import java.util.Scanner;
import java.io.File;

/**
 * Demonstrates how to create File objects, and use them to
 * read the contents from files on the disk.
 */
public class FileInput
{
    /**
     * Reads the first line from the specified file and prints it,
     * if the file exists.  Tells the user the file doesn't exist
     * if it's not there.  
     * 
     * The "throws" part is basically a warning label to users of
     * this method. It tells them that this code might crash if we 
     * try to read from a file that doesn't exist. It won't compile
     * without the label!
     */
    public void peekAtFile(String filename) throws java.io.FileNotFoundException
    {
        File theFile = new File(filename);
        if (theFile.exists()) {
            Scanner scan = new Scanner(theFile);
            String firstLine = scan.nextLine();
            System.out.println("First line is: "+firstLine);
        }
        else {
            System.out.println(filename+" doesn't exist!");
        }
    }

    /**
     * Any method that calls one with a "throws" warning label ALSO
     * needs a warning label.
     */
    public void peekAtInputJava() throws java.io.FileNotFoundException
    {
        peekAtFile("Input.java");
    }

    /**
     * This version doesn't just print the first line -- it keeps
     * reading and printing until it has displayed ALL lines from
     * the file.
     */
    public void printAllLines(String filename) throws java.io.FileNotFoundException
    {
        File theFile = new File(filename);
        if (theFile.exists()) {
            Scanner scan = new Scanner(theFile);
            while(scan.hasNext()) {
                String line = scan.nextLine();
                System.out.println(line);
            }
            System.out.println("Done reading from the file.");
        }
        else {
            System.out.println(filename+" doesn't exist!");
        }
    }

    /**
     * Similar to printAllLines, except we want to read all of the 
     * integers from a file, add them up, and return the sum. It will
     * stop if it encounters non-integer stuff in the file.
     */
    public int addUpIntegers(String filename) throws java.io.FileNotFoundException
    {
        int sum = 0;
        File theFile = new File(filename);
        if (theFile.exists()) {
            Scanner scan = new Scanner(theFile);
            while(scan.hasNextInt()) {
                int num = scan.nextInt();
                sum = sum + num;
            }
        }
        else {
            System.out.println(filename+" doesn't exist!");
        }
        return sum; // For now...
    }
    
    /**
     * Similar to addUpIntegers, except it skips over any non-integer stuff
     * it encounters.
     */
    public int addUpIgnoreText(String filename) throws java.io.FileNotFoundException
    {
        int sum = 0;
        File theFile = new File(filename);
        if (theFile.exists()) {
            Scanner scan = new Scanner(theFile);
            while(scan.hasNext()) {
                if (scan.hasNextInt()) {
                    int num = scan.nextInt();
                    sum = sum + num;
                }
                else {
                    String garbage = scan.next();  // Read the next "word" and discard it
                }
            }
        }
        else {
            System.out.println(filename+" doesn't exist!");
        }
        return sum; // For now...
    }
}