using Xunit;
using Moq;
using System.Text.Json;
using System.Threading.Tasks;
using System.Linq;

namespace OpenHarbor.MCP.Core.Tests;

/// <summary>
/// Unit tests for ToolRegistry following TDD approach.
/// Tests dynamic tool registration and retrieval.
/// </summary>
public class ToolRegistryTests
{
    [Fact]
    public void ToolRegistry_ShouldInitializeEmpty()
    {
        // Arrange & Act
        var registry = new ToolRegistry();

        // Assert
        Assert.NotNull(registry);
        Assert.Empty(registry.GetAllTools());
    }

    [Fact]
    public void ToolRegistry_ShouldAddTool()
    {
        // Arrange
        var registry = new ToolRegistry();
        var mockTool = CreateMockTool("test_tool", "A test tool");

        // Act
        registry.AddTool(mockTool.Object);

        // Assert
        Assert.Single(registry.GetAllTools());
    }

    [Fact]
    public void ToolRegistry_ShouldGetToolByName()
    {
        // Arrange
        var registry = new ToolRegistry();
        var mockTool = CreateMockTool("search_codex", "Search CODEX documents");
        registry.AddTool(mockTool.Object);

        // Act
        var retrieved = registry.GetTool("search_codex");

        // Assert
        Assert.NotNull(retrieved);
        Assert.Equal("search_codex", retrieved.Name);
    }

    [Fact]
    public void ToolRegistry_GetTool_WithInvalidName_ReturnsNull()
    {
        // Arrange
        var registry = new ToolRegistry();
        var mockTool = CreateMockTool("existing_tool", "Exists");
        registry.AddTool(mockTool.Object);

        // Act
        var result = registry.GetTool("nonexistent_tool");

        // Assert
        Assert.Null(result);
    }

    [Fact]
    public void ToolRegistry_ShouldAddMultipleTools()
    {
        // Arrange
        var registry = new ToolRegistry();
        var tool1 = CreateMockTool("tool1", "First tool");
        var tool2 = CreateMockTool("tool2", "Second tool");
        var tool3 = CreateMockTool("tool3", "Third tool");

        // Act
        registry.AddTool(tool1.Object);
        registry.AddTool(tool2.Object);
        registry.AddTool(tool3.Object);

        // Assert
        var allTools = registry.GetAllTools();
        Assert.Equal(3, allTools.Count());
    }

    [Fact]
    public void ToolRegistry_ShouldPreventDuplicateToolNames()
    {
        // Arrange
        var registry = new ToolRegistry();
        var tool1 = CreateMockTool("duplicate", "First");
        var tool2 = CreateMockTool("duplicate", "Second");

        registry.AddTool(tool1.Object);

        // Act & Assert
        var exception = Assert.Throws<ArgumentException>(() =>
            registry.AddTool(tool2.Object)
        );
        Assert.Contains("already registered", exception.Message);
        Assert.Single(registry.GetAllTools());
    }

    [Fact]
    public void ToolRegistry_ShouldRemoveTool()
    {
        // Arrange
        var registry = new ToolRegistry();
        var mockTool = CreateMockTool("temp_tool", "Temporary");
        registry.AddTool(mockTool.Object);

        // Act
        var removed = registry.RemoveTool("temp_tool");

        // Assert
        Assert.True(removed);
        Assert.Empty(registry.GetAllTools());
        Assert.Null(registry.GetTool("temp_tool"));
    }

    [Fact]
    public void ToolRegistry_RemoveTool_WithInvalidName_ReturnsFalse()
    {
        // Arrange
        var registry = new ToolRegistry();

        // Act
        var removed = registry.RemoveTool("nonexistent");

        // Assert
        Assert.False(removed);
    }

    [Fact]
    public void ToolRegistry_ShouldListAllToolNames()
    {
        // Arrange
        var registry = new ToolRegistry();
        registry.AddTool(CreateMockTool("tool_a", "A").Object);
        registry.AddTool(CreateMockTool("tool_b", "B").Object);
        registry.AddTool(CreateMockTool("tool_c", "C").Object);

        // Act
        var names = registry.GetToolNames();

        // Assert
        Assert.Equal(3, names.Count());
        Assert.Contains("tool_a", names);
        Assert.Contains("tool_b", names);
        Assert.Contains("tool_c", names);
    }

    [Fact]
    public void ToolRegistry_ShouldHaveTool()
    {
        // Arrange
        var registry = new ToolRegistry();
        registry.AddTool(CreateMockTool("exists", "Tool").Object);

        // Act & Assert
        Assert.True(registry.HasTool("exists"));
        Assert.False(registry.HasTool("not_exists"));
    }

    [Fact]
    public void ToolRegistry_ShouldClearAllTools()
    {
        // Arrange
        var registry = new ToolRegistry();
        registry.AddTool(CreateMockTool("tool1", "1").Object);
        registry.AddTool(CreateMockTool("tool2", "2").Object);

        // Act
        registry.Clear();

        // Assert
        Assert.Empty(registry.GetAllTools());
        Assert.Empty(registry.GetToolNames());
    }

    [Fact]
    public void ToolRegistry_GetAllTools_ShouldReturnReadOnlyCollection()
    {
        // Arrange
        var registry = new ToolRegistry();
        registry.AddTool(CreateMockTool("tool", "Tool").Object);

        // Act
        var tools = registry.GetAllTools();

        // Assert
        Assert.NotNull(tools);
        // Ensure modifying returned collection doesn't affect registry
        Assert.IsAssignableFrom<System.Collections.Generic.IEnumerable<IMcpTool>>(tools);
    }

    // Helper method to create mock tools
    private Mock<IMcpTool> CreateMockTool(string name, string description)
    {
        var mockTool = new Mock<IMcpTool>();
        mockTool.Setup(t => t.Name).Returns(name);
        mockTool.Setup(t => t.Description).Returns(description);
        mockTool.Setup(t => t.Schema).Returns(JsonDocument.Parse("""{"type": "object"}"""));
        mockTool.Setup(t => t.ExecuteAsync(It.IsAny<JsonDocument>()))
                .ReturnsAsync(JsonDocument.Parse("""{"status": "ok"}"""));
        return mockTool;
    }
}