//! Comprehensive Unit Tests for DQN Reward Function
//!
//! This test suite is designed to catch three critical bugs that were discovered in production:
//! - Bug #2: Empty portfolio features → P&L always 0.0
//! - Bug #3: Wrong defaults (hold_penalty=0.0, threshold=0.0)
//! - Bug #4: Close price misinterpretation (log return vs price)
//!
//! These tests serve as regression tests to prevent future occurrences.

use ml::dqn::agent::{TradingAction, TradingState};
use ml::dqn::reward::{RewardConfig, RewardFunction};
use rust_decimal::Decimal;

// ============================================================================
// CATEGORY A: Portfolio Feature Validation (catch Bug #2)
// ============================================================================

/// Helper to create a state with empty portfolio features (Bug #2 scenario)
fn create_empty_portfolio_state() -> TradingState {
    TradingState {
        price_features: vec![5900.0, 5905.0, 5895.0, 5900.0], // ES futures OHLC
        technical_indicators: vec![0.5, 0.5, 0.5, 0.5],
        market_features: vec![0.25, 10000.0, 0.0, 0.0], // ES typical spread
        portfolio_features: vec![],                     // EMPTY - Bug #2
    }
}

/// Helper to create a state with portfolio growth
fn create_portfolio_with_gain(initial_value: f32, gain_pct: f32) -> (TradingState, TradingState) {
    let normalized_initial = initial_value / 10000.0; // Normalize to [0, 1]
    let normalized_final = (initial_value * (1.0 + gain_pct)) / 10000.0;

    let current_state = TradingState {
        price_features: vec![5900.0, 5905.0, 5895.0, 5900.0],
        technical_indicators: vec![0.5, 0.5, 0.5, 0.5],
        market_features: vec![0.25, 10000.0, 0.0, 0.0],
        portfolio_features: vec![normalized_initial, 0.5, 0.0, 0.0], // [value, position, ...]
    };

    let next_state = TradingState {
        price_features: vec![5910.0, 5915.0, 5905.0, 5910.0],
        technical_indicators: vec![0.5, 0.5, 0.5, 0.5],
        market_features: vec![0.25, 10000.0, 0.0, 0.0],
        portfolio_features: vec![normalized_final, 0.6, 0.0, 0.0], // Portfolio grew
    };

    (current_state, next_state)
}

/// Test A1: Verify error or zero reward when portfolio features are empty (Bug #2)
#[test]
fn test_pnl_reward_requires_portfolio_features() -> anyhow::Result<()> {
    // BUG #2: Empty portfolio_features caused P&L to always be 0.0
    // This test would have caught it by asserting non-zero reward for BUY action

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    let current_state = create_empty_portfolio_state();
    let next_state = create_empty_portfolio_state();

    // Calculate reward for BUY action (should depend on portfolio P&L)
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Buy,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // With empty portfolio_features, reward should be 0.0 (fallback behavior)
    // This catches Bug #2: If portfolio_features is empty, P&L calculation returns 0
    assert_eq!(
        reward,
        Decimal::ZERO,
        "BUG #2 CATCH: Empty portfolio_features should give zero P&L reward, got {}",
        reward
    );

    Ok(())
}

/// Test A2: Verify positive reward for portfolio growth (Buy action with profit)
#[test]
fn test_pnl_reward_positive_gain() -> anyhow::Result<()> {
    // BUG #2: Would fail if portfolio_features were empty (always 0.0 reward)
    // This verifies that non-empty portfolio features produce non-zero rewards

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    // Create states with 5% portfolio gain
    let (current_state, next_state) = create_portfolio_with_gain(10000.0, 0.05);
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Buy,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected: P&L reward = (next_value - current_value) / current_value
    // = (10500 - 10000) / 10000 = 0.05 = 5% gain
    // With pnl_weight=1.0, risk_weight=0.1, cost_weight=0.05
    // Reward ≈ 0.05 (P&L component dominates)

    assert!(
        reward > Decimal::ZERO,
        "BUG #2 CATCH: Portfolio gain should produce positive reward, got {}",
        reward
    );

    // Verify reward is approximately 5% (within tolerance)
    let expected = Decimal::try_from(0.05).unwrap();
    let tolerance = Decimal::try_from(0.01).unwrap(); // 1% tolerance for penalties

    assert!(
        (reward - expected).abs() < tolerance,
        "Expected reward ~{} for 5% gain, got {}",
        expected,
        reward
    );

    Ok(())
}

/// Test A3: Verify negative reward for portfolio loss (Sell action with profit)
#[test]
fn test_pnl_reward_negative_loss() -> anyhow::Result<()> {
    // BUG #2: Would always return 0.0 if portfolio_features were empty

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    // Create states with -3% portfolio loss
    let (current_state, next_state) = create_portfolio_with_gain(10000.0, -0.03);
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Sell,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected: P&L reward = (9700 - 10000) / 10000 = -0.03 = -3% loss
    // With penalties, reward should be negative

    assert!(
        reward < Decimal::ZERO,
        "BUG #2 CATCH: Portfolio loss should produce negative reward, got {}",
        reward
    );

    Ok(())
}

/// Test A4: Verify P&L reward normalization (percentage-based)
#[test]
fn test_pnl_reward_normalization() -> anyhow::Result<()> {
    // BUG #2: Percentage calculation relies on non-zero portfolio value
    // This verifies normalization works correctly

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    // Small portfolio: 1000 → 1020 (+2%)
    let (current_small, next_small) = create_portfolio_with_gain(1000.0, 0.02);

    // Large portfolio: 100000 → 102000 (+2%)
    let (current_large, next_large) = create_portfolio_with_gain(100000.0, 0.02);
    let recent_actions = vec![]; // No action history for unit test
    let reward_small = reward_fn.calculate_reward(
        TradingAction::Buy,
        &current_small,
        &next_small,
        &recent_actions,
    )?;
    let recent_actions = vec![]; // No action history for unit test
    let reward_large = reward_fn.calculate_reward(
        TradingAction::Buy,
        &current_large,
        &next_large,
        &recent_actions,
    )?;

    // Rewards should be approximately equal (percentage-based normalization)
    let tolerance = Decimal::try_from(0.001).unwrap();

    assert!(
        (reward_small - reward_large).abs() < tolerance,
        "BUG #2 CATCH: Rewards should be normalized by portfolio value. Small: {}, Large: {}",
        reward_small,
        reward_large
    );

    Ok(())
}

// ============================================================================
// CATEGORY B: Default Hyperparameter Validation (catch Bug #3)
// ============================================================================

/// Test B1: Assert default diversity_weight = 0.01 (Bug #3)
#[test]
fn test_default_hyperparameters_hold_penalty() {
    // BUG #3: Original code had diversity_weight=0.0 (wrong default)
    // This test ensures default is correctly set to 0.01

    let config = RewardConfig::default();

    let expected = Decimal::try_from(0.01).unwrap();

    assert_eq!(
        config.diversity_weight, expected,
        "BUG #3 CATCH: Default diversity_weight should be 0.01, got {}",
        config.diversity_weight
    );
}

/// Test B2: Assert default movement_threshold = 0.02 (Bug #3)
#[test]
fn test_default_hyperparameters_movement_threshold() {
    // BUG #3: Original code had movement_threshold=0.0 (wrong default)
    // This test ensures default is correctly set to 0.02 (2%)

    let config = RewardConfig::default();

    let expected = Decimal::try_from(0.02).unwrap();

    assert_eq!(
        config.movement_threshold, expected,
        "BUG #3 CATCH: Default movement_threshold should be 0.02 (2%), got {}",
        config.movement_threshold
    );
}

/// Test B3: Verify custom hyperparameters override defaults
#[test]
fn test_custom_hyperparameters_override() {
    // Ensure custom values can be set (not hardcoded to defaults)

    let custom_config = RewardConfig {
        pnl_weight: Decimal::ONE,
        risk_weight: Decimal::try_from(0.2).unwrap(),
        cost_weight: Decimal::try_from(0.1).unwrap(),
        hold_reward: Decimal::try_from(0.005).unwrap(),
        diversity_weight: Decimal::try_from(0.05).unwrap(), // Custom: 5x default
        movement_threshold: Decimal::try_from(0.01).unwrap(), // Custom: 1% instead of 2%
    };

    assert_eq!(
        custom_config.diversity_weight,
        Decimal::try_from(0.05).unwrap(),
        "Custom diversity_weight should be 0.05"
    );

    assert_eq!(
        custom_config.movement_threshold,
        Decimal::try_from(0.01).unwrap(),
        "Custom movement_threshold should be 0.01"
    );
}

// ============================================================================
// CATEGORY C: HOLD Penalty Calculation (catch Bug #4)
// ============================================================================

/// Helper to create states with specific ES futures prices
fn create_state_with_es_price(close_price: f32) -> TradingState {
    TradingState {
        price_features: vec![
            close_price,
            close_price + 5.0,
            close_price - 5.0,
            close_price,
        ], // OHLC
        technical_indicators: vec![0.5, 0.5, 0.5, 0.5],
        market_features: vec![0.25, 10000.0, 0.0, 0.0], // ES typical spread
        portfolio_features: vec![1.0, 0.0, 0.0, 0.0],
    }
}

/// Test C1: HOLD penalty with high volatility (>2% movement) - Bug #4
#[test]
fn test_hold_penalty_with_high_volatility() -> anyhow::Result<()> {
    // BUG #4: Original code used log returns, giving wrong penalty calculation
    // Correct: Use actual price change percentage

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config.clone());

    // ES futures: 5900 → 6020 (+120 points = +2.03% movement)
    let current_state = create_state_with_es_price(5900.0);
    let next_state = create_state_with_es_price(6020.0);
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Hold,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected: Movement 2.03% > threshold 2.0% → penalty applies
    // Excess: 2.03% - 2.0% = 0.03% = 0.0003
    // Reward: 0.001 - (0.01 * 0.0003) = 0.001 - 0.000003 ≈ 0.001

    // The penalty should be very small (just above threshold)
    assert!(
        reward < config.hold_reward,
        "BUG #4 CATCH: HOLD penalty should apply when movement > 2%, got reward {}",
        reward
    );

    // Verify it's still positive (small excess movement)
    assert!(
        reward > Decimal::ZERO,
        "Reward should be positive for small excess movement: {}",
        reward
    );

    Ok(())
}

/// Test C2: HOLD penalty with low volatility (<2% movement) - Bug #4
#[test]
fn test_hold_penalty_with_low_volatility() -> anyhow::Result<()> {
    // BUG #4: Would give wrong penalty if using log returns

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config.clone());

    // ES futures: 5900 → 5910 (+10 points = +0.17% movement)
    let current_state = create_state_with_es_price(5900.0);
    let next_state = create_state_with_es_price(5910.0);
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Hold,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected: Movement 0.17% < threshold 2.0% → NO penalty
    // Reward should equal hold_reward (0.001)

    assert_eq!(
        reward, config.hold_reward,
        "BUG #4 CATCH: No penalty when movement < 2% (movement: 0.17%), got reward {}",
        reward
    );

    Ok(())
}

/// Test C3: HOLD penalty calculation accuracy - Bug #4
#[test]
fn test_hold_penalty_calculation_accuracy() -> anyhow::Result<()> {
    // BUG #4: Verify exact math for penalty calculation
    // Log return: ln(6000/5900) ≈ 0.0167 = 1.67%  (WRONG)
    // Price change: (6000-5900)/5900 ≈ 0.0169 = 1.69%  (CORRECT)

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config.clone());

    // ES futures: 5900 → 6000 (+100 points = +1.69% movement)
    let current_state = create_state_with_es_price(5900.0);
    let next_state = create_state_with_es_price(6000.0);
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Hold,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected: Movement 1.69% < threshold 2.0% → NO penalty
    assert_eq!(
        reward, config.hold_reward,
        "BUG #4 CATCH: 1.69% movement (100 pts on ES 5900) should not trigger penalty, got {}",
        reward
    );

    // Now test with exact 2% boundary
    let next_state_2pct = create_state_with_es_price(6018.0); // Exactly +2%
    let recent_actions = vec![]; // No action history for unit test
    let reward_2pct = reward_fn.calculate_reward(
        TradingAction::Hold,
        &current_state,
        &next_state_2pct,
        &recent_actions,
    )?;

    assert_eq!(
        reward_2pct, config.hold_reward,
        "BUG #4 CATCH: Exactly 2% movement should not trigger penalty (not exceeding), got {}",
        reward_2pct
    );

    Ok(())
}

/// Test C4: HOLD penalty uses actual price change, not log returns - Bug #4
#[test]
fn test_hold_penalty_uses_actual_price_change() -> anyhow::Result<()> {
    // BUG #4: Critical test to verify we're NOT using log returns
    // Log return: ln(new/old) ≈ (new-old)/old for small changes
    // But diverges significantly for large moves

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config.clone());

    // Large price swing: 5900 → 7080 (+1180 points = +20% movement)
    let current_state = create_state_with_es_price(5900.0);
    let next_state = create_state_with_es_price(7080.0);
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Hold,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected price change: (7080-5900)/5900 = 0.20 = 20%
    // Log return: ln(7080/5900) ≈ 0.182 = 18.2% (WRONG - we should NOT use this)

    // Excess: 20% - 2% = 18% = 0.18
    // Penalty: 0.001 - (0.01 * 0.18) = 0.001 - 0.0018 = -0.0008
    let expected = Decimal::try_from(-0.0008).unwrap();
    let tolerance = Decimal::try_from(0.0001).unwrap();

    assert!(
        (reward - expected).abs() < tolerance,
        "BUG #4 CATCH: Penalty should use actual price change (20%), not log return (18.2%). Expected {}, got {}",
        expected,
        reward
    );

    // Verify reward is negative (strong penalty for 20% move)
    assert!(
        reward < Decimal::ZERO,
        "BUG #4 CATCH: 20% movement should produce negative reward, got {}",
        reward
    );

    Ok(())
}

/// Test C5: HOLD penalty with price drop (verify abs value) - Bug #4
#[test]
fn test_hold_penalty_price_drop_abs_value() -> anyhow::Result<()> {
    // BUG #4: Verify penalty applies to |price_change|, not signed change

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config.clone());

    // Price drop: 5900 → 5605 (-295 points = -5% movement)
    let current_state = create_state_with_es_price(5900.0);
    let next_state = create_state_with_es_price(5605.0);
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Hold,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected: |−5%| = 5% > 2% → penalty applies
    // Excess: 5% - 2% = 3% = 0.03
    // Penalty: 0.001 - (0.01 * 0.03) = 0.001 - 0.0003 = 0.0007
    let expected = Decimal::try_from(0.0007).unwrap();
    let tolerance = Decimal::try_from(0.0001).unwrap();

    assert!(
        (reward - expected).abs() < tolerance,
        "BUG #4 CATCH: Penalty should use |−5%| = 5%, got reward {}",
        reward
    );

    Ok(())
}

// ============================================================================
// CATEGORY D: Integration Tests
// ============================================================================

/// Test D1: Full reward function workflow with all actions
#[test]
fn test_reward_function_end_to_end() -> anyhow::Result<()> {
    // Comprehensive end-to-end test covering all three actions

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    // Setup: Portfolio with moderate gain
    let (current_state, next_state) = create_portfolio_with_gain(10000.0, 0.03);

    // Test BUY action (should get positive reward for 3% gain)
    let recent_actions = vec![]; // No action history for unit test
    let buy_reward = reward_fn.calculate_reward(
        TradingAction::Buy,
        &current_state,
        &next_state,
        &recent_actions,
    )?;
    assert!(
        buy_reward > Decimal::ZERO,
        "BUY with 3% gain should be positive: {}",
        buy_reward
    );

    // Test SELL action (gets same P&L reward - direction-agnostic)
    // Note: BUY and SELL use portfolio P&L, not price direction
    // The reward function doesn't penalize wrong directional bets in the P&L component
    let recent_actions = vec![]; // No action history for unit test
    let sell_reward = reward_fn.calculate_reward(
        TradingAction::Sell,
        &current_state,
        &next_state,
        &recent_actions,
    )?;
    // SELL should get same reward as BUY (both use portfolio P&L)
    assert_eq!(
        sell_reward, buy_reward,
        "SELL and BUY should have same reward (portfolio-based, not direction-based): SELL={}, BUY={}",
        sell_reward,
        buy_reward
    );

    // Test HOLD action with low volatility
    let hold_state_current = create_state_with_es_price(5900.0);
    let hold_state_next = create_state_with_es_price(5910.0); // +0.17%
    let recent_actions = vec![]; // No action history for unit test
    let hold_reward = reward_fn.calculate_reward(
        TradingAction::Hold,
        &hold_state_current,
        &hold_state_next,
        &recent_actions,
    )?;
    assert!(
        hold_reward > Decimal::ZERO,
        "HOLD with low volatility should be slightly positive: {}",
        hold_reward
    );

    Ok(())
}

/// Test D2: Reward consistency across episodes (deterministic behavior)
#[test]
fn test_reward_consistency_across_episodes() -> anyhow::Result<()> {
    // Verify same state transitions produce same rewards (no randomness)

    let config = RewardConfig::default();

    let (current_state, next_state) = create_portfolio_with_gain(10000.0, 0.05);

    // Episode 1
    let mut reward_fn_1 = RewardFunction::new(config.clone());
    let recent_actions = vec![]; // No action history for unit test
    let reward_1 = reward_fn_1.calculate_reward(
        TradingAction::Buy,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Episode 2 (fresh reward function)
    let mut reward_fn_2 = RewardFunction::new(config.clone());
    let recent_actions = vec![]; // No action history for unit test
    let reward_2 = reward_fn_2.calculate_reward(
        TradingAction::Buy,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    assert_eq!(
        reward_1, reward_2,
        "Reward function should be deterministic: Episode1={}, Episode2={}",
        reward_1, reward_2
    );

    Ok(())
}

/// Test D3: Verify reward history tracking
#[test]
fn test_reward_history_tracking() -> anyhow::Result<()> {
    // Ensure reward_history is populated correctly

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    let (current_state, next_state) = create_portfolio_with_gain(10000.0, 0.02);

    // Calculate 5 rewards
    for _ in 0..5 {
        let recent_actions = vec![]; // No action history for unit test
        reward_fn.calculate_reward(
            TradingAction::Buy,
            &current_state,
            &next_state,
            &recent_actions,
        )?;
    }

    // Verify history has 5 entries
    let stats = reward_fn.get_stats();
    assert_eq!(
        stats.total_rewards, 5,
        "Should have 5 rewards in history, got {}",
        stats.total_rewards
    );

    Ok(())
}

/// Test D4: Edge case - Zero portfolio value
#[test]
fn test_zero_portfolio_value_edge_case() -> anyhow::Result<()> {
    // BUG #2 catch: Ensure division by zero is handled

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    let current_state = TradingState {
        price_features: vec![5900.0, 5905.0, 5895.0, 5900.0],
        technical_indicators: vec![0.5, 0.5, 0.5, 0.5],
        market_features: vec![0.25, 10000.0, 0.0, 0.0],
        portfolio_features: vec![0.0, 0.0, 0.0, 0.0], // Zero portfolio value
    };

    let next_state = TradingState {
        price_features: vec![5910.0, 5915.0, 5905.0, 5910.0],
        technical_indicators: vec![0.5, 0.5, 0.5, 0.5],
        market_features: vec![0.25, 10000.0, 0.0, 0.0],
        portfolio_features: vec![100.0 / 10000.0, 0.5, 0.0, 0.0], // Portfolio grew from zero
    };

    // Should not panic, P&L component should be zero (current_value = 0 fallback)
    // But total reward may be negative due to cost/risk penalties
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Buy,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // P&L component is zero, but risk penalty (position 0.5 is over threshold 0.0)
    // and cost penalty apply, so total reward is slightly negative
    // The key is that it doesn't panic (division by zero protection works)
    assert!(
        reward <= Decimal::ZERO,
        "Zero portfolio value: P&L=0 but penalties apply, got {}",
        reward
    );

    Ok(())
}

/// Test D5: Realistic ES futures scenario
#[test]
fn test_realistic_es_futures_scenario() -> anyhow::Result<()> {
    // Simulate realistic ES futures trading scenario

    let config = RewardConfig::default();
    let mut reward_fn = RewardFunction::new(config);

    // Scenario: BUY at 5900, price moves to 5925 (+25 points = +0.42%)
    let current_state = TradingState {
        price_features: vec![5900.0, 5905.0, 5895.0, 5900.0],
        technical_indicators: vec![0.52, 0.48, 0.55, 0.50], // Slightly bullish indicators
        market_features: vec![0.25, 12000.0, 0.0, 0.0],     // Normal ES spread and volume
        portfolio_features: vec![0.95, 0.3, 0.0, 0.0],      // 95% portfolio value, 30% position
    };

    let next_state = TradingState {
        price_features: vec![5925.0, 5930.0, 5920.0, 5925.0],
        technical_indicators: vec![0.55, 0.50, 0.58, 0.53],
        market_features: vec![0.25, 11500.0, 0.0, 0.0],
        portfolio_features: vec![0.96, 0.35, 0.0, 0.0], // Portfolio value increased slightly
    };
    let recent_actions = vec![]; // No action history for unit test
    let reward = reward_fn.calculate_reward(
        TradingAction::Buy,
        &current_state,
        &next_state,
        &recent_actions,
    )?;

    // Expected: Small positive reward (portfolio grew ~1%)
    assert!(
        reward > Decimal::ZERO,
        "Profitable ES futures trade should give positive reward: {}",
        reward
    );

    // Verify reward is reasonable magnitude (not extreme)
    let max_reasonable = Decimal::try_from(0.1).unwrap(); // 10% is max reasonable
    assert!(
        reward < max_reasonable,
        "Reward should be reasonable magnitude, got {}",
        reward
    );

    Ok(())
}