#!/usr/bin/env rust-script
//! Simple RED phase verification for Router Z-loss implementation

// Minimal tensor simulation for testing
#[derive(Debug, Clone)]
pub struct Tensor;

#[derive(Debug, Clone)]
pub struct Device;

#[derive(Debug, Clone)]
pub enum DType {
    F32,
}

impl Device {
    pub const CPU: Device = Device;
}

// Minimal error types
#[derive(Debug)]
pub struct TransformerError(String);

impl TransformerError {
    pub fn config(msg: String) -> Self {
        Self(msg)
    }
}

type Result<T> = std::result::Result<T, TransformerError>;

/// Configuration for Router Z-loss regularization
#[derive(Debug, Clone)]
pub struct RouterZLossConfig {
    pub z_loss_weight: f32,
    pub entropy_regularization_weight: f32,
    pub gradient_penalty_weight: f32,
    pub temperature: f32,
    pub epsilon: f32,
}

impl Default for RouterZLossConfig {
    fn default() -> Self {
        Self {
            z_loss_weight: 1e-3,
            entropy_regularization_weight: 1e-4,
            gradient_penalty_weight: 1e-5,
            temperature: 1.0,
            epsilon: 1e-8,
        }
    }
}

/// Router Z-loss regularization for MoE training stability
pub struct RouterZLoss {
    config: RouterZLossConfig,
    device: Device,
}

impl RouterZLoss {
    /// Create a new Router Z-loss regularizer
    pub fn new(config: RouterZLossConfig, device: Device) -> Result<Self> {
        config.validate()?;
        
        Ok(Self {
            config,
            device,
        })
    }

    /// Compute Z-loss - should fail in RED phase
    pub fn compute_loss(&mut self, _router_logits: &Tensor) -> Result<Tensor> {
        Err(TransformerError::config("Router Z-loss not yet implemented".to_string()))
    }

    /// Apply normalization - should fail in RED phase
    fn normalize_logits(&self, _logits: &Tensor) -> Result<Tensor> {
        Err(TransformerError::config("Logit normalization not yet implemented".to_string()))
    }

    /// Get current configuration
    pub fn config(&self) -> &RouterZLossConfig {
        &self.config
    }
}

impl RouterZLossConfig {
    /// Validate the Router Z-loss configuration
    pub fn validate(&self) -> Result<()> {
        if self.z_loss_weight < 0.0 {
            return Err(TransformerError::config(
                "z_loss_weight must be non-negative".to_string()
            ));
        }

        if self.entropy_regularization_weight < 0.0 {
            return Err(TransformerError::config(
                "entropy_regularization_weight must be non-negative".to_string()
            ));
        }

        if self.gradient_penalty_weight < 0.0 {
            return Err(TransformerError::config(
                "gradient_penalty_weight must be non-negative".to_string()
            ));
        }

        if self.temperature <= 0.0 {
            return Err(TransformerError::config(
                "temperature must be positive".to_string()
            ));
        }

        if self.epsilon <= 0.0 {
            return Err(TransformerError::config(
                "epsilon must be positive".to_string()
            ));
        }

        Ok(())
    }
}

fn main() {
    println!("Router Z-loss TDD RED Phase Verification");
    println!("========================================");
    
    // Test 1: Configuration validation passes
    println!("\n1. Testing RouterZLossConfig validation...");
    let config = RouterZLossConfig::default();
    match config.validate() {
        Ok(_) => println!("✓ Default config validation PASSED"),
        Err(_) => {
            println!("✗ Default config validation FAILED");
            return;
        }
    }
    
    // Test configuration failures
    let mut bad_config = RouterZLossConfig::default();
    bad_config.z_loss_weight = -0.1;
    match bad_config.validate() {
        Err(_) => println!("✓ Negative z_loss_weight validation FAILED (expected)"),
        Ok(_) => {
            println!("✗ Negative z_loss_weight validation should have FAILED");
            return;
        }
    }
    
    // Test 2: RouterZLoss creation passes
    println!("\n2. Testing RouterZLoss creation...");
    let device = Device::CPU;
    let zloss = RouterZLoss::new(config.clone(), device);
    match zloss {
        Ok(zloss) => {
            println!("✓ RouterZLoss creation PASSED");
            assert_eq!(zloss.config().z_loss_weight, config.z_loss_weight);
            println!("✓ Config access works");
        },
        Err(_) => {
            println!("✗ RouterZLoss creation FAILED");
            return;
        }
    }
    
    // Test 3: Methods should fail (RED phase)
    println!("\n3. Testing that computation methods fail in RED phase...");
    let mut zloss = RouterZLoss::new(config, Device::CPU).unwrap();
    let router_logits = Tensor;
    
    // compute_loss should fail
    match zloss.compute_loss(&router_logits) {
        Err(_) => println!("✓ compute_loss FAILED (expected in RED phase)"),
        Ok(_) => {
            println!("✗ compute_loss should FAIL in RED phase");
            return;
        }
    }
    
    // normalize_logits should fail
    match zloss.normalize_logits(&router_logits) {
        Err(_) => println!("✓ normalize_logits FAILED (expected in RED phase)"),
        Ok(_) => {
            println!("✗ normalize_logits should FAIL in RED phase");
            return;
        }
    }
    
    println!("\n🎉 RED PHASE VERIFICATION COMPLETE!");
    println!("All tests behave as expected:");
    println!("  - Configuration validation works");
    println!("  - Router creation works");  
    println!("  - All computation methods fail (as expected in RED phase)");
    println!("\n✅ Ready to proceed to GREEN phase implementation!");
}