import * as mathjs from 'mathjs';

interface Range {
    x0: number;
    y0: number;
    x1: number;
    y1: number;
}

// my first attempt at this
function lineSegmentIntersection(l0: Range, l1: Range): boolean {
    // convert to y = mx + b
    const m0 = mathjs.fraction(l0.y1 - l0.y0, l0.x1 - l0.x0);
    const m1 = mathjs.fraction(l1.y1 - l1.y0, l1.x1 - l1.x0);

    const b0 = mathjs.subtract(l0.y0, mathjs.multiply(m0, l0.x0));
    const b1 = mathjs.subtract(l1.y1, mathjs.multiply(m1, l1.x1));

    if (mathjs.equal(m0, m1)) {
        if (mathjs.equal(b0, b1)) {
            // parallel lines with equal intersect
            return (
                (l1.x0 >= l0.x0 && l1.x0 <= l0.x1) ||
                (l1.x1 >= l1.x0 && l1.x1 <= l1.x1)
            );
        } else {
            // parallel lines with different y-intersect will never intersect
            return false;
        }
    }

    // solve for l0 = l1
    const M = mathjs.subtract(m0, m1);
    const B = mathjs.subtract(b0, b1);

    // MX + B = 0 -> X = -B/M
    const X = mathjs.divide(mathjs.unaryMinus(B), M);
    const X_num = mathjs.number(X as mathjs.Fraction);

    const intersects =
        X_num >= Math.min(l0.x0, l0.x1) &&
        X_num <= Math.max(l0.x0, l0.x1) &&
        X_num >= Math.min(l1.x0, l1.x1) &&
        X_num <= Math.max(l1.x0, l1.x1);

    // const Y = mathjs.add(mathjs.multiply(m0, X), b0);
    // const Y_num = mathjs.number(Y as mathjs.Fraction);
    // if (intersects) {
    //     console.log('intersects at', X_num, Y_num);
    // } else {
    //     console.log('would have intersected at', X_num, Y_num, l0, l1);
    // }

    // to test
    // useEffect(() => {
    //     const l0 = { x0: 2, y0: 8, x1: 6, y1: 5, stroke: '' };
    //     const l1 = { x0: 3, y0: 9, x1: 7, y1: 8, stroke: '' };
    //     console.log('intersection:', l0, l1, lineSegmentIntersection(l0, l1));
    // }, []);

    return intersects;
}