Caching & Permission-Gating Paid Market Data

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

struct Quote {
    std::string symbol;
    double bid;
    double ask;
};

struct MarketDepth {
    std::string symbol;
    std::vector<double> bidPrices;
    std::vector<double> askPrices;
};

// Naive: Direct remote feed without caching or access protection.
class RemoteMarketDataFeed {
    int paidApiCalls_{0};

public:
    Quote fetchQuote(const std::string& symbol) {
        ++paidApiCalls_;
        // Simulates expensive network latency and ₹0.50 vendor charge per call
        std::println("[REMOTE FEED] Fetching paid quote for {} (Total API calls: {}, Incurred fee: Rs.{:.2f})",
                     symbol, paidApiCalls_, paidApiCalls_ * 0.50);
        return Quote{symbol, 2450.0, 2451.5};
    }

    MarketDepth fetchLevel2Depth(const std::string& symbol) {
        ++paidApiCalls_;
        std::println("[REMOTE FEED] Fetching Level-2 depth for {} (Total API calls: {})",
                     symbol, paidApiCalls_);
        return MarketDepth{symbol, {2450.0, 2449.5, 2449.0}, {2451.5, 2452.0, 2452.5}};
    }

    int totalCalls() const noexcept { return paidApiCalls_; }
};

// Callers directly call the remote feed, duplicating access checks and failing to cache
class NaiveClientDesk {
    RemoteMarketDataFeed& feed_;
    std::string userTier_; // "BASIC" or "PRO"

public:
    NaiveClientDesk(RemoteMarketDataFeed& feed, std::string tier)
        : feed_(feed), userTier_(std::move(tier)) {}

    void renderScreen(const std::string& symbol) {
        // Repeated calls hit the network every single time!
        auto q1 = feed_.fetchQuote(symbol);
        auto q2 = feed_.fetchQuote(symbol); // Duplicate network call

        // Ad-hoc permission check scattered in caller code: easy to forget or bypass!
        if (userTier_ == "PRO") {
            auto depth = feed_.fetchLevel2Depth(symbol);
            std::println("Rendered Level-2 depth with {} bid levels.", depth.bidPrices.size());
        } else {
            std::println("Level-2 depth skipped for basic user.");
        }
    }
};

int main() {
    RemoteMarketDataFeed feed;
    NaiveClientDesk desk(feed, "BASIC");

    desk.renderScreen("RELIANCE");
    desk.renderScreen("RELIANCE");
    return 0;
}