Metrics.cs

// Licensed to Elasticsearch B.V under one or more agreements.
// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information.

using System;
using System.Collections.Generic;
using Elastic.Transport;

namespace Elastic.Clients.Elasticsearch;

/// <summary>
/// Represents a collection of unique metric names to be included in URL paths to limit the request.
/// </summary>
public sealed class Metrics : IEquatable<Metrics>, IUrlParameter
{
	private static readonly HashSet<string> EmptyMetrics = new();

	/// <summary>
	/// An instance of <see cref="Metrics"/> representing all statistics.
	/// </summary>
	public static Metrics All { get; } = new("_all");

	/// <summary>
	///	Initializes a new instance of the <see cref="Metrics"/> class containing a single metric name.
	/// </summary>
	public Metrics(string metric)
	{
		if (string.IsNullOrEmpty(metric))
			Values = EmptyMetrics;

		Values = new HashSet<string>()
		{
			metric
		};
	}

	/// <summary>
	///	Initializes a new instance of the <see cref="Metrics"/> class containing a collection of metric names.
	/// </summary>
	public Metrics(IEnumerable<string> metrics)
	{
		if (metrics is null)
			Values = EmptyMetrics;

		Values = new HashSet<string>(metrics);
	}

	private HashSet<string> Values { get; }

	/// <inheritdoc />
	public bool Equals(Metrics other)
	{
		if (other is null) return false;

		// Equality is true when both instances have the same metric names.
		return Values.SetEquals(other.Values);
	}

	string IUrlParameter.GetString(ITransportConfiguration settings) => GetString();

	/// <inheritdoc />
	public override string ToString() => GetString();

	private string GetString()
	{
		if (Values == EmptyMetrics)
			return string.Empty;

		return string.Join(",", Values);
	}

	/// <inheritdoc />
	public override int GetHashCode()
	{
		// Lifting the minimal target framework to .NET Standard 2.1
		// would be the best solution ever due to the HashCode type.
		var hashCode = 0;
		foreach (var metric in Values)
			hashCode = (hashCode * 397) ^ metric.GetHashCode();

		return hashCode;
	}

	public static bool operator ==(Metrics left, Metrics right) => Equals(left, right);
	public static bool operator !=(Metrics left, Metrics right) => !Equals(left, right);

	public static implicit operator Metrics(string metric) => new(metric);
	public static implicit operator Metrics(string[] metrics) => new(metrics);

	/// <inheritdoc />
	public override bool Equals(object obj)
	{
		if (obj is not Metrics metrics) return false;

		return Equals(metrics);
	}
}