import java.util.List;
import java.util.Stack;

/**
 *
 *  TODO class to mimic the browsing of a website
 *  TODO uses stacks to imitate each webpage, has methods to scroll through
 *  each line/webpage
 *
 *  @author  Sean Lee
 *  @version Jan 20, 2020
 *  @author  Period: TODO
 *  @author  Assignment: JMCh21_3Browsing
 *
 *  @author  Sources: TODO
 */
public class BrowserModel
{
    private BrowserView view;
    private Stack<Integer> backStk;
    private Stack<Integer> forwardStk;
    private int topLine;

    /**
     * constructor
     * @param view - top of the page
     */
    public BrowserModel(BrowserView view)
    {
        backStk = new Stack<Integer>();
        forwardStk = new Stack<Integer>();
        this.view = view;
        view.update(0);
        backStk.add( 0 );
    }

    /**
     *
     * TODO goes to the back line/link
     */
    public void back()
    {
        if (hasBack())
        {
            int n = backStk.pop();
            forwardStk.add( n );
            topLine = backStk.peek();
            view.update(topLine);
        }
    }

    /**
     *
     * TODO goes to the forward line/link
     */
    public void forward()
    {
        if (hasForward())
        {
            topLine = forwardStk.peek();
            int n = forwardStk.pop();
            backStk.add( n );
            view.update(topLine);
        }
    }

    /**
     *
     * TODO goes to line 0 at the top
     */
    public void home()
    {
        if (topLine != 0)
        {
            backStk.add( 0 );
            topLine = 0;
            view.update(topLine);
        }
    }

    /**
     *
     * TODO goes to the line directed by the link
     * @param n - line to go to
     */
    public void followLink(int n)
    {
        backStk.add( n );
        topLine = n;
        view.update(topLine);
    }

    /**
     *
     * TODO method to see if it is possible to go back
     * @return - true if can go back, false if can't go back
     */
    public boolean hasBack()
    {
        System.out.println("back stack size:" + backStk.size() + backStk);
        if (backStk.size() == 1 && backStk.peek() == 0)
        {
            return false;
        }
        return !backStk.isEmpty();
    }

    /**
     *
     * TODO method to see if it is possible to go forward
     * @return - true if can go forward, false if can't go forward
     */
    public boolean hasForward()
    {
        System.out.println("fwd stack size:" + forwardStk.size() + forwardStk);
        return !forwardStk.isEmpty();
    }

    // The following are for test purposes only
    /**
     *
     * TODO testing method
     * @return backStk
     */
    public Stack<Integer> getBackStk()
    {
        return backStk;
    }

    /**
     *
     * TODO testing method
     * @return forwardStk
     */
    public Stack<Integer> getForwardStk()
    {
        return forwardStk;
    }

    /**
     *
     * TODO testing method
     * @return topline
     */
    public int getTopLine()
    {
        return topLine;
    }
}