Category on NSDate to get current time in current timezone (instead of GMT) and also set time component of date to midnight (useful in comparing dates for "same day" situations)

NSDate+DateExtensions.m

#import "NSDate+DateExtensions.h"

@implementation NSDate (DateExtensions)

+ (NSDate *) currentDateInSystemTimezone
{
    NSDate* sourceDate = [NSDate date];
    
    NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
    NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
    
    NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
    NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
    NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
    
    NSDate* destinationDate = [[NSDate alloc] initWithTimeInterval:interval sinceDate:sourceDate];
    
    return destinationDate;
}

- (NSDate *)dateAtBeginningOfDayForDate:(NSDate *)inputDate
{
    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier: NSGregorianCalendar];
    NSDateComponents *components = [gregorian components: NSUIntegerMax fromDate: inputDate];
    [components setHour: 0];
    [components setMinute: 0];
    [components setSecond: 0];
    
    NSDate *sourceDate = [gregorian dateFromComponents: components];
    
    NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
    NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
    
    NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
    NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
    NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
    
    NSDate* destinationDate = [[NSDate alloc] initWithTimeInterval:-interval sinceDate:sourceDate];
    
    return destinationDate;
    
}