export function nearestPointOnProjectedLine()

in modules/edit-modes/src/utils.ts [114:181]

• 52 lines of code
• 4 McCabe index (conditional complexity)

export function nearestPointOnProjectedLine(
  line: FeatureOf<LineString>,
  inPoint: FeatureOf<Point>,
  viewport: Viewport
): NearestPointType {
  const wmViewport = new WebMercatorViewport(viewport);
  // Project the line to viewport, then find the nearest point
  const coordinates: Array<Array<number>> = line.geometry.coordinates as any;
  const projectedCoords = coordinates.map(([x, y, z = 0]) => wmViewport.project([x, y, z]));
  const [x, y] = wmViewport.project(inPoint.geometry.coordinates);
  // console.log('projectedCoords', JSON.stringify(projectedCoords));

  let minDistance = Infinity;
  let minPointInfo = {};

  projectedCoords.forEach(([x2, y2], index) => {
    if (index === 0) {
      return;
    }

    const [x1, y1] = projectedCoords[index - 1];

    // line from projectedCoords[index - 1] to projectedCoords[index]
    // convert to Ax + By + C = 0
    const A = y1 - y2;
    const B = x2 - x1;
    const C = x1 * y2 - x2 * y1;

    // https://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line
    const div = A * A + B * B;
    const distance = Math.abs(A * x + B * y + C) / Math.sqrt(div);

    // TODO: Check if inside bounds

    if (distance < minDistance) {
      minDistance = distance;
      minPointInfo = {
        index,
        x0: (B * (B * x - A * y) - A * C) / div,
        y0: (A * (-B * x + A * y) - B * C) / div,
      };
    }
  });
  // @ts-ignore
  const { index, x0, y0 } = minPointInfo;
  const [x1, y1, z1 = 0] = projectedCoords[index - 1];
  const [x2, y2, z2 = 0] = projectedCoords[index];

  // calculate what ratio of the line we are on to find the proper z
  const lineLength = distance2d(x1, y1, x2, y2);
  const startToPointLength = distance2d(x1, y1, x0, y0);
  const ratio = startToPointLength / lineLength;
  const z0 = mix(z1, z2, ratio);

  return {
    type: 'Feature',
    geometry: {
      type: 'Point',
      // @ts-expect-error
      coordinates: wmViewport.unproject([x0, y0, z0]),
    },
    properties: {
      // TODO: calculate the distance in proper units
      dist: minDistance,
      index: index - 1,
    },
  };
}