Matching Buyers and Sellers Through an Order Book

#include <print>
#include <string>
#include <vector>

// Naive design: Trading desks maintain direct references to every other desk.
// For N desks, this creates N * (N - 1) / 2 connections (O(N^2) mesh).
class NaiveTradingDesk {
    std::string deskId_;
    std::vector<NaiveTradingDesk*> counterparties_;

public:
    explicit NaiveTradingDesk(std::string id) : deskId_(std::move(id)) {}

    void addCounterparty(NaiveTradingDesk* other) {
        counterparties_.push_back(other);
    }

    const std::string& id() const { return deskId_; }

    // Direct peer-to-peer negotiation: Desk A interrogates Desk B directly.
    bool directMatch(const std::string& symbol, double price, int qty, const std::string& buyerId) {
        // Hardcoded matching check: Desk answers for itself without any centralized price discovery
        if (symbol == "TCS" && price >= 3500.0 && qty <= 100) {
            std::println("[DIRECT MATCH] Seller {} traded {} shares with Buyer {} at Rs.{:.2f}",
                         deskId_, qty, buyerId, price);
            return true;
        }
        return false;
    }

    void submitBuyOrder(const std::string& symbol, double price, int qty) {
        std::println("{} searching {} counterparties for best price...", deskId_, counterparties_.size());
        for (auto* peer : counterparties_) {
            if (peer->directMatch(symbol, price, qty, deskId_)) {
                return; // Matched first peer found, ignoring price-time priority of other desks!
            }
        }
        std::println("{} found no matching counterparty.", deskId_);
    }
};

int main() {
    NaiveTradingDesk deskA("Desk-Alpha");
    NaiveTradingDesk deskB("Desk-Bravo");
    NaiveTradingDesk deskC("Desk-Charlie");

    // Tangled N^2 mesh setup: Every desk must know every other desk
    deskA.addCounterparty(&deskB);
    deskA.addCounterparty(&deskC);
    deskB.addCounterparty(&deskA);
    deskB.addCounterparty(&deskC);
    deskC.addCounterparty(&deskA);
    deskC.addCounterparty(&deskB);

    deskA.submitBuyOrder("TCS", 3550.0, 50);
}