telegram-bot/Core/Core.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;

namespace Kruzya.TelegramBot.Core
{
    public sealed class Core
    {
        /// <summary>
        /// The Core API version.
        /// </summary>
        public UInt32 ApiVersion => 1;

        /// <summary>
        /// The array that contains all modules instances.
        /// </summary>
        public Module[] Modules => _modules.ToArray();

        /// <summary>
        /// The current bot configuration.
        /// </summary>
        public IConfiguration Configuration => _configuration;

        #region Private properties

        /// <summary>
        /// The array that contains all modules instances.
        /// </summary>
        private List<Module> _modules = new List<Module>();
        
        /// <summary>
        /// The current bot configuration.
        /// </summary>
        private IConfiguration _configuration;

        /// <summary>
        /// The all directories for loading our module assemblies.
        /// </summary>
        private List<string> _directories
        {
            get
            {
                // For start, load all assemblies in required directory.
                // And register in internal temporary array.
                var modulesDirectory = new List<string>(new string[]
                {
                    Path.Join(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "modules"),
                    Path.Join(Environment.CurrentDirectory, "modules")
                });
                
                // Also lookup load directories from config.
                modulesDirectory.AddRange(_configuration.GetSection("ModuleDirectories").GetChildren().Select(q => q.Value)
                    .ToList());

                return modulesDirectory;
            }
        }

        #endregion

        public Core(IConfiguration configuration)
        {
            _configuration = configuration;

            HookAppDomain();
            Start();
        }

        /// <summary>
        /// Initializes all required submodules.
        /// </summary>
        private void Start()
        {
            var types = new List<Type>();
            foreach (var directory in _directories)
            {
                if (!Directory.Exists(directory))
                {
                    continue;
                }

                foreach (var file in Directory.EnumerateFiles(directory, "*.dll", SearchOption.AllDirectories))
                {
                    var assemblyTypes = LoadAssembly(file);
                    if (assemblyTypes == null)
                    {
                        continue;
                    }

                    types.AddRange(assemblyTypes);
                }
            }
            
            // Instantiate them.
            foreach (var module in types)
            {
                EnsureLoaded(module);
            }
        }

        /// <summary>
        /// Loads the assembly and appends all Module types to list.
        /// </summary>
        /// <param name="path">The full path to assembly file</param>
        /// <returns><see cref="IEnumerable{T}"/> if success, null otherwise.</returns>
        private IEnumerable<Type> LoadAssembly(string path)
        {
            Assembly assembly;
            try
            {
                assembly = Assembly.LoadFile(path);
            }
            catch (Exception)
            {
                // don't load any invalid module.
                return null;
            }

            return assembly.GetExportedTypes().Where(x => !x.IsAbstract && x.IsSubclassOf(typeof(Module)));
        }

        /// <summary>
        /// Ensures if module is loaded and started. Note that call can change module event chain.
        /// </summary>
        /// <typeparam name="T">The Module type.</typeparam>
        /// <returns>Module instance.</returns>
        public T EnsureLoaded<T>()
            where T : Module
        {
            return (T) EnsureLoaded(typeof(T));
        }
        
        /// <summary>
        /// Ensures if module is loaded and started. Note that call can change module event chain.
        /// </summary>
        /// <param name="moduleType">The Module type.</param>
        /// <returns>Module instance.</returns>
        /// <exception cref="Exception">The given type is not extends the Module class</exception>
        public Module EnsureLoaded(Type moduleType)
        {
            if (!moduleType.IsSubclassOf(typeof(Module)))
            {
                throw new Exception("Received incorrect module type");
            }

            var module = _modules.FirstOrDefault(module => module.GetType() == moduleType);
            if (module == null)
            {
                module = (Module) Activator.CreateInstance(moduleType, this);
                Console.WriteLine($"Started module {module.GetType().Name}");
                _modules.Add(module);
            }

            return module;
        }

        private void HookAppDomain()
        {
            var appDomain = AppDomain.CurrentDomain;
            
            appDomain.AssemblyResolve += delegate(object? sender, ResolveEventArgs args)
            {
                var basePath = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
                var assemblyPath = Path.Combine(basePath, new AssemblyName(args.Name).Name + ".dll");
                if (!File.Exists(assemblyPath))
                {
                    return null;
                }

                return Assembly.LoadFrom(assemblyPath);
            };
        }
    }
}