import java.util.ArrayList;
import java.util.List;
import java.util.Iterator;
import java.util.HashMap;

/**
 * A simple model of a mail server. The server is able to receive
 * mail items for storage, and deliver them to clients on demand.
 *
 * @author David J. Barnes and Michael Kölling
 * @version 2011.07.31
 */
public class MailServer
{
    // Storage for the arbitrary number of mail items to be stored
    // on the server.
    private HashMap<String, ArrayList<MailItem>> mailServer;

    /**
     * Construct a mail server.
     */
    public MailServer()
    {
        mailServer = new HashMap<String, ArrayList<MailItem>>();
    }

    /**
     * Create a mailbox for a single user
     * @param   the name of the new user
     * @return  1 if the creation succeeded
     *          0 if a mailbox with that same name already exists
     */
    public int createMailbox(String user)
    {
        if (mailServer.containsKey(user)) {
            return 0;
        }
        else {
            ArrayList<MailItem> mailBox = new ArrayList<MailItem>();
            mailServer.put(user, mailBox);
            return 1;
        }
    }

    /**
     * Create mailboxes for users
     * @param   an array containing the names of the new users
     * @return  the number of successfully created mailboxes
     *          this number will be less than the number of
     *          specified users if some mailboxes already existed
     */
    public int createMailbox(String[] users)
    {
        int oldSize = mailServer.size();
        for (String u : users) {
            ArrayList<MailItem> mailBox = new ArrayList<MailItem>();
            mailServer.put(u, mailBox);
        }
        return mailServer.size() - oldSize;
    }

    /**
     * Retrieves the mailbox for a user
     *
     * @param   who the owner of the requested mailbox
     * @return  the mailbox belonging to who,
     *          null if it does not exist
     */
    private ArrayList getMailbox(String who)
    {
        return mailServer.get(who);
    }

    /**
     * Return how many mail items are waiting for a user.
     * @param who The user to check for.
     * @return How many items are waiting.
     */
    public int howManyMailItems(String who)
    {
        return getMailbox(who).size();
    }

    /**
     * Return the next mail item for a user or null if there
     * are none.
     * @param who The user requesting their next item.
     * @return The user's next item.
     */
    public MailItem getNextMailItem(String who)
    {
        Iterator<MailItem> it = getMailbox(who).iterator();
        while(it.hasNext())
        {
            MailItem item = it.next();
            it.remove();
            return item;
        }
        return null;
    }

    private boolean ignore(MailItem item)
    {
        return (item.getFrom().equals("") || item.getTo().equals(""));
    }

    /**
     * Add the given mail item to the message list.
     * @param item The mail item to be stored on the server.
     */
    public void post(MailItem item)
    {
        if (!ignore(item))
        {
            for (String rec : item.getTo()) {
                if (mailServer.containsKey(rec)) {
                    getMailbox(rec).add(0, item);
                }
            }
        }
    }

    public int howManyMessages()
    {
        int nMsg = 0;
        for (ArrayList<MailItem> mailBox : mailServer.values()) {
            nMsg = nMsg + mailBox.size();
        }
        return nMsg;
    }
}