using System.Linq;
using ChatBot.Models.Configuration;
using ChatBot.Models.Dto;
using ChatBot.Services;
using ChatBot.Services.Interfaces;
using ChatBot.Tests.TestUtilities;
using FluentAssertions;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Moq;
using OllamaSharp.Models.Chat;

namespace ChatBot.Tests.Services;

public class HistoryCompressionServiceTests : UnitTestBase
{
    private readonly Mock<ILogger<HistoryCompressionService>> _loggerMock;
    private readonly Mock<IOllamaClient> _ollamaClientMock;
    private readonly AISettings _aiSettings;
    private readonly HistoryCompressionService _compressionService;

    public HistoryCompressionServiceTests()
    {
        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<HistoryCompressionService>();
        _ollamaClientMock = TestDataBuilder.Mocks.CreateOllamaClientMock();
        _aiSettings = TestDataBuilder.Configurations.CreateAISettings();

        var optionsMock = TestDataBuilder.Mocks.CreateOptionsMock(_aiSettings);

        _compressionService = new HistoryCompressionService(
            _loggerMock.Object,
            optionsMock.Object,
            _ollamaClientMock.Object
        );
    }

    [Fact]
    public void ShouldCompress_ShouldReturnTrue_WhenMessageCountExceedsThreshold()
    {
        // Arrange
        var messageCount = 15;
        var threshold = 10;

        // Act
        var result = _compressionService.ShouldCompress(messageCount, threshold);

        // Assert
        result.Should().BeTrue();
    }

    [Fact]
    public void ShouldCompress_ShouldReturnFalse_WhenMessageCountIsBelowThreshold()
    {
        // Arrange
        var messageCount = 5;
        var threshold = 10;

        // Act
        var result = _compressionService.ShouldCompress(messageCount, threshold);

        // Assert
        result.Should().BeFalse();
    }

    [Fact]
    public void ShouldCompress_ShouldReturnFalse_WhenMessageCountEqualsThreshold()
    {
        // Arrange
        var messageCount = 10;
        var threshold = 10;

        // Act
        var result = _compressionService.ShouldCompress(messageCount, threshold);

        // Assert
        result.Should().BeFalse();
    }

    [Fact]
    public async Task CompressHistoryAsync_ShouldReturnCompressedMessages_WhenSuccessful()
    {
        // Arrange
        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(10);
        var targetCount = 5;
        var expectedResponse = "Compressed summary of previous messages";

        _ollamaClientMock
            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
            .Returns(
                TestDataBuilder.Mocks.CreateAsyncEnumerable(
                    new List<OllamaSharp.Models.Chat.ChatResponseStream>
                    {
                        new OllamaSharp.Models.Chat.ChatResponseStream
                        {
                            Message = new Message(ChatRole.Assistant, expectedResponse),
                        },
                    }
                )
            );

        // Act
        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);

        // Assert
        result.Should().NotBeNull();
        result.Should().HaveCount(7); // 2 compressed messages + 5 recent messages
        result.Should().Contain(m => m.Role == ChatRole.User && m.Content.Contains("[Сжато:"));
        result.Should().Contain(m => m.Role == ChatRole.Assistant && m.Content.Contains("[Сжато:"));
        result.Should().Contain(m => m.Role == ChatRole.User && m.Content == "User message 9");
        result
            .Should()
            .Contain(m => m.Role == ChatRole.Assistant && m.Content == "Assistant response 9");
    }

    [Fact]
    public async Task CompressHistoryAsync_ShouldFallbackToSimpleTrimming_WhenOllamaClientThrows()
    {
        // Arrange
        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(10);
        var targetCount = 5;

        _ollamaClientMock
            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
            .Returns(ThrowAsyncEnumerable(new Exception("Ollama client error")));

        // Act
        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);

        // Assert
        result.Should().NotBeNull();
        result.Should().HaveCount(7); // 2 compressed messages + 5 recent messages (exception is caught and handled)
        result.Should().Contain(m => m.Role == ChatRole.User && m.Content.Contains("[Сжато:"));
        result.Should().Contain(m => m.Role == ChatRole.Assistant && m.Content.Contains("[Сжато:"));
        result.Should().Contain(m => m.Role == ChatRole.User && m.Content == "User message 9");
        result
            .Should()
            .Contain(m => m.Role == ChatRole.Assistant && m.Content == "Assistant response 9");
    }

    [Fact]
    public async Task CompressHistoryAsync_ShouldReturnOriginalMessages_WhenTargetCountIsGreaterThanOrEqual()
    {
        // Arrange
        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(5);
        var targetCount = 10;

        // Act
        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);

        // Assert
        result.Should().BeEquivalentTo(messages);
        _ollamaClientMock.Verify(
            x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()),
            Times.Never
        );
    }

    [Fact]
    public async Task CompressHistoryAsync_ShouldHandleEmptyMessages()
    {
        // Arrange
        var messages = new List<ChatMessage>();
        var targetCount = 5;

        // Act
        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);

        // Assert
        result.Should().BeEmpty();
        _ollamaClientMock.Verify(
            x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()),
            Times.Never
        );
    }

    private static IAsyncEnumerable<OllamaSharp.Models.Chat.ChatResponseStream> ThrowAsyncEnumerable(
        Exception exception
    )
    {
        return new ThrowingAsyncEnumerable(exception);
    }

    private class ThrowingAsyncEnumerable
        : IAsyncEnumerable<OllamaSharp.Models.Chat.ChatResponseStream>
    {
        private readonly Exception _exception;

        public ThrowingAsyncEnumerable(Exception exception)
        {
            _exception = exception;
        }

        public IAsyncEnumerator<OllamaSharp.Models.Chat.ChatResponseStream> GetAsyncEnumerator(
            CancellationToken cancellationToken = default
        )
        {
            return new ThrowingAsyncEnumerator(_exception);
        }
    }

    private class ThrowingAsyncEnumerator
        : IAsyncEnumerator<OllamaSharp.Models.Chat.ChatResponseStream>
    {
        private readonly Exception _exception;

        public ThrowingAsyncEnumerator(Exception exception)
        {
            _exception = exception;
        }

        public OllamaSharp.Models.Chat.ChatResponseStream Current =>
            throw new InvalidOperationException();

        public ValueTask DisposeAsync()
        {
            return ValueTask.CompletedTask;
        }

        public ValueTask<bool> MoveNextAsync()
        {
            throw _exception;
        }
    }
}