/*
 *  Copyright 1999-2004 The Apache Software Foundation
 *
 *  Licensed 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.tomcat.facade;

import javax.servlet.Servlet;
import javax.servlet.SingleThreadModel;
import javax.servlet.UnavailableException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.tomcat.core.BaseInterceptor;
import org.apache.tomcat.core.Container;
import org.apache.tomcat.core.Context;
import org.apache.tomcat.core.Handler;
import org.apache.tomcat.core.Request;
import org.apache.tomcat.core.Response;
import org.apache.tomcat.core.TomcatException;
import org.apache.tomcat.util.collections.SimplePool;

/**
 * Handler for servlets. It'll implement all servlet-specific
 * requirements ( init, Unavailable exception, etc).
 *
 * It is also used for Jsps ( since a Jsp is a servlet ), but
 * requires the Jsp interceptor to make sure that indeed a Jsp is
 * a servlet ( and set the class name ).
 * 
 * The old Jsp hack is no longer supported ( i.e. declaring a servlet
 * with the name jsp, mapping *.jsp -> jsp will work as required
 * by the servlet spec - no special hook is provided for initialization ).
 * Note that JspServlet doesn't work without special cases in ServletWrapper.
 * 
 * @author James Duncan Davidson [duncan@eng.sun.com]
 * @author Jason Hunter [jch@eng.sun.com]
 * @author James Todd [gonzo@eng.sun.com]
 * @author Harish Prabandham
 * @author Costin Manolache
 */
public final class ServletHandler extends Handler {

    /** 
     * If init() fails or preInit() detects the handler is still
     * unavailable.
     */
    public static final int STATE_DELAYED_INIT=2;

    /** The handler has been succesfully initialized and is ready to
     * serve requests. If the handler is not in this state a 500 error
     * should be reported. ( customize - may be 404 )
     * To ADDED by calling destroy()
     * To DISABLED if permanent UnavailableException in service()
     * FROM ADDED by calling init()
     *
     * Note: Once this state is reached, only UnavailableExceptions are
     * stored in errorException.
     */
    public static final int STATE_READY=3;

    // -------------------- Properties --------------------
    
    // extra informations - if the servlet is declared in web.xml
    private ServletInfo sw;

    private String servletClassName;

    private SimplePool stmPool=null;
    private int stmPoolSize=SimplePool.DEFAULT_SIZE;
    private int stmInstances=0;
    private boolean useStmPool=true;

    protected Class servletClass;
    protected Servlet servlet;
    protected Context context;
    
    // If init() fails, Handler.errorException will hold the reason.
    // In the case of an UnavailableException, this field will hold
    // the expiration time if UnavailableException is not permanent.
    long unavailableTime=-1;
    
    public ServletHandler() {
	super();
    }

    public String toString() {
	return "ServletH " + name + "(" + sw  + ")";
    }

    public void setServletInfo( ServletInfo sw ) {
	this.sw=sw;
    }

    public void setUseSTMPool(boolean useP){
	useStmPool = useP;
    }
    public void setSTMPoolSize(int size) {
	stmPoolSize = size;
    }

    public ServletInfo getServletInfo() {
	if( sw==null ) {
	    // it is possible to create a handler without ServletInfo
	    // defaults are used.
	    sw=new ServletInfo(this);
	}
	return sw;
    }

    /**
     */
    public void setContext( Context context) {
        this.context = context;
    }

    /** Return the context associated with the handler
     */
    public Context getContext() {
	return context;
    }


    public void setServletClassName( String servletClassName) {
	servlet=null; // reset the servlet, if it was set
	servletClass=null;
	this.servletClassName=servletClassName;
	if( debug>0 && sw!=null && sw.getJspFile()!=null)
	    log( context, "setServletClassName for " + sw.getJspFile() +
		 ": " + servletClassName);
    }

    public String getServletClassName() {
	if( servletClassName == null )
	    servletClassName=name;
        return servletClassName;
    }

    // -------------------- Init/destroy --------------------
    // from Handler

    /** Destroy a handler, and notify all the interested interceptors
     */
    public final void destroy() {
	if ( state!=STATE_READY ) {
	    // reset exception
	    errorException = null;
	    return;// already destroyed or not init.
	}
	// XXX if we are being destroyed due to permanent UnavailableException
	// thrown in service(), we probably don't want to go to ADDED state.
	// may need a STATE_DISABLE_PERM?
	setState( STATE_ADDED );

	// XXX post will not be called if any error happens in destroy.
	// That's how tomcat worked before - I think it's a bug !
	try {
	    doDestroy();
	} catch( Exception ex ) {
	    log(context,  "Error during destroy ", ex );
	}
	

	errorException=null;
    }


    /** Call the init method, and notify all interested listeners.
     *  This is a final method to insure consistent behavior on errors.
     *  It also saves handlers from dealing with synchronization issues.
     */
    public final synchronized void init()
    {
	// we use getState() as a workaround for bugs in VMs
	
	if( getState() == STATE_READY || getState() == STATE_DISABLED )
	    return;

	try {
	    // special preInit() hook
	    preInit();
	    // preInit may either throw exception or setState DELAYED_INIT
	} catch( ClassNotFoundException ex ) {
	    log( context, "Class not found: " + servletClassName);
	    setErrorException(ex);
	    setState(STATE_DISABLED);
	    return;
	} catch( Exception ex ) {
	    // save error, assume permanent
	    log(context, "Exception in preInit " + ex.getMessage(), ex );
	    setErrorException(ex);
	    setState(STATE_DISABLED);
	    return;
	}
	    
	// we'll try again later 
	if( getState() == STATE_DELAYED_INIT ||
	    getState()==STATE_DISABLED ) { // or disabled 
	    return;
	}
	// preInit have no exceptions and doesn't delay us
	// We can run init hooks and init

	// Call pre, doInit and post
	BaseInterceptor cI[]=context.getContainer().getInterceptors();
	for( int i=0; i< cI.length; i++ ) {
	    try {
		cI[i].preServletInit( context, this );
	    } catch( TomcatException ex) {
		// log, but ignore.
		log(context, "preServletInit" , ex);
	    }
	}
		
	try {
	    doInit();
	    // if success, we are ready to serve
	} catch( Exception ex ) {
	    // save error, assume permanent
	    log(context, "Exception in init  " + ex.getMessage(), ex );
	    setErrorException(ex);
	    state=STATE_DISABLED;
	}
	    
	for( int i=0; i< cI.length; i++ ) {
	    try {
		cI[i].postServletInit( context, this );
	    } catch( TomcatException ex) {
		log(context, "postServletInit" , ex);
	    }
	}

	// Now that both pre/post hooks have been called, the
	// servlet is ready to serve.

	// if no error happened and if doInit didn't put us in
	// a special state, we are ready
	if( state!=STATE_DISABLED &&
		getErrorException() == null ) {
	    state=STATE_READY;
	}
    }

    private void log( Context ctx, String s ) {
	if( ctx==null )
	    log( s );
	else
	    ctx.log( s );
    }

    private void log( Context ctx, String s, Throwable t ) {
	if( ctx==null )
	    log( s, t );
	else
	    ctx.log( s, t );
    }
    
    // -------------------- --------------------

    public void reload() {
	if( getState()==STATE_READY ) {
	    try {
		destroy();
	    } catch(Exception ex ) {
		log(context,  "Error in destroy ", ex );
	    }
	}

	if( sw.getServletClassName() != null ) {
	    // I can survive reload
	    servlet=null;
	    servletClass=null;
	}
	setState( STATE_ADDED );
    }
    
    // -------------------- 

    public Servlet getServlet() 
	throws ClassNotFoundException, InstantiationException,
	IllegalAccessException
    {
	if(servlet!=null)
	    return servlet;

	if( debug>0)
	    log(context, "LoadServlet " + name + " " +
		sw.getServletName() + " " +
		sw.getServletClassName() + " " + servletClass );

	// default
	if( servletClassName==null )
	    servletClassName=name;
	
	if (servletClass == null) {
	    servletClass=context.getClassLoader().loadClass(servletClassName);
	}
	
	servlet = (Servlet)servletClass.newInstance();
	if (useStmPool && ( servlet instanceof SingleThreadModel )) {
	    if(stmPool == null){
		stmPool = new SimplePool(stmPoolSize);
	    }
	    stmPool.put(servlet);
	    stmInstances++;
	}
	return servlet;
    }

    // -------------------- Destroy --------------------
    
    protected void doDestroy() throws TomcatException {
	synchronized (this) {
	    try {
		if( servlet!=null) {
		    BaseInterceptor cI[]=context.
			getContainer().getInterceptors();
		    for( int i=0; i< cI.length; i++ ) {
			try {
			    cI[i].preServletDestroy( context, this );
			} catch( TomcatException ex) {
			    log(context, "preServletDestroy", ex);
			}
		    }
		    if(useStmPool && (servlet instanceof SingleThreadModel)){
			Servlet sl=null;
			while((sl = (Servlet)stmPool.get()) != null){
			    sl.destroy();
			}
			stmInstances=0;
		    } else {
			servlet.destroy();
		    }

		    for( int i=0; i< cI.length; i++ ) {
			try {
			    cI[i].postServletDestroy( context, this );
			} catch( TomcatException ex) {
			    log(context, "postServletDestroy", ex);
			}
		    }
		}
	    } catch(Exception ex) {
		// Should never come here...
		log(context, "Error in destroy ", ex );
	    }
	}
    }

    // Special hook
    protected void preInit() throws Exception
    {
	if( debug > 0 )
	    log(context, "preInit " + servlet + " " + sw.getJspFile() + " " +
		 servletClassName);

	// Deal with Unavailable errors
	if( ! checkAvailable() ) {
	    // remain in STATE_DELAYED_INIT state
	    return;
	}
	// clear STATE_DELAYED_INIT if set
	setState( STATE_ADDED );
	
	// For JSPs we rely on JspInterceptor to set the servlet class name.
	// We make no distinction between servlets and jsps.
	getServlet();
    }

    
    protected void doInit()
	throws Exception
    {
	try {
	    servlet.init( getServletInfo().getServletConfig() );
	} catch( UnavailableException ex ) {
	    // Implement the "UnavailableException" specification
	    // servlet exception state
	    setErrorException( ex );
	    if ( ex.isPermanent() ) {
		setState( STATE_DISABLED );
	    } else {
		setState( STATE_DELAYED_INIT );
		setServletUnavailable( ex );
	    }
	    servlet=null;
	    // we have set the exception and state, okay to just return
	}

	// other exceptions are just thrown -
	// init() will deal with them.
    }

    // Overrides the default handler
    public void service ( Request req, Response res )
	throws Exception
    {
        BaseInterceptor ri[];
	ri=context.getContainer().
	    getInterceptors(Container.H_preInitCheck);
	for( int i=0; i< ri.length; i++ ) {
	    int status = ri[i].preInitCheck(req, this);
	    if(status != 0) {
		if(status >= 300){
		    contextM.handleStatus(req, res, status);
		}
		return;
	    }
	}
	if( state!=STATE_READY ) {
	    if( state!= STATE_DISABLED ) {
		init();
	    }
	    if( state== STATE_DISABLED || state==STATE_DELAYED_INIT ) {
		// the init failed because of an exception
		Exception ex=getErrorException();
		// save error info
		res.setErrorException(ex);
		res.setErrorURI(null);
		handleInitError( req, res, ex );
		return;
	    } 
	}
	ri=context.getContainer().
	    getInterceptors(Container.H_postInitCheck);
	for( int i=0; i< ri.length; i++ ) {
	    int status = ri[i].postInitCheck(req, this);
	    if(status != 0) {
		contextM.handleStatus(req, res, status);
		return;
	    }
	}

	super.service( req, res );
    }

    protected void doSTMService(HttpServletRequest reqF, HttpServletResponse resF) 
	throws Exception {
	Servlet sl = null;
	try {
	    boolean newInstance = false;
	    if ((sl = (Servlet)stmPool.get()) == null) {
		synchronized (this) {
		    if (stmInstances < stmPoolSize) {
			stmInstances++;
			newInstance = true;
		    }
		}
		if (newInstance) {
		    sl = (Servlet)servletClass.newInstance();
		    sl.init(getServletInfo().getServletConfig());
		} else {
		 /* The pool is full, just synchronize on the initial instance.
		    Ideally, we would the pain across all pooled instances
		    to avoid a bottleneck on a single instance. */
		    sl = servlet;
		}
	    }
	    /* Since this may be the initial instance, we still need to
	       synchronize here */
	    synchronized(sl) {
		sl.service(reqF, resF);
	    }
	} finally {
	    if (sl != null) {
		stmPool.put(sl);
	    }
	}
    }
         
    protected void doService(Request req, Response res)
	throws Exception
    {
	//  case
	String jspFile=sw.getJspFile();
	if( jspFile!=null ) {
	    if( jspFile.startsWith("/"))
		req.setAttribute( "javax.servlet.include.request_uri",
				  req.getContext().getPath()  + jspFile );
	    else
		req.setAttribute( "javax.servlet.include.request_uri",
				  req.getContext().getPath()  + "/" +jspFile );
	    req.setAttribute( "javax.servlet.include.servlet_path", jspFile );
	}


	// if unavailable
	if( ! checkAvailable( req, res ) ) {
	    handleServiceError( req, res, res.getErrorException());
	    return; // we can't handle it
	}

	// Get facades - each req have one facade per context
	// the facade itself is very light.

	// For big servers ( with >100s of webapps ) we can
	// use a pool or other technique. Right now there
	// are many other ( much more expensive ) resources
	// associated with contexts ( like the session thread)

	// XXX
	HttpServletRequest reqF= (HttpServletRequest)req.getFacade();
	HttpServletResponse resF= (HttpServletResponse)res.getFacade();
	if( reqF == null || resF == null ||
	    ! (reqF instanceof HttpServletRequestFacade) ) {
	    reqF=new HttpServletRequestFacade(req);
	    resF=new HttpServletResponseFacade(res);
	    req.setFacade( reqF );
	    res.setFacade( resF );
	}

	try {
	    // We are initialized and fine
	    if (servlet instanceof SingleThreadModel) {
		if(useStmPool) {
		    doSTMService(reqF,resF);
		} else {
		    synchronized(servlet) {
			servlet.service(reqF, resF);
		    }
		}
	    } else {
		servlet.service(reqF, resF);
	    }
	    // catch just UnavailableException, so we can set a timer if needed
	    // other exceptions will be thrown
	} catch ( UnavailableException ex ) {
	    // if new exception, save and set timer if necessary
	    if ( res.getErrorException() != ex ) {
		res.setErrorException(ex);
		res.setErrorURI(null);
		if ( ex.isPermanent() ) {
		    setState( STATE_DISABLED );
		    // XXX spec says we must destroy the servlet
		}
		if ( null == getErrorException() ) {
		    synchronized(this) {
			if ( null == getErrorException() ) {
			    if ( state == STATE_DISABLED )
				// set the permanet exception for future use
				setErrorException( ex );
			    else
				// set expiration
				setServletUnavailable((UnavailableException)ex );
			}
		    }
		}
	    }
	    handleServiceError( req, res, ex );
	    return;
	}
	
	// clear any error exception since none were thrown
	res.setErrorException(null);
	res.setErrorURI(null);
    }

    private void handleError( Request req, Response res, Throwable t ) {
	if (t instanceof UnavailableException) {
	    int unavailableTime = -1;
	    if ( !((UnavailableException)t).isPermanent() ) {
		unavailableTime = ((UnavailableException)t).getUnavailableSeconds();
		// if unavailable time not known, use 1 second
		if ( unavailableTime <= 0 )
		    unavailableTime = 1;
		res.setHeader("Retry-After", Integer.toString(unavailableTime));
	    }
	    String msg=t.getMessage();
	    String logMsg="UnavailableException in: " + req +
		", time remaining " + unavailableTime + " seconds : " + msg;
	    log( context, logMsg, t);
	    req.setAttribute("javax.servlet.error.message", msg );
            req.setAttribute("tomcat.servlet.error.service.unavailableTime", new Integer(unavailableTime));
	    contextM.handleStatus( req, res, HttpServletResponse.SC_SERVICE_UNAVAILABLE );
	    return;
	} else {
	    contextM.handleError( req, res, t );
	}
    }

    protected void handleInitError( Request req, Response res, Throwable t )
    {
	// if in included, defer handling to higher level
	if (res.isIncluded()) return;
	if( t instanceof ClassNotFoundException )
	    contextM.handleStatus( req, res, 404 );
	else
	    handleError( req, res, t );
    }

    protected void handleServiceError( Request req, Response res, Throwable t )
	throws Exception
    {
	// if in included, defer handling to higher level
	if (res.isIncluded()) {
	    throw (Exception)t;
	}
	// only for top-level servlets
	handleError( req, res, t );
    }

    // -------------------- Unavailable --------------------

    /** Set unavailable time
     */
    private void setServletUnavailable( UnavailableException ex ) {
	unavailableTime=System.currentTimeMillis() +
	    ex.getUnavailableSeconds() * 1000;
	setErrorException( ex );
    }

    /** Check if unavailable timer is present and if so, has the
	unavailable time expired.  Two versions are needed.  The
	first is used in init() handling which is itself synchronized.
	The second is used in service() handling after initialization
	is successful.  It needs its own synchronization since
	multiple requests could try to expire the unavailable error.
     */
    private boolean checkAvailable() {
	if( unavailableTime == -1 )
	    return true;
	
	// if permanent exception this code isn't called
	// if timer not expired
	if ( (unavailableTime - System.currentTimeMillis()) < 0) {
	    // disable the error - it expired
	    unavailableTime=-1;
	    setErrorException(null);
	    log(context, getName()+" unavailable time expired, trying again ");
	    return true;
	}
	// still unavailable
	return false;
    }

    private boolean checkAvailable( Request req, Response res ) {
	if( unavailableTime == -1 )
	    return true;

	// save a copy of current UnavailableException
	Exception ex = getErrorException();	
	// if permanent exception this code isn't called
	long moreTime = unavailableTime - System.currentTimeMillis();
	// if timer expired
	if ( moreTime < 0) {
	    synchronized(this) {
		// if another request hasn't expired the error
		if ( unavailableTime != -1 ) {
		    // disable the error - it expired
		    setErrorException(null);
		    unavailableTime=-1;
		    log(context, getName() +
			" unavailable time expired, trying again ");
		}
		return true;
	    }
	}
	// get seconds remaining with minimum of 1 second
	int secs=1;
	if( moreTime > 0 )
	    secs = (int)((moreTime + 999) / 1000);
	// save error info
	res.setErrorException(new UnavailableException(ex.getMessage(), secs));
	res.setErrorURI(null);
	// still unavailable
	return false;
    }

    /** The handler may return a set of classes it depends on
     */
    public String [] _getDepends() {
	return null;
    }

}