOps.Graph.Api.Services;

public sealed class InMemoryGraphRepository
{
    private static readonly string[] CompatibilityKinds = ["artifact", "component", "vuln"];
    private static readonly DateTimeOffset FixedSnapshotAt = new(2026, 4, 4, 0, 0, 0, TimeSpan.Zero);
    private readonly List<NodeTile> _nodes;
    private readonly List<EdgeTile> _edges;
    private readonly Dictionary<string, (List<NodeTile> Nodes, List<EdgeTile> Edges)> _snapshots;

    public InMemoryGraphRepository(IEnumerable<NodeTile>? seed = null, IEnumerable<EdgeTile>? edges = null)
    {
        _nodes = seed?.ToList() ?? new List<NodeTile>
        {
            new() { Id = "gn:acme:component:example", Kind = "component", Tenant = "acme", Attributes = new() { ["purl"] = "pkg:npm/example@1.0.0", ["ecosystem"] = "npm", ["displayName"] = "example", ["version"] = "1.0.0" } },
            new() { Id = "gn:acme:component:widget", Kind = "component", Tenant = "acme", Attributes = new() { ["purl"] = "pkg:npm/widget@2.0.0", ["ecosystem"] = "npm", ["displayName"] = "widget", ["version"] = "2.0.0" } },
            new() { Id = "gn:acme:artifact:sha256:abc", Kind = "artifact", Tenant = "acme", Attributes = new() { ["digest"] = "sha256:abc", ["ecosystem"] = "container", ["displayName"] = "auth-service", ["version"] = "2026.04.04" } },
            new() { Id = "gn:acme:sbom:sha256:sbom-a", Kind = "sbom", Tenant = "acme", Attributes = new() { ["sbom_digest"] = "sha256:sbom-a", ["artifact_digest"] = "sha256:abc", ["format"] = "cyclonedx" } },
            new() { Id = "gn:acme:sbom:sha256:sbom-b", Kind = "sbom", Tenant = "acme", Attributes = new() { ["sbom_digest"] = "sha256:sbom-b", ["artifact_digest"] = "sha256:abc", ["format"] = "spdx" } },
            new() { Id = "gn:acme:component:gamma", Kind = "component", Tenant = "acme", Attributes = new() { ["purl"] = "pkg:nuget/Gamma@3.1.4", ["ecosystem"] = "nuget", ["displayName"] = "gamma", ["version"] = "3.1.4" } },
            new() { Id = "gn:acme:vuln:CVE-2026-1234", Kind = "vuln", Tenant = "acme", Attributes = new() { ["displayName"] = "CVE-2026-1234", ["severity"] = "critical", ["cveId"] = "CVE-2026-1234" } },
            new() { Id = "gn:acme:vuln:CVE-2026-5678", Kind = "vuln", Tenant = "acme", Attributes = new() { ["displayName"] = "CVE-2026-5678", ["severity"] = "high", ["cveId"] = "CVE-2026-5678" } },
            new() { Id = "gn:bravo:component:widget", Kind = "component", Tenant = "bravo", Attributes = new() { ["purl"] = "pkg:npm/widget@2.0.0", ["ecosystem"] = "npm", ["displayName"] = "widget", ["version"] = "2.0.0" } },
            new() { Id = "gn:bravo:artifact:sha256:def", Kind = "artifact", Tenant = "bravo", Attributes = new() { ["digest"] = "sha256:def", ["ecosystem"] = "container", ["displayName"] = "transform-service", ["version"] = "2026.04.04" } },
            new() { Id = "gn:bravo:vuln:CVE-2026-9001", Kind = "vuln", Tenant = "bravo", Attributes = new() { ["displayName"] = "CVE-2026-9001", ["severity"] = "medium", ["cveId"] = "CVE-2026-9001" } },
        };

        _edges = edges?.ToList() ?? new List<EdgeTile>
        {
            new() { Id = "ge:acme:artifact->component", Kind = "builds", Tenant = "acme", Source = "gn:acme:artifact:sha256:abc", Target = "gn:acme:component:example", Attributes = new() { ["reason"] = "sbom" } },
            new() { Id = "ge:acme:component->component", Kind = "depends_on", Tenant = "acme", Source = "gn:acme:component:example", Target = "gn:acme:component:widget", Attributes = new() { ["scope"] = "runtime" } },
            new() { Id = "ge:acme:component->component:gamma", Kind = "depends_on", Tenant = "acme", Source = "gn:acme:component:widget", Target = "gn:acme:component:gamma", Attributes = new() { ["scope"] = "runtime" } },
            new() { Id = "ge:acme:component->vuln:widget", Kind = "affects", Tenant = "acme", Source = "gn:acme:component:widget", Target = "gn:acme:vuln:CVE-2026-1234", Attributes = new() { ["scope"] = "runtime" } },
            new() { Id = "ge:acme:component->vuln:gamma", Kind = "affects", Tenant = "acme", Source = "gn:acme:component:gamma", Target = "gn:acme:vuln:CVE-2026-5678", Attributes = new() { ["scope"] = "runtime" } },
            new() { Id = "ge:acme:sbom->artifact", Kind = "SBOM_VERSION_OF", Tenant = "acme", Source = "gn:acme:sbom:sha256:sbom-b", Target = "gn:acme:artifact:sha256:abc", Attributes = new() { ["relationship"] = "version_of" } },
            new() { Id = "ge:acme:sbom->sbom", Kind = "SBOM_LINEAGE_PARENT", Tenant = "acme", Source = "gn:acme:sbom:sha256:sbom-b", Target = "gn:acme:sbom:sha256:sbom-a", Attributes = new() { ["relationship"] = "parent" } },
            new() { Id = "ge:bravo:artifact->component", Kind = "builds", Tenant = "bravo", Source = "gn:bravo:artifact:sha256:def", Target = "gn:bravo:component:widget", Attributes = new() { ["reason"] = "sbom" } },
            new() { Id = "ge:bravo:component->vuln:widget", Kind = "affects", Tenant = "bravo", Source = "gn:bravo:component:widget", Target = "gn:bravo:vuln:CVE-2026-9001", Attributes = new() { ["scope"] = "runtime" } },
        };

        // Drop edges whose endpoints aren't present in the current node set to avoid invalid graph seeds in tests.
        var nodeIds = _nodes.Select(n => n.Id).ToHashSet(StringComparer.Ordinal);
        _edges = _edges.Where(e => nodeIds.Contains(e.Source) && nodeIds.Contains(e.Target)).ToList();

        _snapshots = SeedSnapshots();
    }

    public IEnumerable<NodeTile> Query(string tenant, GraphSearchRequest request)
    {
        var queryable = _nodes
            .Where(n => n.Tenant.Equals(tenant, StringComparison.Ordinal))
            .Where(n => request.Kinds is null || request.Kinds.Length == 0 || request.Kinds.Contains(n.Kind, StringComparer.OrdinalIgnoreCase));

        if (!string.IsNullOrWhiteSpace(request.Query))
        {
            queryable = queryable.Where(n => MatchesQuery(n, request.Query!));
        }

        if (request.Filters is not null)
        {
            queryable = queryable.Where(n => FiltersMatch(n, request.Filters!));
        }

        return queryable;
    }

    public (IReadOnlyList<NodeTile> Nodes, IReadOnlyList<EdgeTile> Edges) QueryGraph(string tenant, GraphQueryRequest request)
    {
        var nodes = Query(tenant, new GraphSearchRequest
        {
            Kinds = request.Kinds,
            Query = request.Query,
            Filters = request.Filters,
            Limit = request.Limit,
            Cursor = request.Cursor
        }).ToList();

        var nodeIds = nodes.Select(n => n.Id).ToHashSet(StringComparer.Ordinal);
        var edges = request.IncludeEdges
            ? _edges.Where(e => e.Tenant.Equals(tenant, StringComparison.Ordinal) && nodeIds.Contains(e.Source) && nodeIds.Contains(e.Target))
                .OrderBy(e => e.Id, StringComparer.Ordinal)
                .ToList()
            : new List<EdgeTile>();

        return (nodes, edges);
    }

    public (IReadOnlyList<NodeTile> Nodes, IReadOnlyList<EdgeTile> Edges) GetLineage(string tenant, GraphLineageRequest request)
    {
        ArgumentNullException.ThrowIfNull(request);

        var maxDepth = request.MaxDepth ?? 3;
        if (maxDepth < 1)
        {
            maxDepth = 1;
        }

        var allowedKinds = BuildLineageKindFilter(request.RelationshipKinds);
        var tenantNodes = _nodes
            .Where(n => n.Tenant.Equals(tenant, StringComparison.Ordinal))
            .ToList();

        if (tenantNodes.Count == 0)
        {
            return (Array.Empty<NodeTile>(), Array.Empty<EdgeTile>());
        }

        var nodeById = tenantNodes.ToDictionary(n => n.Id, StringComparer.Ordinal);
        var seedIds = new HashSet<string>(StringComparer.Ordinal);

        if (!string.IsNullOrWhiteSpace(request.ArtifactDigest))
        {
            var digest = request.ArtifactDigest.Trim();
            foreach (var node in tenantNodes.Where(n => HasAttribute(n, "artifact_digest", digest)))
            {
                seedIds.Add(node.Id);
            }
        }

        if (!string.IsNullOrWhiteSpace(request.SbomDigest))
        {
            var digest = request.SbomDigest.Trim();
            foreach (var node in tenantNodes.Where(n => HasAttribute(n, "sbom_digest", digest)))
            {
                seedIds.Add(node.Id);
            }
        }

        if (seedIds.Count == 0)
        {
            return (Array.Empty<NodeTile>(), Array.Empty<EdgeTile>());
        }

        var tenantEdges = _edges
            .Where(e => e.Tenant.Equals(tenant, StringComparison.Ordinal))
            .Where(e => IsLineageEdgeAllowed(e, allowedKinds))
            .ToList();

        var adjacency = new Dictionary<string, List<EdgeTile>>(StringComparer.Ordinal);
        foreach (var edge in tenantEdges)
        {
            AddAdjacency(adjacency, edge.Source, edge);
            AddAdjacency(adjacency, edge.Target, edge);
        }

        var visitedNodes = new HashSet<string>(seedIds, StringComparer.Ordinal);
        var visitedEdges = new HashSet<string>(StringComparer.Ordinal);
        var frontier = new HashSet<string>(seedIds, StringComparer.Ordinal);

        for (var depth = 0; depth < maxDepth && frontier.Count > 0; depth++)
        {
            var next = new HashSet<string>(StringComparer.Ordinal);
            foreach (var nodeId in frontier)
            {
                if (!adjacency.TryGetValue(nodeId, out var edges))
                {
                    continue;
                }

                foreach (var edge in edges)
                {
                    if (visitedEdges.Add(edge.Id))
                    {
                        var other = string.Equals(edge.Source, nodeId, StringComparison.Ordinal)
                            ? edge.Target
                            : edge.Source;
                        if (visitedNodes.Add(other))
                        {
                            next.Add(other);
                        }
                    }
                }
            }

            frontier = next;
        }

        var resultNodes = new List<NodeTile>();
        foreach (var nodeId in visitedNodes.OrderBy(id => id, StringComparer.Ordinal))
        {
            if (nodeById.TryGetValue(nodeId, out var node))
            {
                resultNodes.Add(node);
            }
        }

        var resultEdges = tenantEdges
            .Where(edge => visitedEdges.Contains(edge.Id))
            .Where(edge => visitedNodes.Contains(edge.Source) && visitedNodes.Contains(edge.Target))
            .OrderBy(edge => edge.Id, StringComparer.Ordinal)
            .ToList();

        return (resultNodes, resultEdges);
    }

    public (IReadOnlyList<NodeTile> Nodes, IReadOnlyList<EdgeTile> Edges)? GetSnapshot(string tenant, string snapshotId)
    {
        if (_snapshots.TryGetValue($"{tenant}:{snapshotId}", out var snap))
        {
            return (snap.Nodes, snap.Edges);
        }
        return null;
    }

    public IReadOnlyList<NodeTile> GetCompatibilityNodes(string tenant)
        => _nodes
            .Where(node => node.Tenant.Equals(tenant, StringComparison.Ordinal))
            .Where(node => CompatibilityKinds.Contains(node.Kind, StringComparer.OrdinalIgnoreCase))
            .OrderBy(node => node.Id, StringComparer.Ordinal)
            .ToList();

    public IReadOnlyList<EdgeTile> GetCompatibilityEdges(string tenant)
    {
        var nodeIds = GetCompatibilityNodes(tenant).Select(node => node.Id).ToHashSet(StringComparer.Ordinal);
        return _edges
            .Where(edge => edge.Tenant.Equals(tenant, StringComparison.Ordinal))
            .Where(edge => nodeIds.Contains(edge.Source) && nodeIds.Contains(edge.Target))
            .OrderBy(edge => edge.Id, StringComparer.Ordinal)
            .ToList();
    }

    public static string BuildGraphId(string tenant)
        => $"graph::{tenant}::main";

    public bool GraphExists(string tenant, string graphId)
        => string.Equals(BuildGraphId(tenant), graphId, StringComparison.OrdinalIgnoreCase);

    public NodeTile? GetNode(string tenant, string nodeId)
        => _nodes.FirstOrDefault(node =>
            node.Tenant.Equals(tenant, StringComparison.Ordinal)
            && node.Id.Equals(nodeId, StringComparison.Ordinal));

    public (IReadOnlyList<EdgeTile> Incoming, IReadOnlyList<EdgeTile> Outgoing) GetAdjacency(string tenant, string nodeId)
    {
        var edges = GetCompatibilityEdges(tenant);
        var incoming = edges.Where(edge => edge.Target.Equals(nodeId, StringComparison.Ordinal)).ToList();
        var outgoing = edges.Where(edge => edge.Source.Equals(nodeId, StringComparison.Ordinal)).ToList();
        return (incoming, outgoing);
    }

    public (IReadOnlyList<NodeTile> Nodes, IReadOnlyList<EdgeTile> Edges)? FindCompatibilityPath(string tenant, string sourceId, string targetId, int maxDepth)
    {
        var nodes = GetCompatibilityNodes(tenant).ToDictionary(node => node.Id, StringComparer.Ordinal);
        if (!nodes.ContainsKey(sourceId) || !nodes.ContainsKey(targetId))
        {
            return null;
        }

        var edges = GetCompatibilityEdges(tenant);
        var adjacency = new Dictionary<string, List<EdgeTile>>(StringComparer.Ordinal);
        foreach (var edge in edges)
        {
            if (!adjacency.TryGetValue(edge.Source, out var list))
            {
                list = new List<EdgeTile>();
                adjacency[edge.Source] = list;
            }

            list.Add(edge);
        }

        var queue = new Queue<(string NodeId, List<EdgeTile> PathEdges)>();
        var visited = new HashSet<string>(StringComparer.Ordinal) { sourceId };
        queue.Enqueue((sourceId, new List<EdgeTile>()));

        while (queue.Count > 0)
        {
            var (nodeId, pathEdges) = queue.Dequeue();
            if (nodeId.Equals(targetId, StringComparison.Ordinal))
            {
                var pathNodes = BuildNodeListFromEdges(nodes, sourceId, pathEdges);
                return (pathNodes, pathEdges);
            }

            if (pathEdges.Count >= maxDepth || !adjacency.TryGetValue(nodeId, out var outgoing))
            {
                continue;
            }

            foreach (var edge in outgoing.OrderBy(edge => edge.Id, StringComparer.Ordinal))
            {
                if (!visited.Add(edge.Target))
                {
                    continue;
                }

                var nextEdges = new List<EdgeTile>(pathEdges.Count + 1);
                nextEdges.AddRange(pathEdges);
                nextEdges.Add(edge);
                queue.Enqueue((edge.Target, nextEdges));
            }
        }

        return null;
    }

    public DateTimeOffset GetSnapshotTimestamp()
        => FixedSnapshotAt;

    private Dictionary<string, (List<NodeTile> Nodes, List<EdgeTile> Edges)> SeedSnapshots()
    {
        var dict = new Dictionary<string, (List<NodeTile>, List<EdgeTile>)>(StringComparer.Ordinal);

        dict["acme:snapA"] = (new List<NodeTile>(_nodes), new List<EdgeTile>(_edges));

        var updatedNodes = new List<NodeTile>(_nodes.Select(n => n with
        {
            Attributes = new Dictionary<string, object?>(n.Attributes)
        }));

        var widget = updatedNodes.FirstOrDefault(n => n.Id == "gn:acme:component:widget");
        if (widget is null)
        {
            // Custom seeds may not include the default widget node; skip optional snapshot wiring in that case.
            return dict;
        }

        widget.Attributes["purl"] = "pkg:npm/widget@2.1.0";
        widget.Attributes["version"] = "2.1.0";

        updatedNodes.Add(new NodeTile
        {
            Id = "gn:acme:component:newlib",
            Kind = "component",
            Tenant = "acme",
            Attributes = new() { ["purl"] = "pkg:npm/newlib@1.0.0", ["ecosystem"] = "npm", ["displayName"] = "newlib", ["version"] = "1.0.0" }
        });

        var updatedEdges = new List<EdgeTile>(_edges)
        {
            new()
            {
                Id = "ge:acme:component->component:new",
                Kind = "depends_on",
                Tenant = "acme",
                Source = widget.Id,
                Target = "gn:acme:component:newlib",
                Attributes = new() { ["scope"] = "runtime" }
            }
        };

        dict["acme:snapB"] = (updatedNodes, updatedEdges);
        return dict;
    }

    private static bool HasAttribute(NodeTile node, string key, string expected)
    {
        if (!node.Attributes.TryGetValue(key, out var value) || value is null)
        {
            return false;
        }

        return string.Equals(value.ToString(), expected, StringComparison.OrdinalIgnoreCase);
    }

    private static HashSet<string> BuildLineageKindFilter(string[]? relationshipKinds)
    {
        if (relationshipKinds is null || relationshipKinds.Length == 0)
        {
            return new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        }

        var set = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        foreach (var value in relationshipKinds)
        {
            if (string.IsNullOrWhiteSpace(value))
            {
                continue;
            }

            set.Add(value.Trim());
        }

        return set;
    }

    private static bool IsLineageEdgeAllowed(EdgeTile edge, HashSet<string> allowedKinds)
    {
        if (allowedKinds.Count == 0)
        {
            return edge.Kind.StartsWith("SBOM_LINEAGE_", StringComparison.OrdinalIgnoreCase)
                || string.Equals(edge.Kind, "SBOM_VERSION_OF", StringComparison.OrdinalIgnoreCase);
        }

        if (allowedKinds.Contains(edge.Kind))
        {
            return true;
        }

        if (edge.Attributes.TryGetValue("relationship", out var relationship) && relationship is not null)
        {
            return allowedKinds.Contains(relationship.ToString() ?? string.Empty);
        }

        return false;
    }

    private static void AddAdjacency(Dictionary<string, List<EdgeTile>> adjacency, string nodeId, EdgeTile edge)
    {
        if (!adjacency.TryGetValue(nodeId, out var list))
        {
            list = new List<EdgeTile>();
            adjacency[nodeId] = list;
        }

        list.Add(edge);
    }

    private static bool MatchesQuery(NodeTile node, string query)
    {
        var q = query.ToLowerInvariant();
        return node.Id.ToLowerInvariant().Contains(q)
            || node.Attributes.Values.OfType<string>().Any(v => v.Contains(q, StringComparison.OrdinalIgnoreCase));
    }

    private static bool FiltersMatch(NodeTile node, IReadOnlyDictionary<string, object> filters)
    {
        foreach (var kvp in filters)
        {
            if (!node.Attributes.TryGetValue(kvp.Key, out var value))
            {
                return false;
            }
            if (kvp.Value is null)
            {
                continue;
            }
            if (!kvp.Value.ToString()!.Equals(value?.ToString(), StringComparison.OrdinalIgnoreCase))
            {
                return false;
            }
        }
        return true;
    }

    private static IReadOnlyList<NodeTile> BuildNodeListFromEdges(
        IDictionary<string, NodeTile> nodes,
        string sourceId,
        IReadOnlyList<EdgeTile> edges)
    {
        var list = new List<NodeTile>();
        if (nodes.TryGetValue(sourceId, out var firstNode))
        {
            list.Add(firstNode);
        }

        foreach (var edge in edges)
        {
            if (nodes.TryGetValue(edge.Target, out var node))
            {
                list.Add(node);
            }
        }

        return list;
    }
}

internal static class CursorCodec
{
    public static string Encode(int offset) => Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(offset.ToString()));

    public static int Decode(string? token)
    {
        if (string.IsNullOrWhiteSpace(token)) return 0;
        try
        {
            var text = System.Text.Encoding.UTF8.GetString(Convert.FromBase64String(token));
            return int.TryParse(text, out var value) ? value : 0;
        }
        catch
        {
            return 0;
        }
    }
}