NSDate+Justaway.m

#import "NSDate+Justaway.h"

@implementation NSDate (Justaway)

+ (instancetype)dateWithString:(NSString *)string
{
    static NSDateFormatter *formatter;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        formatter = NSDateFormatter.new;
        formatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
        formatter.dateFormat = @"EEE MMM dd HH:mm:ss Z yyyy";
    });
    
    return [formatter dateFromString:string];
}

- (NSString *)absoluteDescription
{
    static NSDateFormatter *formatter;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        formatter = [[NSDateFormatter alloc] init];
        formatter.locale = [NSLocale currentLocale];
        formatter.dateFormat = @"yyyy/MM/dd HH:mm:ss";
    });
    
    return [formatter stringFromDate:self];
}

- (NSString *)relativeDescription
{
    NSTimeInterval diff = [[NSDate date] timeIntervalSinceDate:self];
    if (diff < 1) {
        return @"now";
    } else if (diff < 60) {
        return [NSString stringWithFormat:@"%ds", (int) diff];
    } else if (diff < 3600) {
        return [NSString stringWithFormat:@"%dm", (int) (diff / 60)];
    } else if (diff < 86400) {
        return [NSString stringWithFormat:@"%dh", (int) (diff / 3600)];
    } else {
        return [NSString stringWithFormat:@"%dd", (int) (diff / 86400)];
    }
}

@end

TEST_NSDate+Justaway.m

#import <XCTest/XCTest.h>
#import "NSDate+Justaway.h"

@interface NSDate_Justaway : XCTestCase

@end

@implementation NSDate_Justaway

- (void)setUp
{
    [super setUp];
    // Put setup code here. This method is called before the invocation of each test method in the class.
}

- (void)tearDown
{
    // Put teardown code here. This method is called after the invocation of each test method in the class.
    [super tearDown];
}

- (void)testExample
{
    // relativeDescription
    XCTAssertEqualObjects([[NSDate date] relativeDescription], @"now");
    XCTAssertEqualObjects([[NSDate dateWithTimeIntervalSinceNow:-3] relativeDescription], @"3s");
    XCTAssertEqualObjects([[NSDate dateWithTimeIntervalSinceNow:-3*60] relativeDescription], @"3m");
    XCTAssertEqualObjects([[NSDate dateWithTimeIntervalSinceNow:-3*60*60] relativeDescription], @"3h");
    XCTAssertEqualObjects([[NSDate dateWithTimeIntervalSinceNow:-3*60*60*24] relativeDescription], @"3d");
    
    // absoluteDescription
    XCTAssertEqualObjects([[NSDate dateWithString:@"Wed Jun 06 20:07:10 +0900 2012"] absoluteDescription], @"2012/06/06 20:07:10");
    XCTAssertEqualObjects([[NSDate dateWithString:@"Wed Jun 06 20:07:10 +0000 2012"] absoluteDescription], @"2012/06/07 05:07:10");
}

@end