Method romanNumeralsToDecimal

src/Encoder/NumeralSystem.js:247–276

* Translates given roman numerals to decimal. * @protected * @param {string} romanNumerals * @return {?number} Decimal or null, if not defined.

(romanNumerals)

   * @return {?number} Decimal or null, if not defined.
   */
  static romanNumeralsToDecimal (romanNumerals) {
    romanNumerals = romanNumerals.toString().toUpperCase()

    let index = 0
    let decimal = 0
    let error = false

    let previousNumeral = 0
    let numeral

    while (!error && index < romanNumerals.length) {
      // Find first roman numeral with the highest value
      numeral = romanNumeralSymbols.findIndex(symbol =>
        romanNumerals.substr(index, symbol.length) === symbol)

      if (numeral !== -1 && numeral >= previousNumeral) {
        // Append roman numeral
        decimal += romanNumeralValues[numeral]
        // Move cursor
        index += romanNumeralSymbols[numeral].length
        // Track previous numeral
        previousNumeral = numeral
      } else {
        // Unexpected numeral
        error = true
      }
    }

    return !error ? decimal : null
  }
}