/*
 * Hermite resize - fast image resize/resample using Hermite filter.
 * https://github.com/viliusle/Hermite-resize
 */

export function resizeCanvas(canvas: HTMLCanvasElement, width: number, height: number) {
  const width_source = canvas.width;
  const height_source = canvas.height;
  width = Math.round(width);
  height = Math.round(height);

  const ratio_w = width_source / width;
  const ratio_h = height_source / height;
  const ratio_w_half = Math.ceil(ratio_w / 2);
  const ratio_h_half = Math.ceil(ratio_h / 2);

  const ctx = canvas.getContext('2d');
  if (ctx) {
    const img = ctx.getImageData(0, 0, width_source, height_source);
    const img2 = ctx.createImageData(width, height);
    const data = img.data;
    const data2 = img2.data;

    for (let j = 0; j < height; j++) {
      for (let i = 0; i < width; i++) {
        const x2 = (i + j * width) * 4;
        const center_y = j * ratio_h;
        let weight = 0;
        let weights = 0;
        let weights_alpha = 0;
        let gx_r = 0;
        let gx_g = 0;
        let gx_b = 0;
        let gx_a = 0;

        const xx_start = Math.floor(i * ratio_w);
        const yy_start = Math.floor(j * ratio_h);
        let xx_stop = Math.ceil((i + 1) * ratio_w);
        let yy_stop = Math.ceil((j + 1) * ratio_h);
        xx_stop = Math.min(xx_stop, width_source);
        yy_stop = Math.min(yy_stop, height_source);

        for (let yy = yy_start; yy < yy_stop; yy++) {
          const dy = Math.abs(center_y - yy) / ratio_h_half;
          const center_x = i * ratio_w;
          const w0 = dy * dy; //pre-calc part of w
          for (let xx = xx_start; xx < xx_stop; xx++) {
            const dx = Math.abs(center_x - xx) / ratio_w_half;
            const w = Math.sqrt(w0 + dx * dx);
            if (w >= 1) {
              //pixel too far
              continue;
            }
            //hermite filter
            weight = 2 * w * w * w - 3 * w * w + 1;
            const pos_x = 4 * (xx + yy * width_source);
            //alpha
            gx_a += weight * data[pos_x + 3];
            weights_alpha += weight;
            //colors
            if (data[pos_x + 3] < 255) weight = (weight * data[pos_x + 3]) / 250;
            gx_r += weight * data[pos_x];
            gx_g += weight * data[pos_x + 1];
            gx_b += weight * data[pos_x + 2];
            weights += weight;
          }
        }
        data2[x2] = gx_r / weights;
        data2[x2 + 1] = gx_g / weights;
        data2[x2 + 2] = gx_b / weights;
        data2[x2 + 3] = gx_a / weights_alpha;
      }
    }

    canvas.width = width;
    canvas.height = height;

    //draw
    ctx.putImageData(img2, 0, 0);
  }
}