const { SQRT2, round, abs, log2, sqrt, ceil } = Math;


const SQRT3 = sqrt(3);

/** Number of buckets per unit */
const NUM_BUCKETS_PER_UNIT = ceil(log2(1/(SQRT3/6/SQRT2)));
// Must be smaller than half the minimum distance (divided by sqrt(2)) between
// any two shape centroids i,e smaller than
// `(SQRT3/6)/SQRT2 === 0.20412414523193148 and a power of 2
const BUCKET_SIZE = 2**-NUM_BUCKETS_PER_UNIT;


/**
 * Guessed maximum floating point error after all transformations.
 * * A high value was chosen to be sure but it is possible to calculate it
 * exactly though the calculation would be very tedious.
 */
const MAX_ABS_ERROR = 2**-16;


/**
 * Perform a location sensitive hash (called buckets)
 * 
 * * points close to zero are automatically put into bucket 0
 *
 * @param v 
 */
function getCoordinateBuckets(
        c: number): number[] {

    const buckets: number[] = [];

    const c_ = c;
    const c__ = c_/BUCKET_SIZE;

    const b1 = round(c__);

    buckets.push(b1);  // usually there's only one bucket per coordinate

    const d = abs(c__ - b1);

    if (d >= 0.5 - MAX_ABS_ERROR) {  // too close to call - put into two buckets
        const b2 = c__ > b1
            ? b1 + 1   // we rounded down
            : b1 - 1;  // we rounded up

        buckets.push(b2);
    }

    return buckets;
}


export { getCoordinateBuckets }