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// *                                                                                                                         *
// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
// *                                                                                                                         *
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// ***************************************************************************************************************************
package org.apache.juneau.rest;

import static java.util.logging.Level.*;
import static javax.servlet.http.HttpServletResponse.*;
import static org.apache.juneau.internal.StringUtils.*;
import static org.apache.juneau.rest.HttpRuntimeException.*;
import static org.apache.juneau.rest.annotation.HookEvent.*;

import java.io.*;
import java.lang.reflect.Method;
import java.text.*;
import java.util.*;
import java.util.function.*;
import java.util.logging.*;

import javax.servlet.*;
import javax.servlet.http.*;

import org.apache.juneau.internal.*;
import org.apache.juneau.reflect.*;
import org.apache.juneau.rest.annotation.*;
import org.apache.juneau.cp.*;
import org.apache.juneau.dto.swagger.*;
import org.apache.juneau.http.exception.*;

/**
 * Servlet implementation of a REST resource.
 *
 * <ul class='seealso'>
 *    <li class='link'>{@doc RestServlet}
 * </ul>
 */
public abstract class RestServlet extends HttpServlet implements RestInfoProvider, RestCallLogger, RestResourceResolver, ResourceFinder {

   private static final long serialVersionUID = 1L;

   private RestContextBuilder builder;
   private volatile RestContext context;
   private volatile Exception initException;
   private boolean isInitialized = false;  // Should not be volatile.
   private volatile RestResourceResolver resourceResolver = new BasicRestResourceResolver();
   private Logger logger = Logger.getLogger(getClass().getName());
   private RestInfoProvider infoProvider;
   private RestCallLogger callLogger;
   private ResourceFinder resourceFinder;

   @Override /* Servlet */
   public final synchronized void init(ServletConfig servletConfig) throws ServletException {
      try {
         if (context != null)
            return;
         builder = RestContext.create(servletConfig, this.getClass(), null);
         if (resourceResolver != null)
            builder.resourceResolver(resourceResolver);
         builder.init(this);
         super.init(servletConfig);
         builder.servletContext(this.getServletContext());
         setContext(builder.build());
         context.postInitChildFirst();
      } catch (ServletException e) {
         initException = e;
         log(SEVERE, e, "Servlet init error on class ''{0}''", getClass().getName());
         throw e;
      } catch (Throwable e) {
         initException = toHttpException(e, InternalServerError.class);
         log(SEVERE, e, "Servlet init error on class ''{0}''", getClass().getName());
      }
   }

   /*
    * Bypasses the init(ServletConfig) method and just calls the super.init(ServletConfig) method directly.
    * Used when subclasses of RestServlet are attached as child resources.
    */
   synchronized void innerInit(ServletConfig servletConfig) throws ServletException {
      super.init(servletConfig);
   }

   /**
    * Sets the context object for this servlet.
    *
    * @param context Sets the context object on this servlet.
    * @throws ServletException If error occurred during post-initialiation.
    */
   public synchronized void setContext(RestContext context) throws ServletException {
      this.builder = context.builder;
      this.context = context;
      isInitialized = true;
      infoProvider = new BasicRestInfoProvider(context);
      callLogger = new BasicRestCallLogger(context);
      resourceFinder = new RecursiveResourceFinder();
      context.postInit();
   }

   /**
    * Returns <jk>true</jk> if this servlet has been initialized and {@link #getContext()} returns a value.
    *
    * @return <jk>true</jk> if this servlet has been initialized and {@link #getContext()} returns a value.
    */
   public synchronized boolean isInitialized() {
      return isInitialized;
   }

   /**
    * Sets the resource resolver to use for this servlet and all child servlets.
    * <p>
    * This method can be called immediately following object construction, but must be called before {@link #init(ServletConfig)} is called.
    * Otherwise calling this method will have no effect.
    *
    * @param resourceResolver The resolver instance.  Can be <jk>null</jk>.
    * @return This object (for method chaining).
    */
   public synchronized RestServlet setRestResourceResolver(RestResourceResolver resourceResolver) {
      this.resourceResolver = resourceResolver;
      return this;
   }

   /**
    * Returns the path defined on this servlet if it's defined via {@link Rest#path()}.
    *
    * @return The path defined on this servlet, or an empty string if not specified.
    */
   @SuppressWarnings("deprecation")
   public synchronized String getPath() {
      if (context != null)
         return context.getPath();
      ClassInfo ci = ClassInfo.of(getClass());
      String path = "";
      for (Rest rr : ci.getAnnotations(Rest.class))
         if (! rr.path().isEmpty())
            path = trimSlashes(rr.path());
      if (! path.isEmpty())
         return path;
      for (RestResource rr : ci.getAnnotations(RestResource.class))
         if (! rr.path().isEmpty())
            path = trimSlashes(rr.path());
      return "";
   }

   @Override /* GenericServlet */
   public synchronized RestContextBuilder getServletConfig() {
      return builder;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Context methods.
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Returns the read-only context object that contains all the configuration information about this resource.
    *
    * <p>
    * This object is <jk>null</jk> during the call to {@link #init(ServletConfig)} but is populated by the time
    * {@link #init()} is called.
    *
    * <p>
    * Resource classes that don't extend from {@link RestServlet} can add the following method to their class to get
    * access to this context object:
    * <p class='bcode w800'>
    *    <jk>public void</jk> init(RestServletContext context) <jk>throws</jk> Exception;
    * </p>
    *
    * @return The context information on this servlet.
    */
   public synchronized RestContext getContext() {
      if (context == null)
         throw new InternalServerError("RestContext object not set on resource.");
      return context;
   }

   /**
    * Convenience method for calling <c>getContext().getProperties();</c>
    *
    * @return The resource properties as an {@link RestContextProperties}.
    * @see RestContext#getProperties()
    */
   public RestContextProperties getProperties() {
      return getContext().getProperties();
   }


   //-----------------------------------------------------------------------------------------------------------------
   // Convenience logger methods
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Log a message at {@link Level#INFO} level.
    *
    * <p>
    * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
    *
    * @param msg The message to log.
    */
   @Override /* GenericServlet */
   public void log(String msg) {
      doLog(Level.INFO, null, () -> msg);
   }

   /**
    * Log a message.
    *
    * <p>
    * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
    *
    * @param msg The message to log.
    * @param cause The cause.
    */
   @Override /* GenericServlet */
   public void log(String msg, Throwable cause) {
      doLog(Level.INFO, null, () -> msg);
   }

   /**
    * Log a message.
    *
    * <p>
    * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
    *
    * @param level The log level.
    * @param msg The message to log.
    * @param args Optional {@link MessageFormat}-style arguments.
    */
   public void log(Level level, String msg, Object...args) {
      doLog(level, null, () -> StringUtils.format(msg, args));
   }

   /**
    * Log a message.
    *
    * <p>
    * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
    *
    * @param level The log level.
    * @param cause The cause.
    * @param msg The message to log.
    * @param args Optional {@link MessageFormat}-style arguments.
    */
   public void log(Level level, Throwable cause, String msg, Object...args) {
      doLog(level, cause, () -> StringUtils.format(msg, args));
   }

   /**
    * Main logger method.
    *
    * <p>
    * The default behavior logs a message to the Java logger of the class name.
    *
    * <p>
    * Subclasses can override this method to implement their own logger handling.
    *
    * @param level The log level.
    * @param cause Optional throwable.
    * @param msg The message to log.
    */
   protected void doLog(Level level, Throwable cause, Supplier<String> msg) {
      logger.log(level, cause, msg);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Lifecycle methods
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * The main service method.
    *
    * <p>
    * Subclasses can optionally override this method if they want to tailor the behavior of requests.
    */
   @Override /* Servlet */
   public void service(HttpServletRequest r1, HttpServletResponse r2) throws ServletException, InternalServerError, IOException {
      try {
         // To avoid checking the volatile field context on every call, use the non-volatile isInitialized field as a first-check check.
         if (! isInitialized) {
            if (initException != null)
               throw initException;
            if (context == null)
               throw new InternalServerError("Servlet {0} not initialized.  init(ServletConfig) was not called.  This can occur if you've overridden this method but didn't call super.init(RestConfig).", getClass().getName());
            isInitialized = true;
         }

         context.execute(r1, r2);

      } catch (Throwable e) {
         r2.sendError(SC_INTERNAL_SERVER_ERROR, e.getLocalizedMessage());
      }
   }

   @Override /* GenericServlet */
   public synchronized void destroy() {
      if (context != null)
         context.destroy();
      super.destroy();
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Hook events
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Method that gets called during servlet initialization.
    *
    * <p>
    * This method is called from within the {@link Servlet#init(ServletConfig)} method after the {@link RestContextBuilder}
    * object has been created and initialized with the annotations defined on the class, but before the
    * {@link RestContext} object has been created.
    *
    * <p>
    * An example of this is the <c>PetStoreResource</c> class that uses an init method to perform initialization
    * of an internal data structure.
    *
    * <h5 class='figure'>Example:</h5>
    * <p class='bcode w800'>
    *    <ja>@Rest</ja>(...)
    *    <jk>public class</jk> PetStoreResource <jk>extends</jk> ResourceJena {
    *
    *       <jc>// Our database.</jc>
    *       <jk>private</jk> Map&lt;Integer,Pet&gt; <jf>petDB</jf>;
    *
    *       <ja>@Override</ja>
    *       <jk>public void</jk> onInit(RestContextBuilder builder) <jk>throws</jk> Exception {
    *          <jc>// Load our database from a local JSON file.</jc>
    *          <jf>petDB</jf> = JsonParser.<jsf>DEFAULT</jsf>.parse(getClass().getResourceAsStream(<js>"PetStore.json"</js>), LinkedHashMap.<jk>class</jk>, Integer.<jk>class</jk>, Pet.<jk>class</jk>);
    *       }
    *    }
    * </p>
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple INIT methods can be defined on a class.
    *       <br>INIT methods on parent classes are invoked before INIT methods on child classes.
    *       <br>The order of INIT method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       The method can throw any exception causing initialization of the servlet to fail.
    * </ul>
    *
    * @param builder Context builder which can be used to configure the servlet.
    * @throws Exception Any exception thrown will cause servlet to fail startup.
    */
   @RestHook(INIT)
   public void onInit(RestContextBuilder builder) throws Exception {}

   /**
    * Method that gets called immediately after servlet initialization.
    *
    * <p>
    * This method is called from within the {@link Servlet#init(ServletConfig)} method after the {@link RestContext}
    * object has been created.
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple POST_INIT methods can be defined on a class.
    *       <br>POST_INIT methods on parent classes are invoked before POST_INIT methods on child classes.
    *       <br>The order of POST_INIT method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       The method can throw any exception causing initialization of the servlet to fail.
    * </ul>
    *
    * @param context The initialized context object.
    * @throws Exception Any exception thrown will cause servlet to fail startup.
    */
   @RestHook(POST_INIT)
   public void onPostInit(RestContext context) throws Exception {}

   /**
    * Identical to {@link #onPostInit(RestContext)} except the order of execution is child-resources first.
    *
    * <p>
    * Use this method if you need to perform any kind of initialization on child resources before the parent resource.
    *
    * <p>
    * This method is called from within the {@link Servlet#init(ServletConfig)} method after the {@link RestContext}
    * object has been created and after the {@link HookEvent#POST_INIT} methods have been called.
    *
    * <p>
    * The only valid parameter type for this method is {@link RestContext} which can be used to retrieve information
    * about the servlet.
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple POST_INIT_CHILD_FIRST methods can be defined on a class.
    *       <br>POST_INIT_CHILD_FIRST methods on parent classes are invoked before POST_INIT_CHILD_FIRST methods on child classes.
    *       <br>The order of POST_INIT_CHILD_FIRST method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       The method can throw any exception causing initialization of the servlet to fail.
    * </ul>
    *
    * @param context The initialized context object.
    * @throws Exception Any exception thrown will cause servlet to fail startup.
    */
   @RestHook(POST_INIT_CHILD_FIRST)
   public void onPostInitChildFirst(RestContext context) throws Exception {}

   /**
    * Method that gets called during servlet destroy.
    *
    * <p>
    * This method is called from within the {@link Servlet#destroy()}.
    *
    * <h5 class='figure'>Example:</h5>
    * <p class='bcode w800'>
    *    <ja>@Rest</ja>(...)
    *    <jk>public class</jk> PetStoreResource <jk>extends</jk> ResourceJena {
    *
    *       <jc>// Our database.</jc>
    *       <jk>private</jk> Map&lt;Integer,Pet&gt; <jf>petDB</jf>;
    *
    *       <ja>@Override</ja>
    *       <jk>public void</jk> onDestroy(RestContext context) {
    *          <jf>petDB</jf> = <jk>null</jk>;
    *       }
    *    }
    * </p>
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple DESTROY methods can be defined on a class.
    *       <br>DESTROY methods on child classes are invoked before DESTROY methods on parent classes.
    *       <br>The order of DESTROY method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       In general, destroy methods should not throw any exceptions, although if any are thrown, the stack trace will be
    *       printed to <c>System.err</c>.
    * </ul>
    *
    * @param context The initialized context object.
    * @throws Exception Any exception thrown will cause stack trace to be printed to <c>System.err</c>.
    */
   @RestHook(DESTROY)
   public void onDestroy(RestContext context) throws Exception {}

   /**
    * A method that is called immediately after the <c>HttpServlet.service(HttpServletRequest, HttpServletResponse)</c>
    * method is called.
    *
    * <p>
    * Note that you only have access to the raw request and response objects at this point.
    *
    * <h5 class='figure'>Example:</h5>
    * <p class='bcode w800'>
    *    <ja>@Rest</ja>(...)
    *    <jk>public class</jk> MyResource <jk>extends</jk> BasicRestServlet {
    *
    *       <jc>// Add a request attribute to all incoming requests.</jc>
    *       <ja>@Override</ja>
    *       <jk>public void</jk> onStartCall(HttpServletRequest req, HttpServletResponse res) {
    *          req.setAttribute(<js>"foobar"</js>, <jk>new</jk> FooBar());
    *       }
    *    }
    * </p>
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple START_CALL methods can be defined on a class.
    *       <br>START_CALL methods on parent classes are invoked before START_CALL methods on child classes.
    *       <br>The order of START_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       The method can throw any exception.
    *       <br>{@link HttpException HttpExceptions} can be thrown to cause a particular HTTP error status code.
    *       <br>All other exceptions cause an HTTP 500 error status code.
    * </ul>
    *
    * @param req The HTTP servlet request object.
    * @param res The HTTP servlet response object.
    * @throws Exception Any exception.
    */
   @RestHook(START_CALL)
   public void onStartCall(HttpServletRequest req, HttpServletResponse res) throws Exception {}

   /**
    * Method that gets called immediately before the <ja>@RestMethod</ja> annotated method gets called.
    *
    * <p>
    * At this point, the {@link RestRequest} object has been fully initialized, and all {@link RestGuard} and
    * {@link RestMatcher} objects have been called.
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple PRE_CALL methods can be defined on a class.
    *       <br>PRE_CALL methods on parent classes are invoked before PRE_CALL methods on child classes.
    *       <br>The order of PRE_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       The method can throw any exception.
    *       <br>{@link HttpException HttpExceptions} can be thrown to cause a particular HTTP error status code.
    *       <br>All other exceptions cause an HTTP 500 error status code.
    *    <li>
    *       It's advisable not to mess around with the HTTP body itself since you may end up consuming the body
    *       before the actual REST method has a chance to use it.
    * </ul>
    *
    * @param req The request object.
    * @param res The response object.
    * @throws Exception Any exception.
    */
   @RestHook(PRE_CALL)
   public void onPreCall(RestRequest req, RestResponse res) throws Exception {}

   /**
    * Method that gets called immediately after the <ja>@RestMethod</ja> annotated method gets called.
    *
    * <p>
    * At this point, the output object returned by the method call has been set on the response, but
    * {@link RestConverter RestConverters} have not yet been executed and the response has not yet been written.
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple POST_CALL methods can be defined on a class.
    *       <br>POST_CALL methods on parent classes are invoked before POST_CALL methods on child classes.
    *       <br>The order of POST_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       The method can throw any exception, although at this point it is too late to set an HTTP error status code.
    * </ul>
    *
    * @param req The request object.
    * @param res The response object.
    * @throws Exception Any exception.
    */
   @RestHook(POST_CALL)
   public void onPostCall(RestRequest req, RestResponse res) throws Exception {}

   /**
    * Method that gets called right before we exit the servlet service method.
    *
    * <p>
    * At this point, the output has been written and flushed.
    *
    * <p>
    * The following attributes are set on the {@link HttpServletRequest} object that can be useful for logging purposes:
    * <ul>
    *    <li><js>"Exception"</js> - Any exceptions thrown during the request.
    *    <li><js>"ExecTime"</js> - Execution time of the request.
    * </ul>
    *
    * <ul class='notes'>
    *    <li>
    *       The default implementation of this method is a no-op.
    *    <li>
    *       Multiple END_CALL methods can be defined on a class.
    *       <br>END_CALL methods on parent classes are invoked before END_CALL methods on child classes.
    *       <br>The order of END_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
    *    <li>
    *       The method can throw any exception, although at this point it is too late to set an HTTP error status code.
    *    <li>
    *       Note that if you override a parent method, you probably need to call <code><jk>super</jk>.parentMethod(...)</code>.
    *       <br>The method is still considered part of the parent class for ordering purposes even though it's
    *       overridden by the child class.
    * </ul>
    *
    * @param req The HTTP servlet request object.
    * @param res The HTTP servlet response object.
    * @throws Exception Any exception.
    */
   @RestHook(END_CALL)
   public void onEndCall(HttpServletRequest req, HttpServletResponse res) throws Exception {}

   //-----------------------------------------------------------------------------------------------------------------
   // Other methods.
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Returns the current HTTP request.
    *
    * @return The current HTTP request, or <jk>null</jk> if it wasn't created.
    */
   public synchronized RestRequest getRequest() {
      return getContext().getRequest();
   }

   /**
    * Returns the current HTTP response.
    *
    * @return The current HTTP response, or <jk>null</jk> if it wasn't created.
    */
   public synchronized RestResponse getResponse() {
      return getContext().getResponse();
   }


   //-----------------------------------------------------------------------------------------------------------------
   // RestInfoProvider
   //-----------------------------------------------------------------------------------------------------------------

   @Override /* RestInfoProvider */
   public Swagger getSwagger(RestRequest req) throws Exception {
      return infoProvider.getSwagger(req);
   }

   @Override /* RestInfoProvider */
   public String getSiteName(RestRequest req) throws Exception {
      return infoProvider.getSiteName(req);
   }

   @Override /* RestInfoProvider */
   public String getTitle(RestRequest req) throws Exception {
      return infoProvider.getTitle(req);
   }

   @Override /* RestInfoProvider */
   public String getDescription(RestRequest req) throws Exception {
      return infoProvider.getDescription(req);
   }

   @Override /* RestInfoProvider */
   public String getMethodSummary(Method method, RestRequest req) throws Exception {
      return infoProvider.getMethodSummary(method, req);
   }

   @Override /* RestInfoProvider */
   public String getMethodDescription(Method method, RestRequest req) throws Exception {
      return infoProvider.getMethodDescription(method, req);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // RestCallLogger
   //-----------------------------------------------------------------------------------------------------------------

   @Override /* RestCallLogger */
   public void log(RestCallLoggerConfig config, HttpServletRequest req, HttpServletResponse res) {
      callLogger.log(config, req, res);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // ClasspathResourceFinder
   //-----------------------------------------------------------------------------------------------------------------

   @Override /* ClasspathResourceFinder */
   public InputStream findResource(Class<?> baseClass, String name, Locale locale) throws IOException {
      return resourceFinder.findResource(baseClass, name, locale);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // RestResourceResolver
   //-----------------------------------------------------------------------------------------------------------------

   @Override /* RestResourceResolver */
   public <T> T resolve(Object parent, Class<T> c, Object... args) {
      return resourceResolver.resolve(parent, c, args);
   }

   @Override /* RestResourceResolver */
   public <T> T resolve(Object parent, Class<T> c, RestContextBuilder builder, Object... args) throws Exception {
      return resourceResolver.resolve(parent, c, builder, args);
   }
}