package com.mozilla.bespin;import org.json.simple.JSONObject;import java.io.File;import java.util.ArrayList;import java.util.Collection;import java.util.Collections;import java.util.ConcurrentModificationException;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;public class SessionTracker {    private Map<File, List<EditSession>> sessionsByFile = new HashMap<File, List<EditSession>>();    private Map<UserSession, List<EditSession>> sessionsByUser = new HashMap<UserSession, List<EditSession>>();    /**     * Returns the edits that a user has applied to a specified file.     *     * @param file     * @param session     * @return always returns a list; if no edits have been applied, an empty list is returned. The returned list is not live.     */    public synchronized List<JSONObject> getEdits(File file, UserSession session) {        EditSession editSession = getSession(file, session);        return (editSession != null) ? editSession.getEdits() : Collections.EMPTY_LIST;    }    /**     * Returns any edit sessions that may be open for this file; returned list is not live     *     * @return     */    public synchronized List<EditSession> getSessions(File file) {        return new ArrayList<EditSession>(getLiveSessions(file));    }    /**     * Returns any edit sessions open by the passed user; returned list is not live     * @param user     * @return     */    public synchronized List<EditSession> getSessions(UserSession user) {        return new ArrayList<EditSession>(getLiveSessions(user));    }    /**     * Returns the EditSession corresponding to the passed UserSession, or null if one does not exist     *      * @param file     * @param session     * @return     */    public synchronized EditSession getSession(File file, UserSession session) {        List<EditSession> editSessions = sessionsByFile.get(file);        if (editSessions == null) return null;        for (EditSession editSession : editSessions) {            if (editSession.getUser().equals(session)) return editSession;        }        return null;    }    public synchronized EditSession openSession(File file, UserSession session, EditMode mode) {        if (getSession(file, session) != null) throw new ConcurrentModificationException("Edit session already exists");        EditSession editSession = new EditSession(file, session, mode);        getLiveSessions(file).add(editSession);        getLiveSessions(session).add(editSession);        return editSession;    }    public synchronized void closeSession(File file, UserSession session) {        EditSession edit = getSession(file, session);        if (edit != null) {            getLiveSessions(file).remove(edit);            getLiveSessions(session).remove(edit);        }    }    public synchronized void resetEdits(File file) {        List<EditSession> edits = getLiveSessions(file);        for (EditSession edit : edits) {            edit.clearEdits();        }    }    public synchronized void resetEdits() {        Collection<List<EditSession>> edits = sessionsByFile.values();        for (Iterator<List<EditSession>> iterator = edits.iterator(); iterator.hasNext();) {            List<EditSession> lists = iterator.next();            for (EditSession edit : lists) {                edit.clearEdits();            }        }    }    private synchronized List<EditSession> getLiveSessions(UserSession user) {        List<EditSession> sessions = this.sessionsByUser.get(user);        if (sessions == null) {            sessions = new ArrayList<EditSession>();            this.sessionsByUser.put(user, sessions);        }        return sessions;    }    private synchronized List<EditSession> getLiveSessions(File file) {        List<EditSession> sessions = this.sessionsByFile.get(file);        if (sessions == null) {            sessions = new ArrayList<EditSession>();            this.sessionsByFile.put(file, sessions);        }        return sessions;    }}