// -----------------------------------------------------------------------------
// DeterminismValidationTests.cs
// Sprint: SPRINT_3500_0004_0003_integration_tests_corpus
// Task: T5 - Determinism Validation Suite
// Description: Tests to validate scoring determinism across runs, platforms, and time
// -----------------------------------------------------------------------------

using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using FluentAssertions;
using Xunit;

namespace StellaOps.Integration.Determinism;

/// <summary>
/// Determinism validation tests for the scoring engine.
/// Ensures identical inputs produce identical outputs across:
/// - Multiple runs
/// - Different timestamps (with frozen time)
/// - Parallel execution
/// </summary>
public class DeterminismValidationTests
{
    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        WriteIndented = false
    };

    #region T5-AC1: Same input produces identical score hash

    [Fact]
    public void IdenticalInput_ProducesIdenticalHash_AcrossRuns()
    {
        // Arrange
        var input = new ScoringInput
        {
            ScanId = "test-scan-001",
            SbomHash = "sha256:abc123",
            RulesHash = "sha256:def456",
            PolicyHash = "sha256:ghi789",
            FeedHash = "sha256:jkl012",
            Timestamp = DateTimeOffset.Parse("2024-01-01T00:00:00Z")
        };

        // Act - Compute hash multiple times
        var hash1 = ComputeInputHash(input);
        var hash2 = ComputeInputHash(input);
        var hash3 = ComputeInputHash(input);

        // Assert
        hash1.Should().Be(hash2);
        hash2.Should().Be(hash3);
    }

    [Fact]
    public void DifferentInput_ProducesDifferentHash()
    {
        // Arrange
        var input1 = new ScoringInput
        {
            ScanId = "scan-001",
            SbomHash = "sha256:abc",
            RulesHash = "sha256:def",
            PolicyHash = "sha256:ghi",
            FeedHash = "sha256:jkl",
            Timestamp = DateTimeOffset.Parse("2024-01-01T00:00:00Z")
        };

        var input2 = new ScoringInput
        {
            ScanId = "scan-001",
            SbomHash = "sha256:DIFFERENT", // Changed
            RulesHash = "sha256:def",
            PolicyHash = "sha256:ghi",
            FeedHash = "sha256:jkl",
            Timestamp = DateTimeOffset.Parse("2024-01-01T00:00:00Z")
        };

        // Act
        var hash1 = ComputeInputHash(input1);
        var hash2 = ComputeInputHash(input2);

        // Assert
        hash1.Should().NotBe(hash2);
    }

    #endregion

    #region T5-AC2: Cross-platform determinism

    [Fact]
    public void HashComputation_IsConsistent_WithKnownVector()
    {
        // Arrange - Known test vector for cross-platform verification
        var input = new ScoringInput
        {
            ScanId = "determinism-test-001",
            SbomHash = "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
            RulesHash = "sha256:0000000000000000000000000000000000000000000000000000000000000000",
            PolicyHash = "sha256:ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
            FeedHash = "sha256:1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef",
            Timestamp = DateTimeOffset.Parse("2024-06-15T12:00:00Z")
        };

        // Act
        var hash = ComputeInputHash(input);

        // Assert - This hash should be identical on any platform
        hash.Should().NotBeNullOrEmpty();
        hash.Should().HaveLength(64); // SHA-256 hex = 64 chars
        hash.Should().MatchRegex("^[a-f0-9]{64}$");
    }

    [Fact]
    public void CanonicalJson_ProducesStableOutput()
    {
        // Arrange - Same data, different property order
        var obj1 = new Dictionary<string, object>
        {
            ["zebra"] = "last",
            ["alpha"] = "first",
            ["middle"] = 123
        };

        var obj2 = new Dictionary<string, object>
        {
            ["alpha"] = "first",
            ["middle"] = 123,
            ["zebra"] = "last"
        };

        // Act
        var json1 = ToCanonicalJson(obj1);
        var json2 = ToCanonicalJson(obj2);

        // Assert - Canonical JSON should sort keys
        json1.Should().Be(json2);
    }

    #endregion

    #region T5-AC3: Timestamp independence (frozen time tests)

    [Fact]
    public void ScoringWithFrozenTime_IsDeterministic()
    {
        // Arrange - Freeze timestamp
        var frozenTime = DateTimeOffset.Parse("2024-06-15T00:00:00Z");

        var input1 = new ScoringInput
        {
            ScanId = "frozen-time-001",
            SbomHash = "sha256:sbom",
            RulesHash = "sha256:rules",
            PolicyHash = "sha256:policy",
            FeedHash = "sha256:feed",
            Timestamp = frozenTime
        };

        var input2 = new ScoringInput
        {
            ScanId = "frozen-time-001",
            SbomHash = "sha256:sbom",
            RulesHash = "sha256:rules",
            PolicyHash = "sha256:policy",
            FeedHash = "sha256:feed",
            Timestamp = frozenTime
        };

        // Act
        var hash1 = ComputeInputHash(input1);
        var hash2 = ComputeInputHash(input2);

        // Assert
        hash1.Should().Be(hash2);
    }

    [Fact]
    public void DifferentTimestamps_ProduceDifferentHashes()
    {
        // Arrange
        var input1 = new ScoringInput
        {
            ScanId = "time-test-001",
            SbomHash = "sha256:same",
            RulesHash = "sha256:same",
            PolicyHash = "sha256:same",
            FeedHash = "sha256:same",
            Timestamp = DateTimeOffset.Parse("2024-01-01T00:00:00Z")
        };

        var input2 = new ScoringInput
        {
            ScanId = "time-test-001",
            SbomHash = "sha256:same",
            RulesHash = "sha256:same",
            PolicyHash = "sha256:same",
            FeedHash = "sha256:same",
            Timestamp = DateTimeOffset.Parse("2024-01-02T00:00:00Z") // Different
        };

        // Act
        var hash1 = ComputeInputHash(input1);
        var hash2 = ComputeInputHash(input2);

        // Assert
        hash1.Should().NotBe(hash2);
    }

    #endregion

    #region T5-AC4: Parallel execution determinism

    [Fact]
    public async Task ParallelExecution_ProducesIdenticalHashes()
    {
        // Arrange
        var input = new ScoringInput
        {
            ScanId = "parallel-test-001",
            SbomHash = "sha256:parallel",
            RulesHash = "sha256:parallel",
            PolicyHash = "sha256:parallel",
            FeedHash = "sha256:parallel",
            Timestamp = DateTimeOffset.Parse("2024-01-01T00:00:00Z")
        };

        // Act - Compute hash in parallel 100 times
        var tasks = Enumerable.Range(0, 100)
            .Select(_ => Task.Run(() => ComputeInputHash(input)))
            .ToArray();

        var hashes = await Task.WhenAll(tasks);

        // Assert - All hashes should be identical
        hashes.Should().AllBe(hashes[0]);
    }

    [Fact]
    public async Task ConcurrentScoring_MaintainsDeterminism()
    {
        // Arrange - Multiple different inputs
        var inputs = Enumerable.Range(0, 50)
            .Select(i => new ScoringInput
            {
                ScanId = $"concurrent-{i:D3}",
                SbomHash = $"sha256:sbom{i:D3}",
                RulesHash = "sha256:rules",
                PolicyHash = "sha256:policy",
                FeedHash = "sha256:feed",
                Timestamp = DateTimeOffset.Parse("2024-01-01T00:00:00Z")
            })
            .ToArray();

        // Act - Run twice in parallel
        var hashes1 = await Task.WhenAll(inputs.Select(i => Task.Run(() => ComputeInputHash(i))));
        var hashes2 = await Task.WhenAll(inputs.Select(i => Task.Run(() => ComputeInputHash(i))));

        // Assert - Both runs should produce identical results
        hashes1.Should().BeEquivalentTo(hashes2);
    }

    #endregion

    #region T5-AC5: Replay after code changes produces same result

    [Fact]
    public void GoldenVectorReplay_ProducesExpectedHash()
    {
        // Arrange - Golden test vector (version-locked)
        // This test ensures code changes don't break determinism
        var goldenInput = new ScoringInput
        {
            ScanId = "golden-vector-001",
            SbomHash = "sha256:goldensbom0000000000000000000000000000000000000000000000000",
            RulesHash = "sha256:goldenrule0000000000000000000000000000000000000000000000000",
            PolicyHash = "sha256:goldenpoli0000000000000000000000000000000000000000000000000",
            FeedHash = "sha256:goldenfeed0000000000000000000000000000000000000000000000000",
            Timestamp = DateTimeOffset.Parse("2024-01-01T00:00:00Z")
        };

        // Act
        var hash = ComputeInputHash(goldenInput);

        // Assert - This is the expected hash for the golden vector
        // If this test fails after a code change, it indicates a breaking change to determinism
        hash.Should().NotBeNullOrEmpty();
        
        // The actual expected hash would be computed once and stored here:
        // hash.Should().Be("expected_golden_hash_here");
        
        // For now, verify it's a valid hash format
        hash.Should().MatchRegex("^[a-f0-9]{64}$");
    }

    [Fact]
    public void MerkleRoot_IsStable_ForSameNodes()
    {
        // Arrange
        var nodes = new[]
        {
            "sha256:node1",
            "sha256:node2",
            "sha256:node3",
            "sha256:node4"
        };

        // Act - Compute merkle root multiple times
        var root1 = ComputeMerkleRoot(nodes);
        var root2 = ComputeMerkleRoot(nodes);
        var root3 = ComputeMerkleRoot(nodes);

        // Assert
        root1.Should().Be(root2);
        root2.Should().Be(root3);
    }

    [Fact]
    public void MerkleRoot_ChangesWhenNodeChanges()
    {
        // Arrange
        var nodes1 = new[] { "sha256:a", "sha256:b", "sha256:c" };
        var nodes2 = new[] { "sha256:a", "sha256:DIFFERENT", "sha256:c" };

        // Act
        var root1 = ComputeMerkleRoot(nodes1);
        var root2 = ComputeMerkleRoot(nodes2);

        // Assert
        root1.Should().NotBe(root2);
    }

    #endregion

    #region Helper Methods

    private static string ComputeInputHash(ScoringInput input)
    {
        var canonical = ToCanonicalJson(input);
        return ComputeSha256(canonical);
    }

    private static string ToCanonicalJson<T>(T obj)
    {
        // Sort keys for canonical JSON
        if (obj is IDictionary<string, object> dict)
        {
            var sorted = dict.OrderBy(kvp => kvp.Key, StringComparer.Ordinal)
                .ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
            return JsonSerializer.Serialize(sorted, JsonOptions);
        }

        return JsonSerializer.Serialize(obj, JsonOptions);
    }

    private static string ComputeSha256(string input)
    {
        var bytes = Encoding.UTF8.GetBytes(input);
        var hash = SHA256.HashData(bytes);
        return Convert.ToHexStringLower(hash);
    }

    private static string ComputeMerkleRoot(string[] nodes)
    {
        if (nodes.Length == 0)
            return ComputeSha256("");

        if (nodes.Length == 1)
            return nodes[0];

        var current = nodes.ToList();

        while (current.Count > 1)
        {
            var next = new List<string>();

            for (var i = 0; i < current.Count; i += 2)
            {
                var left = current[i];
                var right = i + 1 < current.Count ? current[i + 1] : left;
                var combined = left + right;
                next.Add("sha256:" + ComputeSha256(combined));
            }

            current = next;
        }

        return current[0];
    }

    #endregion

    #region DTOs

    private sealed record ScoringInput
    {
        public required string ScanId { get; init; }
        public required string SbomHash { get; init; }
        public required string RulesHash { get; init; }
        public required string PolicyHash { get; init; }
        public required string FeedHash { get; init; }
        public required DateTimeOffset Timestamp { get; init; }
    }

    #endregion
}