using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

namespace ImageTuner
{
    class Program
    {
        static void Main(string[] args)
        {
            string originalImageFile = "<image image file>.jpg";
            string scaledImageFile = "<downsized image file>.jpg";
            bool imageMatchCriterion = false;
            bool imageStillTooBig = false;

            float resolutionScaleFactor = 0.95f;
            long jpegQualityLevel = 100L;

            using (var originalImage = new Bitmap(originalImageFile))
            {
                while (!imageMatchCriterion)
                {
                    Console.WriteLine("Image doesn't match size criterion. Resizing.");
                    int scaledHeight = (int)(originalImage.Height * resolutionScaleFactor);
                    int scaledWidth = (int)(originalImage.Width * resolutionScaleFactor);

                    using (var toCompress = new Bitmap(originalImage, new Size(height: scaledHeight, width: scaledWidth)))
                    {
                        var jpgEncoder = GetEncoder(ImageFormat.Jpeg);
                        var myEncoder = Encoder.Quality;
                        var myEncoderParameters = new EncoderParameters(1);

                        var myEncoderParameter = new EncoderParameter(myEncoder, jpegQualityLevel);
                        myEncoderParameters.Param[0] = myEncoderParameter;

                        using (var tempStream = new MemoryStream())
                        {
                            //Save the image byte to memory first.
                            toCompress.Save(tempStream, jpgEncoder, myEncoderParameters);
                            byte[] imageSize = tempStream.ToArray();
                            //Check the image size in memory. If it's too big, continue to loop.
                            if (imageSize.Length <= 512000)
                            {
                                imageMatchCriterion = true;
                                using (var saveStream = new FileStream(scaledImageFile, FileMode.Create))
                                {
                                    toCompress.Save(saveStream, jpgEncoder, myEncoderParameters);
                                }
                            }
                            else
                            {
                                if (resolutionScaleFactor > 0.60f)
                                {
                                    //Reduce the resolution of the image by 10 percent each time.
                                    resolutionScaleFactor -= 0.10f;
                                }
                                else
                                {
                                    //When the resolution scaling already reach 60%, time to look at reducing the quality level by 5 each time.
                                    if (jpegQualityLevel > 50)
                                    {
                                        jpegQualityLevel -= 5L;
                                    }
                                    else
                                    {
                                        //Cannot drop the image quality below 50 percent. Once that happen, the image is almost unusable.
                                        imageStillTooBig = true;
                                        break;
                                    }
                                }
                            }
                        }
                    }
                }
            }
            if (imageStillTooBig)
            {
                Console.WriteLine("Image resizing failed.");
            }
            else
            {
                Console.WriteLine("Image resizing completed.");
            }
            

        }

        private static ImageCodecInfo GetEncoder(ImageFormat format)
        {
            ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
            foreach (ImageCodecInfo codec in codecs)
            {
                if (codec.FormatID == format.Guid)
                {
                    return codec;
                }
            }
            return null;
        }
    }
}