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package Torello.Java;

class DotDots
{
    static String parentDir(
            final String    directoryStr,
            final char      separator,
            final short     nLevels
        )
    {
        if (nLevels < 1) throw new IllegalArgumentException(
            "The parameter nLevels may not be less than 1, nor negative.  You have passed: " +
            nLevels
        );

        if ((separator != '/') && (separator != '\\')) throw new IllegalArgumentException(
            "The separator character provided to this method must be either a forward-slash '/' " +
            "or a back-slash ('\\') character.  You have provided: ['" + separator + "']."
        );

        int count = 0;

        for (int i=directoryStr.length() - 1; i >= 0; i--)

            if (directoryStr.charAt(i) == separator)
                if (++count == (nLevels + 1))
                    return directoryStr.substring(0, i + 1);

        throw new IllegalArgumentException(
            "The parameter nLevels was: " + nLevels + ", but unfortunately there only were: " +
            count + "'" + separator + "' characters found in the directory-string."
        );
    }

    static String specifiedAncestor(
            final String    fileName,
            final String    ancestorDirectory,
            final char      separator
        )
    {
        if ((separator != '/') && (separator != '\\')) throw new IllegalArgumentException(
            "The separator character provided to this method must be either a forward-slash '/' " +
            "or a back-slash ('\\') character.  You have provided: ['" + separator + "']."
        );

        if (! fileName.startsWith(ancestorDirectory)) throw new IllegalArgumentException(
            "The file-name you have provided [" + fileName + "] is a String that does " +
            "start with the ancestorDirectory String [" + ancestorDirectory + "].  " +
            "Therefore there is no relative path using the dot-dot construct to the named " +
            "ancestor directory fromm the directory where the named file resides."
        );

        int levelsDeep = StringParse.countCharacters(fileName, separator) - 
            StringParse.countCharacters(ancestorDirectory, separator);

        String dotDots = "";

        while (levelsDeep-- > 0) dotDots = dotDots + ".." + separator;

        return dotDots;
    }

}