namespace ScadaLink.DataConnectionLayer.Adapters;

/// <summary>
/// WP-7: Abstraction over OPC UA client library for testability.
/// The real implementation would wrap an OPC UA SDK (e.g., OPC Foundation .NET Standard Library).
/// </summary>
public interface IOpcUaClient : IAsyncDisposable
{
    Task ConnectAsync(string endpointUrl, CancellationToken cancellationToken = default);
    Task DisconnectAsync(CancellationToken cancellationToken = default);
    bool IsConnected { get; }

    /// <summary>
    /// Creates a monitored item subscription for a node. Returns a subscription handle.
    /// </summary>
    Task<string> CreateSubscriptionAsync(
        string nodeId,
        Action<string, object?, DateTime, uint> onValueChanged,
        CancellationToken cancellationToken = default);

    Task RemoveSubscriptionAsync(string subscriptionHandle, CancellationToken cancellationToken = default);

    Task<(object? Value, DateTime SourceTimestamp, uint StatusCode)> ReadValueAsync(
        string nodeId, CancellationToken cancellationToken = default);

    Task<uint> WriteValueAsync(string nodeId, object? value, CancellationToken cancellationToken = default);
}

/// <summary>
/// Factory for creating IOpcUaClient instances.
/// </summary>
public interface IOpcUaClientFactory
{
    IOpcUaClient Create();
}

/// <summary>
/// Default factory that creates stub OPC UA clients.
/// In production, this would create real OPC UA SDK client instances.
/// </summary>
public class DefaultOpcUaClientFactory : IOpcUaClientFactory
{
    public IOpcUaClient Create() => new StubOpcUaClient();
}

/// <summary>
/// Stub OPC UA client for development/testing. A real implementation would
/// wrap the OPC Foundation .NET Standard Library.
/// </summary>
internal class StubOpcUaClient : IOpcUaClient
{
    public bool IsConnected { get; private set; }

    public Task ConnectAsync(string endpointUrl, CancellationToken cancellationToken = default)
    {
        IsConnected = true;
        return Task.CompletedTask;
    }

    public Task DisconnectAsync(CancellationToken cancellationToken = default)
    {
        IsConnected = false;
        return Task.CompletedTask;
    }

    public Task<string> CreateSubscriptionAsync(
        string nodeId, Action<string, object?, DateTime, uint> onValueChanged,
        CancellationToken cancellationToken = default)
    {
        return Task.FromResult(Guid.NewGuid().ToString());
    }

    public Task RemoveSubscriptionAsync(string subscriptionHandle, CancellationToken cancellationToken = default)
    {
        return Task.CompletedTask;
    }

    public Task<(object? Value, DateTime SourceTimestamp, uint StatusCode)> ReadValueAsync(
        string nodeId, CancellationToken cancellationToken = default)
    {
        return Task.FromResult<(object?, DateTime, uint)>((null, DateTime.UtcNow, 0));
    }

    public Task<uint> WriteValueAsync(string nodeId, object? value, CancellationToken cancellationToken = default)
    {
        return Task.FromResult<uint>(0); // Good status
    }

    public ValueTask DisposeAsync()
    {
        IsConnected = false;
        return ValueTask.CompletedTask;
    }
}