/*
    *  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.mina.statemachine;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Deque;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  import java.util.concurrent.ConcurrentLinkedDeque;
  
  import org.apache.mina.statemachine.context.StateContext;
  import org.apache.mina.statemachine.event.Event;
  import org.apache.mina.statemachine.event.UnhandledEventException;
  import org.apache.mina.statemachine.transition.SelfTransition;
  import org.apache.mina.statemachine.transition.Transition;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Represents a complete state machine. Contains a collection of {@link State}
   * objects connected by {@link Transition}s. Normally you wouldn't create 
   * instances of this class directly but rather use the 
   * {@link org.apache.mina.statemachine.annotation.State} annotation to define
   * your states and then let {@link StateMachineFactory} create a 
   * {@link StateMachine} for you.
   *
   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
   */
  public class StateMachine {
      private static final Logger LOGGER = LoggerFactory.getLogger(StateMachine.class);
  
      private static final String CALL_STACK = StateMachine.class.getName() + ".callStack";
  
      private final State startState;
  
      private final Map<String, State> states;
  
      private final ThreadLocal<Boolean> processingThreadLocal = new ThreadLocal<Boolean>() {
          @Override
          protected Boolean initialValue() {
              return Boolean.FALSE;
          }
      };
  
      private final ThreadLocal<LinkedList<Event>> eventQueueThreadLocal = new ThreadLocal<LinkedList<Event>>() {
          @Override
          protected LinkedList<Event> initialValue() {
              return new LinkedList<>();
          }
      };
  
      /**
       * Creates a new instance using the specified {@link State}s and start
       * state.
       * 
       * @param states the {@link State}s.
       * @param startStateId the id of the start {@link State}.
       */
      public StateMachine(State[] states, String startStateId) {
          this.states = new HashMap<>();
          
          for (State s : states) {
              this.states.put(s.getId(), s);
          }
          
          this.startState = getState(startStateId);
      }
  
      /**
       * Creates a new instance using the specified {@link State}s and start
       * state.
       * 
       * @param states the {@link State}s.
       * @param startStateId the id of the start {@link State}.
       */
      public StateMachine(Collection<State> states, String startStateId) {
          this(states.toArray(new State[0]), startStateId);
      }
  
     /**
      * Returns the {@link State} with the specified id.
      * 
      * @param id the id of the {@link State} to return.
      * @return the {@link State}
      * @throws NoSuchStateException if no matching {@link State} could be found.
      */
     public State getState(String id) {
         State state = states.get(id);
         
         if (state == null) {
             throw new NoSuchStateException(id);
         }
         
         return state;
     }
 
     /**
      * @return an unmodifiable {@link Collection} of all {@link State}s used by
      * this {@link StateMachine}.
      */
     public Collection<State> getStates() {
         return Collections.unmodifiableCollection(states.values());
     }
 
     /**
      * Processes the specified {@link Event} through this {@link StateMachine}.
      * Normally you wouldn't call this directly but rather use
      * {@link StateMachineProxyBuilder} to create a proxy for an interface of
      * your choice. Any method calls on the proxy will be translated into
      * {@link Event} objects and then fed to the {@link StateMachine} by the
      * proxy using this method.
      * 
      * @param event the {@link Event} to be handled.
      */
     public void handle(Event event) {
         StateContext context = event.getContext();
 
         synchronized (context) {
             LinkedList<Event> eventQueue = eventQueueThreadLocal.get();
             eventQueue.addLast(event);
 
             if (processingThreadLocal.get()) {
                 /*
                  * This thread is already processing an event. Queue this 
                  * event.
                  */
                 if (LOGGER.isDebugEnabled()) {
                     LOGGER.debug("State machine called recursively. Queuing event {} for later processing.", event);
                 }
             } else {
                 processingThreadLocal.set(true);
                 
                 try {
                     if (context.getCurrentState() == null) {
                         context.setCurrentState(startState);
                     }
                     
                     processEvents(eventQueue);
                 } finally {
                     processingThreadLocal.set(false);
                 }
             }
         }
     }
 
     private void processEvents(LinkedList<Event> eventQueue) {
         while (!eventQueue.isEmpty()) {
             Event event = eventQueue.removeFirst();
             StateContext context = event.getContext();
             handle(context.getCurrentState(), event);
         }
     }
 
     private void handle(State state, Event event) {
         StateContext context = event.getContext();
 
         for (Transition t : state.getTransitions()) {
             if (LOGGER.isDebugEnabled()) {
                 LOGGER.debug("Trying transition {}", t);
             }
 
             try {
                 if (t.execute(event)) {
                     if (LOGGER.isDebugEnabled()) {
                         LOGGER.debug("Transition {} executed successfully.", t);
                     }
                     
                     setCurrentState(context, t.getNextState());
 
                     return;
                 }
             } catch (BreakAndContinueException bace) {
                 if (LOGGER.isDebugEnabled()) {
                     LOGGER.debug("BreakAndContinueException thrown in transition {}. Continuing with next transition.", t);
                 }
             } catch (BreakAndGotoException bage) {
                 State newState = getState(bage.getStateId());
 
                 if (bage.isNow()) {
                     if (LOGGER.isDebugEnabled()) {
                         LOGGER.debug("BreakAndGotoException thrown in transition {}. Moving to state {} now", t,
                             newState.getId());
                     }
                     
                     setCurrentState(context, newState);
                     handle(newState, event);
                 } else {
                     if (LOGGER.isDebugEnabled()) {
                         LOGGER.debug("BreakAndGotoException thrown in transition {}. Moving to state {} next.",
                                 t, newState.getId());
                     }
                     
                     setCurrentState(context, newState);
                 }
                 
                 return;
             } catch (BreakAndCallException bace) {
                 State newState = getState(bace.getStateId());
 
                 Deque<State> callStack = getCallStack(context);
                 State returnTo = bace.getReturnToStateId() != null ? getState(bace.getReturnToStateId()) : context
                         .getCurrentState();
                 callStack.push(returnTo);
 
                 if (bace.isNow()) {
                     if (LOGGER.isDebugEnabled()) {
                         LOGGER.debug("BreakAndCallException thrown in transition {}. Moving to state {} now.",
                                 t, newState.getId());
                     }
                     
                     setCurrentState(context, newState);
                     handle(newState, event);
                 } else {
                     if (LOGGER.isDebugEnabled()) {
                         LOGGER.debug("BreakAndCallException thrown in transition {}. Moving to state {} next.",
                                 t, newState.getId());
                     }
                     
                     setCurrentState(context, newState);
                 }
                 
                 return;
             } catch (BreakAndReturnException bare) {
                 Deque<State> callStack = getCallStack(context);
                 State newState = callStack.pop();
 
                 if (bare.isNow()) {
                     if (LOGGER.isDebugEnabled()) {
                         LOGGER.debug("BreakAndReturnException thrown in transition {}. Moving to state {} now.",
                                 t, newState.getId());
                     }
                     
                     setCurrentState(context, newState);
                     handle(newState, event);
                 } else {
                     if (LOGGER.isDebugEnabled()) {
                         LOGGER.debug("BreakAndReturnException thrown in transition {}. Moving to state {} next.",
                                 t, newState.getId());
                     }
                     
                     setCurrentState(context, newState);
                 }
                 
                 return;
             }
         }
 
         /*
          * No transition could handle the event. Try with the parent state if
          * there is one.
          */
         if (state.getParent() != null) {
             handle(state.getParent(), event);
         } else {
             throw new UnhandledEventException(event);
         }
     }
 
     private Deque<State> getCallStack(StateContext context) {
         @SuppressWarnings("unchecked")
         Deque<State> callStack = (Deque<State>) context.getAttribute(CALL_STACK);
         
         if (callStack == null) {
             callStack = new ConcurrentLinkedDeque<>();
             context.setAttribute(CALL_STACK, callStack);
         }
         
         return callStack;
     }
 
     private void setCurrentState(StateContext context, State newState) {
         if (newState != null) {
             if (LOGGER.isDebugEnabled()) {
                 if (newState != context.getCurrentState()) {
                     LOGGER.debug("Leaving state {}", context.getCurrentState().getId());
                     LOGGER.debug("Entering state {}", newState.getId());
                 }
             }
             
             executeOnExits(context, context.getCurrentState());
             executeOnEntries(context, newState);
             context.setCurrentState(newState);
         }
     }
 
     void executeOnExits(StateContext context, State state) {
         List<SelfTransition> onExits = state.getOnExitSelfTransitions();
         boolean isExecuted = false;
 
         if (onExits != null) {
             for (SelfTransition selfTransition : onExits) {
                 selfTransition.execute(context, state);
                 
                 if (LOGGER.isDebugEnabled()) {
                     isExecuted = true;
                     LOGGER.debug("Executing onEntry action for {}", state.getId());
                 }
             }
         }
         
         if (LOGGER.isDebugEnabled() && !isExecuted) {
             LOGGER.debug("No onEntry action for {}", state.getId());
 
         }
     }
 
     void executeOnEntries(StateContext context, State state) {
         List<SelfTransition> onEntries = state.getOnEntrySelfTransitions();
         boolean isExecuted = false;
 
         if (onEntries != null) {
             for (SelfTransition selfTransition : onEntries) {
                 selfTransition.execute(context, state);
                 
                 if (LOGGER.isDebugEnabled()) {
                     isExecuted = true;
                     LOGGER.debug("Executing onExit action for {}", state.getId());
                 }
             }
         }
         
         if (LOGGER.isDebugEnabled() && !isExecuted) {
             LOGGER.debug("No onEntry action for {}", state.getId());
         }
     }
 }