using System.Text;
using EntKube.Clusters.Domain;
using k8s;
using k8s.Models;
using Microsoft.Extensions.Logging;

namespace EntKube.Clusters.Features.AdoptCluster.Components.Istio;

/// <summary>
/// Checks whether Istio service mesh with Gateway API support is installed.
/// The Terraform bootstrap installs three layers:
/// 1. Gateway API CRDs (standard + experimental)
/// 2. istio-base (Istio CRDs + namespace)
/// 3. istiod (control plane with PILOT_ENABLE_GATEWAY_API=true)
///
/// This check verifies all three layers are present and healthy.
/// </summary>
public class IstioCheck : IAdoptionCheck
{
    private readonly ILogger<IstioCheck> logger;

    public string ComponentName => "istio";
    public string DisplayName => "Istio Service Mesh + Gateway API";

    public IstioCheck(ILogger<IstioCheck> logger)
    {
        this.logger = logger;
    }

    public async Task<ComponentCheckResult> CheckAsync(KubernetesCluster cluster, CancellationToken ct = default)
    {
        Kubernetes client = BuildClient(cluster);
        List<string> details = new();
        List<string> missing = new();

        // Check 1: Gateway API CRDs installed (gateways.gateway.networking.k8s.io)

        bool gatewayApiCrd = await CrdExists(client, "gateways.gateway.networking.k8s.io", ct);

        if (gatewayApiCrd)
        {
            details.Add("Gateway API CRDs present");
        }
        else
        {
            missing.Add("Gateway API CRDs not installed (gateways.gateway.networking.k8s.io)");
        }

        // Check 2: istio-system namespace with istiod pods running

        List<string> istiodPods = await FindIstiodPods(client, ct);

        if (istiodPods.Count > 0)
        {
            details.AddRange(istiodPods.Select(p => $"Pod running: {p}"));
        }
        else
        {
            missing.Add("No istiod pods found in istio-system namespace");
        }

        // Check 3: Istio CRDs (VirtualService or Gateway) — confirms istio-base installed

        bool istioCrd = await CrdExists(client, "virtualservices.networking.istio.io", ct);

        if (istioCrd)
        {
            details.Add("Istio CRDs present (networking.istio.io)");
        }
        else
        {
            missing.Add("Istio base CRDs not installed (networking.istio.io)");
        }

        // Determine status

        if (istiodPods.Count == 0 && !istioCrd)
        {
            return new ComponentCheckResult(ComponentName, ComponentStatus.NotInstalled, details, missing);
        }

        // Discover configuration from running pods

        string? version = await GetIstiodVersion(client, ct);

        DiscoveredConfiguration config = new(
            Version: version,
            Namespace: "istio-system",
            HelmReleaseName: "istiod",
            Values: new Dictionary<string, string>
            {
                ["pilotReplicas"] = istiodPods.Count.ToString(),
                ["gatewayApiEnabled"] = gatewayApiCrd.ToString(),
                ["istioCrdsInstalled"] = istioCrd.ToString()
            });

        if (missing.Count > 0)
        {
            return new ComponentCheckResult(ComponentName, ComponentStatus.Degraded, details, missing, config);
        }

        return new ComponentCheckResult(ComponentName, ComponentStatus.Installed, details, missing, config);
    }

    private async Task<string?> GetIstiodVersion(Kubernetes client, CancellationToken ct)
    {
        try
        {
            V1PodList podList = await client.CoreV1.ListNamespacedPodAsync(
                "istio-system", labelSelector: "app=istiod", cancellationToken: ct);

            foreach (V1Pod pod in podList.Items)
            {
                if (pod.Spec?.Containers?.Count > 0)
                {
                    string? image = pod.Spec.Containers[0].Image;

                    if (image?.Contains(':') == true)
                    {
                        return image.Split(':').Last().TrimStart('v');
                    }
                }
            }
        }
        catch { }

        return null;
    }

    private async Task<List<string>> FindIstiodPods(Kubernetes client, CancellationToken ct)
    {
        List<string> pods = new();

        try
        {
            V1PodList podList = await client.CoreV1.ListNamespacedPodAsync(
                "istio-system",
                labelSelector: "app=istiod",
                cancellationToken: ct);

            foreach (V1Pod pod in podList.Items)
            {
                if (pod.Status?.Phase == "Running")
                {
                    pods.Add(pod.Metadata.Name);
                }
            }
        }
        catch (k8s.Autorest.HttpOperationException ex) when (ex.Response.StatusCode == System.Net.HttpStatusCode.NotFound)
        {
            logger.LogDebug("istio-system namespace not found");
        }
        catch (Exception ex)
        {
            logger.LogWarning(ex, "Error checking for istiod pods");
        }

        return pods;
    }

    private async Task<bool> CrdExists(Kubernetes client, string crdName, CancellationToken ct)
    {
        try
        {
            await client.ApiextensionsV1.ReadCustomResourceDefinitionAsync(crdName, cancellationToken: ct);
            return true;
        }
        catch
        {
            return false;
        }
    }

    private static Kubernetes BuildClient(KubernetesCluster cluster)
    {
        byte[] kubeConfigBytes = Encoding.UTF8.GetBytes(cluster.KubeConfig);
        using MemoryStream stream = new(kubeConfigBytes);
        KubernetesClientConfiguration config = KubernetesClientConfiguration.BuildConfigFromConfigFile(stream, cluster.ContextName);
        return new Kubernetes(config);
    }
}