YASM (Yet Another State Machine)

A modern, efficient deterministic finite state machine library for Rust 2024 edition.

✨ Key Features

• ⚡ Deterministic: One state + input = one next state (guaranteed)
• 🔒 Type Safe: Compile-time prevention of invalid transitions
• 🚀 Callback System: React to state changes with flexible event hooks
• 🔧 Macro-Driven: Clean declarative syntax for state machine definition
• 📊 Visualization: Auto-generate Mermaid diagrams and documentation
• 🔍 Analysis Tools: Pathfinding, reachability, and connectivity analysis
• 📈 Memory Efficient: Ring buffer with configurable history (default: 512)
• 📦 Optional Serde: Serialization support with serde feature

📦 Installation

[dependencies]
yasm = "0.4.1"

# With serialization support
yasm = { version = "0.4.1", features = ["serde"] }

🚀 Quick Start

Define a State Machine

use yasm::*;

define_state_machine! {
    name: DoorStateMachine,
    states: { Closed, Open, Locked },
    inputs: { OpenDoor, CloseDoor, Lock, Unlock },
    initial: Closed,
    transitions: {
        Closed + OpenDoor => Open,
        Open + CloseDoor => Closed,
        Closed + Lock => Locked,
        Locked + Unlock => Closed
    }
}

Basic Usage

fn main() {
    let mut door = StateMachineInstance::<DoorStateMachine>::new();
    
    println!("Current: {:?}", door.current_state()); // Closed
    
    door.transition(Input::OpenDoor).unwrap();
    println!("After opening: {:?}", door.current_state()); // Open
    
    // Check what's possible next
    println!("Valid inputs: {:?}", door.valid_inputs()); // [CloseDoor]
}

🔥 Core Features

1. Callback System

React to state machine events with flexible callback hooks:

let mut door = StateMachineInstance::<DoorStateMachine>::new();

// React to specific state entries
door.on_state_entry(State::Open, |state| {
    println!("Door opened! Turning on lights...");
});

// React to specific transitions
door.on_transition(State::Closed, Input::Lock, |from, input, to| {
    println!("Security system activated: {from:?} --{input:?}--> {to:?}");
});

// Global monitoring
door.on_any_transition(|from, input, to| {
    println!("State change: {from:?} → {to:?}");
});

// Now all transitions will trigger callbacks
door.transition(Input::OpenDoor).unwrap(); // Triggers callbacks

2. Query & Analysis

Analyze your state machine structure:

// Find reachable states
let reachable = StateMachineQuery::<DoorStateMachine>::reachable_states(&State::Closed);
println!("From Closed, can reach: {reachable:?}");

// Check connectivity
let has_path = StateMachineQuery::<DoorStateMachine>::has_path(
    &State::Open, 
    &State::Locked
);
println!("Open can reach Locked: {has_path}");

// Find shortest path
if let Some(path) = StateMachineQuery::<DoorStateMachine>::shortest_path(
    &State::Open, 
    &State::Locked
) {
    println!("Shortest path: {path:?}");
}

3. Documentation Generation

Generate visual documentation automatically:

// Mermaid state diagram
let diagram = StateMachineDoc::<DoorStateMachine>::generate_mermaid();
println!("{diagram}");

// Transition table
let table = StateMachineDoc::<DoorStateMachine>::generate_transition_table();
println!("{table}");

4. History Management

Track transitions with efficient ring buffer:

// Custom history size
let mut door = StateMachineInstance::<DoorStateMachine>::with_max_history(100);

// Make some transitions
door.transition(Input::OpenDoor).unwrap();
door.transition(Input::CloseDoor).unwrap();

// View history
println!("History: {:?}", door.history());
println!("History length: {}", door.history_len());

🛠️ Advanced Features

Hidden Operations

Use underscore-prefixed inputs for internal operations that won't appear in documentation:

define_state_machine! {
    name: ServerStateMachine,
    states: { Active, Maintenance },
    inputs: { Maintain, Restore, _Debug, _AdminReset }, // Hidden inputs
    initial: Active,
    transitions: {
        Active + Maintain => Maintenance,
        Maintenance + Restore => Active,
        // Hidden transitions (functional but not documented)
        Active + _Debug => Active,
        Maintenance + _AdminReset => Active
    }
}

Multiple Callback Types

The callback system supports various event types:

let mut workflow = StateMachineInstance::<WorkflowStateMachine>::new();

// State-specific callbacks
workflow.on_state_entry(State::Review, |state| { /* ... */ });
workflow.on_state_exit(State::Draft, |state| { /* ... */ });

// Transition-specific callbacks  
workflow.on_transition(State::Draft, Input::Submit, |from, input, to| { /* ... */ });

// Global callbacks
workflow.on_any_state_entry(|state| { /* ... */ });
workflow.on_any_state_exit(|state| { /* ... */ });
workflow.on_any_transition(|from, input, to| { /* ... */ });

// Callback management
println!("Total callbacks: {}", workflow.callback_count());
workflow.clear_callbacks();

Feature Flags

Serde Support

Enable with the serde feature for serialization:

[dependencies]
yasm = { version = "0.4.1", features = ["serde"] }

#[cfg(feature = "serde")]
{
    let state = State::Open;
    let json = serde_json::to_string(&state).unwrap();
    let restored: State = serde_json::from_str(&json).unwrap();
}

📚 Examples

Run comprehensive examples:

# Basic usage patterns
cargo run --example basic_demo

# Advanced features and analysis
cargo run --example advanced_usage

# Callback system demonstration  
cargo run --example callback_demo

# Simple callback examples
cargo run --example simple_callback_demo

# Documentation generation
cargo run --example generate_docs

🏗️ Architecture

src/
├── lib.rs          # Public API and comprehensive tests
├── core.rs         # StateMachine trait definition
├── instance.rs     # StateMachineInstance with history & callbacks
├── callbacks.rs    # Callback registry and event system
├── query.rs        # Analysis algorithms (paths, reachability)
├── doc.rs          # Documentation generation utilities
└── macros.rs       # define_state_machine! macro implementation

🔧 API Overview

Core Types

• StateMachine - Core trait defining state machine behavior
• StateMachineInstance<SM> - Runtime instance with state and history
• CallbackRegistry<SM> - Event callback management system
• StateMachineQuery<SM> - Analysis and pathfinding utilities
• StateMachineDoc<SM> - Documentation generation tools

Key Methods

// Instance management
let mut sm = StateMachineInstance::<MyStateMachine>::new();
let mut sm = StateMachineInstance::<MyStateMachine>::with_max_history(256);

// State operations
sm.transition(input)?;           // Execute transition
sm.current_state();              // Get current state
sm.valid_inputs();               // Get valid inputs
sm.can_accept(&input);           // Check if input is valid

// Callback registration  
sm.on_state_entry(state, callback);
sm.on_transition(from, input, callback);
sm.on_any_transition(callback);

// History access
sm.history();                    // Get transition history
sm.history_len();                // History length
sm.reset();                      // Reset to initial state

// Analysis
StateMachineQuery::<SM>::reachable_states(&from);
StateMachineQuery::<SM>::shortest_path(&from, &to);
StateMachineQuery::<SM>::has_path(&from, &to);

// Documentation
StateMachineDoc::<SM>::generate_mermaid();
StateMachineDoc::<SM>::generate_transition_table();

🧪 Testing

# Run all tests
cargo test

# Test with features
cargo test --features serde

# Test specific functionality
cargo test callbacks

📄 License

MIT License. See LICENSE for details.

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