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package com.vladsch.flexmark.util.format;

/*
   taken from: http://math.hws.edu/eck/cs124/javanotes3/c9/ex-9-3-answer.html

   An object of type RomanNumeral is an integer between 1 and 3999.  It can
   be constructed either from an integer or from a string that represents
   a Roman numeral in this range.  The function toString() will return a
   standardized Roman numeral representation of the number.  The function
   toInt() will return the number as a value of type int.
*/

import java.util.regex.Pattern;

public class RomanNumeral {
  private final int num; // The number represented by this Roman numeral.

  /*
     The following arrays are used by the toString() function to construct
     the standard Roman numeral representation of the number.  For each i,
     the number numbers[i] is represented by the corresponding string, letters[i].
  */

  private static final int[] numbers = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
  private static final String[] letters = {
    "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"
  };

  public static final Pattern ROMAN_NUMERAL =
      Pattern.compile(
          "M{0,3}(?:CM|DC{0,3}|CD|C{1,3})?(?:XC|LX{0,3}|XL|X{1,3})?(?:IX|VI{0,3}|IV|I{1,3})?");
  public static final Pattern LOWERCASE_ROMAN_NUMERAL =
      Pattern.compile(
          "m{0,3}(?:cm|dc{0,3}|cd|c{1,3})?(?:xc|lx{0,3}|xl|x{1,3})?(?:ix|vi{0,3}|iv|i{1,3})?");
  public static final Pattern LIMITED_ROMAN_NUMERAL =
      Pattern.compile("(?:X{1,3})?(?:IX|VI{0,3}|IV|I{1,3})?");
  public static final Pattern LIMITED_LOWERCASE_ROMAN_NUMERAL =
      Pattern.compile("(?:x{1,3})?(?:ix|vi{0,3}|iv|i{1,3})?");

  public RomanNumeral(int arabic) {
    // Constructor.  Creates the Roman number with the int value specified
    // by the parameter.  Throws a NumberFormatException if arabic is
    // not in the range 1 to 3999 inclusive.
    if (arabic < 1) {
      throw new NumberFormatException("Value of RomanNumeral must be positive.");
    }
    if (arabic > 3999) {
      throw new NumberFormatException("Value of RomanNumeral must be 3999 or less.");
    }
    num = arabic;
  }

  public RomanNumeral(String roman) {
    // Constructor.  Creates the Roman number with the given representation.
    // For example, RomanNumeral("xvii") is 17.  If the parameter is not a
    // legal Roman numeral, a NumberFormatException is thrown.  Both upper and
    // lower case letters are allowed.

    if (roman.length() == 0)
      throw new NumberFormatException("An empty string does not define a Roman numeral.");

    roman = roman.toUpperCase();

    int i = 0; // A position in the string, roman;
    int arabic =
        0; // Arabic numeral equivalent of the part of the string that has been converted so far.

    while (i < roman.length()) {
      char letter = roman.charAt(i);
      int number = letterToNumber(letter);

      if (number < 0)
        throw new NumberFormatException("Illegal character \"" + letter + "\" in roman numeral.");

      i++;

      if (i == roman.length()) {
        // There is no letter in the string following the one we have just processed.
        // So just add the number corresponding to the single letter to arabic.
        arabic += number;
      } else {
        // Look at the next letter in the string.  If it has a larger Roman numeral
        // equivalent than number, then the two letters are counted together as
        // a Roman numeral with value (nextNumber - number).
        int nextNumber = letterToNumber(roman.charAt(i));
        if (nextNumber > number) {
          // Combine the two letters to get one value, and move on to next position in string.
          arabic += (nextNumber - number);
          i++;
        } else {
          // Don't combine the letters.  Just add the value of the one letter onto the number.
          arabic += number;
        }
      }
    }

    if (arabic > 3999)
      throw new NumberFormatException("Roman numeral must have value 3999 or less.");

    num = arabic;
  }

  private static int letterToNumber(char letter) {
    // Find the integer value of letter considered as a Roman numeral.  Return
    // -1 if letter is not a legal Roman numeral.  The letter must be upper case.
    switch (letter) {
      case 'I':
        return 1;
      case 'V':
        return 5;
      case 'X':
        return 10;
      case 'L':
        return 50;
      case 'C':
        return 100;
      case 'D':
        return 500;
      case 'M':
        return 1000;
      default:
        return -1;
    }
  }

  @Override
  public String toString() {
    // Return the standard representation of this Roman numeral.
    StringBuilder roman = new StringBuilder();
    int n = num;
    for (int i = 0; i < numbers.length; i++) {
      while (n >= numbers[i]) {
        roman.append(letters[i]);
        n -= numbers[i];
      }
    }
    return roman.toString();
  }

  public int toInt() {
    // Return the value of this Roman numeral as an int.
    return num;
  }
}