export interface Point { x: number; y: number; z: number }
export interface Charge extends Point { coulombs: number }
export const COULOMB_CONSTANT = 8.9875517923e9;

/** SI units: positions in metres, charges in coulombs, output in N/C.
 * Samples inside 0.18 m of a charge are omitted to avoid visual singularities.
 */
export function electricField(point: Point, charges: readonly Charge[]): Point {
  const field = { x: 0, y: 0, z: 0 };
  for (const charge of charges) {
    const dx = point.x - charge.x;
    const dy = point.y - charge.y;
    const dz = point.z - charge.z;
    const r2 = dx * dx + dy * dy + dz * dz;
    if (r2 < 0.18 ** 2) continue;
    const factor = COULOMB_CONSTANT * charge.coulombs / (r2 * Math.sqrt(r2));
    field.x += factor * dx;
    field.y += factor * dy;
    field.z += factor * dz;
  }
  return field;
}