using FluentAssertions;
using Microsoft.Extensions.Options;
using StellaOps.Router.Common.Enums;
using StellaOps.Router.Common.Models;
using StellaOps.Router.Gateway.Configuration;
using StellaOps.Router.Gateway.Routing;
using Xunit;

namespace StellaOps.Router.Gateway.Tests;

public sealed class DefaultRoutingPluginTests
{
    [Fact]
    public async Task ChooseInstanceAsync_WhenNoCandidates_ReturnsNull()
    {
        var plugin = CreatePlugin(gatewayRegion: "eu1");

        var decision = await plugin.ChooseInstanceAsync(
            new RoutingContext
            {
                Method = "GET",
                Path = "/items",
                Headers = new Dictionary<string, string>(),
                Endpoint = new EndpointDescriptor
                {
                    ServiceName = "inventory",
                    Version = "1.0.0",
                    Method = "GET",
                    Path = "/items"
                },
                AvailableConnections = [],
                GatewayRegion = "eu1",
                RequestedVersion = null,
                CancellationToken = CancellationToken.None
            },
            CancellationToken.None);

        decision.Should().BeNull();
    }

    [Fact]
    public async Task ChooseInstanceAsync_WhenRequestedVersionDoesNotMatch_ReturnsNull()
    {
        var plugin = CreatePlugin(
            gatewayRegion: "eu1",
            options: new RoutingOptions
            {
                StrictVersionMatching = true,
                DefaultVersion = null
            });

        var candidates = new List<ConnectionState>
        {
            CreateConnection("inv-1", "inventory", "1.0.0", region: "eu1", status: InstanceHealthStatus.Healthy)
        };

        var decision = await plugin.ChooseInstanceAsync(
            CreateContext(
                requestedVersion: "2.0.0",
                candidates: candidates),
            CancellationToken.None);

        decision.Should().BeNull();
    }

    [Fact]
    public async Task ChooseInstanceAsync_PrefersHealthyOverDegraded()
    {
        var plugin = CreatePlugin(
            gatewayRegion: "eu1",
            options: new RoutingOptions
            {
                StrictVersionMatching = true,
                DefaultVersion = null,
                PreferLocalRegion = true,
                AllowDegradedInstances = true,
                TieBreaker = TieBreakerMode.RoundRobin
            });

        var degraded = CreateConnection("inv-degraded", "inventory", "1.0.0", region: "eu1", status: InstanceHealthStatus.Degraded);
        degraded.AveragePingMs = 1;

        var healthy = CreateConnection("inv-healthy", "inventory", "1.0.0", region: "eu1", status: InstanceHealthStatus.Healthy);
        healthy.AveragePingMs = 50;

        var decision = await plugin.ChooseInstanceAsync(
            CreateContext(
                requestedVersion: "1.0.0",
                candidates: [degraded, healthy]),
            CancellationToken.None);

        decision.Should().NotBeNull();
        decision!.Connection.ConnectionId.Should().Be("inv-healthy");
    }

    [Fact]
    public async Task ChooseInstanceAsync_PrefersLocalRegionOverRemote()
    {
        var plugin = CreatePlugin(
            gatewayRegion: "eu1",
            options: new RoutingOptions
            {
                StrictVersionMatching = true,
                DefaultVersion = null,
                PreferLocalRegion = true,
                AllowDegradedInstances = true,
                TieBreaker = TieBreakerMode.RoundRobin
            });

        var remote = CreateConnection("inv-us1", "inventory", "1.0.0", region: "us1", status: InstanceHealthStatus.Healthy);
        var local = CreateConnection("inv-eu1", "inventory", "1.0.0", region: "eu1", status: InstanceHealthStatus.Healthy);

        var decision = await plugin.ChooseInstanceAsync(
            CreateContext(
                requestedVersion: "1.0.0",
                candidates: [remote, local]),
            CancellationToken.None);

        decision.Should().NotBeNull();
        decision!.Connection.ConnectionId.Should().Be("inv-eu1");
    }

    [Fact]
    public async Task ChooseInstanceAsync_WhenNoLocal_UsesNeighborRegion()
    {
        var plugin = CreatePlugin(
            gatewayRegion: "eu1",
            gatewayNeighbors: ["eu2"],
            options: new RoutingOptions
            {
                StrictVersionMatching = true,
                DefaultVersion = null,
                PreferLocalRegion = true,
                AllowDegradedInstances = true,
                TieBreaker = TieBreakerMode.RoundRobin
            });

        var neighbor = CreateConnection("inv-eu2", "inventory", "1.0.0", region: "eu2", status: InstanceHealthStatus.Healthy);
        var remote = CreateConnection("inv-us1", "inventory", "1.0.0", region: "us1", status: InstanceHealthStatus.Healthy);

        var decision = await plugin.ChooseInstanceAsync(
            CreateContext(
                requestedVersion: "1.0.0",
                candidates: [remote, neighbor]),
            CancellationToken.None);

        decision.Should().NotBeNull();
        decision!.Connection.ConnectionId.Should().Be("inv-eu2");
    }

    [Fact]
    public async Task ChooseInstanceAsync_WhenTied_UsesRoundRobin()
    {
        var plugin = CreatePlugin(
            gatewayRegion: "eu1",
            options: new RoutingOptions
            {
                StrictVersionMatching = true,
                DefaultVersion = null,
                PreferLocalRegion = false,
                AllowDegradedInstances = true,
                TieBreaker = TieBreakerMode.RoundRobin,
                PingToleranceMs = 1_000
            });

        var heartbeat = DateTime.UtcNow;

        var a = CreateConnection("inv-a", "inventory", "1.0.0", region: "us1", status: InstanceHealthStatus.Healthy);
        a.AveragePingMs = 10;
        a.LastHeartbeatUtc = heartbeat;

        var b = CreateConnection("inv-b", "inventory", "1.0.0", region: "us1", status: InstanceHealthStatus.Healthy);
        b.AveragePingMs = 10;
        b.LastHeartbeatUtc = heartbeat;

        var ctx = CreateContext(requestedVersion: "1.0.0", candidates: [a, b]);

        var decision1 = await plugin.ChooseInstanceAsync(ctx, CancellationToken.None);
        var decision2 = await plugin.ChooseInstanceAsync(ctx, CancellationToken.None);

        decision1.Should().NotBeNull();
        decision2.Should().NotBeNull();

        decision1!.Connection.ConnectionId.Should().Be("inv-a");
        decision2!.Connection.ConnectionId.Should().Be("inv-b");
    }

    private static DefaultRoutingPlugin CreatePlugin(
        string gatewayRegion,
        RoutingOptions? options = null,
        IReadOnlyList<string>? gatewayNeighbors = null)
    {
        options ??= new RoutingOptions
        {
            StrictVersionMatching = true,
            DefaultVersion = null,
            PreferLocalRegion = true,
            AllowDegradedInstances = true,
            TieBreaker = TieBreakerMode.RoundRobin
        };

        var node = new RouterNodeConfig
        {
            Region = gatewayRegion,
            NeighborRegions = gatewayNeighbors?.ToList() ?? []
        };

        return new DefaultRoutingPlugin(
            Options.Create(options),
            Options.Create(node));
    }

    private static RoutingContext CreateContext(
        string? requestedVersion,
        IReadOnlyList<ConnectionState> candidates)
    {
        return new RoutingContext
        {
            Method = "GET",
            Path = "/items",
            Headers = new Dictionary<string, string>(),
            Endpoint = new EndpointDescriptor
            {
                ServiceName = "inventory",
                Version = "1.0.0",
                Method = "GET",
                Path = "/items"
            },
            AvailableConnections = candidates,
            GatewayRegion = "eu1",
            RequestedVersion = requestedVersion,
            CancellationToken = CancellationToken.None
        };
    }

    private static ConnectionState CreateConnection(
        string connectionId,
        string serviceName,
        string version,
        string region,
        InstanceHealthStatus status)
    {
        return new ConnectionState
        {
            ConnectionId = connectionId,
            Instance = new InstanceDescriptor
            {
                InstanceId = connectionId,
                ServiceName = serviceName,
                Version = version,
                Region = region
            },
            Status = status,
            LastHeartbeatUtc = DateTime.UtcNow,
            TransportType = TransportType.InMemory
        };
    }
}