/**
    * 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.hadoop.hbase.procedure2;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.util.ArrayList;
  import java.util.Arrays;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.protobuf.generated.ProcedureProtos.StateMachineProcedureData;
  
  /**
   * Procedure described by a series of steps.
   *
   * The procedure implementor must have an enum of 'states', describing
   * the various step of the procedure.
   * Once the procedure is running, the procedure-framework will call executeFromState()
   * using the 'state' provided by the user. The first call to executeFromState()
   * will be performed with 'state = null'. The implementor can jump between
   * states using setNextState(MyStateEnum.ordinal()).
   * The rollback will call rollbackState() for each state that was executed, in reverse order.
   */
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public abstract class StateMachineProcedure<TEnvironment, TState>
      extends Procedure<TEnvironment> {
    private Flow stateFlow = Flow.HAS_MORE_STATE;
    private int stateCount = 0;
    private int[] states = null;
  
    private ArrayList<Procedure> subProcList = null;
  
    protected enum Flow {
      HAS_MORE_STATE,
      NO_MORE_STATE,
    }
  
    /**
     * called to perform a single step of the specified 'state' of the procedure
     * @param state state to execute
     * @return Flow.NO_MORE_STATE if the procedure is completed,
     *         Flow.HAS_MORE_STATE if there is another step.
     */
    protected abstract Flow executeFromState(TEnvironment env, TState state)
      throws ProcedureYieldException, InterruptedException;
  
    /**
     * called to perform the rollback of the specified state
     * @param state state to rollback
     * @throws IOException temporary failure, the rollback will retry later
     */
    protected abstract void rollbackState(TEnvironment env, TState state)
      throws IOException, InterruptedException;
  
    /**
     * Convert an ordinal (or state id) to an Enum (or more descriptive) state object.
     * @param stateId the ordinal() of the state enum (or state id)
     * @return the state enum object
     */
    protected abstract TState getState(int stateId);
  
    /**
     * Convert the Enum (or more descriptive) state object to an ordinal (or state id).
     * @param state the state enum object
     * @return stateId the ordinal() of the state enum (or state id)
     */
    protected abstract int getStateId(TState state);
  
    /**
     * Return the initial state object that will be used for the first call to executeFromState().
     * @return the initial state enum object
     */
    protected abstract TState getInitialState();
  
    /**
     * Set the next state for the procedure.
     * @param state the state enum object
     */
    protected void setNextState(final TState state) {
      setNextState(getStateId(state));
   }
 
   /**
    * By default, the executor will try ro run all the steps of the procedure start to finish.
    * Return true to make the executor yield between execution steps to
    * give other procedures time to run their steps.
    * @param state the state we are going to execute next.
    * @return Return true if the executor should yield before the execution of the specified step.
    *         Defaults to return false.
    */
   protected boolean isYieldBeforeExecuteFromState(TEnvironment env, TState state) {
     return false;
   }
 
   /**
    * Add a child procedure to execute
    * @param subProcedure the child procedure
    */
   protected void addChildProcedure(Procedure... subProcedure) {
     if (subProcList == null) {
       subProcList = new ArrayList<Procedure>(subProcedure.length);
     }
     for (int i = 0; i < subProcedure.length; ++i) {
       subProcList.add(subProcedure[i]);
     }
   }
 
   @Override
   protected Procedure[] execute(final TEnvironment env)
       throws ProcedureYieldException, InterruptedException {
     updateTimestamp();
     try {
       if (!hasMoreState()) return null;
 
       TState state = getCurrentState();
       if (stateCount == 0) {
         setNextState(getStateId(state));
       }
 
       stateFlow = executeFromState(env, state);
 
       if (subProcList != null && subProcList.size() != 0) {
         Procedure[] subProcedures = subProcList.toArray(new Procedure[subProcList.size()]);
         subProcList = null;
         return subProcedures;
       }
 
       return (isWaiting() || isFailed() || !hasMoreState()) ? null : new Procedure[] {this};
     } finally {
       updateTimestamp();
     }
   }
 
   @Override
   protected void rollback(final TEnvironment env)
       throws IOException, InterruptedException {
     try {
       updateTimestamp();
       rollbackState(env, getCurrentState());
       stateCount--;
     } finally {
       updateTimestamp();
     }
   }
 
   @Override
   protected boolean isYieldAfterExecutionStep(final TEnvironment env) {
     return isYieldBeforeExecuteFromState(env, getCurrentState());
   }
 
   private boolean hasMoreState() {
     return stateFlow != Flow.NO_MORE_STATE;
   }
 
   private TState getCurrentState() {
     return stateCount > 0 ? getState(states[stateCount-1]) : getInitialState();
   }
 
   /**
    * Set the next state for the procedure.
    * @param stateId the ordinal() of the state enum (or state id)
    */
   private void setNextState(final int stateId) {
     if (states == null || states.length == stateCount) {
       int newCapacity = stateCount + 8;
       if (states != null) {
         states = Arrays.copyOf(states, newCapacity);
       } else {
         states = new int[newCapacity];
       }
     }
     states[stateCount++] = stateId;
   }
 
   @Override
   protected void toStringState(StringBuilder builder) {
     super.toStringState(builder);
     if (!isFinished() && getCurrentState() != null) {
       builder.append(":").append(getCurrentState());
     }
   }
 
   @Override
   protected void serializeStateData(final OutputStream stream) throws IOException {
     StateMachineProcedureData.Builder data = StateMachineProcedureData.newBuilder();
     for (int i = 0; i < stateCount; ++i) {
       data.addState(states[i]);
     }
     data.build().writeDelimitedTo(stream);
   }
 
   @Override
   protected void deserializeStateData(final InputStream stream) throws IOException {
     StateMachineProcedureData data = StateMachineProcedureData.parseDelimitedFrom(stream);
     stateCount = data.getStateCount();
     if (stateCount > 0) {
       states = new int[stateCount];
       for (int i = 0; i < stateCount; ++i) {
         states[i] = data.getState(i);
       }
     } else {
       states = null;
     }
   }
 }