using System;
using Junction.Core.Monitoring;
using Junction.Core.Plugins;
using Junction.Core.Polling;
using Microsoft.Extensions.DependencyInjection;

namespace Junction.Core
{
    /// <summary>
    /// DI registration for the Junction.Core orchestration stack.
    /// </summary>
    public static class ServiceCollectionExtensions
    {
        /// <summary>
        /// Registers the Core services:
        /// <list type="bullet">
        /// <item><see cref="IPluginLoader"/> → <see cref="PluginLoader"/> (singleton; scanned once at startup).</item>
        /// <item><see cref="IPollingEngine"/> → <see cref="PollingEngine"/> (transient; one loop per machine),
        /// plus a <see cref="Func{IPollingEngine}"/> factory the monitor uses to build engines on demand.</item>
        /// <item><see cref="IMachineMonitor"/> → <see cref="MachineMonitor"/> (singleton; the app-wide hub).</item>
        /// </list>
        /// Does NOT register <c>IMachineRepository</c> (that is <c>AddJunctionPersistence</c>) nor any concrete
        /// logging provider (the app host wires NLog). Logging is consumed via the
        /// <c>Microsoft.Extensions.Logging</c> abstractions only.
        /// </summary>
        /// <param name="services">The service collection to add to.</param>
        /// <returns>The same collection, for chaining.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="services"/> is null.</exception>
        public static IServiceCollection AddJunctionCore(this IServiceCollection services)
        {
            if (services is null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            services.AddSingleton<IPluginLoader, PluginLoader>();

            // One engine per machine: transient, plus a factory the monitor calls per machine.
            services.AddTransient<IPollingEngine, PollingEngine>();
            services.AddSingleton<Func<IPollingEngine>>(sp => () => sp.GetRequiredService<IPollingEngine>());

            services.AddSingleton<IMachineMonitor, MachineMonitor>();

            return services;
        }
    }
}