src/application/services/routing.rs

use crate::application::services::pricing::LogisticsZone;
use crate::infrastructure::db::DbPool;
use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize, Clone, sqlx::FromRow)]
pub struct CarrierRecord {
    pub carrier_id: String,
    pub name: String,
    pub service_type: String,
    pub base_rate: f64,
    pub per_kg_rate: f64,
}

pub struct RoutingService {
    pool: DbPool,
}

impl RoutingService {
    pub fn new(pool: DbPool) -> Self {
        Self { pool }
    }

    pub async fn select_optimal_carrier(
        &self,
        zone: LogisticsZone,
        weight_grams: f64,
    ) -> Result<CarrierRecord, sqlx::Error> {
        let service_type = match zone {
            LogisticsZone::Local => "LOCAL",
            LogisticsZone::Regional => "REGIONAL",
            LogisticsZone::National => "NATIONAL",
        };

        let carriers = sqlx::query_as::<_, CarrierRecord>(
            "SELECT carrier_id, name, service_type, base_rate, per_kg_rate FROM carrier_registry WHERE service_type = $1 AND is_active = TRUE"
        )
        .bind(service_type)
        .fetch_all(&self.pool)
        .await?;

        // Simple cost-based selection: base_rate + (kg * per_kg_rate)
        let weight_kg = weight_grams / 1000.0;

        let best_carrier = carriers.into_iter().min_by(|a, b| {
            let cost_a = a.base_rate + (weight_kg * a.per_kg_rate);
            let cost_b = b.base_rate + (weight_kg * b.per_kg_rate);
            cost_a
                .partial_cmp(&cost_b)
                .unwrap_or(std::cmp::Ordering::Equal)
        });

        best_carrier.ok_or_else(|| sqlx::Error::RowNotFound)
    }
}