samples/utils/src/main/java/org/apache/edgent/samples/utils/sensor/SimpleSimulatedSensor.java

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to you under the Apache License, Version 2.0 (the
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package org.apache.edgent.samples.utils.sensor;

import java.text.DecimalFormat;
import java.util.Random;

import org.apache.edgent.analytics.sensors.Range;
import org.apache.edgent.function.Supplier;

/**
 * A simple simulated sensor.
 * <p>
 * The sensor starts off with an initial value.
 * Each call to {@link #get()} changes the current value by
 * a random amount between plus/minus {@code deltaFactor}.
 * The new current value is limited to a {@code range}
 * and then rounded to 1 fractional digit. 
 * See {@link #setNumberFractionalDigits(int)}.
 * </p><p>
 * Sample use:
 * <pre>{@code
 * Topology t = ...;
 * // a miles-per-gallon sensor
 * SimpleSimulatedSensor avgMpgSensor = new SimpleSimulatedSensor(10.5, 0.4,
 *                                          Ranges<Double>.closed(7.0,14.0));
 * TStream<Double> avgMpg = t.poll(avgMpgSensor, 1, TimeUnit.SECONDS);
 * 
 * // an integer valued sensor
 * SimpleSimulatedSensor doubleSensor = new SimpleSimulatedSensor();
 * TStream<Integer> intSensor = t.poll(() -> doubleSensor.get().intValue(),
 *                                          1, TimeUnit.SECONDS);
 * }</pre>
 */
public class SimpleSimulatedSensor implements Supplier<Double> {
    private static final long serialVersionUID = 1L;
    private int numFracDigits;
    private volatile DecimalFormat df;
    private Random r = new Random();
    private final Range<Double> range;
    private final double deltaFactor;
    private double currentValue;
   
    /**
     * Create a sensor.
     * <p>
     * Same as {@code SimpleSimulatedSensor(0.0, 1.0, null)};
     * </p>
     */
    public SimpleSimulatedSensor() {
        this(0.0, 1.0, null);
    }
    
    /**
     * Create a sensor.
     * <p>
     * Same as {@code SimpleSimulatedSensor(initialValue, 1.0, null)};
     * </p>
     * @param initialValue the initial value
     */
    public SimpleSimulatedSensor(double initialValue) {
        this(initialValue, 1.0, null);
    }
    
    /**
     * Create a sensor.
     * 
     * <p>
     * Same as {@code SimpleSimulatedSensor(initialValue, deltaFactor, null)};
     * </p>
     * @param initialValue the initial value.
     * @param deltaFactor maximum plus/minus change on each {@code get()}.
     *              e.g., 1.0 to limit change to +/- 1.0.
     *              Must be &gt; 0.0
     */
    public SimpleSimulatedSensor(double initialValue, double deltaFactor) {
        this(initialValue, deltaFactor, null);
    }
    
    /**
     * Create a sensor.
     * 
     * @param initialValue the initial value.  Must be within range.
     * @param deltaFactor maximum plus/minus change on each {@link #get()}.
     *              e.g., 1.0 to limit change to +/- 1.0.
     *              Must be &gt; 0.0
     * @param range maximum sensor value range. Unlimited if null.
     */
    public SimpleSimulatedSensor(double initialValue,
            double deltaFactor, Range<Double> range) {
        if (range!=null && !range.contains(initialValue))
            throw new IllegalArgumentException("initialValue");
        if (deltaFactor <= 0.0)
            throw new IllegalArgumentException("deltaFactor");
        this.currentValue = initialValue;
        this.deltaFactor = deltaFactor;
        this.range = range;
        setNumberFractionalDigits(1);
    }
    
    /**
     * Set number of fractional digits to round sensor values to.
     * <p>
     * This class offers rounding as a convenience and because
     * ancestors of this implementation had such a scheme.
     * </p>
     * @param numFracDigits  if &lt;= 0, no rounding will be performed
     */
    public void setNumberFractionalDigits(int numFracDigits) {
        this.numFracDigits = numFracDigits;
        if (numFracDigits <= 0) {
            df = null;
        }
        else {
            String fracPattern = "";
            for (int i = 0; i < numFracDigits; i++)
                fracPattern += "#";
            df = new DecimalFormat("#."+fracPattern);
        }
    }
    
    /** Get the number of fractional digits setting
     * @return the value
     */
    public int getNumberFractionalDigits() {
        return numFracDigits;
    }
    
    /** Get the range setting
     * @return the value
     */
    public Range<Double> getRange() {
        return range;
    }
    
    /** Get the deltaFactor setting
     * @return the value
     */
    public double getDeltaFactor() {
        return deltaFactor;
    }
    
    /** Get the next sensor value as described in the class documentation. */
    @Override
    public Double get() {
        double delta = 2 * r.nextDouble() - 1.0; // between -1.0 and 1.0
        double nextValue = currentValue + delta * deltaFactor;
        if (range!=null && !range.contains(nextValue)) {
            nextValue = nextValue > currentValue
                        ? range.upperEndpoint()
                        : range.lowerEndpoint();
        }
        if (df != null)
            nextValue = Double.valueOf(df.format(nextValue));
        currentValue = nextValue;
        return currentValue;
    }
}