/*
    * Copyright 2005 the original author or authors.
    * 
    * 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 net.sf.sensor.meter;
  
  /***
   * 
   *
   */
  class MeterData {
  
    // ==========================================================================
    // Fields
    // ==========================================================================
    
    /*** The label that uniquely identifies an instance of this class. */
    private final String label;
    
    /*** Lazy-initialized hierarchical (tree) view on this instance. */
    private MeterStatistics meterStatistics;
    
    
    // ==========================================================================
    // Statistics Fields
    // ==========================================================================
    
    private long currentValue = 0L;
    private long sumOfValues = 0L;
    private long averageValue = 0L;
    private long minimumValue = 0L;
    private long maximumValue = 0L;
    private long standardDeviation = 0L;
    
    private long numberOfValueChanges = 0L;
    private long sumOfSquaresOfValues = 0L;
    
    private long timeOfFirstUpdate = 0L;
    private long timeOfLastUpdate = 0L;
    
    
    // ==========================================================================
    // Constructors
    // ==========================================================================
    
    /***
     * Creates a new MeterData instance uniquely identified by the specified label.
     * 
     * @param runtime the associated {@link MeterRuntime}.
     * @param label the label that uniquely identifies an instance of this class.
     */
    MeterData(String label) {
      this.label = label;
    }
    
    
    // ==========================================================================
    // Basic API
    // ==========================================================================
    
    /***
     * Returns the label.
     * @return Returns the label.
     */
    String getLabel() {
      return label;
    }
    
    /***
     * Resets all statistics data.
     */
    synchronized void reset() {
      currentValue = 0L;
      sumOfValues  = 0L;
      averageValue = 0L;
      minimumValue = 0L;
      maximumValue = 0L;
      standardDeviation = 0L;
      
      timeOfFirstUpdate = 0L;
      timeOfLastUpdate  = 0L;
      
      numberOfValueChanges = 0L;
      sumOfSquaresOfValues = 0L;
    }
    
    
   // ==========================================================================
   // Tree structure-related methods (package private) 
   // ==========================================================================
   
   /***
    * Creates a new instance of Meter linked to this MeterData instance.
    * @return a new instance of Meter linked to this MeterData instance.
    */
   Meter createMeter() {
     return new Meter(this);
   }
   
   /***
    * Callback method used by Meter instances to report back a timing measurement.
    * @param newValue the time (in milliseconds) it took to execute the code that was being measured.
    */
   synchronized void updateFromMeter(long newValue) {
     // update the internal statistics
     numberOfValueChanges++;
     currentValue         = newValue;
     sumOfValues          = sumOfValues + newValue;
     averageValue         = sumOfValues / numberOfValueChanges;
     sumOfSquaresOfValues = sumOfSquaresOfValues + (newValue * newValue);
     
     // the time of the last update is always the last call to this method.
     timeOfLastUpdate = System.currentTimeMillis();
     
     if (numberOfValueChanges == 1L) {
       minimumValue      = newValue;
       maximumValue      = newValue;
       timeOfFirstUpdate = timeOfLastUpdate;
     } else {
       if (newValue < minimumValue) {
         minimumValue = newValue;
       }
     
       if (newValue > maximumValue) {
         maximumValue = newValue;
       }
     }
     
     // calculate the standard deviation
     long nMinus1 = (numberOfValueChanges <= 1) ? 1 : numberOfValueChanges - 1; // avoid 0 divides
     long numerator = sumOfSquaresOfValues - ((sumOfValues * sumOfValues) / numberOfValueChanges);
     
     standardDeviation = (long) java.lang.Math.sqrt(numerator / nMinus1);
   }
   
   /***
    * Returns a hierarchical statistical view of this instance of MeterData.
    * @return a hierarchical statistical view of this instance of MeterData.
    */
   MeterStatistics getStatistics() {
     if (meterStatistics == null) {
       meterStatistics = new MeterStatistics(this);
     }
     
     // refresh the statistics
     refreshStatistics();
     
     return meterStatistics;
   }
   
   /***
    * Callback method used by {@link MeterStatistics#refresh()} to extract
    * the latest data from this instance.
    * This method is synchronized to prevent half-updated data, etc.
    * The reason for this elaborate callback mechanism is to get all internal
    * values out of this instance in one synchronized call instead of calling
    * a number of synchronized getters from the statistics class. The latter
    * could lead to inconsistent data.
    */
   synchronized void refreshStatistics() {
     meterStatistics.refreshFromData(
         currentValue,
         numberOfValueChanges ,
         sumOfValues,
         averageValue,
         standardDeviation,
         minimumValue,
         maximumValue,
         timeOfFirstUpdate,
         timeOfLastUpdate,
         sumOfSquaresOfValues);
   }
 
   
   // ==========================================================================
   // Internal statistics getters.
   // FOR TESTING PURPOSES ONLY !! 
   // THESE METHODS ARE NOT THREAD SAFE !!
   // ==========================================================================
   
   /***
    * Returns the currentValue.
    * @return Returns the currentValue.
    */
   long getCurrentValue() {
     return currentValue;
   }
   
   /***
    * Returns the numberOfValueChanges.
    * @return Returns the numberOfValueChanges.
    */
   long getNumberOfValueChanges() {
     return numberOfValueChanges;
   }
   
   /***
    * Returns the sumOfValues.
    * @return Returns the sumOfValues.
    */
   long getSumOfValues() {
     return sumOfValues;
   }
   
   /***
    * Returns the averageValue.
    * @return Returns the averageValue.
    */
   long getAverageValue() {
     return averageValue;
   }
   
   /***
    * Returns the sumOfSquaresOfValues.
    * @return Returns the sumOfSquaresOfValues.
    */
   long getSumOfSquaresOfValues() {
     return sumOfSquaresOfValues;
   }
   
   /***
    * Returns the standardDeviation.
    * @return Returns the standardDeviation.
    */
   long getStandardDeviation() {
     return standardDeviation;
   }
   
   /***
    * Returns the minimumValue.
    * @return Returns the minimumValue.
    */
   long getMinimumValue() {
     return minimumValue;
   }
   
   /***
    * Returns the maximumValue.
    * @return Returns the maximumValue.
    */
   long getMaximumValue() {
     return maximumValue;
   }
   
   /***
    * Returns the timeOfFirstUpdate.
    * @return Returns the timeOfFirstUpdate.
    */
   long getTimeOfFirstUpdate() {
     return timeOfFirstUpdate;
   }
   
   /***
    * Returns the timeOfLastUpdate.
    * @return Returns the timeOfLastUpdate.
    */
   long getTimeOfLastUpdate() {
     return timeOfLastUpdate;
   }
 
   
   // ==========================================================================
   // Standard Object method overrides and simple debugging methods
   // ==========================================================================
   
   /***
    * @see java.lang.Object#toString()
    */
   public String toString() {
     return "Current value: "              + currentValue
          + ", Number of value changes: "  + numberOfValueChanges
          + ", Sum of values: "            + sumOfValues
          + ", Average value: "            + averageValue
          + ", Standard deviation: "       + standardDeviation
          + ", Minimum value: "            + minimumValue
          + ", Maximum value: "            + maximumValue
          + ", Time of first update: "     + timeOfFirstUpdate
          + ", Time of last update: "      + timeOfLastUpdate
          + ", Sum of squares of values: " + sumOfSquaresOfValues;
   }
   
 }