// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using Microsoft.Extensions.Primitives;
 
namespace Microsoft.Extensions.Configuration
{
    /// <summary>
    /// Represents a set of key/value application configuration properties.
    /// </summary>
    public interface IConfiguration
    {
        /// <summary>
        /// Gets or sets a configuration value.
        /// </summary>
        /// <param name="key">The configuration key.</param>
        /// <returns>The configuration value.</returns>
        string? this[string key] { get; set; }
 
        /// <summary>
        /// Gets a configuration sub-section with the specified key.
        /// </summary>
        /// <param name="key">The key of the configuration section.</param>
        /// <returns>The <see cref="IConfigurationSection"/>.</returns>
        /// <remarks>
        ///     This method will never return <c>null</c>. If no matching sub-section is found with the specified key,
        ///     an empty <see cref="IConfigurationSection"/> will be returned.
        /// </remarks>
        IConfigurationSection GetSection(string key);
 
        /// <summary>
        /// Gets the immediate descendant configuration sub-sections.
        /// </summary>
        /// <returns>The configuration sub-sections.</returns>
        IEnumerable<IConfigurationSection> GetChildren();
 
        /// <summary>
        /// Returns a <see cref="IChangeToken"/> that can be used to observe when this configuration is reloaded.
        /// </summary>
        /// <returns>An <see cref="IChangeToken"/> token if this provider supports change tracking; otherwise, <see langword="null" />.</returns>
        IChangeToken GetReloadToken();
    }
}