typopo/src/modules/words/case.js

Fix frequent microtypography errors in multiple languages. Write neat texts without bothering about typography rules. Typopo works for English, German, Slovak, Czech and Rusyn language.

import { base } from "../../const.js";

/**
  Corrects accidental uppercase

  Best-effort function to fix most common accidental uppercase errors, namely:
  [1] 2 first uppercase letters (ie. UPpercase)
  [2] Swapped cases (ie. uPPERCASE)

  Algorithm does not fix other uppercase eventualities,
  e.g. mixed case (UppERcaSe) as there are many cases for corporate brands
  that could potentially match the algorithm as false positive.

  @param {string} string — input text for identification
  @returns {string} — output with corrected accidental uppercase
*/
export function fixCase(string) {
  /* [1] two first uppercase letters (i.e. UPpercase) */
  // prettier-ignore
  string = string.replace(
    new RegExp(
      `([^${base.allChars}]|^)` + 
      `([${base.uppercaseChars}]{2})` + 
      `([${base.lowercaseChars}]{2,})`, 
      "g"
    ), 
    function ($0, $1, $2, $3) {
      return `${$1}${$2.substring(0, 1)}${$2.substring(1).toLowerCase()}${$3}`;
    }
  );

  /* [2] Swapped cases (n-letter cases, i.e. uPPERCASE)
      There is one exception excluded from swapping → iOS
      If needed, update this code to exclude the list of other popular names.
  */
  // prettier-ignore
  return string.replace(
    new RegExp(
      `(\\b)` + 
      `(?!iOS)` + 
      `([${base.lowercaseChars}])` + 
      `([${base.uppercaseChars}]{2,})`, 
      "g"
    ), 
    function ($0, $1, $2, $3) {
      return `${$1}${$2.toUpperCase()}${$3.toLowerCase()}`;
    }
  );
}