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 source-generated 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 [Reactive] attribute for source-generated observable properties
• 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 reactive properties and 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

Quick Start

1. Define a ViewModel

using System.Reactive.Linq;
using Termina.Input;
using Termina.Reactive;

public partial class CounterViewModel : ReactiveViewModel
{
    [Reactive] private int _count;
    [Reactive] private string _message = "Press Up/Down to change count";

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

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

The [Reactive] attribute generates:

• A BehaviorSubject<T> backing field
• A public property Count with get/set
• An IObservable<T> property CountChanged for subscriptions

2. Define a Page

using System.Reactive.Linq;
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.CountChanged
                            .Select(count => new TextNode($"Count: {count}")
                                .WithForeground(Color.BrightCyan))
                            .AsLayout())
                    .Height(5))
            .WithChild(
                ViewModel.MessageChanged
                    .Select(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 IObservable<string> StreamOutput => _streamOutput.AsObservable();
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.