gabrielbull/react-aim

import findCorners, { boundaries } from './corners';
import pointInPolygon from './utils/pointInPolygon';

export function distance(source, target) {
  const a = source.x - target.x;
  const b = source.y - target.y;
  return Math.sqrt(a * a + b * b);
}

export function side(corners) {
  if (corners[0] === 'top-right' && corners[1] === 'bottom-right') return 'right';
  else if (corners[0] === 'top-left' && corners[1] === 'bottom-right') return 'top-right';
  else if (corners[0] === 'top-left' && corners[1] === 'top-right') return 'top';
  else if (corners[0] === 'bottom-left' && corners[1] === 'top-right') return 'top-left';
  else if (corners[0] === 'bottom-left' && corners[1] === 'top-left') return 'left';
  else if (corners[0] === 'bottom-right' && corners[1] === 'top-left') return 'bottom-left';
  else if (corners[0] === 'bottom-right' && corners[1] === 'bottom-left') return 'bottom';
  else if (corners[0] === 'top-right' && corners[1] === 'bottom-left') return 'bottom-right';
}

export function bullseye(corners, boundaries, mousePosition) {
  switch(side(corners)) {
  case 'right':
    return {
      x: boundaries[0].x,
      y: mousePosition.y
    };
  case 'top-right':
    return {
      x: boundaries[1].x,
      y: boundaries[0].y
    };
  case 'top':
    return {
      x: mousePosition.x,
      y: boundaries[0].y
    };
  case 'top-left':
    return {
      x: boundaries[0].x,
      y: boundaries[1].y
    };
  case 'left':
    return {
      x: boundaries[0].x,
      y: mousePosition.y
    };
  case 'bottom-left':
    return {
      x: boundaries[1].x,
      y: boundaries[0].y
    };
  case 'bottom':
    return {
      x: mousePosition.x,
      y: boundaries[0].y
    };
  case 'bottom-right':
    return {
      x: boundaries[0].x,
      y: boundaries[1].y
    };
  }
}

function formatPoints(points) {
  const finalPoints = [];
  for (let i = 0, len = points.length; i < len; ++i) {
    finalPoints.push([points[i].x, points[i].y]);
  }
  return finalPoints;
}

export default function aiming(e, mousePosition, prevMousePosition, target, alreadyAiming) {
  if (!prevMousePosition) return false;
  else if (!alreadyAiming && mousePosition.x === prevMousePosition.x && mousePosition.y === prevMousePosition.y) {
    return false;
  }

  const corners = findCorners(e, target);
  const bound = boundaries(corners, prevMousePosition, target);

  if (
    pointInPolygon(
      [mousePosition.x, mousePosition.y],
      formatPoints(bound)
    )
  ) {
    const dist = Math.round(distance(mousePosition, bullseye(corners, bound, mousePosition)));
    return Math.max(dist, 1);
  }
  return false;
}