type PickingCircleCallback = (x: number, y: number, idx: number) => boolean | null;

function traversePickingCircle(radius: number, callback: PickingCircleCallback) {
    // iterate on radius so we get closer to the mouse
    // results first.
    // Result traversal order for radius=2
    // --3--
    // -323-
    // 32123
    // -323
    // --3--
    let prevSq: number | undefined = undefined;

    for (let r = 0; r <= radius; r++) {
        const sq = r * r;
        for (let x = -r; x <= r; x++) {
            const sqx = x * x;
            for (let y = -r; y <= r; y++) {
                const dist = sqx + y * y;
                // skip if too far
                if (dist > sq) {
                    continue;
                }
                // skip if belongs to previous
                if (prevSq != null && dist <= prevSq) {
                    continue;
                }

                const realX = radius + x;
                const realY = radius + y;
                const idx = realY * (2 * radius) + realX;
                if (callback(realX, realY, idx) === false) {
                    return;
                }
            }
        }
        prevSq = sq;
    }
}

export default traversePickingCircle;