#region License

// Copyright 2005-2019 Paul Kohler (https://github.com/paulkohler/minisqlquery). All rights reserved.
// This source code is made available under the terms of the GNU Lesser General Public License v3.0
// https://github.com/paulkohler/minisqlquery/blob/master/LICENSE

#endregion

using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;

namespace MiniSqlQuery.Core
{
    /// <summary>
    /// 	Helper class for loading external plugins.
    /// </summary>
    public class PlugInUtility
    {
        /// <summary>
        /// 	Search <paramref name = "baseDir" /> for files that match the pattern <paramref name = "searchPattern" />
        /// 	and return an array of instances.
        /// </summary>
        /// <returns>An array of instances of the plugins found.</returns>
        /// <typeparam name = "T">The type (interface or class) to find instances of.</typeparam>
        /// <param name = "baseDir">The search base.</param>
        /// <param name = "searchPattern">Search pattern, e.g. "*.dll".</param>
        public static T[] GetInstances<T>(string baseDir, string searchPattern)
        {
            var tmpInstances = new List<T>();
            Assembly pluginAssembly;

            try
            {
                // perform the file search
                string[] files = Directory.GetFiles(baseDir, searchPattern, SearchOption.TopDirectoryOnly);

                // load each asembly and inspect for instances of T
                foreach (string file in files)
                {
                    pluginAssembly = Assembly.LoadFrom(file);
                    Type[] assemblyTypes = pluginAssembly.GetTypes();

                    // check each assembly to se it it implements the interface T
                    foreach (Type assemblyType in assemblyTypes)
                    {
                        Type instanceType = assemblyType.GetInterface(typeof(T).FullName);
                        if (instanceType != null)
                        {
                            // this instance type matches T, create an instance of the class and add it to the list
                            tmpInstances.Add((T)Activator.CreateInstance(assemblyType));
                        }
                    }
                }
            }
            catch (TargetInvocationException exp)
            {
                if (exp.InnerException != null)
                {
                    throw exp.InnerException;
                }
            }

            return tmpInstances.ToArray();
        }
    }
}