//! Stress testing for portfolios.
//!
//! Applies historical and hypothetical scenarios to estimate P&L impact.

use riskflow_shared::{Portfolio, StressTestResult};

/// Stress tester.
#[derive(Debug)]
pub struct StressTester {
    /// Predefined scenarios.
    scenarios: Vec<StressScenario>,
}

/// A stress test scenario.
#[derive(Debug, Clone)]
pub struct StressScenario {
    /// Scenario name.
    pub name: String,
    /// Description.
    pub description: String,
    /// Market shock (%).
    pub market_shock: f64,
    /// Sector-specific shocks.
    pub sector_shocks: Vec<(String, f64)>,
}

impl Default for StressTester {
    fn default() -> Self {
        Self::new()
    }
}

impl StressTester {
    /// Create a new stress tester with predefined scenarios.
    #[must_use]
    pub fn new() -> Self {
        Self {
            scenarios: default_scenarios(),
        }
    }

    /// Run all stress tests.
    #[must_use]
    pub fn run_all(&self, portfolio: &Portfolio) -> Vec<StressTestResult> {
        self.scenarios
            .iter()
            .map(|scenario| self.run_scenario(portfolio, scenario))
            .collect()
    }

    /// Run a single stress test scenario.
    fn run_scenario(&self, portfolio: &Portfolio, scenario: &StressScenario) -> StressTestResult {
        let total_value = portfolio
            .positions
            .iter()
            .map(|p| p.market_value)
            .sum::<f64>();

        let mut position_impacts = Vec::with_capacity(portfolio.positions.len());
        let mut total_pnl: f64 = 0.0;

        for position in &portfolio.positions {
            // Calculate position-level impact
            let beta_impact = position.beta * scenario.market_shock;

            // Add sector-specific shock
            let sector_shock = scenario
                .sector_shocks
                .iter()
                .find(|(s, _)| s == &position.sector)
                .map_or(0.0, |(_, shock)| *shock);

            let position_pnl = position.market_value * (beta_impact + sector_shock) / 100.0;
            total_pnl += position_pnl;

            let position_return = beta_impact + sector_shock;
            position_impacts.push((position.symbol.clone(), position_return));
        }

        let pnl_impact = if total_value > 0.0 {
            total_pnl / total_value * 100.0
        } else {
            0.0
        };

        StressTestResult {
            scenario: scenario.name.clone(),
            description: scenario.description.clone(),
            pnl_impact,
            position_impacts,
        }
    }

    /// Add a custom scenario.
    pub fn add_scenario(&mut self, scenario: StressScenario) {
        self.scenarios.push(scenario);
    }

    /// Get all scenarios.
    #[must_use]
    pub fn scenarios(&self) -> &[StressScenario] {
        &self.scenarios
    }
}

/// Default stress test scenarios.
fn default_scenarios() -> Vec<StressScenario> {
    vec![
        StressScenario {
            name: "2008 Financial Crisis".to_string(),
            description: "Sharp market decline with financial sector stress".to_string(),
            market_shock: -40.0,
            sector_shocks: vec![
                ("Financials".to_string(), -25.0),
                ("Technology".to_string(), 5.0),
                ("Consumer Staples".to_string(), 10.0),
            ],
        },
        StressScenario {
            name: "COVID-19 Crash".to_string(),
            description: "Rapid 30% market decline".to_string(),
            market_shock: -30.0,
            sector_shocks: vec![
                ("Technology".to_string(), 10.0),
                ("Healthcare".to_string(), 5.0),
                ("Energy".to_string(), -20.0),
            ],
        },
        StressScenario {
            name: "Tech Correction".to_string(),
            description: "Technology sector bubble burst".to_string(),
            market_shock: -15.0,
            sector_shocks: vec![
                ("Technology".to_string(), -30.0),
                ("Communications".to_string(), -15.0),
                ("Financials".to_string(), 5.0),
            ],
        },
        StressScenario {
            name: "Rising Rates".to_string(),
            description: "Sharp increase in interest rates".to_string(),
            market_shock: -10.0,
            sector_shocks: vec![
                ("Financials".to_string(), 10.0),
                ("Technology".to_string(), -15.0),
                ("Consumer Staples".to_string(), -5.0),
            ],
        },
        StressScenario {
            name: "Inflation Spike".to_string(),
            description: "Unexpected inflation acceleration".to_string(),
            market_shock: -8.0,
            sector_shocks: vec![
                ("Energy".to_string(), 15.0),
                ("Technology".to_string(), -10.0),
                ("Consumer Staples".to_string(), -5.0),
            ],
        },
        StressScenario {
            name: "Flash Crash".to_string(),
            description: "Sudden market liquidity crisis".to_string(),
            market_shock: -10.0,
            sector_shocks: vec![],
        },
    ]
}

#[cfg(test)]
mod tests {
    use super::*;
    use riskflow_shared::get_sample_portfolio;

    #[test]
    fn test_stress_tester_creation() {
        let tester = StressTester::new();
        assert!(!tester.scenarios.is_empty());
    }

    #[test]
    fn test_run_all() {
        let tester = StressTester::new();
        let portfolio = get_sample_portfolio();

        let results = tester.run_all(&portfolio);
        assert!(!results.is_empty());

        // All results should have P&L impact
        for result in &results {
            assert!(!result.scenario.is_empty());
            // P&L should be negative for crisis scenarios (most are)
        }
    }

    #[test]
    fn test_crisis_scenario_negative_pnl() {
        let tester = StressTester::new();
        let portfolio = get_sample_portfolio();

        let results = tester.run_all(&portfolio);
        let crisis = results.iter().find(|r| r.scenario.contains("2008"));

        assert!(crisis.is_some());
        assert!(crisis.unwrap().pnl_impact < 0.0); // Should be negative
    }

    #[test]
    fn test_add_custom_scenario() {
        let mut tester = StressTester::new();
        let initial_count = tester.scenarios().len();

        tester.add_scenario(StressScenario {
            name: "Custom Test".to_string(),
            description: "Test scenario".to_string(),
            market_shock: -5.0,
            sector_shocks: vec![],
        });

        assert_eq!(tester.scenarios().len(), initial_count + 1);
    }

    #[test]
    fn test_position_impacts() {
        let tester = StressTester::new();
        let portfolio = get_sample_portfolio();

        let results = tester.run_all(&portfolio);
        let result = &results[0];

        // Should have impact for each position
        assert_eq!(result.position_impacts.len(), portfolio.positions.len());
    }
}