/**
 * Given the number of words (`word`), the number of sentences (`sentence`),
 * and the number of unique unfamiliar words in a document (`difficultWord`),
 * returns the score associated with the document.
 *
 * @param {Counts} counts
 *   Counts from input document.
 * @return {number}
 *   Score representing ease of reading.
 *
 *   Pass it to `daleChallGradeLevel` to get grade levels.
 */
export function daleChallFormula(counts: Counts): number
/**
 * Turn a dale–chall score into U.S. grade levels.
 *
 * @param {number} score
 *   Score representing ease of reading.
 * @returns {[number, number]}
 *   Grade levels.
 *
 *   |        Score | Corresponding grade level               | Return value     |
 *   | -----------: | --------------------------------------- | ---------------- |
 *   |  Less than 5 | Grade 4 and lower                       | `[0, 4]`         |
 *   |  Less than 6 | Grades 5 and 6                          | `[5, 6]`         |
 *   |  Less than 7 | Grades 7 and 8                          | `[7, 8]`         |
 *   |  Less than 8 | Grades 9 and 10                         | `[9, 10]`        |
 *   |  Less than 9 | Grades 11 and 12                        | `[11, 12]`       |
 *   | Less than 10 | Grades 13 and 15 (College)              | `[13, 15]`       |
 *   |       Higher | Grades 16 and higher (College Graduate) | `[16, Infinity]` |
 */
export function daleChallGradeLevel(score: number): [number, number]
/**
 * Counts from input document.
 */
export type Counts = {
  /**
   *   Number of sentences.
   */
  sentence: number
  /**
   *   Number of words.
   */
  word: number
  /**
   * Number of difficult words.
   */
  difficultWord?: number | undefined
}
/**
 * Deprecated: please use the `Counts` type instead.
 */
export type DaleChallFormulaCounts = Counts