session-ios/Signal/src/NotificationTracker.m

#import "NotificationTracker.h"
#import "CryptoTools.h"
#import "FunctionalUtil.h"

#define MAX_NOTIFICATIONS_TO_TRACK 100
#define NOTIFICATION_PAYLOAD_KEY @"m"

@implementation NotificationTracker {
    NSMutableArray* _witnessedNotifications;
}

+(NotificationTracker*) notificationTracker {
    NotificationTracker* notificationTracker = [NotificationTracker new];
    notificationTracker->_witnessedNotifications = [NSMutableArray new];
    return notificationTracker;
}

-(BOOL) shouldProcessNotification:(NSDictionary*) notification {
    BOOL should = ![self wasNotificationProcessed:notification];
    if (should) {
        [self markNotificationAsProcessed:notification];
    }
    return should;
}

-(void) markNotificationAsProcessed:(NSDictionary*) notification {
    NSData* data = [self getIdForNotification:notification];
    [_witnessedNotifications insertObject:data atIndex:0];
    
    while(MAX_NOTIFICATIONS_TO_TRACK < _witnessedNotifications.count){
        [_witnessedNotifications removeLastObject];
    }
}

-(BOOL) wasNotificationProcessed:(NSDictionary*) notification {
    NSData* data = [self getIdForNotification:notification];
    
    return [_witnessedNotifications any:^int(NSData* previousData) {
        return [data isEqualToData:previousData];
    }];
}

// Uniquely Identify a notification by the hash of the message payload.
-(NSData*) getIdForNotification:(NSDictionary*) notification {
    NSData* data = [notification[NOTIFICATION_PAYLOAD_KEY] dataUsingEncoding:NSUTF8StringEncoding];
    NSData* notificationHash = [data hashWithSha256];
    return notificationHash;
}

@end