using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.CodeDom.Compiler;
using System.Reflection;

namespace HS.Comm.Utility
{
    /// <summary>
    /// JS動態語法解析
    /// </summary>
    public class Evaluator
    {
        /// <summary>
        /// 靜態建構函式
        
 
/// </summary>
        static Evaluator()
        {
            //構造JScript的編譯驅動程式碼
            CodeDomProvider provider = CodeDomProvider.CreateProvider("JScript");

            CompilerParameters parameters;
            parameters = new CompilerParameters();
            parameters.GenerateInMemory 
 
= true;

            CompilerResults results;
            results = provider.CompileAssemblyFromSource(parameters, _jscriptSource);

            Assembly assembly = results.CompiledAssembly;
            _evaluatorType = assembly.GetType("Evaluator");

            _evaluator = Activator.CreateInstance(_evaluatorType);
        }

        
 
/// <summary>
        /// 計算結果,如果表示式出錯則丟擲異常
        /// </summary>
        /// <param name="statement">表示式,如"1+2+3+4"</param>
        /// <returns>結果</returns>
        public static object Eval(string statement)
        {
            try
            {
                object obj = _evaluatorType.InvokeMember("Eval", BindingFlags.InvokeMethod, null, _evaluator, new object[] { statement });
                return obj;
            }
            catch
            {
                return string.Empty;
            }
        }

        private static object _evaluator = null;
        private static Type _evaluatorType = null;
        /// <summary>
        /// JScript程式碼
        /// </summary>
        private static readonly string _jscriptSource = @"class Evaluator
               {
                   public function Eval(expr : String) : String 
                   { 
                      return eval(expr); 
                   }
               }";
    }
}