normalCase.ts

import lowerCase from "./lowerCase.ts";

import nonWordRegexp from "./vendor/nonWordRegexp.ts";
import camelCaseRegexp from "./vendor/camelCaseRegexp.ts";
import camelCaseUpperRegexp from "./vendor/camelCaseUpperRegexp.ts";

/**
 * Convert a `string` to normal case.
 *
 * Example:
 *
 * ```ts
 * normalCase("test string");
 * //=> "test string"
 *
 * normalCase("testString");
 * //=> "test string"
 *
 * normalCase("Test-String");
 * //=> "test string"
 * ```
 */
export default function normalCase(
  str: string,
  locale?: string,
  replacement?: string,
): string {
  if (str == null) {
    return "";
  }

  replacement = typeof replacement !== "string" ? " " : replacement;

  function replace(match: string, index: number, value: string): string {
    if (index === 0 || index === value.length - match.length) {
      return "";
    }

    return replacement!;
  }

  str = String(str)
    // Support camel case ("camelCase" -> "camel Case").
    .replace(camelCaseRegexp, "$1 $2")
    // Support odd camel case ("CAMELCase" -> "CAMEL Case").
    .replace(camelCaseUpperRegexp, "$1 $2")
    // Remove all non-word characters and replace with a single space.
    .replace(nonWordRegexp, replace);

  // Lower case the entire string.
  return lowerCase(str, locale);
}