Extensions.Configuration.EntityFrameworkCore/RAIC.Extensions.Configuration.EntityFrameworkCore.SqlServer/Extensions/ServiceCollectionExtensions.cs

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using Options = RAIC.Extensions.Configuration.EntityFrameworkCore.SqlServer.SqlServerNotificationConfigurationReloaderOptions;

namespace RAIC.Extensions.Configuration.EntityFrameworkCore.SqlServer.Extensions;

public static class ServiceCollectionExtensions
{
    /// <summary>
    /// Adds <see cref="SqlServerNotificationConfigurationReloader{,}"/> (a <see cref="Microsoft.Extensions.Hosting.IHostedService"/> implementation)
    /// and supporting services to the <see cref="IServiceCollection"/>, obtaining its connection string from a <typeparamref name="TDbContext"/> instance.
    /// </summary>
    /// <typeparam name="TDbContext">Type of the <see cref="DbContext"/> which implements <see cref="ISettingsDbContext{TSettingDbSet, TSetting}"/></typeparam>
    /// <typeparam name="TSetting">Concrete type which implements <see cref="ISetting"/></typeparam>
    /// <param name="services">The service collection to add the services too</param>
    /// <returns>The service collection it was called on now with added services</returns>
    /// <remarks>If your connection string contains a password then this method may not work, please use another overload</remarks>
    /// <exception cref="NullReferenceException">If your <typeparamref name="TDbContext"/> does not have a connection string</exception>
    public static IServiceCollection AddSqlServerNotificationConfigurationReloadService<TDbContext, TSetting>(this IServiceCollection services)
        where TDbContext : DbContext, ISettingsDbContext<DbSet<TSetting>, TSetting>
        where TSetting : class, ISetting
    {
        var optionsBuilder = services.AddCoreServices<TDbContext, TSetting>();

        optionsBuilder.Configure<TDbContext>((options, dependency) =>
        {
            options.ConnectionString = dependency.Database.GetConnectionString() ?? throw new NullReferenceException($"{typeof(TDbContext).Name} ConnectionString is null");
        });

        return services;
    }

    /// <summary>
    /// Adds <see cref="SqlServerNotificationConfigurationReloader{,}"/> (a <see cref="Microsoft.Extensions.Hosting.IHostedService"/> implementation)
    /// and supporting services to the <see cref="IServiceCollection"/>.
    /// </summary>
    /// <typeparam name="TDbContext">Type of the <see cref="DbContext"/> which implements <see cref="ISettingsDbContext{,}"/></typeparam>
    /// <typeparam name="TSetting">Concrete type which implements <see cref="ISetting"/></typeparam>
    /// <param name="services">The service collection to add the services too</param>
    /// <param name="configure">
    /// Action to manually configure the <see cref="Options"/> instance consumed by <see cref="SqlServerNotificationConfigurationReloader{,}"/> eg.
    /// <code>
    /// options => {
    ///     options.ConnectionString = context.Configuration.GetConnectionString("Default");
    /// }
    /// </code>
    /// </param>
    /// <returns>The service collection it was called on now with added services</returns>
    public static IServiceCollection AddSqlServerNotificationConfigurationReloadService<TDbContext, TSetting>(this IServiceCollection services, Action<Options> configure)
        where TDbContext : DbContext, ISettingsDbContext<DbSet<TSetting>, TSetting>
        where TSetting : class, ISetting
    {
        var optionsBuilder = services.AddCoreServices<TDbContext, TSetting>();

        optionsBuilder.Configure(configure);

        return services;
    }


    private static OptionsBuilder<Options> AddCoreServices<TDbContext, TSetting>(this IServiceCollection services)
        where TDbContext : DbContext, ISettingsDbContext<DbSet<TSetting>, TSetting>
        where TSetting : class, ISetting
    {
        services.AddSingleton(static provider =>
        {
            var configRoot = (IConfigurationRoot)provider.GetRequiredService<IConfiguration>(); // DEBT: Is this cast always safe?
            return configRoot.Providers.OfType<IEntityFrameworkCoreDbSetConfigurationProvider>().Single();
        });

        return services.AddHostedService<SqlServerNotificationConfigurationReloader<TDbContext, TSetting>>()
                       .AddOptions<Options>().ValidateDataAnnotations().ValidateOnStart();
    }
}