Supporting NSE and BSE Without Mixing Components

#include <cstdint>
#include <format>
#include <memory>
#include <print>
#include <string>
#include <string_view>

// Naive implementation: Components are instantiated piecemeal via scattered conditionals.
// There is zero type safety or compile-time guarantee preventing an engineer from
// pairing an NSE router with a BSE fee calculator or BSE symbol validator.

class NaiveNseRouter {
public:
    std::string route(std::string_view symbol, int qty) {
        return std::format("[NSE-NEAT] Routed {} of {}", qty, symbol);
    }
};

class NaiveBseRouter {
public:
    std::string route(std::string_view symbol, int qty) {
        return std::format("[BSE-BOLT] Routed {} of {}", qty, symbol);
    }
};

class NaiveNseFeeCalc {
public:
    int64_t calculate(int64_t turnoverPaise) {
        return (turnoverPaise * 325) / 10'000'000; // NSE rate
    }
};

class NaiveBseFeeCalc {
public:
    int64_t calculate(int64_t turnoverPaise) {
        return (turnoverPaise * 375) / 10'000'000; // BSE rate
    }
};

int main() {
    std::string exchange = "NSE";
    std::string feeTier = "BSE"; // Config typo or wrong parameter flag!

    auto nseRouter = std::make_unique<NaiveNseRouter>();
    auto bseFee = std::make_unique<NaiveBseFeeCalc>(); // ACCIDENTAL MISMATCH!

    // The trading session is now running with an NSE router but charging BSE fee schedules!
    int64_t turnoverPaise = 100'000'000; // Rs. 1,000,000
    std::println("{}", nseRouter->route("RELIANCE", 100));
    std::println("Calculated Fee (Wrong Exchange Rate!): {} paise", bseFee->calculate(turnoverPaise));
}