using System;
using System.Windows;
using System.Windows.Media.Imaging;

namespace RBG.Helpers
{
    public class ImageProcessing
    {
        /// <summary>
        /// Returns a copy of the original bitmap with a specified per-channel colour multiplier
        /// Each channel expects a rate 0-1 (will handle other values, with unexpected results)
        /// Defaults to 1.0 for each channel (no modification)
        /// </summary>
        /// <param name="sourceBitmap">The source bitmap</param>
        /// <param name="redRate">The red-channel multiplier</param>
        /// <param name="greenRate">The green-channel multiplier</param>
        /// <param name="blueRate">The blue-channel multiplier</param>
        /// <param name="alphaRate">The alpha-channel multiplier</param>
        /// <returns></returns>
        public static BitmapSource UpdatePixelColours(BitmapSource sourceBitmap, double redRate = 1.0, double greenRate = 1.0, double blueRate = 1.0, double alphaRate = 1.0)
        {
            // Create a writeable bitmap from the source bitmap
            WriteableBitmap wbmp = new(sourceBitmap);
            // Ensure 32 bpp
            if (wbmp.Format.BitsPerPixel != 32) return null;
            // Lock the bitmap so the buffer cannot change
            wbmp.Lock();
            // Enter unsafe code (used over marshalled pointer access so that it is more performant, but has a
            // higher security risk as this is raw [but still bounded] memory access ( => data may be changed by a third party)
            // As the buffer is of a known size, and not terminated by a specific symbol, modified data in the buffer is
            // unlikely to cause a novel vulnerability in the software ( => vulnerability exists in BitmapSource, can be
            // exploited with any bitmap image being loaded)
            unsafe
            {
                // Retrieve the buffer pointer
                int* arrayptr = (int*)wbmp.BackBuffer;
                // Iterate through each pixel
                for (int i = 0; i < wbmp.PixelWidth * wbmp.PixelHeight; i++)
                {
                    // Dereference the exact pixel value
                    int pixel = *(arrayptr + i);
                    // decompose the colour channels
                    int a = (pixel >> 24) & 0xFF;
                    int r = (pixel >> 16) & 0xFF;
                    int g = (pixel >> 8) & 0xFF;
                    int b = pixel & 0xFF;
                    // Calc new values & clamp to a max of 0xFF (8 bits per channel)
                    int newB = (int)Math.Min((uint)(b * blueRate), 255);
                    int newG = (int)Math.Min((uint)(g * greenRate), 255);
                    int newR = (int)Math.Min((uint)(r * redRate), 255);
                    int newA = (int)Math.Min((uint)(a * alphaRate), 255);
                    // Set the pixel to the new value
                    *(arrayptr + i) = (newA << 24) | (newR << 16) | (newG << 8) | newB;
                }
            }
            // Invalidate the full current image, so that the new buffer data is fully applied
            wbmp.AddDirtyRect(new Int32Rect(0, 0, wbmp.PixelWidth, wbmp.PixelHeight));
            // Unlock the image, as everything has finished changing
            wbmp.Unlock();
            return wbmp;
        }

        /// <summary>
        /// Retrieves a cropped area of the provided bitmap
        /// </summary>
        /// <param name="source"></param>
        /// <param name="row"></param>
        /// <param name="col"></param>
        /// <param name="rowSize"></param>
        /// <param name="colSize"></param>
        /// <param name="colsIncluded"></param>
        /// <param name="rowsIncluded"></param>
        /// <returns></returns>
        public static BitmapSource RetrieveSubImage(BitmapSource source, int row, int col, int rowSize, int colSize, int colsIncluded = 1, int rowsIncluded = 1)
        {
            // Get number of pixels per segment
            int rowPixelsPerTile = (source.PixelWidth / rowSize) - 1;
            int colPixelsPerTile = (source.PixelHeight / colSize) - 1;
            // Create a cropping bound
            Int32Rect pixelRect = new(colPixelsPerTile * col, rowPixelsPerTile * row, colPixelsPerTile * colsIncluded, rowPixelsPerTile * rowsIncluded);
            return new CroppedBitmap(source, pixelRect);
        }


    }
}