orderbook.hpp

 // what Does this do ?  --> https://stackoverflow.com/questions/1653958/why-are-ifndef-and-define-used-in-c-header-files

#ifndef ORDERBOOK_HPP
#define ORDERBOOK_HPP

#include <string>
#include <unordered_map>
#include <vector>


std :: string TICKER = "GOOGL"; // ticker for the stock we are trading
struct Balances{
    std:: unordered_map <std :: string,int> balance; // STORES USD : VALUE, GOOGE : VALUE 
    Balances(){
        balance["USD"] = 0;
        balance[TICKER] = 0;
    }
    Balances(std:: string market , int value){
        balance[market] = value;
    }

    std::string addBalance(std:: string market, int value){
        // if balance array contains the market, add the value to the balance
        if(balance.find(market) != balance.end()){
            balance[market] += value;
            return "Balance added successfully";
        }
        balance[market] = value;
        return "Balance added successfully";
    }
};

// stores unique user name and balances for each user
struct User{
    std :: string user_name;
    Balances user_balance;

    User(){};

    User(std::string Username, Balances b){
        user_name = Username;
        user_balance = b;
    }

    User(std::string Username){
        user_name = Username;
        user_balance = Balances(); // default balance is 1000 USD and 0 GOOGL
    }
};


// User can place an order to buy or sell a certain quantity of a stock at a certain price, and this order is stored in the order book or is matched and balances are exchanged 
struct Order{
    std :: string user_name;
    std :: string side;
    int price;
    int quantity;
    static int order_counter_bid; // Declare a static counter to keep track of the order number
    static int order_counter_ask; // Declare a static counter to keep track of the order number
    int insertion_order_bid; // order in which the order was inserted into the order book
    int insertion_order_ask; // order in which the order was inserted into the order book
    Order(std::string Username, std::string Side, int Price, int Quantity){
        user_name = Username;
        side = Side;
        price = Price;
        quantity = Quantity;
        if(side == "bid"){
            insertion_order_bid = order_counter_bid++;
        }
        else{
            insertion_order_ask = order_counter_ask++;
        }
    }
};




class OrderBook{
private:

    std :: vector<Order> bids; // stores all bids in order of price and time --> O(n) lookup
    std :: vector<Order> asks; // stores all asks in order of price and time --> O(n) lookup
    std :: unordered_map <std :: string,User> users; // stores unique user name and balances for each user --> O(1) lookup no need to be in order 
    void flipBalance(const std::string& userId1, const std::string& userId2, double quantity, double price);

    public:
    OrderBook(); // constructor
   ~OrderBook(); // destructor 
    std:: string add_bid(std :: string Username, int Price, int Quantity); // adds a bid or ask to the order book
    std:: string add_ask(std :: string Username, int Price, int Quantity); // adds a bid or ask to the order book
    std:: string getBalance(std::string username); // returns the balance of a user
    std:: string getQuote(int qty); // returns the best bid and ask prices and quantities
    std:: string getDepth(); // returns the entire order book and shows all bids and asks
    std:: string makeUser(std:: string); // creates a new user for people trying to join the market
    std:: string addBalanace(std:: string Username, std:: string market, int value); // adds balance to a user
    void cancelBid(std:: string Username, int Price, int Quantity); // cancels a bid or ask from the order book
    void cancelAsk(std:: string Username, int Price, int Quantity); // cancels a bid or ask from the order book

};


#endif