using System;
using Flee.ExpressionElements.Base;
using Flee.ExpressionElements.MemberElements;
using Flee.InternalTypes;
using Flee.PublicTypes;

namespace Flee.ExpressionElements
{
    internal class AssignmentElement : ExpressionElement
    {
        private readonly string _variableName;
        private readonly ExpressionElement _valueExpression;
        private readonly ExpressionContext _context;

        public AssignmentElement(string variableName, ExpressionElement valueExpression, ExpressionContext context)
        {
            _variableName = variableName;
            _valueExpression = valueExpression;
            _context = context;
            
            // 检查变量是否存在
            if (!_context.Variables.ContainsKey(_variableName))
            {
                this.ThrowCompileException("UndefinedVariable", CompileExceptionReason.UndefinedName, _variableName);
            }
        }

        public override void Emit(FleeILGenerator ilg, IServiceProvider services)
        {
            // 首先计算右侧表达式的值
            _valueExpression.Emit(ilg, services);
            
            // 获取一个临时本地变量来存储值
            var valueType = _valueExpression.ResultType;
            int tempIndex = ilg.GetTempLocalIndex(valueType);
            
            // 存储值到临时变量
            Utility.EmitStoreLocal(ilg, tempIndex);
            
            // 加载变量集合 (arg 2)
            ilg.Emit(System.Reflection.Emit.OpCodes.Ldarg_2); // 加载 VariableCollection
            
            // 加载变量名
            ilg.Emit(System.Reflection.Emit.OpCodes.Ldstr, _variableName);
            
            // 加载要设置的值
            Utility.EmitLoadLocal(ilg, tempIndex);
            
            // 如果值类型是值类型，需要装箱
            if (valueType.IsValueType)
            {
                ilg.Emit(System.Reflection.Emit.OpCodes.Box, valueType);
            }
            
            // 调用 Variables[string] 的 setter
            var indexerSetter = typeof(VariableCollection).GetProperty("Item", new Type[] { typeof(string) }).GetSetMethod();
            ilg.Emit(System.Reflection.Emit.OpCodes.Callvirt, indexerSetter);
            
            // 加载返回值到栈上
            Utility.EmitLoadLocal(ilg, tempIndex);
        }

        public override Type ResultType
        {
            get { return _valueExpression.ResultType; }
        }
    }
}