import org.apache.commons.lang.StringUtils;

import java.util.LinkedList;
import java.util.List;

public class StringHideUtils {

    /**
     * @param str - string to replace
     * @param ch  - character for replacement
     * @param n   - count of the first characters to show
     * @return
     */
    public static String showFirstChars(String str, char ch, int n) {
        if (str == null || n > str.length()) {
            return str;
        }
        char[] word = hideChars(str.toCharArray(), ch, n, str.length());
        return new String(word);
    }


    /**
     * @param str - string to replace
     * @param ch  - character for replacement
     * @param n   - count of the last characters to show
     * @return
     */
    public static String showLastChars(String str, char ch, int n) {
        if (str == null || n > str.length()) {
            return str;
        }
        char[] word = hideChars(str.toCharArray(), ch, 0, str.length() - n);
        return new String(word);
    }


    /**
     * @param str   - string to replace
     * @param ch    - character for replacement
     * @param first - count of the first characters to show
     * @param last  - count of the last characters to show
     * @return
     */
    public static String hideMiddleChars(String str, char ch, int first, int last) {
        if (str == null || first > str.length() || last > str.length()) {
            return str;
        }
        Integer[] indexes = findEmptyCharIndex(str);
        str = str.replaceAll("\\s", "");

        char[] word = hideChars(str.toCharArray(), ch, first, str.length() - last);

        return indexes.length == 0 ? new String(word) : mergeWhitespacesToString(word, indexes);
    }

    private static Integer[] findEmptyCharIndex(String str) {
        List<Integer> emptyCharIndex = new LinkedList<>();
        for (int i = 0; i < str.length(); i++) {
            if (str.charAt(i) == ' ') {
                emptyCharIndex.add(i);
            }
        }
        return emptyCharIndex.toArray(new Integer[emptyCharIndex.size()]);
    }

    private static String mergeWhitespacesToString(char[] word, Integer[] whiteSpacesIndexes) {
        LinkedList<Character> charList = new LinkedList<>();
        for (char letter : word) {
            charList.add(letter);
        }
        for (Integer whtIx : whiteSpacesIndexes) {
            charList.add(whtIx, ' ');
        }
        return StringUtils.join(charList.toArray());
    }

    //skip empty char
    private static char[] hideChars(char[] word, char ch, int start, int end) {
        for (int i = start; i < end; i++) {
            word[i] = ch;
        }
        return word;
    }
}