/*
 * 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>
/// Family of metrics with labels.
/// </summary>
public abstract class Family<TMetricType> where TMetricType : class
{
    /// <summary>
    /// Family instance that does nothing. Safe for use in static initializers.
    /// </summary>
    public static Family<TMetricType> Null()
    {
        return new NullFamily<TMetricType>();
    }

    /// <summary>
    /// Adds a metric instance with the specified labels.
    /// </summary>
    public abstract TMetricType Add(Dictionary<string, string> labels);
}

/// <summary>
/// Null implementation of family that does nothing.
/// </summary>
internal class NullFamily<TMetricType> : Family<TMetricType> where TMetricType : class
{
    public override TMetricType Add(Dictionary<string, string> labels)
    {
        // Return null metric instance
        if (typeof(TMetricType) == typeof(Counter))
            return (TMetricType)(object)Counter.Null();
        if (typeof(TMetricType) == typeof(Gauge))
            return (TMetricType)(object)Gauge.Null();
        if (typeof(TMetricType) == typeof(Histogram))
            return (TMetricType)(object)Histogram.Null();
        return null!;
    }
}

/// <summary>
/// Factory for creating metric families.
/// </summary>
public abstract class FamilyFactory
{
    /// <summary>
    /// Creates a new counter family.
    /// </summary>
    public abstract Family<Counter> NewCounterFamily(string name, string description);

    /// <summary>
    /// Creates a new gauge family.
    /// </summary>
    public abstract Family<Gauge> NewGaugeFamily(string name, string description);

    /// <summary>
    /// Creates a new histogram family.
    /// </summary>
    public abstract Family<Histogram> NewHistogramFamily(
        string name,
        string description,
        Histogram.BucketBoundaries boundaries);
}