decode time aware polyline in objective-c

main.m

// main.m
#import <Foundation/Foundation.h>

// Main methods declaration
NSArray *getDecodedPolyline(NSString *);
NSArray *getLocationsTillTime(NSArray *, NSDate *);

// Helper methods declaration
NSArray *getDecodedDimensionFromPolyline(NSString *, int);
NSArray *getFormattedDimensions(NSNumber *, NSNumber *, NSNumber *);
NSArray *getMidLocation(NSArray *, NSDate *);

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSString *polyline = @"spxsBsdb|Lymo`qvAx@TKvAr@K";
        NSArray *decoded = getDecodedPolyline(polyline);
        NSLog(@"decoded %@", decoded);

        NSDate *startTime = decoded[0][2];
        NSDate *queryTime = [startTime dateByAddingTimeInterval:5];
        NSArray *locations = getLocationsTillTime(decoded, queryTime);
        NSLog(@"locations %@", locations);
    }
    return 0;
}

// Implementation

// returns decoded polyline from string
NSArray *getDecodedPolyline(NSString *polyline) {
    
    NSMutableArray *gpxLogs = [[NSMutableArray alloc] init];
    NSNumber *index = 0, *latPart = 0, *lngPart = 0, *timePart = 0;
    NSNumber *polylineLength = [NSNumber numberWithInt:[polyline length]];
    
    while (index < polylineLength) {
        NSNumber *indexOffset, *latOffset, *lngOffset, *timeOffset;
        NSArray *decodedDimension;

        // assign index and latPart
        decodedDimension = getDecodedDimensionFromPolyline(polyline, index.intValue);
        indexOffset = decodedDimension[0];
        latOffset = decodedDimension[1];
        index = @(indexOffset.intValue);
        latPart = @(latPart.intValue + latOffset.intValue);
        
        // assign index and lngPart
        decodedDimension = getDecodedDimensionFromPolyline(polyline, index.intValue);
        indexOffset = decodedDimension[0];
        lngOffset = decodedDimension[1];
        index = @(indexOffset.intValue);
        lngPart = @(lngPart.intValue + lngOffset.intValue);
        
        // assign index and timePart
        decodedDimension = getDecodedDimensionFromPolyline(polyline, index.intValue);
        indexOffset = decodedDimension[0];
        timeOffset = decodedDimension[1];
        index = @(indexOffset.intValue);
        timePart = @(timePart.intValue + timeOffset.intValue);
        
        NSArray *decodedDimensions = getFormattedDimensions(latPart, lngPart, timePart);
        [gpxLogs addObject:decodedDimensions];
    }
    
    return gpxLogs;

}

// returns locations [[lat, lng] ..] till timestamp from decoded polyline
NSArray *getLocationsTillTime(NSArray *decoded, NSDate *queryTime) {
    NSMutableArray *locationsElapsed = [[NSMutableArray alloc] init];
    int decodedLength = [decoded count];
    
    if (queryTime == nil) {
        return nil;
    }
    
    if (decoded == nil || [decoded count] == 0) {
        return locationsElapsed;
    }
    
    NSDate *startTime = decoded[0][2];
    
    if( [queryTime timeIntervalSinceDate:startTime] <= 0 ) {
        // queryTime is before start time
        NSArray *locations = @[decoded[0][0], decoded[0][1]];
        [locationsElapsed addObject:locations];
        return locationsElapsed;
    }
    
    NSMutableArray *currentPair = [[NSMutableArray alloc] init];
    
    for (int index = 0; index < decodedLength; index++) {
        [currentPair addObject:decoded[index]];
        
        if ([currentPair count] == 2) {
            NSDate *startTime = currentPair[0][2];
            NSDate *endTime = currentPair[1][2];
            
            if ([queryTime timeIntervalSinceDate:startTime] > 0 &&
                [queryTime timeIntervalSinceDate:endTime] <= 0) {
                // location is in between the current pair
                NSArray *midLocation = getMidLocation(currentPair, queryTime);
                [locationsElapsed addObject:midLocation];
                return locationsElapsed;
            } else {
                // remove first element from current pair
                [currentPair removeObjectAtIndex:0];
            }
        }
        
        NSArray *currentLocation = @[currentPair[0][0], currentPair[0][1]];
        [locationsElapsed addObject:currentLocation];
    }
    
    return locationsElapsed;
}

// helper method for decoding
NSArray *getDecodedDimensionFromPolyline(NSString *polyline, int index) {
    long result = 1, shift = 0, correctedResult = 1;
    
    while (TRUE) {
        unichar polylineChar = [polyline characterAtIndex:index] - 63 - 1;
        index += 1;
        result += polylineChar << shift;
        shift += 5;
        
        if (polylineChar < 0x1f) {
            break;
        }
    }
    
    if ((result & 1) != 0) {
        correctedResult = ~result >> 1;
    } else {
        correctedResult = result >> 1;
    }
    
    NSNumber *indexNumber = [NSNumber numberWithInt:index];
    NSNumber *resultNumber = [NSNumber numberWithInt:correctedResult];
    NSArray *arrayResult = @[indexNumber, resultNumber];
    return arrayResult;
}

// helper method for modifying format of decoded elements
NSArray *getFormattedDimensions(NSNumber *lat, NSNumber *lng, NSNumber *time) {
    NSTimeInterval unixTimeStamp = [time doubleValue];
    return @[@([lat floatValue] / 100000.0),
             @([lng floatValue] / 100000.0),
             [NSDate dateWithTimeIntervalSince1970:unixTimeStamp]];
}

// helper method to find mid location in a pair on a timestamp
NSArray *getMidLocation(NSArray *currentPair, NSDate *queryTime) {
    NSDate *startTime = currentPair[0][2];
    NSDate *endTime = currentPair[1][2];
    double timeSinceStart = [queryTime timeIntervalSinceDate:startTime];
    double intervalLength = [endTime timeIntervalSinceDate:startTime];
    float ratio = timeSinceStart / intervalLength;
    NSNumber *startLat = currentPair[0][0], *startLng = currentPair[0][1];
    NSNumber *endLat = currentPair[1][0], *endLng = currentPair[1][1];
    
    return @[@(startLat.floatValue * (1 - ratio) + endLat.floatValue * ratio),
             @(startLng.floatValue * (1 - ratio) + endLng.floatValue * ratio)];
}

To run

clang main.m -fobjc-arc -fmodules -mmacosx-version-min=10.6 -o main
./main