/*
 * Copyright 2018 The Cartographer 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.
 */

namespace CartographerSharp.Metrics;

/// <summary>
/// Gauge metric for tracking values that can go up and down.
/// </summary>
public abstract class Gauge
{
    /// <summary>
    /// Gauge instance that does nothing. Safe for use in static initializers.
    /// </summary>
    public static Gauge Null()
    {
        return new NullGauge();
    }

    /// <summary>
    /// Increments the gauge by 1.
    /// </summary>
    public abstract void Increment();

    /// <summary>
    /// Increments the gauge by the specified value.
    /// </summary>
    public abstract void Increment(double byValue);

    /// <summary>
    /// Decrements the gauge by 1.
    /// </summary>
    public abstract void Decrement();

    /// <summary>
    /// Decrements the gauge by the specified value.
    /// </summary>
    public abstract void Decrement(double byValue);

    /// <summary>
    /// Sets the gauge to the specified value.
    /// </summary>
    public abstract void Set(double value);
}

/// <summary>
/// Null implementation of gauge that does nothing.
/// </summary>
internal class NullGauge : Gauge
{
    public override void Increment()
    {
        // Do nothing
    }

    public override void Increment(double byValue)
    {
        // Do nothing
    }

    public override void Decrement()
    {
        // Do nothing
    }

    public override void Decrement(double byValue)
    {
        // Do nothing
    }

    public override void Set(double value)
    {
        // Do nothing
    }
}