/*

     File: NotificationObserve.c

 Abstract: Implements the code to add and remove observers for the stock price

 change notification, using CFNotificationCenter.

  Version: 1.2

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#import <CoreFoundation/CoreFoundation.h>

extern void StockPriceChanged(void *observer, CFStringRef stockSymbol, double newPrice);

// Callback for the notification

// This repackages the data and sends it to the observer as a StockPriceChanged() callback.

void myCallback(CFNotificationCenterRef center, void *observer, CFStringRef name, const void *object, CFDictionaryRef userInfo) {

    double newPrice = 0.0;

    CFStringRef stockSymbol = NULL;

    // We get the new price out of the user info dictionary

    // We also get the stock symbol out of there (true, the object is also

    //   the stock symbol, but that can be NULL, if the registry was made for "all")

    if (userInfo) {

        CFNumberRef newPriceNum = CFDictionaryGetValue(userInfo, CFSTR("New Price"));

    if (newPriceNum) CFNumberGetValue(newPriceNum, kCFNumberDoubleType, &newPrice);

        stockSymbol = CFDictionaryGetValue(userInfo, CFSTR("Stock Symbol"));

    }

    StockPriceChanged(observer, stockSymbol, newPrice);

}

// Pass in "all" stockSymbol to register for all stocks; this will cause the notification

// to be registered for with a NULL object, meaning it will be delivered no matter

// what the object.

void AddStockNotificationObserver(const void *observer, CFStringRef stockSymbol) {

    CFNotificationCenterRef center = CFNotificationCenterGetDistributedCenter();

    // Register for the notification with the global notification center

    // Arguments are:

    // Caller supplied arbitrary observer (which is used as the callback object)

    // Name of notification, in this case "Stock Price Changed Notification"

    // And the object, in this case the stock symbol (NULL for all)

    // The suspension behavior --- determines when the notification center process

    //   delivers the notifications to this process. For notifications that don't

    //   require non-frontmost apps to react, then you can pass 

    //   CFNotificationSuspensionBehaviorHold or CFNotificationSuspensionBehaviorCoalesce

    if (CFEqual(stockSymbol, CFSTR("all"))) stockSymbol = NULL;

    CFNotificationCenterAddObserver(center, observer, myCallback, CFSTR("Stock Price Changed Notification"),  stockSymbol, CFNotificationSuspensionBehaviorDeliverImmediately);

}

void RemoveStockNotificationObserver(const void *observer, CFStringRef stockSymbol) {

    CFNotificationCenterRef center = CFNotificationCenterGetDistributedCenter();

    if (CFEqual(stockSymbol, CFSTR("all"))) stockSymbol = NULL;

    CFNotificationCenterRemoveObserver(center, observer, CFSTR("Stock Price Changed Notification"),  stockSymbol);

}

extern void RemoveObserverForAllStocks(const void *observer) {

    CFNotificationCenterRef center = CFNotificationCenterGetDistributedCenter();

    CFNotificationCenterRemoveEveryObserver(center, observer);

}