/**
 * Merges the range defined by the provided start and end into the list of
 * existing ranges. The merge is done in place on the existing range for
 * performance and is also returned.
 *
 * @param ranges Existing range list
 * @param newRangeStart Start position of the range to merge, inclusive
 * @param newRangeEnd End position of range to merge, exclusive
 */
export default function mergeRange(ranges: [number, number][], newRangeStart: number, newRangeEnd: number): [number, number][] {
  let inRange = false;
  for (let i = 0; i < ranges.length; i++) {
    const range = ranges[i];
    if (!inRange) {
      if (newRangeEnd <= range[0]) {
        // Case 1: New range is before the search range
        ranges.splice(i, 0, [newRangeStart, newRangeEnd]);
        return ranges;
      }
      if (newRangeEnd <= range[1]) {
        // Case 2: New range is either wholly contained within the
        // search range or overlaps with the front of it
        range[0] = Math.min(newRangeStart, range[0]);
        return ranges;
      }
      if (newRangeStart < range[1]) {
        // Case 3: New range either wholly contains the search range
        // or overlaps with the end of it
        range[0] = Math.min(newRangeStart, range[0]);
        inRange = true;
      } else {
        // Case 4: New range starts after the search range
        continue;
      }
    } else {
      if (newRangeEnd <= range[0]) {
        // Case 5: New range extends from previous range but doesn't
        // reach the current one
        ranges[i - 1][1] = newRangeEnd;
        return ranges;
      }
      if (newRangeEnd <= range[1]) {
        // Case 6: New range extends from prvious range into the
        // current range
        ranges[i - 1][1] = Math.max(newRangeEnd, range[1]);
        ranges.splice(i, 1);
        return ranges;
      }
      // Case 7: New range extends from previous range past the
      // end of the current range
      ranges.splice(i, 1);
      i--;
    }
  }

  if (inRange) {
    // Case 8: New range extends past the last existing range
    ranges[ranges.length - 1][1] = newRangeEnd;
  } else {
    // Case 9: New range starts after the last existing range
    ranges.push([newRangeStart, newRangeEnd]);
  }

  return ranges;
}