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

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using Options = RAIC.Extensions.Configuration.EntityFrameworkCore.PostgreSQL.PostgreSQLNotificationConfigurationReloaderOptions;

namespace RAIC.Extensions.Configuration.EntityFrameworkCore.PostgreSQL.Extensions;

public static class ServiceCollectionExtensions
{

    public delegate OptionsBuilder<T> OptionsTransformer<T>(OptionsBuilder<T> transform) where T : class;


    /// <summary>
    /// Adds <see cref="PostgreSQLNotificationConfigurationReloader"/> (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"/> to use to obtain the underlying database connection</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>
    public static IServiceCollection AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(this IServiceCollection services)
        where TDbContext : DbContext
    {
        return services.AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(static _ => { });
    }

    /// <summary>
    /// Adds <see cref="PostgreSQLNotificationConfigurationReloader"/> (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"/> to use to obtain the underlying database connection</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="PostgreSQLNotificationConfigurationReloader"/> eg.
    /// <code>
    /// options => {
    ///     options.DebounceInterval = TimeSpan.FromSeconds(2);
    ///     options.ChannelName = "awesome_channel";
    /// }
    /// </code>
    /// </param>
    /// <returns>The service collection it was called on now with added services</returns>
    public static IServiceCollection AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(this IServiceCollection services, Action<Options> configure)
        where TDbContext : DbContext
    {
        var optionsBuilder = services.AddCoreServices<TDbContext>();

        optionsBuilder.Configure(configure);

        return services;
    }

    /// <summary>
    /// Adds <see cref="PostgreSQLNotificationConfigurationReloader"/> (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"/> to use to obtain the underlying database connection</typeparam>
    /// <param name="services">The service collection to add the services too</param>
    /// <param name="optionsTransform">
    /// Transformer delegate to apply to the <see cref="Options"/> instance consumed by <see cref="PostgreSQLNotificationConfigurationReloader"/> eg.
    /// <code>
    ///  optionsBuilder => optionsBuilder.Bind(context.Configuration)
    /// </code>
    /// </param>
    /// <returns>The service collection it was called on now with added services</returns>
    public static IServiceCollection AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(this IServiceCollection services, OptionsTransformer<Options> optionsTransform)
        where TDbContext : DbContext
    {
        var optionsBuilder = services.AddCoreServices<TDbContext>();

        optionsTransform(optionsBuilder);

        return services;
    }


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

        return services.AddOptions<Options>().ValidateDataAnnotations().ValidateOnStart();
    }
}


/* 
 * 
CREATE OR REPLACE FUNCTION settings_poc.notify_setting_change()
RETURNS trigger AS $$
BEGIN
PERFORM pg_notify('setting_channel', concat(NEW.key,'=',NEW.value));
RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION settings_poc.notify_setting_remove()
RETURNS trigger AS $$
BEGIN
PERFORM pg_notify('setting_channel', OLD.key);
RETURN OLD;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER setting_insert_trigger
AFTER INSERT ON settings_poc.settings
FOR EACH ROW EXECUTE FUNCTION settings_poc.notify_setting_change();

CREATE TRIGGER setting_update_trigger
AFTER UPDATE ON settings_poc.settings
FOR EACH ROW WHEN (NEW.value <> OLD.value) EXECUTE FUNCTION settings_poc.notify_setting_change();

CREATE TRIGGER setting_delete_trigger
AFTER DELETE ON settings_poc.settings
FOR EACH ROW EXECUTE FUNCTION settings_poc.notify_setting_remove();

 * 
 */