package Q3;

import java.util.*;

public class CreditCard {
  private int evenSum;
  private int oddSum;
  private int sum;
  private String ccNumber;
  private String company;

  public CreditCard(String num) {
    this.ccNumber = num;
    this.company = this.identifyCompany(num);
    this.calculateSums(num);
  }

  public int getEvenSum() {
    return evenSum;
  }

  public int getOddSum() {
    return oddSum;
  }

  public int getSum() {
    return sum;
  }

  public String getCcNumber() {
    return this.ccNumber;
  }

  public String getCompany() {
    return this.company;
  }

  public boolean isValid() {
    return this.validateCompany()
        && this.validateLength()
        && this.validateNumber()
        && this.validateSums()
        && this.isDivisibleBy10();
  }

  public boolean isDivisibleBy10() {
    return ((this.evenSum + this.oddSum) % 10) == 0;
  }

  public boolean validateCompany() {
    return this.ccNumber.startsWith("4")
        || this.ccNumber.startsWith("5")
        || this.ccNumber.startsWith("37")
        || this.ccNumber.startsWith("6");
  }

  public boolean validateLength() {
    return this.ccNumber.length() >= 13 && this.ccNumber.length() <= 16;
  }

  public boolean validateNumber() {
    for (int i = 0; i < this.ccNumber.length(); i++)
      if (!Character.isDigit(this.ccNumber.charAt(i))) return false;
    return true;
  }

  public boolean validateSums() {
    return this.evenSum > 0 && this.oddSum > 0;
  }

  private String identifyCompany(String number) {
    if (validateCompany())
      switch (number.charAt(0)) {
        case '3':
          return "American Express";
        case '4':
          return "Visa";
        case '5':
          return "MasterCard";
        case '6':
          return "Discover";
      }

    return "Unknown";
  }

  private void calculateSums(String number) {
    if (!validateNumber()) return;

    String reversed = this.reverseString(number);
    for (int i = 0; i < reversed.length(); i++) {
      int digit = this.digitFrom(reversed, i);
      if (this.isOdd(i + 1)) this.oddSum += digit;
      else {
        String value = String.valueOf(digit * 2);
        for (int j = 0; j < value.length(); j++) this.evenSum += this.digitFrom(value, j);
      }
    }
  }

  private String reverseString(String value) {
    return new StringBuilder(value).reverse().toString();
  }

  private boolean isEven(int number) {
    return number % 2 == 0;
  }

  private boolean isOdd(int number) {
    return !this.isEven(number);
  }

  private int digitFrom(String input, int index) {
    return Character.getNumericValue(input.charAt(index));
  }

  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    System.out.println("Enter credit card #:");
    CreditCard creditCard = new CreditCard(in.next());
    if (creditCard.isValid())
      System.out.println(
          String.format("%s is offerred by %s", creditCard.getCcNumber(), creditCard.getCompany()));
    else System.out.println(String.format("%s in invalid", creditCard.getCcNumber()));
  }
}