/**
 * Assignment 2, COMP268 Class: CreditCard.java
 *
 * @description Provides an implementation of Luhn's algorithm
 * @author: mo khan Student ID: 3431709
 * @date Jun 9, 2019
 * @version 1.0
 */
package Q3;

import java.util.*;

public class CreditCard {
  private int evenSum = 0;
  private int oddSum = 0;
  private int sum = 0;
  private String ccNumber;
  private String company;

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

  /**
   * Returns the sum of the even digits
   *
   * @return the sum of the even digits
   */
  public int getEvenSum() {
    return evenSum;
  }

  /**
   * Returns the sum of the odd digits
   *
   * @return the sum of the odd digits
   */
  public int getOddSum() {
    return oddSum;
  }

  /**
   * Returns the sum of all the digits
   *
   * @return the sum of the even and odd digits.
   */
  public int getSum() {
    return sum;
  }

  /**
   * Return the credit card number
   *
   * @return the credit card number.
   */
  public String getCcNumber() {
    return this.ccNumber;
  }

  /**
   * Return the company that issues this credit card number.
   *
   * @return the name of the company that owns this credit card number.
   */
  public String getCompany() {
    return this.company;
  }

  /** @return true if the credit card # is valid, otherwise returns false. */
  public boolean isValid() {
    return this.validateCompany()
        && this.validateLength()
        && this.validateNumber()
        && this.validateSums()
        && this.isDivisibleBy10();
  }

  /** @return true if the total sum is divisible by 10, otherwise returns false. */
  public boolean isDivisibleBy10() {
    return ((this.getSum()) % 10) == 0;
  }

  /**
   * Validates the company that the credit card number belongs to.
   *
   * @return true if the card belongs to one of the described credit card company, otherwise false.
   */
  public boolean validateCompany() {
    return this.ccNumber.startsWith("4")
        || this.ccNumber.startsWith("5")
        || this.ccNumber.startsWith("37")
        || this.ccNumber.startsWith("6");
  }

  /** @return true if the length of the card number is valid. */
  public boolean validateLength() {
    return this.ccNumber.length() >= 13 && this.ccNumber.length() <= 16;
  }

  /** @return true if each character in the credit card number is a digit. */
  public boolean validateNumber() {
    for (int i = 0; i < this.ccNumber.length(); i++)
      if (!Character.isDigit(this.ccNumber.charAt(i))) return false;
    return true;
  }

  /** @return true if the sum is greater than 0; */
  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);
      }
    }

    this.sum = this.oddSum + this.evenSum;
  }

  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));
  }

  /**
   * The entry point to the console application.
   *
   * @param args the argument vector provided to the console application.
   */
  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()));
  }
}