// Licensed under BUSL-1.1. Copyright (C) 2026 StellaOps Contributors.
// Sprint: SPRINT_20260110_012_008_POLICY
// Task: FCG-004 - FixChain Gate Unit Tests

using System.Collections.Immutable;
using Moq;
using StellaOps.Policy.Confidence.Models;
using StellaOps.Policy.Gates;
using StellaOps.Policy.TrustLattice;
using Xunit;

namespace StellaOps.Policy.Tests.Gates;

/// <summary>
/// Unit tests for <see cref="FixChainGate"/> evaluation scenarios.
/// </summary>
[Trait("Category", "Unit")]
public sealed class FixChainGateTests
{
    private readonly Mock<TimeProvider> _timeProviderMock;
    private readonly DateTimeOffset _fixedTime = new(2026, 1, 11, 12, 0, 0, TimeSpan.Zero);
    private readonly FixChainGateOptions _defaultOptions;

    public FixChainGateTests()
    {
        _timeProviderMock = new Mock<TimeProvider>();
        _timeProviderMock.Setup(t => t.GetUtcNow()).Returns(_fixedTime);

        _defaultOptions = new FixChainGateOptions
        {
            Enabled = true,
            RequiredSeverities = ["critical", "high"],
            MinimumConfidence = 0.85m,
            AllowInconclusive = false,
            GracePeriodDays = 7
        };
    }

    private FixChainGate CreateGate(FixChainGateOptions? options = null)
    {
        return new FixChainGate(options ?? _defaultOptions, _timeProviderMock.Object);
    }

    [Fact]
    public async Task EvaluateAsync_WhenDisabled_ReturnsPass()
    {
        // Arrange
        var options = new FixChainGateOptions { Enabled = false };
        var gate = CreateGate(options);
        var context = CreatePolicyContext("critical");
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.True(result.Passed);
        Assert.Contains("disabled", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_LowSeverity_ReturnsPass()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("low");
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.True(result.Passed);
        Assert.Contains("does not require", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_MediumSeverity_ReturnsPass()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("medium");
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.True(result.Passed);
    }

    [Fact]
    public async Task EvaluateAsync_CriticalSeverity_NoAttestation_ReturnsFail()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("critical");
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
        Assert.Contains("no FixChain attestation", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_HighSeverity_NoAttestation_ReturnsFail()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("high");
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
    }

    [Fact]
    public async Task EvaluateAsync_CriticalSeverity_WithFixedAttestation_ReturnsPass()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.hasAttestation"] = "true",
            ["fixchain.verdict"] = "fixed",
            ["fixchain.confidence"] = "0.95"
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.True(result.Passed);
        Assert.Contains("verified", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_FixedVerdict_BelowMinConfidence_ReturnsFail()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.hasAttestation"] = "true",
            ["fixchain.verdict"] = "fixed",
            ["fixchain.confidence"] = "0.70" // Below 0.85 minimum
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
        Assert.Contains("below minimum", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_PartialVerdict_ReturnsFail()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.hasAttestation"] = "true",
            ["fixchain.verdict"] = "partial",
            ["fixchain.confidence"] = "0.90"
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
        Assert.Contains("Partial fix", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_NotFixedVerdict_ReturnsFail()
    {
        // Arrange
        var gate = CreateGate();
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.hasAttestation"] = "true",
            ["fixchain.verdict"] = "not_fixed",
            ["fixchain.confidence"] = "0.95"
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
        Assert.Contains("NOT fixed", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_InconclusiveVerdict_WhenNotAllowed_ReturnsFail()
    {
        // Arrange
        var options = _defaultOptions with { AllowInconclusive = false };
        var gate = CreateGate(options);
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.hasAttestation"] = "true",
            ["fixchain.verdict"] = "inconclusive",
            ["fixchain.confidence"] = "0.50"
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
        Assert.Contains("inconclusive", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_InconclusiveVerdict_WhenAllowed_ReturnsPass()
    {
        // Arrange
        var options = _defaultOptions with { AllowInconclusive = true };
        var gate = CreateGate(options);
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.hasAttestation"] = "true",
            ["fixchain.verdict"] = "inconclusive",
            ["fixchain.confidence"] = "0.50"
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.True(result.Passed);
        Assert.Contains("allowed by policy", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_WithinGracePeriod_ReturnsPass()
    {
        // Arrange
        var gate = CreateGate();
        var cvePublished = _fixedTime.AddDays(-3); // 3 days ago, within 7-day grace
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.cvePublishedAt"] = cvePublished.ToString("o")
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.True(result.Passed);
        Assert.Contains("grace period", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_AfterGracePeriod_NoAttestation_ReturnsFail()
    {
        // Arrange
        var gate = CreateGate();
        var cvePublished = _fixedTime.AddDays(-10); // 10 days ago, past 7-day grace
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.cvePublishedAt"] = cvePublished.ToString("o")
        });
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
    }

    [Fact]
    public void EvaluateDirect_FixedVerdict_ReturnsAllow()
    {
        // Arrange
        var gate = CreateGate();
        var fixChainContext = new FixChainGateContext
        {
            HasAttestation = true,
            Verdict = "fixed",
            Confidence = 0.95m,
            VerifiedAt = _fixedTime,
            AttestationDigest = "sha256:test"
        };

        // Act
        var result = gate.EvaluateDirect(fixChainContext, "production", "critical");

        // Assert
        Assert.True(result.Passed);
        Assert.Equal(FixChainGateResult.DecisionAllow, result.Decision);
    }

    [Fact]
    public void EvaluateDirect_NoAttestation_ReturnsBlock()
    {
        // Arrange
        var gate = CreateGate();
        var fixChainContext = new FixChainGateContext
        {
            HasAttestation = false
        };

        // Act
        var result = gate.EvaluateDirect(fixChainContext, "production", "critical");

        // Assert
        Assert.False(result.Passed);
        Assert.Equal(FixChainGateResult.DecisionBlock, result.Decision);
    }

    [Fact]
    public void EvaluateDirect_InconclusiveAllowed_ReturnsWarn()
    {
        // Arrange
        var options = _defaultOptions with { AllowInconclusive = true };
        var gate = CreateGate(options);
        var fixChainContext = new FixChainGateContext
        {
            HasAttestation = true,
            Verdict = "inconclusive",
            Confidence = 0.50m
        };

        // Act
        var result = gate.EvaluateDirect(fixChainContext, "production", "critical");

        // Assert
        Assert.True(result.Passed);
        Assert.Equal(FixChainGateResult.DecisionAllow, result.Decision);
    }

    [Fact]
    public async Task EvaluateAsync_ProductionEnvironment_UsesHigherConfidence()
    {
        // Arrange
        var options = new FixChainGateOptions
        {
            Enabled = true,
            RequiredSeverities = ["critical"],
            MinimumConfidence = 0.70m,
            EnvironmentConfidence = new Dictionary<string, decimal>
            {
                ["production"] = 0.95m,
                ["staging"] = 0.80m
            }
        };
        var gate = CreateGate(options);

        // Context with 0.90 confidence - passes staging but not production
        var context = CreatePolicyContext("critical", new Dictionary<string, string>
        {
            ["fixchain.hasAttestation"] = "true",
            ["fixchain.verdict"] = "fixed",
            ["fixchain.confidence"] = "0.90"
        });
        context = context with { Environment = "production" };
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.False(result.Passed);
        Assert.Contains("below minimum", result.Reason);
    }

    [Fact]
    public async Task EvaluateAsync_DevelopmentEnvironment_NoRequirements()
    {
        // Arrange
        var options = new FixChainGateOptions
        {
            Enabled = true,
            RequiredSeverities = ["critical"],
            EnvironmentSeverities = new Dictionary<string, IReadOnlyList<string>>
            {
                ["production"] = ["critical", "high"],
                ["development"] = [] // No requirements
            }
        };
        var gate = CreateGate(options);
        var context = CreatePolicyContext("critical") with { Environment = "development" };
        var mergeResult = CreateMergeResult();

        // Act
        var result = await gate.EvaluateAsync(mergeResult, context);

        // Assert
        Assert.True(result.Passed);
        Assert.Contains("No severity requirements", result.Reason);
    }

    [Fact]
    public void Options_DefaultValues_AreReasonable()
    {
        // Arrange & Act
        var options = new FixChainGateOptions();

        // Assert
        Assert.True(options.Enabled);
        Assert.Contains("critical", options.RequiredSeverities);
        Assert.Contains("high", options.RequiredSeverities);
        Assert.True(options.MinimumConfidence >= 0.80m);
        Assert.False(options.AllowInconclusive);
        Assert.True(options.GracePeriodDays > 0);
    }

    private static PolicyGateContext CreatePolicyContext(
        string severity,
        Dictionary<string, string>? metadata = null)
    {
        return new PolicyGateContext
        {
            Environment = "production",
            Severity = severity,
            CveId = "CVE-2024-1234",
            SubjectKey = "pkg:generic/test@1.0.0",
            Metadata = metadata
        };
    }

    private static MergeResult CreateMergeResult()
    {
        var emptyClaim = new ScoredClaim
        {
            SourceId = "test",
            Status = VexStatus.Affected,
            OriginalScore = 1.0,
            AdjustedScore = 1.0,
            ScopeSpecificity = 1,
            Accepted = true,
            Reason = "test"
        };

        return new MergeResult
        {
            Status = VexStatus.Affected,
            Confidence = 0.9,
            HasConflicts = false,
            AllClaims = [emptyClaim],
            WinningClaim = emptyClaim,
            Conflicts = []
        };
    }
}