快速学习C# 设计模式之职责链模式

internal abstract class ToleranceHandler
{
  protected ToleranceHandler handler;

  public void SetToleranceHandler(ToleranceHandler handler)
  {
    this.handler = handler;
  }

  public abstract Task<Dictionary<string, List<Service>>> HandlerRequestAsync(int request);
}

internal class ConsulHandler : ToleranceHandler
{
  public override async Task<Dictionary<string, List<Service>>> HandlerRequestAsync(int request)
  {
    if (request == 2)
    {
      var result = await this.GetRegisterServiceDictionary();
      return result == null ? await this.handler.HandlerRequestAsync(1) : result;
    }
    else
    {
      return await this.handler.HandlerRequestAsync(request);
    }
  }
}

internal class FileHandler:ToleranceHandler
{
  private static readonly string fileName = "SubscribeService.json";

  public override async Task<Dictionary<string, List<Service>>> HandlerRequestAsync(int request)
  {
    if (request == 0)
    {
      StreamReader sr = File.OpenText(fileName);
      string result = await sr.ReadToEndAsync();

      return result.FromJson<Dictionary<string, List<Service>>>();
    }
    else
    {
      return await this.handler.HandlerRequestAsync(request);
    }
  }
}

internal class InMemoryHandler : ToleranceHandler
{
  public override async Task<Dictionary<string, List<Service>>> HandlerRequestAsync(int request)
  {
    if (request == 1)
    {
      IMemoryCache memoryCache = new MemoryCache(Options.Create(new MemoryCacheOptions()));

      var result = memoryCache.Get<Dictionary<string, List<Service>>>("ServiceRegisterDiscovery:List");

      return result == null ? await this.handler.HandlerRequestAsync(0) : result;
    }

    return await this.handler.HandlerRequestAsync(request);
  }
}

public async Task<List<Service>> GetService(string serviceName)
{
  ToleranceHandler consulHandler = new ConsulHandler();  
  ToleranceHandler fileHandler = new FileHandler();
  ToleranceHandler inMemoryHandler = new InMemoryHandler();

  consulHandler.SetToleranceHandler(fileHandler);
  fileHandler.SetToleranceHandler(inMemoryHandler);

  Dictionary<string, List<Service>> serviceDic = await consulHandler.HandlerRequestAsync(2);

  return serviceDic[serviceName];
}