// <copyright file="RuntimeAgentBaseTests.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under the BUSL-1.1.
// </copyright>

using FluentAssertions;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Time.Testing;
using Xunit;

namespace StellaOps.Signals.RuntimeAgent.Tests;

/// <summary>
/// Tests for <see cref="RuntimeAgentBase"/>.
/// </summary>
[Trait("Category", "Unit")]
public class RuntimeAgentBaseTests
{
    private readonly FakeTimeProvider _timeProvider = new();
    private readonly TestGuidGenerator _guidGenerator = new();

    [Fact]
    public void Constructor_InitializesProperties()
    {
        var agent = CreateAgent();

        agent.AgentId.Should().Be("test-agent");
        agent.Platform.Should().Be(RuntimePlatform.DotNet);
        agent.State.Should().Be(AgentState.Stopped);
        agent.Posture.Should().Be(RuntimePosture.None);
    }

    [Fact]
    public async Task StartAsync_TransitionsToRunning()
    {
        var agent = CreateAgent();
        var options = RuntimeAgentOptions.Development;

        await agent.StartAsync(options, CancellationToken.None);

        agent.State.Should().Be(AgentState.Running);
        agent.Posture.Should().Be(RuntimePosture.ActiveTracing);
    }

    [Fact]
    public async Task StartAsync_WhenAlreadyRunning_Throws()
    {
        var agent = CreateAgent();
        await agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);

        var act = () => agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);

        await act.Should().ThrowAsync<InvalidOperationException>();
    }

    [Fact]
    public async Task StopAsync_TransitionsToStopped()
    {
        var agent = CreateAgent();
        await agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);

        await agent.StopAsync(CancellationToken.None);

        agent.State.Should().Be(AgentState.Stopped);
    }

    [Fact]
    public async Task PauseAsync_TransitionsToPaused()
    {
        var agent = CreateAgent();
        await agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);

        await agent.PauseAsync(CancellationToken.None);

        agent.State.Should().Be(AgentState.Paused);
    }

    [Fact]
    public async Task ResumeAsync_TransitionsBackToRunning()
    {
        var agent = CreateAgent();
        await agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);
        await agent.PauseAsync(CancellationToken.None);

        await agent.ResumeAsync(CancellationToken.None);

        agent.State.Should().Be(AgentState.Running);
    }

    [Fact]
    public async Task SetPostureAsync_ChangesPosture()
    {
        var agent = CreateAgent();
        await agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);

        await agent.SetPostureAsync(RuntimePosture.Sampled, CancellationToken.None);

        agent.Posture.Should().Be(RuntimePosture.Sampled);
    }

    [Fact]
    public async Task GetStatistics_ReturnsStatistics()
    {
        var agent = CreateAgent();
        await agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);

        var stats = agent.GetStatistics();

        stats.AgentId.Should().Be("test-agent");
        stats.State.Should().Be(AgentState.Running);
        stats.TotalEventsCollected.Should().Be(0);
    }

    [Fact]
    public async Task DisposeAsync_StopsAgent()
    {
        var agent = CreateAgent();
        await agent.StartAsync(RuntimeAgentOptions.Development, CancellationToken.None);

        await agent.DisposeAsync();

        agent.State.Should().Be(AgentState.Stopped);
    }

    private DotNetEventPipeAgent CreateAgent()
    {
        return new DotNetEventPipeAgent(
            "test-agent",
            _timeProvider,
            _guidGenerator,
            NullLogger<DotNetEventPipeAgent>.Instance);
    }

    private sealed class TestGuidGenerator : IGuidGenerator
    {
        private int _counter;

        public Guid NewGuid()
        {
            var bytes = new byte[16];
            BitConverter.GetBytes(++_counter).CopyTo(bytes, 0);
            return new Guid(bytes);
        }
    }
}