/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.ki.session.mgt;

import org.apache.ki.session.ExpiredSessionException;
import org.apache.ki.session.InvalidSessionException;
import org.apache.ki.session.StoppedSessionException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.Serializable;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.text.DateFormat;
import java.util.*;


/**
 * Simple {@link org.apache.ki.session.Session} POJO implementation, intended to be used on the business/server tier.
 *
 * @author Les Hazlewood
 * @since 0.1
 */
public class SimpleSession implements ValidatingSession, Serializable {

    //TODO - complete JavaDoc

    protected static final long MILLIS_PER_SECOND = 1000;
    protected static final long MILLIS_PER_MINUTE = 60 * MILLIS_PER_SECOND;
    protected static final long MILLIS_PER_HOUR = 60 * MILLIS_PER_MINUTE;

    private transient static final Logger log = LoggerFactory.getLogger(SimpleSession.class);

    private Serializable id = null;
    private Date startTimestamp = null;
    private Date stopTimestamp = null;
    private Date lastAccessTime = null;
    private long timeout = DefaultSessionManager.DEFAULT_GLOBAL_SESSION_TIMEOUT;
    private boolean expired = false;
    private InetAddress hostAddress = null;

    private Map<Object, Object> attributes = null;

    public SimpleSession() {
        this(getLocalHost());
    }

    public SimpleSession(InetAddress hostAddress) {
        this.startTimestamp = new Date();
        this.lastAccessTime = startTimestamp;
        this.hostAddress = hostAddress;
    }

    private static InetAddress getLocalHost() {
        try {
            return InetAddress.getLocalHost();
        } catch (UnknownHostException e) {
            throw new IllegalStateException(e);
        }
    }

    public Serializable getId() {
        return this.id;
    }

    public void setId(Serializable id) {
        this.id = id;
    }

    public Date getStartTimestamp() {
        return startTimestamp;
    }

    public void setStartTimestamp(Date startTimestamp) {
        this.startTimestamp = startTimestamp;
    }

    /**
     * Returns the time the session was stopped, or <tt>null</tt> if the session is still active.
     * <p/>
     * <p>A session may become stopped under a number of conditions:
     * <ul>
     * <li>If the user logs out of the system, their current session is terminated (released).</li>
     * <li>If the session expires</li>
     * <li>The application explicitly calls {@link #stop() destroy()}</li>
     * <li>If there is an internal system error and the session state can no longer accurately
     * reflect the user's behavior, such in the case of a system crash</li>
     * </ul>
     * </p>
     * <p/>
     * <p>Once stopped, a session may no longer be used.  It is locked from all further activity.
     *
     * @return The time the session was stopped, or <tt>null</tt> if the session is still
     *         active.
     */
    public Date getStopTimestamp() {
        return stopTimestamp;
    }

    public void setStopTimestamp(Date stopTimestamp) {
        this.stopTimestamp = stopTimestamp;
    }

    public Date getLastAccessTime() {
        return lastAccessTime;
    }

    public void setLastAccessTime(Date lastAccessTime) {
        this.lastAccessTime = lastAccessTime;
    }

    /**
     * Returns true if this session has expired, false otherwise.  If the session has
     * expired, no further user interaction with the system may be done under this session.
     *
     * @return true if this session has expired, false otherwise.
     */
    public boolean isExpired() {
        return expired;
    }

    public void setExpired(boolean expired) {
        this.expired = expired;
    }

    public long getTimeout() {
        return timeout;
    }

    public void setTimeout(long timeout) {
        this.timeout = timeout;
    }

    public InetAddress getHostAddress() {
        return hostAddress;
    }

    public void setHostAddress(InetAddress hostAddress) {
        this.hostAddress = hostAddress;
    }

    public Map<Object, Object> getAttributes() {
        touch();
        return attributes;
    }

    public void setAttributes(Map<Object, Object> attributes) {
        touch();
        this.attributes = attributes;
    }

    public void touch() {
        this.lastAccessTime = new Date();
    }

    public void stop() {
        if (this.stopTimestamp == null) {
            this.stopTimestamp = new Date();
        }
    }

    protected boolean isStopped() {
        return getStopTimestamp() != null;
    }

    protected void expire() {
        stop();
        if (!this.expired) {
            this.expired = true;
        }
    }

    /** @since 0.9 */
    public boolean isValid() {
        return !isStopped() && !isExpired();
    }

    /**
     * Determines if this session is expired.
     *
     * @return true if the specified session has expired, false otherwise.
     */
    protected boolean isTimedOut() {

        if (isExpired()) {
            return true;
        }

        long timeout = getTimeout();

        if (timeout >= 0l) {

            Date lastAccessTime = getLastAccessTime();

            if (lastAccessTime == null) {
                String msg = "session.lastAccessTime for session with id [" +
                        getId() + "] is null.  This value must be set at " +
                        "least once, preferably at least upon instantiation.  Please check the " +
                        getClass().getName() + " implementation and ensure " +
                        "this value will be set (perhaps in the constructor?)";
                throw new IllegalStateException(msg);
            }

            // Calculate at what time a session would have been last accessed
            // for it to be expired at this point.  In other words, subtract
            // from the current time the amount of time that a session can
            // be inactive before expiring.  If the session was last accessed
            // before this time, it is expired.
            long expireTimeMillis = System.currentTimeMillis() - timeout;
            Date expireTime = new Date(expireTimeMillis);
            return lastAccessTime.before(expireTime);
        } else {
            if (log.isTraceEnabled()) {
                log.trace("No timeout for session with id [" + getId() +
                        "].  Session is not considered expired.");
            }
        }

        return false;
    }

    public void validate() throws InvalidSessionException {
        //check for stopped:
        if (isStopped()) {
            //timestamp is set, so the session is considered stopped:
            String msg = "Session with id [" + getId() + "] has been " +
                    "explicitly stopped.  No further interaction under this session is " +
                    "allowed.";
            throw new StoppedSessionException(msg, getId());
        }

        //check for expiration
        if (isTimedOut()) {
            expire();

            //throw an exception explaining details of why it expired:
            Date lastAccessTime = getLastAccessTime();
            long timeout = getTimeout();

            Serializable sessionId = getId();

            DateFormat df = DateFormat.getInstance();
            String msg = "Session with id [" + sessionId + "] has expired. " +
                    "Last access time: " + df.format(lastAccessTime) +
                    ".  Current time: " + df.format(new Date()) +
                    ".  Session timeout is set to " + timeout / MILLIS_PER_SECOND + " seconds (" +
                    timeout / MILLIS_PER_MINUTE + " minutes)";
            if (log.isTraceEnabled()) {
                log.trace(msg);
            }
            throw new ExpiredSessionException(msg, sessionId);
        }
    }

    private Map<Object, Object> getAttributesLazy() {
        Map<Object, Object> attributes = getAttributes();
        if (attributes == null) {
            attributes = new HashMap<Object, Object>();
            setAttributes(attributes);
        }
        return attributes;
    }

    public Collection<Object> getAttributeKeys() throws InvalidSessionException {
        Map<Object, Object> attributes = getAttributes();
        if (attributes == null) {
            //noinspection unchecked
            return Collections.EMPTY_SET;
        }
        return attributes.keySet();
    }

    public Object getAttribute(Object key) {
        Map<Object, Object> attributes = getAttributes();
        if (attributes == null) {
            return null;
        }
        return attributes.get(key);
    }

    public void setAttribute(Object key, Object value) {
        if (value == null) {
            removeAttribute(key);
        } else {
            getAttributesLazy().put(key, value);
        }
    }

    public Object removeAttribute(Object key) {
        Map<Object, Object> attributes = getAttributes();
        if (attributes == null) {
            return null;
        } else {
            return attributes.remove(key);
        }
    }

}