Termina

Termina is a reactive terminal UI (TUI) framework for .NET with declarative layouts and surgical region-based rendering. It provides an MVVM architecture with reactive properties, ASP.NET Core-style routing, and seamless integration with Microsoft.Extensions.Hosting.

Documentation

Full Documentation

• Getting Started Guide
• Tutorials
• Component Reference
• Architecture

Features

• Reactive MVVM Architecture - ViewModels with ReactiveProperty<T> for observable state management
• Declarative Layouts - Tree-based layout system with size constraints (Fixed, Fill, Auto, Percent)
• Surgical Rendering - Only changed regions re-render, enabling smooth streaming updates
• ASP.NET Core-Style Routing - Route templates with parameters (/tasks/{id:int}) and type constraints
• Source Generators - AOT-compatible code generation for route parameters
• Streaming Support - Native StreamingTextNode for real-time content like LLM output
• Dependency Injection - Full integration with Microsoft.Extensions.DependencyInjection
• Hosting Integration - Works with Microsoft.Extensions.Hosting for clean lifecycle management

Installation

dotnet add package Termina
dotnet add package Microsoft.Extensions.Hosting

Upgrading to 0.7.0? This release migrates from System.Reactive to R3 with breaking API changes. See the Migration Guide for details.

Quick Start

1. Define a ViewModel

using R3;
using Termina.Input;
using Termina.Reactive;

public class CounterViewModel : ReactiveViewModel
{
    public ReactiveProperty<int> Count { get; } = new(0);
    public ReactiveProperty<string> Message { get; } = new("Press Up/Down to change count");

    public override void OnActivated()
    {
        Input.OfType<IInputEvent, KeyPressed>()
            .Subscribe(HandleKey)
            .DisposeWith(Subscriptions);
    }

    private void HandleKey(KeyPressed key)
    {
        switch (key.KeyInfo.Key)
        {
            case ConsoleKey.UpArrow:
                Count.Value++;
                Message.Value = $"Count: {Count.Value}";
                break;
            case ConsoleKey.DownArrow:
                Count.Value--;
                Message.Value = $"Count: {Count.Value}";
                break;
            case ConsoleKey.Escape:
                Shutdown();
                break;
        }
    }

    public override void Dispose()
    {
        Count.Dispose();
        Message.Dispose();
        base.Dispose();
    }
}

ReactiveProperty<T> is both a value holder and an Observable<T> — subscribe directly in your Page for reactive UI bindings.

2. Define a Page

using R3;
using Termina.Extensions;
using Termina.Layout;
using Termina.Reactive;
using Termina.Rendering;
using Termina.Terminal;

public class CounterPage : ReactivePage<CounterViewModel>
{
    public override ILayoutNode BuildLayout()
    {
        return Layouts.Vertical()
            .WithChild(
                new PanelNode()
                    .WithTitle("Counter Demo")
                    .WithBorder(BorderStyle.Rounded)
                    .WithBorderColor(Color.Cyan)
                    .WithContent(
                        ViewModel.Count
                            .Select<int, ILayoutNode>(count => new TextNode($"Count: {count}")
                                .WithForeground(Color.BrightCyan))
                            .AsLayout())
                    .Height(5))
            .WithChild(
                ViewModel.Message
                    .Select<string, ILayoutNode>(msg => new TextNode(msg))
                    .AsLayout()
                    .Height(1));
    }
}

3. Configure and Run

using Microsoft.Extensions.Hosting;
using Termina.Hosting;

var builder = Host.CreateApplicationBuilder(args);

builder.Services.AddTermina("/counter", termina =>
{
    termina.RegisterRoute<CounterPage, CounterViewModel>("/counter");
});

await builder.Build().RunAsync();

Layout System

Termina uses a declarative tree-based layout system:

Layouts.Vertical()
    .WithChild(header.Height(3))           // Fixed height
    .WithChild(content.Fill())             // Take remaining space
    .WithChild(sidebar.Width(20))          // Fixed width
    .WithChild(footer.Height(1));          // Fixed height

Layouts.Horizontal()
    .WithChild(menu.Width(30))
    .WithChild(main.Fill(2))               // 2x weight
    .WithChild(aside.Fill(1));             // 1x weight

Routing

ASP.NET Core-style route templates with parameter support:

builder.Services.AddTermina("/", termina =>
{
    termina.RegisterRoute<HomePage, HomeViewModel>("/");
    termina.RegisterRoute<TasksPage, TasksViewModel>("/tasks");
    termina.RegisterRoute<TaskDetailPage, TaskDetailViewModel>("/tasks/{id:int}");
    termina.RegisterRoute<UserPage, UserViewModel>("/users/{name}");
});

Route Parameter Injection

public partial class TaskDetailViewModel : ReactiveViewModel
{
    [FromRoute] private int _id;  // Injected from route

    public override void OnActivated()
    {
        LoadTask(Id);  // Id is already populated
    }
}

Navigation

Navigate("/tasks/42");
NavigateWithParams("/tasks/{id}", new { id = 42 });
Shutdown();  // Exit the application

Streaming Content

For real-time content like LLM output, Pages own StreamingTextNode and subscribe to ViewModel observables:

// In Page
private StreamingTextNode _output = null!;

protected override void OnBound()
{
    _output = StreamingTextNode.Create();
    ViewModel.StreamOutput.Subscribe(chunk => _output.Append(chunk));
}

// In ViewModel
public Observable<string> StreamOutput => _streamOutput;
private readonly Subject<string> _streamOutput = new();

private async Task StreamResponse()
{
    await foreach (var chunk in GetStreamingData())
    {
        _streamOutput.OnNext(chunk);  // Character-level updates
    }
}

Testing

VirtualInputSource enables automated testing:

var scriptedInput = new VirtualInputSource();
builder.Services.AddTerminaVirtualInput(scriptedInput);

scriptedInput.EnqueueKey(ConsoleKey.UpArrow);
scriptedInput.EnqueueString("Hello World");
scriptedInput.EnqueueKey(ConsoleKey.Enter);
scriptedInput.Complete();

await host.RunAsync();

Requirements

• .NET 10.0 or later
• AOT-compatible (Native AOT publishing supported)

License

Apache 2.0 - See LICENSE for details.

Contributing

Contributions are welcome! See CONTRIBUTING.md for development setup and guidelines.