using LinFu.AOP.Cecil.Interfaces;
using LinFu.Reflection.Emit;
using Mono.Cecil;
using Mono.Cecil.Cil;

namespace LinFu.AOP.Cecil
{
    /// <summary>
    ///     Represents an instruction emitter that saves the return value from a given method call.
    /// </summary>
    public class SaveReturnValue : IInstructionEmitter
    {
        private readonly TypeReference _returnType;
        private readonly VariableDefinition _returnValue;

        /// <summary>
        ///     Initializes a new instance of the <see cref="SaveReturnValue" /> class.
        /// </summary>
        /// <param name="returnType">The return type.</param>
        /// <param name="returnValue">The return value.</param>
        public SaveReturnValue(TypeReference returnType, VariableDefinition returnValue)
        {
            _returnType = returnType;
            _returnValue = returnValue;
        }


        /// <summary>
        ///     Saves the return value from a given method call.
        /// </summary>
        /// <param name="IL">The <see cref="ILProcessor" /> pointing to the target method body.</param>
        public void Emit(ILProcessor IL)
        {
            var module = IL.Body.Method.DeclaringType.Module;
            
            var voidType = module.ImportType(typeof(void));
            var returnTypeIsValueType = _returnType != voidType && _returnType.IsValueType;

            if (_returnType is GenericParameter || returnTypeIsValueType)
                IL.Create(OpCodes.Box, _returnType);

            if (_returnType != voidType)
                IL.Create(OpCodes.Stloc, _returnValue);
        }
    }
}