using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using Chernobyl.Collections.Generic;

namespace Chernobyl.Extensions.Configuration
{
    /// <summary>
    /// Extensions for Chernobyl settings and related types.
    /// </summary>
    public static class Extensions
    {
        /// <summary>
        /// The default string that is applied to the front of all setting keys.
        /// For example, in "Chernobyl.Plugins", "Chernobyl" is the root.
        /// </summary>
        public static string RootKey = "Chernobyl";

        /// <summary>
        /// The default string that is placed between each element in a settings
        /// key. For example, in "Chernobyl.Plugins" the '.' is the separator.
        /// </summary>
        public static string KeySeparator = ".";

        /// <summary>
        /// The default string that is applied to any settings value that contains
        /// the list of plugin names.
        /// </summary>
        public static string PluginKey = RootKey + KeySeparator + "Plugins";

        /// <summary>
        /// The default character placed between assembly names in the settings 
        /// identified by <see cref="PluginKey"/>.
        /// </summary>
        public static char PluginNameSeparator = ';';

        /// <summary>
        /// Retrieves the <see cref="AssemblyName"/> of plugins identified by
        /// <see cref="PluginKey"/> in the configuration provided.
        /// </summary>
        /// <param name="config">The configuration to look in for the plugin
        /// names.</param>
        /// <returns>The names of the plugin assemblies from <paramref name="config"/>.</returns>
        public static IEnumerable<AssemblyName> GetPluginNames(this global::System.Configuration.Configuration config)
        {
            return config.AppSettings.Settings[PluginKey].Value.EmptyIfNull()
                         .Split(PluginNameSeparator)
                         .Where(str => str.IsEmpty() == false)
                         .Select(str => new AssemblyName(str));
        }

        /// <summary>
        /// Retrieves the plugin <see cref="Assembly"/> instances identified by
        /// <see cref="PluginKey"/> in the configuration provided.
        /// </summary>
        /// <param name="config">The configuration to look in for the plugin
        /// names.</param>
        /// <returns>The <see cref="Assembly"/> instances from 
        /// <paramref name="config"/>.</returns>
        public static IEnumerable<Assembly> GetPluginAssemblies(this global::System.Configuration.Configuration config)
        {
            return config.GetPluginNames().Select(Assembly.Load);
        }
    }
}