/*
 * 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 com.facebook.presto.spi.statistics;

import java.util.Objects;
import java.util.function.Function;

import static java.lang.Double.isNaN;

public final class Estimate
{
    // todo eventually add some notion of statistic reliability
    //      Skipping for now as there hard to compute it properly and so far we do not have
    //      usecase for that.

    private static final double UNKNOWN_VALUE = Double.NaN;

    private final double value;

    public static final Estimate unknownValue()
    {
        return new Estimate(UNKNOWN_VALUE);
    }

    public Estimate(double value)
    {
        this.value = value;
    }

    public static final Estimate zeroValue()
    {
        return new Estimate(0);
    }

    public boolean isValueUnknown()
    {
        return isNaN(value);
    }

    public double getValue()
    {
        return value;
    }

    public Estimate map(Function<Double, Double> mappingFunction)
    {
        if (isValueUnknown()) {
            return this;
        }
        else {
            return new Estimate(mappingFunction.apply(value));
        }
    }

    @Override
    public String toString()
    {
        return String.valueOf(value);
    }

    @Override
    public boolean equals(Object o)
    {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        Estimate estimate = (Estimate) o;
        return Double.compare(estimate.value, value) == 0;
    }

    @Override
    public int hashCode()
    {
        return Objects.hash(value);
    }
}
