import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

/**
 * A class to read a text file (presumably containing a book) 
 * and give the contents of that file to the user one work at a time.
 * The class strips blank spaces and most punctuation. All words are
 * downcased
 * Created: April 20, 2020
 * @author gtowell
 */
public class BookReader {

    /** The reader for the file being read. */
    private BufferedReader bufferedBook;

    /** The current line in the file being read, as an array of words */
    private String[] currentLine;

    /** The position in the currentLine  of the next word */
    private int lineindex;

    /** 
     * Initialize the BookReader
     * @param filename the name of the file contain the book to be read
     * @throws FileNotFoundException is the book file does not exist
     */
    public BookReader(String filename) throws FileNotFoundException {
        bufferedBook = new BufferedReader(new FileReader(filename));
        currentLine=null;
        lineindex=0;
    }

    /**
     * Get the next non-blank line in the file.  
     * Also remove leading and trailing spaces and most punctuation.
     * @return the next line, modified as described. Or null when the file 
     * has been completely read.
     * @throws IOException when there is a problem reading from the fle
     */
    private String getNewLine() throws IOException {
        String nextLine = bufferedBook.readLine();
        while (nextLine!=null && nextLine.length()==0) {
            nextLine = bufferedBook.readLine();
        }
        return nextLine==null?nextLine:nextLine.trim().toLowerCase().replaceAll("[\\.\\'?!,\\\"]", "");
    }

    /**
     * Get the next word in the file.  in all lower case.
     * @return the next word.  Or null if the file has been completely read
     * @throws IOException if there is a problem reading the file
     */
    public String nextWord() throws IOException {
        if (currentLine==null || lineindex>=currentLine.length) {
            String nextLine = getNewLine();
            if (nextLine==null)
                return null;
            currentLine = nextLine.split("\\s+");
            lineindex=0;
        }
        return currentLine[lineindex++];
    }

}