/* This Example is a part of different 
* examples shown in Book: 
* C#2005 Beginners: A Step Ahead
* Written by: Gaurav Arora 
* Reach at : msdotnetheaven*/

// File name : dynamicAssembly.cs
//This demostrates how to build a dynamic assembly

using System;
using System.Reflection;
using System.Reflection.Emit;
namespace CSharp.AStepAhead.dynamicAssembly
{
    class CodeGenerator
    {
        Type t;
        AppDomain currentDomain;
        AssemblyName assemName;
        AssemblyBuilder assemBuilder;
        ModuleBuilder moduleBuilder;
        TypeBuilder typeBuilder;
        MethodBuilder methodBuilder;
        ILGenerator msilG;
        
        public static void Main()
        {
            CodeGenerator codeGen = new CodeGenerator();
            Type myType = codeGen.T;
            if (myType != null)
            {
                object o = Activator.CreateInstance(myType);
                MethodInfo helloWorld =  myType.GetMethod("HelloWorld");
                if (helloWorld != null)
                {
                    // Run the HelloWorld Method
                    helloWorld.Invoke(o, null);
                }
                else  //if method info null
                {
                    Console.WriteLine("Could not retrieve MethodInfo");
                }
            }
            else //if type null
            {
                Console.WriteLine("Could not access the Type");
            }
        } 

        public CodeGenerator()
        {
            // Get the current Application Domain.
            // This is needed when building code.
            currentDomain = AppDomain.CurrentDomain;

            // Create a new Assembly for Methods
            assemName = new AssemblyName();
            assemName.Name = "dynamicAssembly";
            assemBuilder = currentDomain.DefineDynamicAssembly(assemName, AssemblyBuilderAccess.Run);

            // Create a new module within this assembly
            moduleBuilder = assemBuilder.DefineDynamicModule("dynamicAssemblyModule");

            // Create a new type within the module
            typeBuilder = moduleBuilder.DefineType("dynamicAssemblyClass", TypeAttributes.Public);

            // Now add the HelloWorld method to the class that was just created.
            methodBuilder = typeBuilder.DefineMethod("HelloWorld", MethodAttributes.Public, null, null);

            // Now generate some Microsoft Intermediate Language Code that simply 
            // writes a line of text out to the console.
            msilG = methodBuilder.GetILGenerator();
            msilG.EmitWriteLine("Hello! This is a dynamic assembly.");
            msilG.Emit(OpCodes.Ret);

            // Create a type.
            t = typeBuilder.CreateType();
        }
        
        public Type T
        {
            get
            {
                return this.t;
            }
        }
    }
}