IZOSMShortLink

IZOSMShortLink.h

//
//  IZOSMShortLink.h
//  OpenMaps
//
//  Created by Zsombor Szabó on 2/2/10.
//  Copyright 2010 IZE. All rights reserved.
//

#import <Foundation/Foundation.h>


@interface IZOSMShortLink : NSObject {
	NSNumber								*_latitude;
	NSNumber								*_longitude;
	NSNumber								*_zoomlevel;
	NSString								*_string;
}

- (id)initWithLatitude:(NSNumber *)latitude longitude:(NSNumber *)longitude zoomlevel:(NSNumber *)zoomlevel;
- (id)initWithString:(NSString *)string;

@property (nonatomic, retain) NSNumber *latitude;
@property (nonatomic, retain) NSNumber *longitude;
@property (nonatomic, retain) NSNumber *zoomlevel;
@property (nonatomic, retain) NSString *string;

+ (BOOL)isValidShortLinkString:(NSString *)string;
- (NSString *)osmShortURLString;

@end

IZOSMShortLink.m

//
//  IZOSMShortLink.m
//  OpenMaps
//
//  Created by Zsombor Szabó on 2/2/10.
//  Copyright 2010 IZE. All rights reserved.
//

#import "IZOSMShortLink.h"

#import "RegexKitLite.h"

@implementation IZOSMShortLink

@synthesize latitude=_latitude;
@synthesize longitude=_longitude;
@synthesize zoomlevel=_zoomlevel;
@synthesize string=_string;

static NSString *shortLinkCharArray = @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_@";

- (id)initWithLatitude:(NSNumber *)latitude longitude:(NSNumber *)longitude zoomlevel:(NSNumber *)zoomlevel
{
	if (self = [super init])
	{
		self.latitude = latitude;
		self.longitude = longitude;
		self.zoomlevel = zoomlevel;
		
		// Calculate string
		long long x = round(([longitude doubleValue] + 180.0) * ((1 << 30) / 90.0));
		long long y = round(([latitude doubleValue] +  90.0) * ((1 << 30) / 45.0));
		
		long long c1 = 0, c2 = 0;
		for (int i = 31; i > 16; --i)
		{
			c1 = (c1 << 1) | ((x >> i) & 1);
			c1 = (c1 << 1) | ((y >> i) & 1);
		}
		for (int i = 16; i > 1; --i)
		{
			c2 = (c2 << 1) | ((x >> i) & 1);
			c2 = (c2 << 1) | ((y >> i) & 1);
		}
		
		NSMutableString *str = [[NSMutableString alloc] init];
		int zoom = [self.zoomlevel intValue];
		int digit;
		for (int i = 0; i < ceil((zoom + 8) / 3.0) && i < 5; ++i)
		{
			digit = (c1 >> (24 - 6 * i)) & 0x3f;
			[str appendFormat:@"%c", [shortLinkCharArray characterAtIndex:digit]];
		}
		for (int i = 5; i < ceil((zoom + 8) / 3.0); ++i)
		{
			digit = (c2 >> (24 - 6 * (i - 5))) & 0x3f;
			[str appendFormat:@"%c", [shortLinkCharArray characterAtIndex:digit]];
		}
		for (int i = 0; i < ((zoom + 8) % 3); ++i)
		{
			[str appendString:@"-"];
		}
		
		self.string = str;
		[str release];
	}
	return self;
}

+ (BOOL)isValidShortLinkString:(NSString *)string
{
	return [string isMatchedByRegex:@"[A-Za-z0-9_@]+"];
}

- (id)initWithString:(NSString *)string
{
	if (self = [super init])
	{
		self.string = string;
		
		// Calculate latitude, longitude, zoomlevel
		if ([IZOSMShortLink isValidShortLinkString:self.string] == NO)
			return nil;
		
		NSString *m = [self.string stringByMatching:@"[A-Za-z0-9_@]+"];
		int zoom = [m length]*2+[string length]-11;
		
		long long c1 = 0;
		long long c2 = 0;
		for (int i = 0, j = 54; i < [m length]; i++, j-= 6)
		{
			//int bits = [shortLinkCharArray rangeOfString:
			unsigned int bits = [shortLinkCharArray rangeOfString:
						[NSString stringWithFormat:@"%c", [m characterAtIndex:i]]].location;
			if (j <= 30)
				//c1 |= bits >>> (30-j);
				c1 |= bits >> (30-j);
			else if (j > 30)
				c1 |= bits << (j-30);
			if (j < 30)
				//c2 |= (bits & (0x3fffffff >>> j)) << j;
				c2 |= (bits & (0x3fffffff >> j)) << j;
		}

		long long x = 0;
		long long y = 0;
		
		for (int j=29; j>0;)
		{
			x = (x << 1) | ((c1 >> j--) & 1);
			y = (y << 1) | ((c1 >> j--) & 1);
		}
		for (int j=29; j>0;)
		{
			x = (x << 1) | ((c2 >> j--) & 1);
			y = (y << 1) | ((c2 >> j--) & 1);
		}

		x *= 4; // We can’t do <<= 2 here as x and y may be greater than 2³¹ and then the value would become negative
		y *= 4;

		double lon = x*90.0/(1<<30)-180.0;
		double lat = y*45.0/(1<<30)-90.0;

		self.latitude = [NSNumber numberWithDouble:lat];
		self.longitude = [NSNumber numberWithDouble:lon];
		self.zoomlevel = [NSNumber numberWithInt:zoom];
	}
	return self;
}

- (NSString *)osmShortURLString
{
	return [NSString stringWithFormat:@"http://osm.org/go/%@", self.string];
}

- (void)dealloc
{
	self.latitude = nil;
	self.longitude = nil;
	self.zoomlevel = nil;
	self.string = nil;
	
	[super dealloc];
}

@end