import { Filter } from '.';
import { PNG } from 'pngjs';

export default class FloydSteinberg implements Filter {
  process(image: PNG): PNG {
    const width = image.width;
    const height = image.height;
    const new_data = image.data.slice();
    const pixel = new Map<string, number>();
    for (let y = 0; y < height; y++) {
      for (let x = 0; x < width; x++) {
        const red = image.data[y * width * 4 + x * 4 + 0];
        const green = image.data[y * width * 4 + x * 4 + 1];
        const blue = image.data[y * width * 4 + x * 4 + 2];
        const alpha = image.data[y * width * 4 + x * 4 + 3];
        let grey = Math.trunc(red * 0.3 + green * 0.59 + blue * 0.11);
        // Add errors to color if there are
        if (pixel.has(`${x}_${y}`)) {
          grey += pixel.get(`${x}_${y}`);
        }
        const new_color = grey > 127 ? 0xff : 0;
        new_data[y * width * 4 + x * 4 + 0] = new_color; // red
        new_data[y * width * 4 + x * 4 + 1] = new_color; // green
        new_data[y * width * 4 + x * 4 + 2] = new_color; // blue
        new_data[y * width * 4 + x * 4 + 3] = alpha; // alpha
        const error = grey - (new_color & 0xff);
        if (x + 1 < width) {
          const prev = pixel.has(`${x + 1}_${y}`)
            ? pixel.get(`${x + 1}_${y}`)
            : 0;
          const value = prev + ((error * 7) >> 4);
          pixel.set(`${x + 1}_${y}`, value);
        }
        // if we are in the last line
        if (y == height - 1) {
          continue;
        }
        if (x > 0) {
          const prev = pixel.get(`${x - 1}_${y + 1}`);
          pixel.set(`${x - 1}_${y + 1}`, prev + ((error * 3) >> 4));
        }
        const prev = pixel.has(`${x}_${y + 1}`)
          ? pixel.get(`${x}_${y + 1}`)
          : 0;
        pixel.set(`${x}_${y + 1}`, prev + ((error * 5) >> 4));
        if (x < width - 1) {
          pixel.set(`${x + 1}_${y + 1}`, 0 + ((error * 1) >> 4));
        }
      }
    }
    image.data = new_data;
    return image;
  }
}