using System;
using Microsoft.Extensions.Options;
using StellaOps.Policy;
using StellaOps.PolicyDsl;
using StellaOps.Policy.Engine.Options;
using StellaOps.Policy.Engine.Services;
using Xunit;

namespace StellaOps.Policy.Engine.Tests;

public sealed class PolicyCompilationServiceTests
{
    private const string SimplePolicy = """
        policy "Sample" syntax "stella-dsl@1" {
          rule block_high priority 10 {
            when severity.normalized >= "High"
            then status := "blocked"
            because "Block high severity findings"
          }

          rule warn_medium priority 20 {
            when severity.normalized >= "Medium"
            then status := "warn"
            because "Warn on medium severity findings"
          }
        }
        """;

    [Fact]
    public void Compile_ReturnsComplexityReport_WhenWithinLimits()
    {
        var service = CreateService(maxComplexityScore: 1000, maxDurationMilliseconds: 1000, simulatedDurationMilliseconds: 12.3);
        var request = new PolicyCompileRequest(new PolicyDslPayload("stella-dsl@1", SimplePolicy));

        var result = service.Compile(request);

        Assert.True(result.Success);
        Assert.NotNull(result.Digest);
        Assert.NotNull(result.Complexity);
        Assert.True(result.Complexity!.Score > 0);
        Assert.True(result.Complexity.RuleCount >= 2);
        Assert.Equal(13, result.DurationMilliseconds);
        Assert.True(result.Diagnostics.IsDefaultOrEmpty);
    }

    [Fact]
    public void Compile_Fails_WhenComplexityExceedsThreshold()
    {
        var service = CreateService(maxComplexityScore: 1, maxDurationMilliseconds: 1000, simulatedDurationMilliseconds: 2);
        var request = new PolicyCompileRequest(new PolicyDslPayload("stella-dsl@1", SimplePolicy));

        var result = service.Compile(request);

        Assert.False(result.Success);
        Assert.NotNull(result.Complexity);
        Assert.Equal(2, result.DurationMilliseconds);
        var diagnostic = Assert.Single(result.Diagnostics);
        Assert.Equal(PolicyEngineDiagnosticCodes.CompilationComplexityExceeded, diagnostic.Code);
        Assert.Equal(PolicyIssueSeverity.Error, diagnostic.Severity);
    }

    [Fact]
    public void Compile_Fails_WhenDurationExceedsThreshold()
    {
        var service = CreateService(maxComplexityScore: 1000, maxDurationMilliseconds: 1, simulatedDurationMilliseconds: 5.2);
        var request = new PolicyCompileRequest(new PolicyDslPayload("stella-dsl@1", SimplePolicy));

        var result = service.Compile(request);

        Assert.False(result.Success);
        Assert.NotNull(result.Complexity);
        Assert.Equal(6, result.DurationMilliseconds);
        var diagnostic = Assert.Single(result.Diagnostics);
        Assert.Equal(PolicyEngineDiagnosticCodes.CompilationComplexityExceeded, diagnostic.Code);
    }

    private static PolicyCompilationService CreateService(double maxComplexityScore, int maxDurationMilliseconds, double simulatedDurationMilliseconds)
    {
        var compiler = new PolicyCompiler();
        var analyzer = new PolicyComplexityAnalyzer();
        var options = new PolicyEngineOptions();
        options.Compilation.MaxComplexityScore = maxComplexityScore;
        options.Compilation.MaxDurationMilliseconds = maxDurationMilliseconds;
        var optionsMonitor = new StaticOptionsMonitor<PolicyEngineOptions>(options);
        var timeProvider = new FakeTimeProvider(simulatedDurationMilliseconds);
        return new PolicyCompilationService(compiler, analyzer, optionsMonitor, timeProvider);
    }

    private sealed class StaticOptionsMonitor<T> : IOptionsMonitor<T>
        where T : class
    {
        public StaticOptionsMonitor(T value)
        {
            CurrentValue = value ?? throw new ArgumentNullException(nameof(value));
        }

        public T CurrentValue { get; }

        public T Get(string? name) => CurrentValue;

        public IDisposable OnChange(Action<T, string> listener) => Disposable.Instance;

        private sealed class Disposable : IDisposable
        {
            public static readonly Disposable Instance = new();
            public void Dispose()
            {
            }
        }
    }

    private sealed class FakeTimeProvider : TimeProvider
    {
        private readonly long elapsedCounts;
        private readonly long frequency = 1_000_000;
        private bool firstCall = true;

        public FakeTimeProvider(double milliseconds)
        {
            elapsedCounts = (long)Math.Round(milliseconds * frequency / 1000d);
        }

        public override long GetTimestamp()
        {
            if (firstCall)
            {
                firstCall = false;
                return 0;
            }

            return elapsedCounts;
        }

        public override long TimestampFrequency => frequency;
    }
}