Milktea

A Terminal User Interface (TUI) framework for Ruby, inspired by Bubble Tea from Go. Milktea brings the power of the Elm Architecture to Ruby, enabling you to build rich, interactive command-line applications with composable components and reactive state management.

Features

🏗️ Elm Architecture: Immutable state management with predictable message flow
📦 Container Layouts: Flexbox-style layouts for terminal interfaces
🔄 Hot Reloading: Instant feedback during development (similar to web frameworks)
📱 Responsive Design: Automatic adaptation to terminal resize events
🧩 Composable Components: Build complex UIs from simple, reusable models
🎨 Rich Terminal Support: Leverage TTY gems for advanced terminal features

Installation

Add Milktea to your application's Gemfile:

gem 'milktea'

Or install directly:

gem install milktea

For development versions:

gem 'milktea', git: 'https://github.com/elct9620/milktea'

Quick Start

Here's a simple "Hello World" application:

require 'milktea'

class HelloModel < Milktea::Model
  def view
    "Hello, #{state[:name]}! Count: #{state[:count]}"
  end

  def update(message)
    case message
    when Milktea::Message::KeyPress
      case message.value
      when "+"
        [with(count: state[:count] + 1), Milktea::Message::None.new]
      when "q"
        [self, Milktea::Message::Exit.new]
      else
        [self, Milktea::Message::None.new]
      end
    else
      [self, Milktea::Message::None.new]
    end
  end

  private

  def default_state
    { name: "World", count: 0 }
  end
end

# Simple approach using Application class
class MyApp < Milktea::Application
  root "HelloModel"
end

MyApp.boot

Core Concepts

Models & Elm Architecture

Milktea follows the Elm Architecture pattern with three core concepts:

Model: Immutable state container
View: Pure function that renders state to string
Update: Handles messages and returns new state + side effects

class CounterModel < Milktea::Model
  def view
    "Count: #{state[:count]} (Press +/- to change, q to quit)"
  end

  def update(message)
    case message
    when Milktea::Message::KeyPress
      handle_keypress(message)
    when Milktea::Message::Resize
      # Rebuild model with fresh class for new screen dimensions
      [with, Milktea::Message::None.new]
    else
      [self, Milktea::Message::None.new]
    end
  end

  private

  def default_state
    { count: 0 }
  end

  def handle_keypress(message)
    case message.value
    when "+"
      [with(count: state[:count] + 1), Milktea::Message::None.new]
    when "-"
      [with(count: state[:count] - 1), Milktea::Message::None.new]
    when "q"
      [self, Milktea::Message::Exit.new]
    else
      [self, Milktea::Message::None.new]
    end
  end
end

Container Layout System

Milktea provides a flexbox-inspired layout system for building complex terminal interfaces:

class AppLayout < Milktea::Container
  direction :column
  child HeaderModel, flex: 1
  child ContentModel, flex: 3  
  child FooterModel, flex: 1
end

class SidebarLayout < Milktea::Container
  direction :row
  child SidebarModel, flex: 1
  child MainContentModel, flex: 3
end

Key Container Features:

Direction: :row or :column (default: :column)
Flex Properties: Control size ratios between children
State Mapping: Pass specific state portions to children
Bounds Calculation: Automatic layout calculation and propagation

class AdvancedContainer < Milktea::Container
  direction :row
  
  # Pass specific state to children with state mappers
  child SidebarModel, ->(state) { { items: state[:sidebar_items] } }, flex: 1
  child ContentModel, ->(state) { state.slice(:title, :content) }, flex: 2
  child InfoModel, flex: 1
end

Hot Reloading (Development Feature)

Milktea supports hot reloading for rapid development iteration:

# Configure hot reloading
Milktea.configure do |config|
  config.autoload_dirs = ["app/models", "lib/components"]
  config.hot_reloading = true
end

class DevelopmentModel < Milktea::Model
  def update(message)
    case message
    when Milktea::Message::Reload
      # Hot reload detected - rebuild with fresh class
      [with, Milktea::Message::None.new]
    # ... other message handling
    end
  end
end

When files change, Milktea automatically detects the changes and sends Message::Reload events. Simply handle this message by rebuilding your model with [with, Milktea::Message::None.new] to pick up the latest code changes.

Terminal Resize Handling

Milktea automatically detects terminal resize events and provides a simple pattern for responsive layouts:

class ResponsiveApp < Milktea::Container
  direction :column
  child HeaderModel, flex: 1
  child DynamicContentModel, flex: 4

  def update(message)
    case message
    when Milktea::Message::Resize
      # Only root model needs resize handling
      # All children automatically recalculate bounds
      [with, Milktea::Message::None.new]
    when Milktea::Message::KeyPress
      handle_keypress(message)
    else
      [self, Milktea::Message::None.new]
    end
  end
end

Resize Handling Key Points:

Root-Level Only: Only the root model needs to handle Message::Resize
Automatic Cascading: Child components automatically adapt to new dimensions
Bounds Recalculation: Container layouts automatically recalculate flex distributions
Screen Methods: Use screen_width, screen_height, screen_size for responsive logic

Examples

Explore the examples/ directory for comprehensive demonstrations:

Container Layout: Flexbox-style layouts with resize support
Hot Reload Demo: Development workflow with instant updates

Run examples:

ruby examples/container_layout.rb
ruby examples/hot_reload_demo.rb

Advanced Features

Dynamic Child Resolution

Use symbols to dynamically resolve child components:

class DynamicContainer < Milktea::Container
  direction :column
  child :header_component, flex: 1  # Calls header_component method
  child ContentModel, flex: 3       # Direct class reference

  private

  def header_component
    state[:show_advanced] ? AdvancedHeader : SimpleHeader
  end
end

Custom Message Handling

Create custom messages for complex interactions:

# Define custom message
CustomAction = Data.define(:action_type, :payload)

class CustomModel < Milktea::Model
  def update(message)
    case message
    when CustomAction
      handle_custom_action(message)
    # ... standard message handling
    end
  end

  private

  def handle_custom_action(message)
    case message.action_type
    when :save
      # Handle save action
      [with(saved: true), Milktea::Message::None.new]
    when :load
      # Handle load action
      [with(data: message.payload), Milktea::Message::None.new]
    end
  end
end

Application vs Manual Setup

Choose between high-level Application class or manual setup:

# High-level Application approach (recommended)
class MyApp < Milktea::Application
  root "MainModel"
end

MyApp.boot

# Manual setup (advanced)
config = Milktea.configure do |c|
  c.autoload_dirs = ["app/models"]
  c.hot_reloading = true
end

loader = Milktea::Loader.new(config)
loader.hot_reload if config.hot_reloading?

model = MainModel.new
program = Milktea::Program.new(model, config: config)
program.run

API Reference

Core Classes

Milktea::Model: Base class for all UI components
Milktea::Container: Layout container with flexbox-style properties
Milktea::Application: High-level application wrapper
Milktea::Program: Main application runtime
Milktea::Message: Standard message types (KeyPress, Exit, Resize, Reload)

Message System

Message::KeyPress: Keyboard input events
Message::Exit: Application termination
Message::Resize: Terminal size changes
Message::Reload: Hot reload events
Message::None: No-operation message

For detailed API documentation, see the documentation website.

Development

After checking out the repo:

bin/setup                    # Install dependencies
bundle exec rake spec        # Run tests
bundle exec rake rubocop     # Check code style
bundle exec rake             # Run all checks
bin/console                  # Interactive prompt

Testing

Milktea uses RSpec for testing. Run specific tests:

bundle exec rspec spec/milktea/model_spec.rb
bundle exec rspec spec/milktea/container_spec.rb:42  # Specific line

Code Quality

The project uses RuboCop for code formatting:

bundle exec rake rubocop:autocorrect  # Fix auto-correctable issues

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/elct9620/milktea.

Fork the repository
Create your feature branch (git checkout -b feature/my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin feature/my-new-feature)
Create a Pull Request

License

The gem is available as open source under the terms of the MIT License.

Acknowledgments

Inspired by Bubble Tea - Go TUI framework
Built on the TTY toolkit ecosystem
Follows Elm Architecture principles

milktea

Runtime