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

namespace LinFu.AOP.Cecil
{
    /// <summary>
    ///     Represents a class that emits the instructions that obtain the current <see cref="IAroundInvoke" /> instance.
    /// </summary>
    public class GetSurroundingImplementationInstance : IInstructionEmitter
    {
        private readonly VariableDefinition _aroundInvokeProvider;
        private readonly VariableDefinition _invocationInfo;
        private readonly Instruction _skipGetSurroundingImplementation;
        private readonly VariableDefinition _surroundingImplementation;

        /// <summary>
        ///     Initializes a new instance of the <see cref="GetSurroundingImplementationInstance" /> class.
        /// </summary>
        /// <param name="aroundInvokeProvider">The variable that will hold the <see cref="IAroundInvokeProvider" /> instance.</param>
        /// <param name="invocationInfo"></param>
        /// <param name="surroundingImplementation"></param>
        /// <param name="skipGetSurroundingImplementation"></param>
        public GetSurroundingImplementationInstance(VariableDefinition aroundInvokeProvider,
            VariableDefinition invocationInfo,
            VariableDefinition surroundingImplementation,
            Instruction skipGetSurroundingImplementation)
        {
            _aroundInvokeProvider = aroundInvokeProvider;
            _invocationInfo = invocationInfo;
            _surroundingImplementation = surroundingImplementation;
            _skipGetSurroundingImplementation = skipGetSurroundingImplementation;
        }


        /// <summary>
        ///     Emits the instructions that obtain the current <see cref="IAroundInvoke" /> instance.
        /// </summary>
        /// <param name="IL"></param>
        public void Emit(ILProcessor IL)
        {
            var module = IL.Body.Method.DeclaringType.Module;

            IL.Emit(OpCodes.Ldloc, _aroundInvokeProvider);
            IL.Emit(OpCodes.Brfalse, _skipGetSurroundingImplementation);

            // var surroundingImplementation = this.GetSurroundingImplementation(this, invocationInfo);
            var getSurroundingImplementation =
                module.ImportMethod<IAroundInvokeProvider>("GetSurroundingImplementation");
            IL.Emit(OpCodes.Ldloc, _aroundInvokeProvider);
            IL.Emit(OpCodes.Ldloc, _invocationInfo);
            IL.Emit(OpCodes.Callvirt, getSurroundingImplementation);
            IL.Emit(OpCodes.Stloc, _surroundingImplementation);
        }
    }
}