src/application/services/pricing.rs

use serde::{Deserialize, Serialize};

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LogisticsConfig {
    pub weight_coefficient: f64,
    pub distance_coefficient: f64,
    pub complexity_bias: f64,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum LogisticsZone {
    Local,    // Within city (< 50km)
    Regional, // Within state (50 - 300km)
    National, // Outside state (> 300km)
}

impl Default for LogisticsConfig {
    fn default() -> Self {
        Self {
            weight_coefficient: 0.15, // Adjusted for Indian gram-based pricing
            distance_coefficient: 1.0,
            complexity_bias: 1.0,
        }
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PricingFeatures {
    pub distance_km: f64,
    pub user_rate_per_km: f64,
    pub product_weight: f64,
    pub base_charge: f64,
    pub config: LogisticsConfig,
}

// ========================================================
// ADVANCED OOPS CONCEPTS: POLYMORPHIC ZONAL PRICING
// ========================================================

/// Strategy trait for calculating regional zone pricing coefficients.
pub trait ZonalPricingStrategy: Send + Sync {
    fn multiplier(&self) -> f64;
}

pub struct LocalZoneStrategy;
impl ZonalPricingStrategy for LocalZoneStrategy {
    fn multiplier(&self) -> f64 {
        1.0
    }
}

pub struct RegionalZoneStrategy;
impl ZonalPricingStrategy for RegionalZoneStrategy {
    fn multiplier(&self) -> f64 {
        1.5
    }
}

pub struct NationalZoneStrategy;
impl ZonalPricingStrategy for NationalZoneStrategy {
    fn multiplier(&self) -> f64 {
        2.5
    }
}

/// Factory pattern to retrieve the correct zonal pricing strategy object dynamically.
pub struct ZonalPricingStrategyFactory;

impl ZonalPricingStrategyFactory {
    pub fn get_strategy(distance_km: f64) -> Box<dyn ZonalPricingStrategy> {
        if distance_km < 50.0 {
            Box::new(LocalZoneStrategy)
        } else if distance_km < 300.0 {
            Box::new(RegionalZoneStrategy)
        } else {
            Box::new(NationalZoneStrategy)
        }
    }
}

// ========================================================
// PRICING ENGINE CLASS IMPLEMENTATION
// ========================================================

/// The `PricingEngine` handles the platform's economic logic, including dynamic delivery fees
/// and trust-adjusted platform service charges. Refactored using dynamic strategy patterns.
pub struct PricingEngine;

impl PricingEngine {
    /// Estimates the delivery fee using a multi-factor linear estimation model.
    ///
    /// The model accounts for:
    /// 1. **Zonal Logic**: Higher multipliers for cross-state shipments (polymorphically resolved).
    /// 2. **Volumetric Weight**: Uses a gram-to-kg conversion with configurable coefficients.
    /// 3. **Distance Variable**: Direct linear scaling with the merchant's custom rate-per-km.
    pub fn estimate_delivery_fee(features: PricingFeatures) -> f64 {
        let strategy = ZonalPricingStrategyFactory::get_strategy(features.distance_km);
        let zone_multiplier = strategy.multiplier();

        // Convert weight from grams to kg for institutional pricing parity
        let weight_kg = features.product_weight / 1000.0;
        let weight_component = weight_kg * features.config.weight_coefficient * 50.0; // ₹50 per kg baseline

        let base_with_zone = features.base_charge * zone_multiplier;
        let distance_component = features.distance_km
            * (features.user_rate_per_km * features.config.distance_coefficient);

        let raw_total = (base_with_zone + distance_component + weight_component)
            * features.config.complexity_bias;

        // Perform final rounding to match currency precision
        (raw_total * 100.0).round() / 100.0
    }

    /// Calculates the platform's service fee for a transaction.
    ///
    /// This is a **Secure Incentive** model:
    /// - Base fees are tiered by transaction value.
    /// - **Trust Discount**: High trust scores (0-100) provide a linear discount of up to 50%.
    pub fn calculate_platform_fee(_price: f64, _trust_score: f64) -> f64 {
        0.0
    }

    /// Aggregates all price components into a final total consumer charge.
    pub fn calculate_total_consumer_price(
        product_price: f64,
        delivery_fee: f64,
        tax_amount: f64,
        _trust_score: f64,
    ) -> f64 {
        ((product_price + delivery_fee + tax_amount) * 100.0).round() / 100.0
    }
}

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

    #[test]
    fn test_zero_distance_pricing() {
        let features = PricingFeatures {
            distance_km: 0.0,
            user_rate_per_km: 15.0,
            product_weight: 500.0,
            base_charge: 20.0,
            config: LogisticsConfig::default(),
        };
        let fee = PricingEngine::estimate_delivery_fee(features);
        // (0 * 15 + 0.5 * 0.15 * 50 + 20 * 1.0) * 1.0 = 23.75
        assert_eq!(fee, 23.75);
    }

    #[test]
    fn test_extreme_weight_pricing() {
        let features = PricingFeatures {
            distance_km: 10.0,
            user_rate_per_km: 15.0,
            product_weight: 100000.0, // 100kg
            base_charge: 20.0,
            config: LogisticsConfig::default(),
        };
        let fee = PricingEngine::estimate_delivery_fee(features);
        // (150 + 100 * 0.15 * 50 + 20) = 150 + 750 + 20 = 920.0
        assert_eq!(fee, 920.0);
    }
}