using System;
using System.Linq;
using Ninject;
using Ninject.Extensions.Conventions;

/// <summary>
/// Extensions method to handle plugins
/// </summary>
public static class NinjectPlugin
{
    /// <summary>
    /// Bind a DLL to a specified interface
    /// </summary>
    /// <typeparam name="T">T the service interface to bind to</typeparam>
    /// <param name="kernel"></param>
    /// <param name="directorypath">the path to the folder conaining the assemblies</param>
    public static void LoadDll<T>(this IKernel kernel, string directorypath)
    {
        if(!typeof(T).IsInterface)
            throw new InvalidCastException(typeof(T).Name + " Must be an interface");
        kernel.Bind(s => s.FromAssembliesInPath(directorypath)
            .Select(t => t.GetInterfaces().Any(i => i == typeof(T)))
            .BindSingleInterface());
        if (!kernel.CanResolve<T>())
            throw new InvalidOperationException("No assembly inside " + directorypath + " contains an implementation for interface " + typeof (T).Name);
    }

    /// <summary>
    /// Bind a DLL to a specified interface. If the bining fails, bind to a fallback implementation
    /// </summary>
    /// <typeparam name="T">T the service interface to bind to</typeparam>
    /// <typeparam name="TFallback">The fallback implementation of the service</typeparam>
    /// <param name="kernel"></param>
    /// <param name="directorypath">the path to the folder conaining the assemblies</param>
    public static void LoadDll<T, TFallback>(this IKernel kernel, string directorypath)
        where TFallback : T
    {
        try
        {
            kernel.LoadDll<T>(directorypath);
        }
        catch (Exception e)
        {
            if (e is InvalidCastException)
                throw;
            //bind the fallback
            kernel.Bind<T>().To<TFallback>();
        }
    }
}