svrnty-mcp-gateway/tests/Svrnty.MCP.Gateway.Infrastructure.Tests/Routing/ClientBasedStrategyTests.cs

using Xunit;
using Svrnty.MCP.Gateway.Infrastructure.Routing;
using Svrnty.MCP.Gateway.Core.Models;

namespace Svrnty.MCP.Gateway.Infrastructure.Tests.Routing;

/// <summary>
/// Unit tests for ClientBasedStrategy following TDD approach.
/// Tests client-based routing.
/// </summary>
public class ClientBasedStrategyTests
{
    [Fact]
    public async Task SelectServerAsync_WithExactClientMatch_ReturnsMatchedServer()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>
        {
            { "web-client", "server-1" },
            { "mobile-client", "server-2" }
        };
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = true },
            new ServerInfo { Id = "server-2", IsHealthy = true }
        };

        var context = new RoutingContext { ClientId = "web-client" };

        // Act
        var selected = await strategy.SelectServerAsync(servers, context);

        // Assert
        Assert.NotNull(selected);
        Assert.Equal("server-1", selected.Id);
    }

    [Fact]
    public async Task SelectServerAsync_WithDifferentClients_RoutesDifferently()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>
        {
            { "client-a", "server-1" },
            { "client-b", "server-2" }
        };
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = true },
            new ServerInfo { Id = "server-2", IsHealthy = true }
        };

        var context1 = new RoutingContext { ClientId = "client-a" };
        var context2 = new RoutingContext { ClientId = "client-b" };

        // Act
        var selected1 = await strategy.SelectServerAsync(servers, context1);
        var selected2 = await strategy.SelectServerAsync(servers, context2);

        // Assert
        Assert.Equal("server-1", selected1!.Id);
        Assert.Equal("server-2", selected2!.Id);
    }

    [Fact]
    public async Task SelectServerAsync_WithNoMatch_FallsBackToRoundRobin()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>
        {
            { "known-client", "server-1" }
        };
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = true },
            new ServerInfo { Id = "server-2", IsHealthy = true }
        };

        var context = new RoutingContext { ClientId = "unknown-client" };

        // Act
        var selected = await strategy.SelectServerAsync(servers, context);

        // Assert - should fall back to round-robin
        Assert.NotNull(selected);
    }

    [Fact]
    public async Task SelectServerAsync_WhenMappedServerUnhealthy_SelectsNextHealthy()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>
        {
            { "web-client", "server-1" }
        };
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = false },
            new ServerInfo { Id = "server-2", IsHealthy = true }
        };

        var context = new RoutingContext { ClientId = "web-client" };

        // Act
        var selected = await strategy.SelectServerAsync(servers, context);

        // Assert - should select next healthy server
        Assert.NotNull(selected);
        Assert.Equal("server-2", selected.Id);
    }

    [Fact]
    public async Task SelectServerAsync_WithNullClientId_FallsBackToRoundRobin()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>
        {
            { "web-client", "server-1" }
        };
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = true },
            new ServerInfo { Id = "server-2", IsHealthy = true }
        };

        var context = new RoutingContext { ClientId = null };

        // Act
        var selected = await strategy.SelectServerAsync(servers, context);

        // Assert
        Assert.NotNull(selected);
    }

    [Fact]
    public async Task SelectServerAsync_WithEmptyMapping_UsesRoundRobin()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>();
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = true },
            new ServerInfo { Id = "server-2", IsHealthy = true }
        };

        var context = new RoutingContext { ClientId = "any-client" };

        // Act
        var selected = await strategy.SelectServerAsync(servers, context);

        // Assert - should use round-robin
        Assert.NotNull(selected);
    }

    [Fact]
    public async Task SelectServerAsync_SameClientMultipleTimes_RoutesSameServer()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>
        {
            { "sticky-client", "server-1" }
        };
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = true },
            new ServerInfo { Id = "server-2", IsHealthy = true }
        };

        var context = new RoutingContext { ClientId = "sticky-client" };

        // Act
        var selected1 = await strategy.SelectServerAsync(servers, context);
        var selected2 = await strategy.SelectServerAsync(servers, context);
        var selected3 = await strategy.SelectServerAsync(servers, context);

        // Assert - should always route to same server (sticky sessions)
        Assert.Equal("server-1", selected1!.Id);
        Assert.Equal("server-1", selected2!.Id);
        Assert.Equal("server-1", selected3!.Id);
    }

    [Fact]
    public async Task SelectServerAsync_WithNoHealthyServers_ReturnsNull()
    {
        // Arrange
        var clientMapping = new Dictionary<string, string>
        {
            { "web-client", "server-1" }
        };
        var strategy = new ClientBasedStrategy(clientMapping);

        var servers = new List<ServerInfo>
        {
            new ServerInfo { Id = "server-1", IsHealthy = false }
        };

        var context = new RoutingContext { ClientId = "web-client" };

        // Act
        var selected = await strategy.SelectServerAsync(servers, context);

        // Assert
        Assert.Null(selected);
    }
}