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/*
 * Copyright (c) 2019, V12 Technology Ltd.
 * All rights reserved.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the Server Side Public License, version 1,
 * as published by MongoDB, Inc.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * Server Side Public License for more details.
 *
 * You should have received a copy of the Server Side Public License
 * along with this program.  If not, see 
 * .
 */
package com.fluxtion.ext.streaming.api.stream;

import com.fluxtion.api.partition.LambdaReflection.SerializableFunction;
import com.fluxtion.ext.streaming.api.Stateful;

/**
 * Predicates for numeric change in a value.
 *
 * @author Greg Higgins [email protected]
 */
public class PercentPredicates implements Stateful {

    
    public static SerializableFunction ltPercent(double barrier){
        return new PercentPredicates(barrier)::lt;
    }
    
    public static SerializableFunction gtPercent(double barrier){
        return new PercentPredicates(barrier)::gt;
    }
    
    public double previous = Double.NaN;
    private final double changeBarrier;
    private double result = 0;

    public PercentPredicates(double changeBarrier) {
        this.changeBarrier = changeBarrier;
    }

    private double delta(double newVal) {
        result = newVal / previous;
        previous = newVal;
        return result;
    }

    public boolean lt(double newVal) {
        return delta(newVal) < changeBarrier;
    }

    public boolean gt(double newVal) {
        return delta(newVal) > changeBarrier;
    }

    @Override
    public void reset() {
        previous = Double.NaN;
    }

}