//! Convergence Validation Tests for Continuous PPO
//!
//! Focused tests for verifying convergence properties:
//! - Policy loss convergence (monotonic decrease)
//! - Value loss convergence (stabilization)
//! - Exploration decay (log_std decreases)
//! - Reward improvement (increasing returns)
//! - Gradient stability (no explosions/vanishing)

mod ppo_continuous_test_helpers;

use ppo_continuous_test_helpers::{create_test_config, train_continuous_ppo, TrainingMetrics};

use anyhow::Result;

#[test]
fn test_policy_loss_convergence() -> Result<()> {
    println!("\n=== Test: Policy Loss Convergence (20 epochs) ===");

    let config = create_test_config(64);

    // Train for 20 epochs
    let (_ppo, metrics) = train_continuous_ppo(20, config, 10, 20)?;

    println!("  Policy Loss Trajectory:");
    for (i, &loss) in metrics.policy_losses.iter().enumerate() {
        if i % 5 == 0 || i == metrics.policy_losses.len() - 1 {
            println!("    Epoch {:2}: {:.4}", i + 1, loss);
        }
    }

    // Verify monotonic decrease (with tolerance for noise)
    let first_loss = metrics.policy_losses[0];
    let last_loss = *metrics.policy_losses.last().unwrap();

    println!("\n  Convergence Analysis:");
    println!("    Initial loss: {:.4}", first_loss);
    println!("    Final loss: {:.4}", last_loss);
    println!("    Reduction: {:.2}%", ((first_loss - last_loss) / first_loss.abs().max(1e-8)) * 100.0);

    // Assert at least 50% reduction (or final loss < threshold)
    let reduction_ratio = (first_loss - last_loss) / first_loss.abs().max(1e-8);
    assert!(
        reduction_ratio >= 0.5 || last_loss < 1.0,
        "Policy loss should reduce by ≥50% (got {:.2}%) or reach <1.0 (got {:.4})",
        reduction_ratio * 100.0,
        last_loss
    );

    // Verify no divergence (loss doesn't explode)
    for (i, &loss) in metrics.policy_losses.iter().enumerate() {
        assert!(
            loss.is_finite() && loss < 1000.0,
            "Policy loss at epoch {} ({:.4}) should be finite and reasonable",
            i + 1,
            loss
        );
    }

    println!("✓ Policy loss converges successfully");

    Ok(())
}

#[test]
fn test_value_loss_convergence() -> Result<()> {
    println!("\n=== Test: Value Loss Convergence (20 epochs) ===");

    let config = create_test_config(64);

    // Train for 20 epochs
    let (_ppo, metrics) = train_continuous_ppo(20, config, 10, 20)?;

    println!("  Value Loss Trajectory:");
    for (i, &loss) in metrics.value_losses.iter().enumerate() {
        if i % 5 == 0 || i == metrics.value_losses.len() - 1 {
            println!("    Epoch {:2}: {:.4}", i + 1, loss);
        }
    }

    // Verify convergence to stable value
    let window = 5;
    let is_stable = metrics.is_value_loss_stable(window, 0.1);

    println!("\n  Stability Analysis:");
    if metrics.value_losses.len() >= window {
        let recent: Vec<f32> = metrics
            .value_losses
            .iter()
            .rev()
            .take(window)
            .copied()
            .collect();
        let mean = recent.iter().sum::<f32>() / recent.len() as f32;
        let variance = recent.iter().map(|&x| (x - mean).powi(2)).sum::<f32>() / recent.len() as f32;
        let std = variance.sqrt();

        println!("    Last {} epochs mean: {:.4}", window, mean);
        println!("    Standard deviation: {:.4}", std);
        println!("    Stable (std < 0.1): {}", is_stable);
    }

    // Assert stability or decreasing trend
    let first_loss = metrics.value_losses[0];
    let last_loss = *metrics.value_losses.last().unwrap();

    println!("    Initial loss: {:.4}", first_loss);
    println!("    Final loss: {:.4}", last_loss);

    // Value loss should either stabilize or decrease
    assert!(
        is_stable || last_loss < first_loss * 1.1,
        "Value loss should stabilize or decrease (stable={}, first={:.4}, last={:.4})",
        is_stable,
        first_loss,
        last_loss
    );

    println!("✓ Value loss converges to stable value");

    Ok(())
}

#[test]
fn test_exploration_decay() -> Result<()> {
    println!("\n=== Test: Exploration Decay (30 epochs with learnable log_std) ===");

    let mut config = create_test_config(64);
    config.policy_config.learnable_std = true;
    config.policy_config.init_log_std = 0.0; // Start at exp(0) = 1.0 std

    // Train for 30 epochs
    let (_ppo, metrics) = train_continuous_ppo(30, config, 10, 20)?;

    println!("  Log Std Trajectory:");
    for (i, &log_std) in metrics.log_stds.iter().enumerate() {
        if i % 5 == 0 || i == metrics.log_stds.len() - 1 {
            let std = log_std.exp();
            println!("    Epoch {:2}: log_std={:.4}, std={:.4}", i + 1, log_std, std);
        }
    }

    // Verify log_std starts at init value
    let first_log_std = metrics.log_stds[0];
    println!("\n  Exploration Analysis:");
    println!("    Initial log_std: {:.4} (std={:.4})", first_log_std, first_log_std.exp());

    // Verify log_std decreases over time
    let last_log_std = *metrics.log_stds.last().unwrap();
    println!("    Final log_std: {:.4} (std={:.4})", last_log_std, last_log_std.exp());

    let decay_occurred = metrics.is_exploration_decaying();
    println!("    Decay occurred: {}", decay_occurred);

    assert!(
        decay_occurred,
        "Log std should decrease over training (exploration decay)"
    );

    // Verify log_std stabilizes at lower value (not collapsing to -inf)
    assert!(
        last_log_std > -10.0,
        "Log std should not collapse too much (got {:.4})",
        last_log_std
    );

    // Calculate decay magnitude
    let decay_magnitude = first_log_std - last_log_std;
    println!("    Decay magnitude: {:.4}", decay_magnitude);

    assert!(
        decay_magnitude > 0.1,
        "Decay should be significant (got {:.4})",
        decay_magnitude
    );

    println!("✓ Exploration decays properly (log_std decreases)");

    Ok(())
}

#[test]
fn test_reward_improvement() -> Result<()> {
    println!("\n=== Test: Reward Improvement (50 epochs) ===");

    let config = create_test_config(64);

    // Train for 50 epochs
    let (_ppo, metrics) = train_continuous_ppo(50, config, 10, 20)?;

    println!("  Average Reward Trajectory:");
    for (i, &reward) in metrics.avg_rewards.iter().enumerate() {
        if i % 10 == 0 || i == metrics.avg_rewards.len() - 1 {
            println!("    Epoch {:2}: {:.4}", i + 1, reward);
        }
    }

    // Verify monotonic increase (with tolerance)
    let first_reward = metrics.avg_rewards[0];
    let last_reward = *metrics.avg_rewards.last().unwrap();

    println!("\n  Reward Improvement Analysis:");
    println!("    Initial avg reward: {:.4}", first_reward);
    println!("    Final avg reward: {:.4}", last_reward);

    let improvement_factor = last_reward / first_reward.abs().max(1e-8);
    println!("    Improvement factor: {:.2}x", improvement_factor.abs());

    // Verify final reward > 2x initial reward (or positive improvement)
    let improved = metrics.are_rewards_improving(2.0);
    println!("    Meets 2x improvement: {}", improved);

    // More lenient check: just verify learning happened
    let shows_improvement = last_reward > first_reward * 0.9; // Allow 10% variance
    assert!(
        improved || shows_improvement,
        "Reward should improve significantly (first={:.4}, last={:.4}, factor={:.2})",
        first_reward,
        last_reward,
        improvement_factor
    );

    // Verify no catastrophic collapse
    for (i, &reward) in metrics.avg_rewards.iter().enumerate() {
        assert!(
            reward.is_finite(),
            "Reward at epoch {} should be finite (got {:.4})",
            i + 1,
            reward
        );
    }

    println!("✓ Rewards improve over training");

    Ok(())
}

#[test]
fn test_gradient_stability() -> Result<()> {
    println!("\n=== Test: Gradient Stability (20 epochs) ===");

    let mut config = create_test_config(64);
    config.max_grad_norm = 10.0; // Set gradient clipping threshold

    // Train for 20 epochs
    let (_ppo, metrics) = train_continuous_ppo(20, config, 10, 20)?;

    println!("  Loss Trajectory Analysis:");

    // Monitor for gradient explosions via loss spikes
    let mut max_policy_loss = f32::NEG_INFINITY;
    let mut min_policy_loss = f32::INFINITY;
    let mut max_value_loss = f32::NEG_INFINITY;
    let mut min_value_loss = f32::INFINITY;

    for &loss in &metrics.policy_losses {
        max_policy_loss = max_policy_loss.max(loss);
        min_policy_loss = min_policy_loss.min(loss);
    }

    for &loss in &metrics.value_losses {
        max_value_loss = max_value_loss.max(loss);
        min_value_loss = min_value_loss.min(loss);
    }

    println!("    Policy loss range: [{:.4}, {:.4}]", min_policy_loss, max_policy_loss);
    println!("    Value loss range: [{:.4}, {:.4}]", min_value_loss, max_value_loss);

    // Verify no gradient explosions (losses should stay in reasonable range)
    assert!(
        max_policy_loss < 1000.0,
        "Policy loss should not explode (max={:.4})",
        max_policy_loss
    );
    assert!(
        max_value_loss < 1000.0,
        "Value loss should not explode (max={:.4})",
        max_value_loss
    );

    // Verify no gradient vanishing (losses should not be too small)
    assert!(
        max_policy_loss > 1e-6,
        "Policy loss should not vanish (max={:.4})",
        max_policy_loss
    );
    assert!(
        max_value_loss > 1e-6,
        "Value loss should not vanish (max={:.4})",
        max_value_loss
    );

    // Check for sudden spikes in loss (indicator of instability)
    let mut policy_spikes = 0;
    let mut value_spikes = 0;

    for i in 1..metrics.policy_losses.len() {
        let prev = metrics.policy_losses[i - 1];
        let curr = metrics.policy_losses[i];
        if (curr - prev).abs() > prev.abs() * 2.0 {
            policy_spikes += 1;
        }
    }

    for i in 1..metrics.value_losses.len() {
        let prev = metrics.value_losses[i - 1];
        let curr = metrics.value_losses[i];
        if (curr - prev).abs() > prev.abs() * 2.0 {
            value_spikes += 1;
        }
    }

    println!("    Policy loss spikes (>2x change): {}", policy_spikes);
    println!("    Value loss spikes (>2x change): {}", value_spikes);

    // Allow some spikes in early training, but not excessive
    assert!(
        policy_spikes < 5,
        "Too many policy loss spikes ({}), indicates instability",
        policy_spikes
    );
    assert!(
        value_spikes < 5,
        "Too many value loss spikes ({}), indicates instability",
        value_spikes
    );

    println!("✓ Gradients remain stable (no explosions or vanishing)");

    Ok(())
}

#[test]
fn test_long_term_convergence() -> Result<()> {
    println!("\n=== Test: Long-term Convergence (100 epochs) ===");

    let config = create_test_config(64);

    // Train for 100 epochs
    println!("  Training for 100 epochs (this may take a minute)...");
    let (_ppo, metrics) = train_continuous_ppo(100, config, 10, 20)?;

    println!("\n  Final Metrics:");
    println!("    Policy loss: {:.4} → {:.4}",
        metrics.policy_losses[0],
        metrics.policy_losses.last().unwrap()
    );
    println!("    Value loss: {:.4} → {:.4}",
        metrics.value_losses[0],
        metrics.value_losses.last().unwrap()
    );
    println!("    Avg reward: {:.4} → {:.4}",
        metrics.avg_rewards[0],
        metrics.avg_rewards.last().unwrap()
    );
    println!("    Log std: {:.4} → {:.4}",
        metrics.log_stds[0],
        metrics.log_stds.last().unwrap()
    );

    // Verify all convergence criteria
    let policy_converged = metrics.is_policy_loss_converging(0.3);
    let value_stable = metrics.is_value_loss_stable(10, 0.1);
    let rewards_improved = metrics.are_rewards_improving(1.5);
    let exploration_decayed = metrics.is_exploration_decaying();

    println!("\n  Convergence Criteria:");
    println!("    Policy loss converging (≥30% reduction): {}", policy_converged);
    println!("    Value loss stable (last 10 epochs): {}", value_stable);
    println!("    Rewards improved (≥1.5x): {}", rewards_improved);
    println!("    Exploration decayed: {}", exploration_decayed);

    // At least 3 out of 4 criteria should pass
    let passing_criteria = [
        policy_converged,
        value_stable,
        rewards_improved,
        exploration_decayed,
    ]
    .iter()
    .filter(|&&x| x)
    .count();

    println!("    Total passing: {}/4", passing_criteria);

    assert!(
        passing_criteria >= 3,
        "At least 3/4 convergence criteria should pass (got {}/4)",
        passing_criteria
    );

    println!("✓ Long-term convergence verified ({}/4 criteria)", passing_criteria);

    Ok(())
}

#[test]
fn test_convergence_with_different_learning_rates() -> Result<()> {
    println!("\n=== Test: Convergence with Different Learning Rates ===");

    let state_dim = 64;

    // Test 1: Balanced learning rates
    println!("\n  Test 1: Balanced LRs (policy=3e-4, value=3e-4)");
    let mut config1 = create_test_config(state_dim);
    config1.policy_learning_rate = 3e-4;
    config1.value_learning_rate = 3e-4;

    let (_ppo1, metrics1) = train_continuous_ppo(20, config1, 10, 20)?;
    println!("    Final policy loss: {:.4}", metrics1.policy_losses.last().unwrap());
    println!("    Final value loss: {:.4}", metrics1.value_losses.last().unwrap());

    // Test 2: Aggressive value LR (like hyperopt best)
    println!("\n  Test 2: Aggressive value LR (policy=1e-4, value=1e-3)");
    let mut config2 = create_test_config(state_dim);
    config2.policy_learning_rate = 1e-4;
    config2.value_learning_rate = 1e-3;

    let (_ppo2, metrics2) = train_continuous_ppo(20, config2, 10, 20)?;
    println!("    Final policy loss: {:.4}", metrics2.policy_losses.last().unwrap());
    println!("    Final value loss: {:.4}", metrics2.value_losses.last().unwrap());

    // Test 3: Conservative policy LR
    println!("\n  Test 3: Conservative policy LR (policy=1e-5, value=3e-4)");
    let mut config3 = create_test_config(state_dim);
    config3.policy_learning_rate = 1e-5;
    config3.value_learning_rate = 3e-4;

    let (_ppo3, metrics3) = train_continuous_ppo(20, config3, 10, 20)?;
    println!("    Final policy loss: {:.4}", metrics3.policy_losses.last().unwrap());
    println!("    Final value loss: {:.4}", metrics3.value_losses.last().unwrap());

    // Verify all configurations converged (no crashes)
    assert_eq!(metrics1.policy_losses.len(), 20, "Config 1 should complete 20 epochs");
    assert_eq!(metrics2.policy_losses.len(), 20, "Config 2 should complete 20 epochs");
    assert_eq!(metrics3.policy_losses.len(), 20, "Config 3 should complete 20 epochs");

    // Verify losses are finite
    for loss in &metrics1.policy_losses {
        assert!(loss.is_finite(), "Config 1 losses should be finite");
    }
    for loss in &metrics2.policy_losses {
        assert!(loss.is_finite(), "Config 2 losses should be finite");
    }
    for loss in &metrics3.policy_losses {
        assert!(loss.is_finite(), "Config 3 losses should be finite");
    }

    println!("\n✓ All learning rate configurations converge successfully");

    Ok(())
}