/**
 * Resolver Tests
 * Sprint: SPRINT_9100_0001_0001 (Core Resolver Package)
 * Tasks: RESOLVER-9100-019 through RESOLVER-9100-024
 */

using System.Text.Json;
using Xunit;

using StellaOps.TestKit;
namespace StellaOps.Resolver.Tests;

public class DeterministicResolverTests
{
    private readonly Policy _policy = Policy.Empty;
    private readonly IGraphOrderer _orderer = new TopologicalGraphOrderer();
    private readonly ITrustLatticeEvaluator _evaluator = new DefaultTrustLatticeEvaluator();

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Run_SameInputTwice_IdenticalFinalDigest()
    {
        // RESOLVER-9100-020: Replay test
        var graph = CreateTestGraph();
        var resolver = new DeterministicResolver(_policy, _orderer, _evaluator);
        var fixedTime = DateTimeOffset.Parse("2025-12-24T00:00:00Z");

        var result1 = resolver.Run(graph, fixedTime);
        var result2 = resolver.Run(graph, fixedTime);

        Assert.Equal(result1.FinalDigest, result2.FinalDigest);
        Assert.Equal(result1.GraphDigest, result2.GraphDigest);
        Assert.Equal(result1.TraversalSequence.Length, result2.TraversalSequence.Length);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Run_ShuffledNodesAndEdges_IdenticalFinalDigest()
    {
        // RESOLVER-9100-021: Permutation test
        var node1 = Node.Create("package", "pkg:npm/a@1.0.0");
        var node2 = Node.Create("package", "pkg:npm/b@1.0.0");
        var node3 = Node.Create("package", "pkg:npm/c@1.0.0");

        var edge1 = Edge.Create(node1.Id, "depends_on", node2.Id);
        var edge2 = Edge.Create(node2.Id, "depends_on", node3.Id);

        // Create graphs with different input orders
        var graph1 = EvidenceGraph.Create(
            new[] { node1, node2, node3 },
            new[] { edge1, edge2 });

        var graph2 = EvidenceGraph.Create(
            new[] { node3, node1, node2 }, // shuffled
            new[] { edge2, edge1 }); // shuffled

        var resolver = new DeterministicResolver(_policy, _orderer, _evaluator);
        var fixedTime = DateTimeOffset.Parse("2025-12-24T00:00:00Z");

        var result1 = resolver.Run(graph1, fixedTime);
        var result2 = resolver.Run(graph2, fixedTime);

        Assert.Equal(result1.FinalDigest, result2.FinalDigest);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Run_IsIdempotent()
    {
        // RESOLVER-9100-022: Idempotency property test
        var graph = CreateTestGraph();
        var resolver = new DeterministicResolver(_policy, _orderer, _evaluator);
        var fixedTime = DateTimeOffset.Parse("2025-12-24T00:00:00Z");

        var result1 = resolver.Run(graph, fixedTime);
        var result2 = resolver.Run(graph, fixedTime);
        var result3 = resolver.Run(graph, fixedTime);

        Assert.Equal(result1.FinalDigest, result2.FinalDigest);
        Assert.Equal(result2.FinalDigest, result3.FinalDigest);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Run_TraversalSequence_MatchesTopologicalOrder()
    {
        // RESOLVER-9100-023: Traversal order test
        var root = Node.Create("package", "root");
        var child1 = Node.Create("package", "child1");
        var child2 = Node.Create("package", "child2");

        var edge1 = Edge.Create(root.Id, "depends_on", child1.Id);
        var edge2 = Edge.Create(root.Id, "depends_on", child2.Id);

        var graph = EvidenceGraph.Create(
            new[] { root, child1, child2 },
            new[] { edge1, edge2 });

        var resolver = new DeterministicResolver(_policy, _orderer, _evaluator);
        var result = resolver.Run(graph);

        // Children should come before root in topological order (reverse dependency order)
        var rootIndex = result.TraversalSequence.ToList().IndexOf(root.Id);
        var child1Index = result.TraversalSequence.ToList().IndexOf(child1.Id);
        var child2Index = result.TraversalSequence.ToList().IndexOf(child2.Id);

        // Root depends on children, so root should come after children in topological order
        // Wait - our edges go root -> child, so root has no incoming edges
        // Root should actually be first since it has no dependencies
        Assert.True(rootIndex < child1Index || rootIndex < child2Index,
            "Root should appear before at least one child in traversal");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ResolutionResult_CanonicalJsonStructure()
    {
        // RESOLVER-9100-024: Snapshot test for canonical JSON
        var graph = CreateTestGraph();
        var resolver = new DeterministicResolver(_policy, _orderer, _evaluator);
        var fixedTime = DateTimeOffset.Parse("2025-12-24T00:00:00Z");

        var result = resolver.Run(graph, fixedTime);

        // Verify result structure
        Assert.NotNull(result.FinalDigest);
        Assert.NotNull(result.GraphDigest);
        Assert.NotNull(result.PolicyDigest);
        Assert.Equal(64, result.FinalDigest.Length); // SHA256 hex
        Assert.Equal(64, result.GraphDigest.Length);
        Assert.Equal(64, result.PolicyDigest.Length);
        Assert.Equal(fixedTime, result.ResolvedAt);
    }

    private static EvidenceGraph CreateTestGraph()
    {
        var node1 = Node.Create("package", "pkg:npm/test@1.0.0");
        var node2 = Node.Create("vulnerability", "CVE-2024-1234");

        var edge = Edge.Create(node2.Id, "affects", node1.Id);

        return EvidenceGraph.Create(new[] { node1, node2 }, new[] { edge });
    }
}