/**
 * COMP 1711 (Fall 2005)
 *
 * Solution to Challenge Problem #4 (Spam Helper)
 *
 * This class has a static method that takes a potential e-mail address
 * and tests to see if it meets the standards in the problem description.
 *
 * @author  Based on a solution by Andy Hebert
 * @version Dec-08-2005 
 */
public class Problem04
{
    //---------------------------------------------------------------------------
    /**
     * This method takes in a potential address and determines if it is valid.
     * 
     * @param test The email address to test (a String)
     */
    public static boolean isValidEmail(String test)
    {
        String lowerTest = test.toLowerCase();
        boolean testAt = rightAts(lowerTest);
        boolean testDot = rightDots(lowerTest);
        boolean testChar = rightChars(lowerTest);
        
        if (testAt && testDot && testChar)
        {
            return true;
        } // if

        return false;
    } // end isValidEmail(String)
    //---------------------------------------------------------------------------
    /**
     * Private method to test that the input String contains exactly one '@'
     * character, and that this character is neither the first nor the last.
     * 
     * @param at Potential e-mail address to test (a String)
     */
    private static boolean rightAts(String at)
    {
        int size = at.length();
        int firstAt = at.indexOf('@');      // find position of first occurrence of '@'
        int lastAt = at.lastIndexOf('@');   // find position of last occurrence of '@'

        if(firstAt == -1 || (firstAt != lastAt) || firstAt == 0 || lastAt == (size-1))
        {
            return false;
        } // if

        return true;
    } // end rightAts(String)
    //---------------------------------------------------------------------------
    /**
     * Private method to test that the input String has any '.' characters
     * positioned correctly.  This means that '.' cannot be the first or last
     * character, and that the substrings "..", ".@", and "@." cannot occur.
     * 
     * @param dots Potential e-mail address to test (a String)
     */
    private static boolean rightDots(String dots)
    {
         int size = dots.length();
         int firstDot = dots.indexOf('.');      // find position of first occurrence of '.'
         int lastDot = dots.lastIndexOf('.');   // find position of last occurrence of '.'
         int bad1 = dots.indexOf("..");         // find position of first occurrence of substring ".."
         int bad2 = dots.indexOf("@.");         // find position of first occurrence of substring ".@"
         int bad3 = dots.indexOf(".@");         // find position of first occurrence of substring "@."

         if(firstDot == 0 || lastDot == (size - 1) || (bad1 >= 0) || (bad2 >= 0) || (bad3 >= 0))
         {
             return false;
         } // if

         return true;
    } // end rightDots(String)
    //---------------------------------------------------------------------------
    /**
     * Private method to test that all characters in the input String that
     * are not '@' or '.' are uppercase letters, lowercase letters, or digits.
     * 
     * @param chars Potential e-mail address to test (a String)
     */
    private static boolean rightChars(String chars)
    {
        int size = chars.length();
        char ch;

        for(int i = 0; i < size; i ++)
        {
            ch = chars.charAt(i);
            if ((ch != '.') && (ch != '@'))
            {
                boolean isOK = (('a' <= ch) && (ch <= 'z')) || (('0' <= ch) && (ch <= '9'));
                if (!isOK)
                {
                    return false;
                } // if
            } // if
        } // for i

        return true;
    } // end rightChars(String)
    //---------------------------------------------------------------------------
}// end class Problem04