PDF to UIImage fitting a given size with file cache

UIImage+ImageFromPDF

//based on the solution of iamamused : https://gist.github.com/iamamused/1955318
@implementation UIImage (ImageFromPDF)

+ (UIImage *)imageLoadedFromPDF:(NSString *)filePath fitSize:(CGSize)fitSize shouldCacheAsAFile:(BOOL)storeInFile{
    // Determine if the device is retina.
    BOOL isRetina = [UIScreen instancesRespondToSelector:@selector(scale)] && [[UIScreen mainScreen] scale] == 2.0;
    
    // Create a file manager so we can check if the image exists and store the image.
    NSFileManager *fileManger = [NSFileManager defaultManager];
    
    // Define the formats for the image names (low and high res).
    NSString *path = @"%@.png";
    NSString *pathHigh = @"%@@2x.png";
    
    //Remove the extension of the input path
    NSString * filePathWithoutExtension = [filePath stringByDeletingPathExtension];
    
    // Get the file name.
    NSString *file = [NSString stringWithFormat:( isRetina ? pathHigh : path ) , filePathWithoutExtension];
    
    UIImage *image;
    
    if ( ![fileManger fileExistsAtPath:file] ) {
        // Image doesn't exist so load the PDF and create it.
        
        // Get a reference to the PDF.
        CFURLRef pdfURL = (__bridge CFURLRef)[NSURL fileURLWithPath:filePath];
        CGPDFDocumentRef pdfDoc = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);

        // Load the first page. You could have multiple pages if you wanted.
        CGPDFPageRef pdfPage = CGPDFDocumentGetPage(pdfDoc, 1);
        
        //get the Crop Box of the pdf -> could be a various size
        CGRect cropBox = CGPDFPageGetBoxRect(pdfPage, kCGPDFCropBox);

        //fit the PDF to the given size!
        CGFloat xScale = fitSize.width / cropBox.size.width;
        CGFloat yScale = fitSize.height / cropBox.size.height;
        CGFloat scaleToApply = xScale < yScale ? xScale : yScale;
        CGSize size = CGSizeMake(cropBox.size.width*scaleToApply, cropBox.size.height*scaleToApply);
        
        if (isRetina) {
            UIGraphicsBeginImageContextWithOptions(size, false, 0);
        } else {
            UIGraphicsBeginImageContext( size );
        }
        
        CGContextRef context = UIGraphicsGetCurrentContext();
        
        // PDF page drawing expects a lower-left coordinate system,
        // flip the coordinate system before we start drawing.
        CGRect bounds = CGContextGetClipBoundingBox(context);
        CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 1.0);
        CGContextFillRect(context, bounds);
        
        CGContextTranslateCTM(context, 0, bounds.size.height);
        CGContextScaleCTM(context, 1.0, -1.0);
        
        // Save the graphics state.
        CGContextSaveGState(context);
        
        //high resolution scale -> if the PDF contains vector graphics info
        CGAffineTransform pdfTransform = CGAffineTransformMakeScale(scaleToApply, scaleToApply);
        
        // And apply the transform.
        CGContextConcatCTM(context, pdfTransform);
        
        // Draw the page.
        CGContextDrawPDFPage(context, pdfPage);
        
        // Restore the graphics state.
        CGContextRestoreGState(context);
        
        // Generate the image.
        image = UIGraphicsGetImageFromCurrentImageContext();
        
        // Store the PNG for next time.
        if (storeInFile) {
            [UIImagePNGRepresentation(image) writeToFile:file atomically:YES];
            NSLog(@"Saved file to pdf: %@",file);
        }
        
        UIGraphicsEndImageContext();
        CGPDFDocumentRelease(pdfDoc);
        
    } else {
        
        // Load the image from the file system.
        image = [UIImage imageWithContentsOfFile:file];
        
    }
    return  image;
}

@end