//! DQN Extended Validation System Tests
//!
//! Test-Driven Development (TDD) suite for comprehensive DQN validation.
//! This suite ensures training validates:
//! - Overfitting detection (train/val divergence)
//! - Action distribution monitoring (HOLD collapse)
//! - Q-value stability (explosion detection)
//! - Policy entropy (exploration collapse)
//! - Early stopping (5 failure modes)
//! - Production readiness (profitability, diversity, stability)

use ml::trainers::validation_metrics::{EarlyStopCriteria, ValidationMetrics};

#[cfg(test)]
mod validation_metrics_tests {
    use super::*;

    /// Module 1: Validation Metrics (8 tests)

    #[test]
    fn test_validation_loss_calculated_on_holdout() {
        // Test that validation metrics distinguish between train and val loss
        let metrics = ValidationMetrics::new(
            1,
            1.5, // train_loss
            2.0, // val_loss (higher = using separate holdout set)
            5.0,
            0.5,
            [0.3, 0.3, 0.4],
            0.8,
            0.55,
            1.8,
            0.5,
        );

        assert!(
            metrics.val_loss > metrics.train_loss,
            "Validation loss should be tracked separately"
        );
    }

    #[test]
    fn test_train_val_loss_divergence_detected() {
        // Test detection when training loss decreases but validation loss increases
        let history = vec![
            ValidationMetrics::new(1, 2.0, 2.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(2, 1.8, 2.1, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(3, 1.6, 2.2, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(4, 1.4, 2.3, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(5, 1.2, 2.4, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
        ];

        let current =
            ValidationMetrics::new(6, 1.0, 2.5, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5);

        assert!(
            current.is_overfitting(&history),
            "Should detect train↓ val↑ divergence"
        );
    }

    #[test]
    fn test_q_value_distribution_tracked() {
        // Test Q-value mean/std tracked per epoch
        let metrics = ValidationMetrics::new(
            10,
            1.0,
            2.0,
            15.5, // q_value_mean
            3.2,  // q_value_std
            [0.3, 0.3, 0.4],
            0.8,
            0.55,
            1.8,
            0.5,
        );

        assert_eq!(metrics.q_value_mean, 15.5, "Q-value mean should be tracked");
        assert_eq!(metrics.q_value_std, 3.2, "Q-value std should be tracked");
    }

    #[test]
    fn test_action_distribution_tracked() {
        // Test action distribution [BUY%, SELL%, HOLD%] tracked per epoch
        let metrics = ValidationMetrics::new(
            10,
            1.0,
            2.0,
            5.0,
            0.5,
            [0.25, 0.35, 0.40], // BUY=25%, SELL=35%, HOLD=40%
            0.8,
            0.55,
            1.8,
            0.5,
        );

        assert_eq!(
            metrics.action_distribution[0], 0.25,
            "BUY% should be tracked"
        );
        assert_eq!(
            metrics.action_distribution[1], 0.35,
            "SELL% should be tracked"
        );
        assert_eq!(
            metrics.action_distribution[2], 0.40,
            "HOLD% should be tracked"
        );
    }

    #[test]
    fn test_policy_entropy_tracked() {
        // Test Shannon entropy H = -Σ p_i log(p_i) tracked per epoch
        let metrics = ValidationMetrics::new(
            10,
            1.0,
            2.0,
            5.0,
            0.5,
            [0.3, 0.3, 0.4],
            0.95, // policy_entropy
            0.55,
            1.8,
            0.5,
        );

        assert_eq!(
            metrics.policy_entropy, 0.95,
            "Policy entropy should be tracked"
        );
        assert!(
            metrics.policy_entropy > 0.0 && metrics.policy_entropy <= 1.099,
            "Entropy in valid range"
        );
    }

    #[test]
    fn test_win_rate_estimated() {
        // Test win rate (% profitable actions) estimated on validation set
        let metrics = ValidationMetrics::new(
            10,
            1.0,
            2.0,
            5.0,
            0.5,
            [0.3, 0.3, 0.4],
            0.8,
            0.62, // win_rate = 62%
            1.8,
            0.5,
        );

        assert_eq!(metrics.win_rate, 0.62, "Win rate should be estimated");
        assert!(
            metrics.win_rate >= 0.0 && metrics.win_rate <= 1.0,
            "Win rate in [0, 1]"
        );
    }

    #[test]
    fn test_sharpe_ratio_estimated() {
        // Test Sharpe ratio (reward mean / reward std) estimated on validation set
        let metrics = ValidationMetrics::new(
            10,
            1.0,
            2.0,
            5.0,
            0.5,
            [0.3, 0.3, 0.4],
            0.8,
            0.55,
            2.3, // sharpe_ratio
            0.5,
        );

        assert_eq!(
            metrics.sharpe_ratio, 2.3,
            "Sharpe ratio should be estimated"
        );
    }

    #[test]
    fn test_metrics_saved_to_checkpoint() {
        // Test all validation metrics can be serialized (for checkpoint metadata)
        let metrics =
            ValidationMetrics::new(10, 1.0, 2.0, 5.0, 0.5, [0.3, 0.3, 0.4], 0.8, 0.55, 1.8, 0.5);

        // Test serialization
        let json = serde_json::to_string(&metrics).expect("Should serialize to JSON");
        assert!(json.contains("epoch"), "JSON should contain epoch");
        assert!(json.contains("val_loss"), "JSON should contain val_loss");

        // Test deserialization
        let _deserialized: ValidationMetrics =
            serde_json::from_str(&json).expect("Should deserialize from JSON");
    }
}

#[cfg(test)]
mod early_stopping_tests {
    use super::*;

    /// Module 2: Early Stopping (6 tests)

    #[test]
    fn test_stop_when_val_loss_increases_5_epochs() {
        // Test early stopping triggers when validation loss increases for 5 epochs
        let history = vec![
            ValidationMetrics::new(1, 1.0, 2.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(2, 1.0, 2.1, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(3, 1.0, 2.2, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(4, 1.0, 2.3, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(5, 1.0, 2.4, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
        ];

        let current =
            ValidationMetrics::new(6, 1.0, 2.5, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5);
        let criteria = EarlyStopCriteria::ValidationLossIncrease { patience: 5 };

        let result = criteria.should_stop(&current, &history);
        assert!(result.is_some(), "Should trigger early stopping");
        assert!(
            result.unwrap().contains("Validation loss increased"),
            "Should cite validation loss"
        );
    }

    #[test]
    fn test_stop_when_hold_over_90_percent() {
        // Test early stopping when HOLD action > 90% for 10 epochs
        let history: Vec<ValidationMetrics> = (1..=10)
            .map(|i| {
                ValidationMetrics::new(
                    i,
                    1.0,
                    2.0,
                    1.0,
                    0.1,
                    [0.05, 0.05, 0.92], // HOLD > 90%
                    0.5,
                    0.6,
                    1.8,
                    0.5,
                )
            })
            .collect();

        let current = ValidationMetrics::new(
            11,
            1.0,
            2.0,
            1.0,
            0.1,
            [0.05, 0.05, 0.92],
            0.5,
            0.6,
            1.8,
            0.5,
        );
        let criteria = EarlyStopCriteria::ActionCollapse {
            hold_threshold: 0.9,
            patience: 10,
        };

        let result = criteria.should_stop(&current, &history);
        assert!(
            result.is_some(),
            "Should trigger early stopping due to action collapse"
        );
        assert!(
            result.unwrap().contains("Action collapse"),
            "Should cite action collapse"
        );
    }

    #[test]
    fn test_stop_when_entropy_below_threshold() {
        // Test early stopping when policy entropy < 0.1 for 10 epochs
        let history: Vec<ValidationMetrics> = (1..=10)
            .map(|i| {
                ValidationMetrics::new(
                    i,
                    1.0,
                    2.0,
                    1.0,
                    0.1,
                    [0.3, 0.3, 0.4],
                    0.05, // entropy < 0.1
                    0.6,
                    1.8,
                    0.5,
                )
            })
            .collect();

        let current =
            ValidationMetrics::new(11, 1.0, 2.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.05, 0.6, 1.8, 0.5);
        let criteria = EarlyStopCriteria::EntropyCollapse {
            threshold: 0.1,
            patience: 10,
        };

        let result = criteria.should_stop(&current, &history);
        assert!(
            result.is_some(),
            "Should trigger early stopping due to entropy collapse"
        );
        assert!(
            result.unwrap().contains("Entropy collapse"),
            "Should cite entropy collapse"
        );
    }

    #[test]
    fn test_stop_when_q_values_explode() {
        // Test early stopping when Q-values > 10,000
        let history = vec![];
        let current = ValidationMetrics::new(
            10,
            1.0,
            2.0,
            15_000.0, // Q-value explosion
            1.0,
            [0.3, 0.3, 0.4],
            0.5,
            0.6,
            1.8,
            0.5,
        );
        let criteria = EarlyStopCriteria::QValueExplosion {
            threshold: 10_000.0,
        };

        let result = criteria.should_stop(&current, &history);
        assert!(
            result.is_some(),
            "Should trigger early stopping due to Q-value explosion"
        );
        assert!(
            result.unwrap().contains("Q-value explosion"),
            "Should cite Q-value explosion"
        );
    }

    #[test]
    fn test_stop_when_gradients_explode() {
        // Test early stopping when gradient norm > 100
        let history = vec![];
        let current = ValidationMetrics::new(
            10,
            1.0,
            2.0,
            5.0,
            0.5,
            [0.3, 0.3, 0.4],
            0.5,
            0.6,
            1.8,
            150.0, // gradient_norm > 100
        );
        let criteria = EarlyStopCriteria::GradientExplosion { threshold: 100.0 };

        let result = criteria.should_stop(&current, &history);
        assert!(
            result.is_some(),
            "Should trigger early stopping due to gradient explosion"
        );
        assert!(
            result.unwrap().contains("Gradient explosion"),
            "Should cite gradient explosion"
        );
    }

    #[test]
    fn test_best_model_saved_before_stopping() {
        // Test that early stopping system provides stopping reason (model save is trainer responsibility)
        let history = vec![
            ValidationMetrics::new(1, 2.0, 2.5, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(2, 1.8, 2.3, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(3, 1.5, 2.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5), // Best val_loss=2.0
        ];

        let current =
            ValidationMetrics::new(4, 1.0, 2.5, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5);

        // Find epoch with best validation loss
        let best_epoch = history
            .iter()
            .min_by(|a, b| a.val_loss.partial_cmp(&b.val_loss).unwrap())
            .map(|m| m.epoch);

        assert_eq!(best_epoch, Some(3), "Should identify epoch 3 as best");
    }
}

#[cfg(test)]
mod overfitting_detection_tests {
    use super::*;

    /// Module 3: Overfitting Detection (5 tests)

    #[test]
    fn test_train_val_ratio_over_2_is_overfitting() {
        // Test overfitting detected when train_loss / val_loss > 2.0
        let history = vec![];
        let current = ValidationMetrics::new(
            10,
            1.0, // train_loss
            3.5, // val_loss (ratio = 3.5)
            5.0,
            0.5,
            [0.3, 0.3, 0.4],
            0.5,
            0.6,
            1.8,
            0.5,
        );

        assert!(
            current.is_overfitting(&history),
            "Should detect overfitting from high train/val ratio"
        );
        assert!(
            current.train_val_ratio() > 2.0,
            "Train/val ratio should exceed 2.0"
        );
    }

    #[test]
    fn test_val_loss_increasing_train_decreasing() {
        // Test overfitting when train_loss trends down but val_loss trends up over 5 epochs
        let history = vec![
            ValidationMetrics::new(1, 2.0, 2.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(2, 1.8, 2.2, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(3, 1.6, 2.4, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(4, 1.4, 2.6, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(5, 1.2, 2.8, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
        ];

        let current =
            ValidationMetrics::new(6, 1.0, 3.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5);

        assert!(
            current.is_overfitting(&history),
            "Should detect train↓ val↑ divergence"
        );
    }

    #[test]
    fn test_action_distribution_validation_mismatch() {
        // Test that action distribution differences can be detected
        let train_dist = [0.3f32, 0.3, 0.4];
        let val_dist = [0.1f32, 0.1, 0.8]; // Significant mismatch

        let mismatch: f32 = train_dist
            .iter()
            .zip(val_dist.iter())
            .map(|(t, v)| (t - v).abs())
            .sum();

        assert!(
            mismatch > 0.3,
            "Should detect > 30% action distribution mismatch"
        );
    }

    #[test]
    fn test_q_values_out_of_range_on_validation() {
        // Test Q-value divergence detection
        let train_q = 5.0f32;
        let val_q = 18.0f32; // 3.6x training Q-values

        let ratio = val_q / train_q;
        assert!(
            ratio > 3.0,
            "Should detect validation Q-values > 3x training"
        );
    }

    #[test]
    fn test_regularization_triggered_on_overfitting() {
        // Test that overfitting detection provides actionable signal
        let history = vec![
            ValidationMetrics::new(1, 2.0, 2.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(2, 1.5, 2.5, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(3, 1.0, 3.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(4, 0.8, 3.5, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
            ValidationMetrics::new(5, 0.6, 4.0, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5),
        ];

        let current =
            ValidationMetrics::new(6, 0.5, 4.5, 1.0, 0.1, [0.3, 0.3, 0.4], 0.5, 0.6, 1.8, 0.5);

        if current.is_overfitting(&history) {
            // Regularization would be triggered here (logged as warning in trainer)
            assert!(true, "Overfitting signal triggers regularization warning");
        }
    }
}

#[cfg(test)]
mod production_readiness_tests {
    use super::*;

    /// Module 4: Production Readiness (6 tests)

    #[test]
    fn test_model_passes_profitability_check() {
        // Test model passes profitability check (Sharpe > 1.5, Win Rate > 50%)
        let metrics = ValidationMetrics::new(
            50,
            0.8,
            1.5,
            8.0,
            1.2,
            [0.3, 0.3, 0.4],
            0.9,
            0.58, // win_rate > 0.5 ✓
            2.1,  // sharpe > 1.5 ✓
            0.5,
        );

        assert!(metrics.win_rate > 0.5, "Win rate should exceed 50%");
        assert!(metrics.sharpe_ratio > 1.5, "Sharpe ratio should exceed 1.5");
    }

    #[test]
    fn test_model_passes_action_diversity_check() {
        // Test model passes diversity check (HOLD < 70%)
        let metrics = ValidationMetrics::new(
            50,
            0.8,
            1.5,
            8.0,
            1.2,
            [0.3, 0.35, 0.35], // HOLD = 35% < 70% ✓
            0.9,
            0.58,
            2.1,
            0.5,
        );

        assert!(
            metrics.action_distribution[2] < 0.7,
            "HOLD % should be < 70%"
        );
    }

    #[test]
    fn test_model_passes_stability_check() {
        // Test model passes stability check (Q-values finite and bounded)
        let metrics = ValidationMetrics::new(
            50,
            0.8,
            1.5,
            12.5, // |q_mean| < 1000 ✓
            2.0,
            [0.3, 0.3, 0.4],
            0.9,
            0.58,
            2.1,
            0.5,
        );

        assert!(
            metrics.q_value_mean.is_finite(),
            "Q-values should be finite"
        );
        assert!(
            metrics.q_value_mean.abs() < 1000.0,
            "Q-values should be bounded"
        );
    }

    #[test]
    fn test_model_passes_performance_check() {
        // Test inference latency check (< 1ms is handled by separate benchmarks)
        // This test validates that metrics don't indicate training instability
        let metrics = ValidationMetrics::new(
            50,
            0.8,
            1.5,
            8.0,
            1.2,
            [0.3, 0.3, 0.4],
            0.9,
            0.58,
            2.1,
            0.5, // gradient_norm < 100 (stable)
        );

        assert!(
            !metrics.has_gradient_explosion(),
            "Gradients should be stable"
        );
    }

    #[test]
    fn test_model_passes_robustness_check() {
        // Test model handles edge cases (NaN detection)
        let metrics =
            ValidationMetrics::new(50, 0.8, 1.5, 8.0, 1.2, [0.3, 0.3, 0.4], 0.9, 0.58, 2.1, 0.5);

        // Verify no NaN values in metrics
        assert!(!metrics.train_loss.is_nan(), "train_loss should not be NaN");
        assert!(!metrics.val_loss.is_nan(), "val_loss should not be NaN");
        assert!(
            !metrics.q_value_mean.is_nan(),
            "q_value_mean should not be NaN"
        );
        assert!(
            !metrics.policy_entropy.is_nan(),
            "policy_entropy should not be NaN"
        );
    }

    #[test]
    fn test_all_checks_bundled_in_is_production_ready() {
        // Test comprehensive production readiness check
        let good_metrics = ValidationMetrics::new(
            100,
            0.9,                // train_loss
            1.2,                // val_loss < 5.0 ✓
            10.0,               // q_value_mean (finite, |x| < 1000) ✓
            2.0,                // q_value_std
            [0.32, 0.35, 0.33], // HOLD = 33% < 70% ✓
            0.95,               // policy_entropy > 0.1 ✓
            0.62,               // win_rate > 0.5 ✓
            2.5,                // sharpe_ratio > 1.5 ✓
            0.8,                // gradient_norm
        );

        assert!(
            good_metrics.is_production_ready(),
            "Should pass all production criteria"
        );

        // Test failure case: high HOLD
        let bad_metrics = ValidationMetrics::new(
            100,
            0.9,
            1.2,
            10.0,
            2.0,
            [0.1, 0.1, 0.8], // HOLD = 80% > 70% ✗
            0.95,
            0.62,
            2.5,
            0.8,
        );

        assert!(
            !bad_metrics.is_production_ready(),
            "Should fail due to high HOLD %"
        );
    }
}