package observer;

import java.util.ArrayList;
import java.util.List;

/**
 * Subject (Observable) — maintains a list of observers and notifies them
 * when the stock price changes. Observers register and deregister freely.
 */
public class StockMarket {
    private final String ticker;
    private double price;
    private final List<StockObserver> observers = new ArrayList<>();

    public StockMarket(String ticker, double initialPrice) {
        this.ticker = ticker;
        this.price  = initialPrice;
        System.out.println("[Market] " + ticker + " initialised at $" + initialPrice);
    }

    public void subscribe(StockObserver observer)   { observers.add(observer); }
    public void unsubscribe(StockObserver observer) { observers.remove(observer); }

    public void setPrice(double newPrice) {
        double old = this.price;
        this.price = newPrice;
        System.out.printf("[Market] %s price: $%.2f -> $%.2f%n", ticker, old, newPrice);
        notifyObservers(old, newPrice);
    }

    private void notifyObservers(double old, double newPrice) {
        for (StockObserver o : observers) {
            o.onPriceChanged(ticker, old, newPrice);
        }
    }
}