A Plug-in Wizard Framework

using System;
using System.Collections.Generic;
using System.Windows.Forms;

namespace Clifton.Wizard
{
	/// <summary>
	/// The four states of the wizard.
	/// </summary>
	public enum WizardState
	{
		Uninitialized,
		Start,
		Middle,
		End,
	}

	/// <summary>
	/// The plugin manager coordinates the index to the current 
	/// manager and isolates some of the details of managing the
	/// plugins.
	/// </summary>
	public class PluginManager
	{
		protected List<Plugin> pluginList;
		protected int position;
		protected WizardState state;

		/// <summary>
		/// Returns the current state of the wizard.
		/// </summary>
		public WizardState State
		{
			get { return state; }
		}

		/// <summary>
		/// True if the plugin validates itself, indicating that the
		/// "Next" button can be enabled.
		/// </summary>
		public bool IsValid
		{
			get { return pluginList[position].Instance.IsValid; }
		}

		/// <summary>
		/// Constructor.  Initializes the plugin list and state.
		/// </summary>
		public PluginManager()
		{
			pluginList = new List<Plugin>();
			position = -1;
			state = WizardState.Uninitialized;
		}

		/// <summary>
		/// Adds as assembly to the plugin list.
		/// </summary>
		/// <param name="assemblyPath">The full assembly path.</param>
		/// <param name="typeName">The qualifed [namespace].[class] name that is instantiated.</param>
		public void AddAssembly(string assemblyPath, string typeName)
		{
			Plugin plugin = new Plugin(assemblyPath, typeName);
			pluginList.Add(plugin);
		}

		/// <summary>
		/// Loads all plugin assemblies.
		/// </summary>
		public void LoadPlugins()
		{
			if (pluginList.Count == 0)
			{
				throw new ApplicationException("At least one plugin assembly must be added to the plugin manager's collection.");
			}

			LoadPluginAssemblies();
		}

		/// <summary>
		/// Initialize the wizard state.
		/// </summary>
		public void Initialize()
		{
			position = 0;
			SetState();
		}

		/// <summary>
		/// Returns to the previous wizard frame.
		/// </summary>
		public void Previous()
		{
			if (position == 0)
			{
				throw new ApplicationException("The wizard position cannnot be decremented.");
			}

			--position;
			SetState();
		}

		/// <summary>
		/// Calls the current plugin's OnNext method then increments the frame postion
		/// and updates the wizard state.
		/// </summary>
		public void Next()
		{
			if (position == pluginList.Count - 1)
			{
				throw new ApplicationException("The wizard position cannot be incremented.");
			}

			pluginList[position].Instance.OnNext();
			++position;
			SetState();
		}

		/// <summary>
		/// Calls the plugin's OnHelp method (if implemented).  The default behavior is to
		/// do nothing.
		/// </summary>
		public void OnHelp()
		{
			pluginList[position].Instance.OnHelp();
		}

		/// <summary>
		/// Calls the last plugin's OnNext method.
		/// </summary>
		public void Final()
		{
			if (position != pluginList.Count - 1)
			{
				throw new ApplicationException("Final can only be called on the last frame in the wizard plugin list.");
			}

			pluginList[position].Instance.OnNext();
		}

		/// <summary>
		/// Returns the controls specified by the plugin.
		/// </summary>
		public List<Control> GetControls()
		{
			Plugin plugin = pluginList[position];
			List<Control> controls = plugin.GetControls();

			return controls;
		}

		/// <summary>
		/// Hooks the plugin's UpdateStateEvent, allowing the plugin to
		/// notify our wizard controller that the wizard state needs to
		/// be updated.
		/// </summary>
		/// <param name="eventHandler">The event handler sinking the notification.</param>
		public void HookUpdateStateEvent(EventHandler eventHandler)
		{
			foreach (Plugin plugin in pluginList)
			{
				plugin.Instance.UpdateStateEvent += eventHandler;
			}
		}

		/// <summary>
		/// Loads each plugin.
		/// </summary>
		protected void LoadPluginAssemblies()
		{
			foreach (Plugin plugin in pluginList)
			{
				plugin.LoadAndCreate();
			}
		}

		/// <summary>
		/// Sets the wizard state flag.
		/// </summary>
		protected void SetState()
		{
			if (pluginList.Count - 1 == position)
			{
				state = WizardState.End;
			}
			else if (position == 0)
			{
				state = WizardState.Start;
			}
			else
			{
				state = WizardState.Middle;
			}
		}
	}
}