import type { PrePointOnShape } from '../point-on-shape/point-on-shape.js';
import { getOsculatingCircle } from '../point-on-shape/get-osculating-circle.js';

const { sqrt } = Math;


/**
 * 
 * @param angle
 * @param isHoleClosing `true` if this is a hole-closing two-prong, `false` otherwise
 * @param maxOscRadius the maximum that the osculating circle radius can be
 * @param yPos the source point of the 2-prong to be found
 * 
 * @internal
*/
function getInitialX(
        angle: number,
        isHoleClosing: boolean,
        maxOscRadius: number,
        yPos: PrePointOnShape,
        nnorm: number[]): [number[],number] {

    let xO: number[];
    let rO: number;

    const { p: y } = yPos;

    if (isHoleClosing) {
        return [
            [y[0], y[1] - maxOscRadius],  // xO
            maxOscRadius                  // rO
        ];
    }

    if (angle === 0) {
        return getOsculatingCircle(maxOscRadius, yPos, nnorm);
    }
     
    const { p } = yPos;
    const [tx, ty] = nnorm;
    const l = sqrt(tx*tx + ty*ty);
    const scale = maxOscRadius/l;

    const v = [tx*scale, ty*scale];
    xO = [p[0] + v[0], p[1] + v[1]];
    rO = maxOscRadius;

    return [xO,rO];
}


export { getInitialX }