useful NSString functions

NSString+Kahaf.h

#import <Foundation/Foundation.h>

/**
 *  this category contains functions that either work on `NSString` or return `NSString`. The category is called <b>Kahaf</b>
 * because these functions don't exactly fit into any other single category.
 */
@interface NSString (Kahaf)

/**
 *  Creates and returns a new UUID with RFC 4122 version 4 random bytes.
 *
 *  @return a string representation of the generated UUID
 */
+ (NSString *)uniqueID;

/**
 *  returns path to the `Documents` directory
 *
 *  @return `Documents` directory path
 */
+ (NSString *)pathForPublicDocumentDirectory;
/**
 *  returns path to the `Library` directory
 *
 *  @return `Library` directory path
 */
+ (NSString *)pathForPrivateDocumentDirectory;
/**
 *  returns path to the `Cache` directory
 *
 *  @return `Cache` directory path
 */
+ (NSString *)pathForCacheDirectory;
/**
 *  returns path to a temporary directory, it is safe to write to this directory without checking for existing files
 *
 *  @return path to a temporary directory
 */
+ (NSString *)pathForTemporaryDirectory;
/**
 *  prepends path to `Documents` directory to `self` and returns a new `NSString`
 *
 *  @return `NSString` with `Documents` directory prepended
 */
- (NSString *)prependPublicDocumentsDirectory;
/**
 *  prepends path to `Library` directory to `self` and returns a new `NSString`
 *
 *  @return `NSString` with `Library` directory prepended
 */
- (NSString *)prependPrivateDocumentsDirectory;
/**
 *  prepends path to a temporary directory to `self` and returns a new `NSString`
 *
 *  @return `NSString` with path to a temporary directory prepended
 */
- (NSString *)prependTemporaryDirectory;


/**
 *  removes white space from the start and end of the string (left and right trim)
 *
 *  @return a new string with white space from both ends removed
 */
- (NSString *)trimWhitespace;
/**
 *  checks whether string is a valid email
 *
 *  @return returns YES if string is a valid email
 */
- (BOOL)isValidEmail;

- (BOOL)isValidURL;
/**
 *  removes white space from both ends of a string and returns length
 *
 *  @return returns length of the string (after removing whitespace from both ends)
 */
- (NSUInteger)trimmedLength;

- (NSNumber *)numberWithDecimalString;

@end

NSString+Kahaf.m

#import "NSString+Kahaf.h"

@implementation NSString (Kahaf)

+ (NSString *)uniqueID
{
    return [[NSUUID UUID] UUIDString];
}

+ (NSString *)pathForPublicDocumentDirectory
{
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
	NSString *documentsDirectory = [paths objectAtIndex:0];
	return documentsDirectory;
}

+ (NSString*)pathForPrivateDocumentDirectory
{
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);
	NSString *libraryDirectory = [paths objectAtIndex:0];
	return libraryDirectory;
}

+ (NSString *)pathForCacheDirectory
{
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory,NSUserDomainMask, YES);
	NSString *cacheDir = [paths objectAtIndex:0];
	return cacheDir;
}

+ (NSString *)pathForTemporaryDirectory
{
    return NSTemporaryDirectory();
}

- (NSString *)prependPublicDocumentsDirectory
{
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
	NSString *documentsDirectory = [paths objectAtIndex:0];
	NSString *appFile = [documentsDirectory stringByAppendingPathComponent:self];
	return appFile;
}

- (NSString *)prependPrivateDocumentsDirectory
{
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);
	NSString *documentsDirectory = [paths objectAtIndex:0];
	NSString *appFile = [documentsDirectory stringByAppendingPathComponent:self];
	return appFile;
}

- (NSString *)prependTemporaryDirectory
{
	NSString *path = NSTemporaryDirectory();
    return [path stringByAppendingPathComponent:self];
}


- (NSString *)trimWhitespace
{
    return [self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
}

// based on: http://is.gd/rMQNFX
- (BOOL)isValidEmail
{
    NSString *stricterFilterString = @"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}";
    NSPredicate *emailTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", stricterFilterString];
    return [emailTest evaluateWithObject:self];
}

// based on: https://stackoverflow.com/questions/1471201/how-to-validate-an-url-on-the-iphone
- (BOOL)isValidURL
{
    if([self trimmedLength] > 0)
    {
        NSURL *website = [NSURL URLWithString:self];
        if(website && website.scheme && website.host)
        {
            return YES;
        }
    }
    return NO;
}

- (NSUInteger)trimmedLength
{
    return [[self trimWhitespace] length];
}

- (NSNumber *)numberWithDecimalString
{
    static NSNumberFormatter *f = nil;
    if(f == nil)
    {
        f = [[NSNumberFormatter alloc] init];
        [f setNumberStyle:NSNumberFormatterDecimalStyle];
    }
    
   return [f numberFromString:self];
}
@end