using System.IO;
using System.Linq;
using System.Net.Sockets;
using System.Text.Json;
using Grpc.Core;
using Grpc.Net.Client;
using Microsoft.Extensions.Logging;
using StellaOps.Zastava.Observer.Configuration;
using StellaOps.Zastava.Observer.Cri;

namespace StellaOps.Zastava.Observer.ContainerRuntime.Cri;

internal interface ICriRuntimeClient : IAsyncDisposable
{
    ContainerRuntimeEndpointOptions Endpoint { get; }
    Task<CriRuntimeIdentity> GetIdentityAsync(CancellationToken cancellationToken);
    Task<IReadOnlyList<CriContainerInfo>> ListContainersAsync(ContainerState state, CancellationToken cancellationToken);
    Task<CriContainerInfo?> GetContainerStatusAsync(string containerId, CancellationToken cancellationToken);
}

internal sealed class CriRuntimeClient : ICriRuntimeClient
{
    private static readonly object SwitchLock = new();
    private static bool http2SwitchApplied;

    private readonly GrpcChannel channel;
    private readonly RuntimeService.RuntimeServiceClient client;
    private readonly ILogger<CriRuntimeClient> logger;

    public CriRuntimeClient(ContainerRuntimeEndpointOptions endpoint, ILogger<CriRuntimeClient> logger)
    {
        ArgumentNullException.ThrowIfNull(endpoint);
        this.logger = logger ?? throw new ArgumentNullException(nameof(logger));
        Endpoint = endpoint;

        EnsureHttp2Switch();
        channel = CreateChannel(endpoint);
        client = new RuntimeService.RuntimeServiceClient(channel);
    }

    public ContainerRuntimeEndpointOptions Endpoint { get; }

    public async Task<CriRuntimeIdentity> GetIdentityAsync(CancellationToken cancellationToken)
    {
        var response = await client.VersionAsync(new VersionRequest(), cancellationToken: cancellationToken).ConfigureAwait(false);
        return new CriRuntimeIdentity(
            RuntimeName: response.RuntimeName ?? Endpoint.Engine.ToEngineString(),
            RuntimeVersion: response.RuntimeVersion ?? "unknown",
            RuntimeApiVersion: response.RuntimeApiVersion ?? response.Version ?? "unknown");
    }

    public async Task<IReadOnlyList<CriContainerInfo>> ListContainersAsync(ContainerState state, CancellationToken cancellationToken)
    {
        var request = new ListContainersRequest
        {
            Filter = new ContainerFilter
            {
                State = new ContainerStateValue
                {
                    State = state
                }
            }
        };

        try
        {
            var response = await client.ListContainersAsync(request, cancellationToken: cancellationToken).ConfigureAwait(false);
            if (response.Containers is null || response.Containers.Count == 0)
            {
                return Array.Empty<CriContainerInfo>();
            }

            return response.Containers
                .Select(CriConversions.ToContainerInfo)
                .ToArray();
        }
        catch (RpcException ex) when (ex.StatusCode == StatusCode.Unimplemented)
        {
            logger.LogWarning(ex, "Runtime endpoint {Endpoint} does not support ListContainers for state {State}.", Endpoint.Endpoint, state);
            throw;
        }
    }

    public async Task<CriContainerInfo?> GetContainerStatusAsync(string containerId, CancellationToken cancellationToken)
    {
        if (string.IsNullOrWhiteSpace(containerId))
        {
            return null;
        }

        try
        {
            var response = await client.ContainerStatusAsync(new ContainerStatusRequest
            {
                ContainerId = containerId,
                Verbose = true
            }, cancellationToken: cancellationToken).ConfigureAwait(false);

            if (response.Status is null)
            {
                return null;
            }

            var baseline = CriConversions.ToContainerInfo(new Container
            {
                Id = response.Status.Id,
                PodSandboxId = response.Status.Metadata?.Name ?? string.Empty,
                Metadata = response.Status.Metadata,
                Image = response.Status.Image,
                ImageRef = response.Status.ImageRef,
                Labels = { response.Status.Labels },
                Annotations = { response.Status.Annotations },
                CreatedAt = response.Status.CreatedAt
            });

            var merged = CriConversions.MergeStatus(baseline, response.Status);

            if (response.Info is { Count: > 0 } && TryExtractPid(response.Info, out var pid))
            {
                merged = merged with { Pid = pid };
            }

            return merged;
        }
        catch (RpcException ex) when (ex.StatusCode is StatusCode.NotFound or StatusCode.DeadlineExceeded)
        {
            logger.LogDebug(ex, "Container {ContainerId} no longer available when querying status.", containerId);
            return null;
        }
    }

    private static bool TryExtractPid(IDictionary<string, string> info, out int pid)
    {
        if (info.TryGetValue("pid", out var value) && int.TryParse(value, out pid))
        {
            return true;
        }

        foreach (var entry in info.Values)
        {
            if (string.IsNullOrWhiteSpace(entry))
            {
                continue;
            }

            try
            {
                using var document = JsonDocument.Parse(entry);
                if (document.RootElement.TryGetProperty("pid", out var pidElement) && pidElement.TryGetInt32(out pid))
                {
                    return true;
                }
            }
            catch (JsonException)
            {
            }
        }

        pid = default;
        return false;
    }

    public ValueTask DisposeAsync()
    {
        try
        {
            channel.Dispose();
        }
        catch (InvalidOperationException)
        {
            // Channel already disposed.
        }

        return ValueTask.CompletedTask;
    }

    private static void EnsureHttp2Switch()
    {
        if (http2SwitchApplied)
        {
            return;
        }

        lock (SwitchLock)
        {
            if (!http2SwitchApplied)
            {
                AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport", true);
                http2SwitchApplied = true;
            }
        }
    }

    private GrpcChannel CreateChannel(ContainerRuntimeEndpointOptions endpoint)
    {
        if (IsUnixEndpoint(endpoint.Endpoint, out var unixPath))
        {
            var resolvedPath = unixPath;
            var handler = new SocketsHttpHandler
            {
                ConnectCallback = (context, cancellationToken) => ConnectUnixDomainSocketAsync(resolvedPath, cancellationToken),
                EnableMultipleHttp2Connections = true
            };

            if (endpoint.ConnectTimeout is { } timeout && timeout > TimeSpan.Zero)
            {
                handler.ConnectTimeout = timeout;
            }

            return GrpcChannel.ForAddress("http://unix.local", new GrpcChannelOptions
            {
                HttpHandler = handler,
                DisposeHttpClient = true
            });
        }

        return GrpcChannel.ForAddress(endpoint.Endpoint, new GrpcChannelOptions
        {
            DisposeHttpClient = true
        });
    }

    private static bool IsUnixEndpoint(string endpoint, out string path)
    {
        if (endpoint.StartsWith("unix://", StringComparison.OrdinalIgnoreCase))
        {
            path = endpoint["unix://".Length..];
            return true;
        }

        path = string.Empty;
        return false;
    }

    private static async ValueTask<Stream> ConnectUnixDomainSocketAsync(string unixPath, CancellationToken cancellationToken)
    {
        var socket = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.Unspecified)
        {
            NoDelay = true
        };

        try
        {
            var endpoint = new UnixDomainSocketEndPoint(unixPath);
            await socket.ConnectAsync(endpoint, cancellationToken).ConfigureAwait(false);
            return new NetworkStream(socket, ownsSocket: true);
        }
        catch
        {
            socket.Dispose();
            throw;
        }
    }
}