public interface IConfigurationSource
{
    IConfigurationProvider Build(IConfigurationBuilder builder);
}

public interface IConfigurationProvider
{
	//讀取配置
    bool TryGet(string key, out string? value);
    //修改配置
    void Set(string key, string? value);
    //獲取重載配置的Token
    IChangeToken GetReloadToken();
    //載入配置
    void Load();
    //獲取指定父路徑下的直接子節(jié)點Key，然后 Concat(earlierKeys) 一同返回
    IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string? parentPath);
}

public interface IConfigurationBuilder
{
	//保存Build的一些公開的字典屬性，有需要的化可以使用該字段存放一些變量
    IDictionary<string, object> Properties { get; }
    //來自多個地方的配置源集合
    IList<IConfigurationSource> Sources { get; }
    //向Sources屬性中添加一個配置源
    IConfigurationBuilder Add(IConfigurationSource source);
    //基于所有配置源生成一個全局的配置，供程序讀寫，一般我們都是用這個接口對配置進行讀寫。
    IConfigurationRoot Build();
}

 public class ConfigurationBuilder : IConfigurationBuilder
 {
     private readonly List<IConfigurationSource> _sources = new();
     public IList<IConfigurationSource> Sources => _sources;
     public IDictionary<string, object> Properties { get; } = new Dictionary<string, object>();
     public IConfigurationBuilder Add(IConfigurationSource source)
     {
         ThrowHelper.ThrowIfNull(source);
         _sources.Add(source);
         return this;
     }
     public IConfigurationRoot Build()
     {
         var providers = new List<IConfigurationProvider>();
         foreach (IConfigurationSource source in _sources)
         {
             IConfigurationProvider provider = source.Build(this);
             providers.Add(provider);
         }
         return new ConfigurationRoot(providers);
     }
 }

public interface IConfiguration
{
	//獲取或設置配置
    string? this[string key] { get; set; }
	//獲取指定key的配置子節(jié)點
    IConfigurationSection GetSection(string key);
	//獲取當前配置的直接子節(jié)點列表
    IEnumerable<IConfigurationSection> GetChildren();
    //當配置發(fā)生變更時的token
    IChangeToken GetReloadToken();
}

public interface IConfigurationRoot : IConfiguration
{
	//強制重載所有配置
    void Reload();
    //所有配置提供程序
    IEnumerable<IConfigurationProvider> Providers { get; }
}

public class DataBaseConfigurationSource : IConfigurationSource
{
    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        return new DataBaseConfigurationProvider();
    }
}
public class DataBaseConfigurationProvider : ConfigurationProvider
{
    public override void Load()
    {
        base.Load();
        //讀取數(shù)據庫配置
    }
}
public static class DataBaseConfigurationExtensions
{
    public static IConfigurationBuilder AddDb(this IConfigurationBuilder configurationBuilder)
    {
        configurationBuilder.Sources.Add(new DataBaseConfigurationSource());
        return configurationBuilder;
    }
}

static void Main(string[] args)
{
    var builder = new ConfigurationBuilder()
        .AddDb()
        .Build();
    var value = builder["key"];
}