配置系统与 Options 模式

var builder = WebApplication.CreateBuilder(args);

// 默认已经注册了 appsettings.json / 环境变量 / 命令行
// 手动追加自定义 JSON 文件，可选、可刷新
builder.Configuration
    .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
    .AddJsonFile($"appsettings.{builder.Environment.EnvironmentName}.json",
                 optional: true, reloadOnChange: true)
    .AddEnvironmentVariables("APP_")          // 只接收 APP_ 前缀的变量
    .AddCommandLine(args);                     // 命令行参数最高优先级

var app = builder.Build();

// 分层键读取
var conn = app.Configuration.GetConnectionString("Default");
var timeout = app.Configuration.GetValue<int>("Cache:SlidingExpiryMinutes");

{
  "ConnectionStrings": {
    "Default": "Server=db;Database=shop;Trusted_Connection=true;"
  },
  "Cache": {
    "SlidingExpiryMinutes": 20
  }
}

# Linux / macOS
export ASPNETCORE_ENVIRONMENT=Production
dotnet run

# Windows PowerShell
$env:ASPNETCORE_ENVIRONMENT = "Production"
dotnet run

# 命令行注入（最高优先级）
dotnet run --environment Production

// 按环境分支配置
if (app.Environment.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}
else
{
    app.UseExceptionHandler("/error");
}

// 按环境读取开关
var verboseLogging = builder.Configuration.GetValue<bool>("Logging:EnableVerbose");

// IHostEnvironment 注入
public class StartupProbe(IHostEnvironment env)
{
    public string Mode => env.IsProduction() ? "prod" : env.EnvironmentName;
}

// 配置节
// "Cache": { "SlidingExpiryMinutes": 20, "Redis": "..." }

public class CacheOptions
{
    public int SlidingExpiryMinutes { get; set; } = 15;   // 默认值兜底
    public string? Redis { get; set; }
}

// 注册：绑定 Cache 节
builder.Services.Configure<CacheOptions>(
    builder.Configuration.GetSection("Cache"));

// 消费：注入强类型
public class OrderService(IOptions<CacheOptions> cacheOptions)
{
    public int GetExpiry() => cacheOptions.Value.SlidingExpiryMinutes;
}

// 用 OptionsBuilder 链式配置
builder.Services.AddOptions<CacheOptions>()
    .Bind(builder.Configuration.GetSection("Cache"))
    .ValidateDataAnnotations();          // 绑定后校验

public class SmsOptions
{
    [Required, StringLength(32)]
    public string AccessKey { get; set; } = string.Empty;

    [Required]
    public string Secret { get; set; } = string.Empty;

    [Range(1, 60)]
    public int TimeoutSeconds { get; set; } = 10;
}

builder.Services.AddOptions<SmsOptions>()
    .Bind(builder.Configuration.GetSection("Sms"))
    .ValidateDataAnnotations()
    .Validate(o => o.AccessKey != o.Secret,
              "AccessKey 与 Secret 不能相同")
    .ValidateOnStart();     // 应用启动时立即校验

// 备选：完整配置对象 + IValidateOptions
public class ValidateSmsOptions : IValidateOptions<SmsOptions>
{
    public ValidateOptionsResult Validate(string? name, SmsOptions options)
    {
        if (string.IsNullOrWhiteSpace(options.AccessKey))
            return ValidateOptionsResult.Fail("缺少 Sms:AccessKey");
        if (options.TimeoutSeconds is < 1 or > 60)
            return ValidateOptionsResult.Fail("TimeoutSeconds 超出范围");
        return ValidateOptionsResult.Success;
    }
}

// 两个渠道共用同一结构
// "Payment": {
//   "WeChat": { "AppId": "...", "Secret": "..." },
//   "Alipay": { "AppId": "...", "Secret": "..." }
// }

builder.Services.Configure<PaymentChannelOptions>("WeChat",
    builder.Configuration.GetSection("Payment:WeChat"));
builder.Services.Configure<PaymentChannelOptions>("Alipay",
    builder.Configuration.GetSection("Payment:Alipay"));

public class PaymentService(IOptionsSnapshot<PaymentChannelOptions> channels)
{
    public async Task PayAsync(string channel, decimal amount)
    {
        var opts = channels.Get(channel);      // 按名取配置
        // 使用 opts.AppId / opts.Secret 发起支付
    }
}

// 注册：开启重载
builder.Configuration.AddJsonFile("appsettings.json",
    optional: false, reloadOnChange: true);
builder.Services.AddOptions<FeatureFlags>()
    .Bind(builder.Configuration.GetSection("FeatureFlags"))
    .ValidateOnStart();

public class FeatureService(IOptionsMonitor<FeatureFlags> flags)
{
    public bool IsEnabled(string name)
    {
        // CurrentValue 每次读取最新值
        return flags.CurrentValue.Map.GetValueOrDefault(name);
    }

    public void Watch(Action<FeatureFlags> onChange)
    {
        // 配置变更时触发回调
        flags.OnChange(onChange);
    }
}

// 运行时动态更新示例
var flagService = app.Services.GetRequiredService<FeatureService>();
flagService.Watch(f => Console.WriteLine($"新配置: 折扣={f.DiscountPercent}%"));

app.MapGet("/flag/discount", () =>
    flagService.IsEnabled("discount") ? "on" : "off");

# 初始化 User Secrets
dotnet user-secrets init
# 设置密钥
dotnet user-secrets set "Sms:Secret" "dev-only-secret"
# 查看
dotnet user-secrets list

// 开发环境：User Secrets 覆盖 appsettings
if (builder.Environment.IsDevelopment())
{
    builder.Configuration.AddUserSecrets<Program>();
}

// 生产：从密钥服务加载
builder.Configuration.AddAzureKeyVault(
    new Uri("https://myvault.vault.azure.net/"),
    new DefaultAzureCredential());