import UIKit

extension UIImage {
    
    /// Resizes an image to the specified size.
    ///
    /// - Parameters:
    ///     - size: the size we desire to resize the image to.
    ///
    /// - Returns: the resized image.
    ///
    func imageWithSize(size: CGSize) -> UIImage? {
        
        UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.main.scale);
        let rect = CGRect(x: 0.0, y: 0.0, width: size.width, height: size.height);
        draw(in: rect)
        
        let resultingImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        
        return resultingImage
    }
    
    /// Resizes an image to the specified size and adds an extra transparent margin at all sides of
    /// the image.
    ///
    /// - Parameters:
    ///     - size: the size we desire to resize the image to.
    ///     - extraMargin: the extra transparent margin to add to all sides of the image.
    ///
    /// - Returns: the resized image.  The extra margin is added to the input image size.  So that
    ///         the final image's size will be equal to:
    ///         `CGSize(width: size.width + extraMargin * 2, height: size.height + extraMargin * 2)`
    ///
    func imageWithSize(size: CGSize, extraMargin: CGFloat) -> UIImage? {
        
        let imageSize = CGSize(width: size.width + extraMargin * 2, height: size.height + extraMargin * 2)
        
        UIGraphicsBeginImageContextWithOptions(imageSize, false, UIScreen.main.scale);
        let drawingRect = CGRect(x: extraMargin, y: extraMargin, width: size.width, height: size.height)
        draw(in: drawingRect)
        
        let resultingImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        
        return resultingImage
    }
    
    /// Resizes an image to the specified size.
    ///
    /// - Parameters:
    ///     - size: the size we desire to resize the image to.
    ///     - roundedRadius: corner radius
    ///
    /// - Returns: the resized image with rounded corners.
    ///
    func imageWithSize(size: CGSize, roundedRadius radius: CGFloat) -> UIImage? {
        
        UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.main.scale)
        if let currentContext = UIGraphicsGetCurrentContext() {
            let rect = CGRect(origin: .zero, size: size)
            currentContext.addPath(UIBezierPath(roundedRect: rect,
                                                byRoundingCorners: .allCorners,
                                                cornerRadii: CGSize(width: radius, height: radius)).cgPath)
            currentContext.clip()
            
            //Don't use CGContextDrawImage, coordinate system origin in UIKit and Core Graphics are vertical oppsite.
            draw(in: rect)
            currentContext.drawPath(using: .fillStroke)
            let roundedCornerImage = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
            return roundedCornerImage
        }
        return nil
    }
}