UIImage+Extensions.swift

//
//  UIImage+Extensions.swift
//  Slide Widgets
//
//  Created by Jonathan Cole on 9/15/20.
//  Copyright © 2020 Haptic Apps. All rights reserved.
//

import UIKit

extension UIImage {
    /// Average color of the image, nil if it cannot be found
    var averageColor: UIColor? {
        // convert our image to a Core Image Image
        guard let inputImage = CIImage(image: self) else { return nil }

        // Create an extent vector (a frame with width and height of our current input image)
        let extentVector = CIVector(x: inputImage.extent.origin.x,
                                    y: inputImage.extent.origin.y,
                                    z: inputImage.extent.size.width,
                                    w: inputImage.extent.size.height)

        // create a CIAreaAverage filter, this will allow us to pull the average color from the image later on
        guard let filter = CIFilter(name: "CIAreaAverage",
                                  parameters: [kCIInputImageKey: inputImage, kCIInputExtentKey: extentVector]) else { return nil }
        guard let outputImage = filter.outputImage else { return nil }

        // A bitmap consisting of (r, g, b, a) value
        var bitmap = [UInt8](repeating: 0, count: 4)
        let context = CIContext(options: [.workingColorSpace: kCFNull!])

        // Render our output image into a 1 by 1 image supplying it our bitmap to update the values of (i.e the rgba of the 1 by 1 image will fill out bitmap array
        context.render(outputImage,
                       toBitmap: &bitmap,
                       rowBytes: 4,
                       bounds: CGRect(x: 0, y: 0, width: 1, height: 1),
                       format: .RGBA8,
                       colorSpace: nil)

        // Convert our bitmap images of r, g, b, a to a UIColor
        return UIColor(red: CGFloat(bitmap[0]) / 255,
                       green: CGFloat(bitmap[1]) / 255,
                       blue: CGFloat(bitmap[2]) / 255,
                       alpha: CGFloat(bitmap[3]) / 255)
    }
}