Implement state machine patterns in C#/.NET

[Copilot]

Implements three state machine patterns with examples and comprehensive test coverage.

Patterns Implemented

State Pattern (Gang of Four)

• IState<TContext> interface with OnEnter/OnExit/Execute lifecycle
• StateContext<TContext> base class handling state transitions
• Example: Document workflow (Draft → Moderation → Approved → Published)

State Machine with Explicit Transitions

• StateMachine<TState, TTrigger> with configurable allowed transitions
• Entry/Exit actions and transition events
• Validation via CanFire() before state changes
• Example: Traffic light with timed transitions

Hierarchical State Machine

• HierarchicalState supporting nested states
• Event bubbling from child to parent
• Full state path tracking
• Example: Vending machine with sub-states

Usage

// State Machine with Transitions
var sm = new StateMachine<LightState, Trigger>(LightState.Red);

sm.Configure(LightState.Red)
    .Permit(Trigger.TimerExpired, LightState.Green)
    .OnEntry(() => Console.WriteLine("Stop!"));

sm.Fire(Trigger.TimerExpired);  // Red → Green

// State Pattern
var document = new Document("Proposal");
document.Submit();   // Draft → Moderation
document.Approve();  // Moderation → Approved
document.Publish();  // Approved → Published

Structure

StateMachinePatterns.Core/      - Pattern implementations
StateMachinePatterns.Examples/  - Working examples
StateMachinePatterns.Tests/     - 18 unit tests

Type-safe enums, separation of concerns, full test coverage.

Original prompt

State machine patterns by C#/.Net

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