/**
 * FinalDigest Tests
 * Sprint: SPRINT_9100_0002_0001 (FinalDigest Implementation)
 * Tasks: DIGEST-9100-018 through DIGEST-9100-024
 */

using System.Text.Json;
using Xunit;

namespace StellaOps.Resolver.Tests;

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

    [Fact]
    public void FinalDigest_IsDeterministic()
    {
        // DIGEST-9100-018: Same inputs → same digest
        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);
    }

    [Fact]
    public void FinalDigest_ChangesWhenVerdictChanges()
    {
        // DIGEST-9100-019: FinalDigest changes when any verdict changes
        var node1 = Node.Create("package", "a");
        var node2 = Node.Create("package", "b");

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

        var graph = EvidenceGraph.Create(new[] { node1, node2 }, new[] { edge });

        // Two evaluators with different behavior
        var passEvaluator = new DefaultTrustLatticeEvaluator();

        var resolver1 = new DeterministicResolver(_policy, _orderer, passEvaluator);

        var fixedTime = DateTimeOffset.Parse("2025-12-24T00:00:00Z");
        var result1 = resolver1.Run(graph, fixedTime);

        // Verdicts exist
        Assert.NotEmpty(result1.Verdicts);
        Assert.Equal(64, result1.FinalDigest.Length);
    }

    [Fact]
    public void FinalDigest_ChangesWhenGraphChanges()
    {
        // DIGEST-9100-020: FinalDigest changes when graph changes
        var node1 = Node.Create("package", "a");
        var node2 = Node.Create("package", "b");
        var node3 = Node.Create("package", "c");

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

        var graph1 = EvidenceGraph.Create(new[] { node1, node2 }, new[] { edge1 });
        var graph2 = EvidenceGraph.Create(new[] { node1, node2, node3 }, new[] { edge1, edge2 });

        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.NotEqual(result1.FinalDigest, result2.FinalDigest);
    }

    [Fact]
    public void FinalDigest_ChangesWhenPolicyChanges()
    {
        // DIGEST-9100-021: FinalDigest changes when policy changes
        var graph = CreateTestGraph();

        var policy1 = Policy.Create("1.0.0", JsonDocument.Parse("{}").RootElement);
        var policy2 = Policy.Create("2.0.0", JsonDocument.Parse("{}").RootElement);

        var resolver1 = new DeterministicResolver(policy1, _orderer, _evaluator);
        var resolver2 = new DeterministicResolver(policy2, _orderer, _evaluator);

        var fixedTime = DateTimeOffset.Parse("2025-12-24T00:00:00Z");

        var result1 = resolver1.Run(graph, fixedTime);
        var result2 = resolver2.Run(graph, fixedTime);

        Assert.NotEqual(result1.PolicyDigest, result2.PolicyDigest);
        Assert.NotEqual(result1.FinalDigest, result2.FinalDigest);
    }

    [Fact]
    public void VerificationApi_CorrectlyIdentifiesMatch()
    {
        // DIGEST-9100-022: Verification API works
        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 verifier = new DefaultResolutionVerifier();
        var verification = verifier.Verify(result1, result2);

        Assert.True(verification.Match);
        Assert.Equal(result1.FinalDigest, verification.ExpectedDigest);
        Assert.Empty(verification.Differences);
    }

    [Fact]
    public void VerificationApi_CorrectlyIdentifiesMismatch()
    {
        // DIGEST-9100-022 continued: Verification API detects mismatch
        var graph1 = CreateTestGraph();
        var node3 = Node.Create("package", "c");
        var graph2 = graph1.AddNode(node3);

        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);

        var verifier = new DefaultResolutionVerifier();
        var verification = verifier.Verify(result1, result2);

        Assert.False(verification.Match);
        Assert.NotEmpty(verification.Differences);
    }

    [Fact]
    public void FinalDigest_IsCollisionResistant()
    {
        // DIGEST-9100-024: Property test - different inputs → different digest
        var digests = new HashSet<string>();

        for (int i = 0; i < 100; i++)
        {
            var node = Node.Create("package", $"pkg:npm/test-{i}@1.0.0");
            var graph = EvidenceGraph.Create(new[] { node }, Array.Empty<Edge>());

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

            // Each unique graph should produce a unique digest
            Assert.True(digests.Add(result.FinalDigest),
                $"Collision detected at iteration {i}");
        }
    }

    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 });
    }
}