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HTML / CSS / JS

// Configuration system: appsettings.json + environment variables + IOptions<T>

/*
appsettings.json:
{
  "Logging": { "LogLevel": { "Default": "Information" } },
  "Database": {
    "ConnectionString": "Server=localhost;Database=MyApp;",
    "CommandTimeoutSeconds": 30,
    "MaxPoolSize": 100
  },
  "FeatureFlags": {
    "EnableBetaFeatures": false,
    "MaxUploadSizeMb": 10
  }
}
*/

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;

// Strongly-typed option classes
public class DatabaseOptions
{
    public const string Section = "Database";
    public string ConnectionString      { get; set; } = "";
    public int    CommandTimeoutSeconds { get; set; } = 30;
    public int    MaxPoolSize           { get; set; } = 50;
}

public class FeatureFlags
{
    public const string Section = "FeatureFlags";
    public bool EnableBetaFeatures { get; set; }
    public int  MaxUploadSizeMb    { get; set; } = 10;
}

// Wire up in Program.cs
var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddOptions<DatabaseOptions>()
    .Bind(builder.Configuration.GetSection(DatabaseOptions.Section))
    .ValidateDataAnnotations()
    .ValidateOnStart();

builder.Services
    .AddOptions<FeatureFlags>()
    .Bind(builder.Configuration.GetSection(FeatureFlags.Section));

var app = builder.Build();

app.MapGet("/config", (IOptions<DatabaseOptions> db, IOptions<FeatureFlags> ff) =>
    Results.Ok(new
    {
        db.Value.MaxPoolSize,
        db.Value.CommandTimeoutSeconds,
        ff.Value.EnableBetaFeatures,
        ff.Value.MaxUploadSizeMb
    }));

app.Run();