using HeuristicLab.Algorithms.PushGP.Stack;

namespace HeuristicLab.Algorithms.PushGP.Expressions
{
    public class ExecDoRangeExpression : Expression
    {
        public ExecDoRangeExpression() : base(OpCode.ExecDoXRange)
        { }

        public override void Eval(IInterpreterService interpreterService)
        {
            // not enough arguments on stack
            if (interpreterService.IntegerStack.Count < 2 ||
                interpreterService.ExecStack.Count == 0)
                return;

            var destinationIndex = interpreterService.IntegerStack.Pop();
            var currentIndex = interpreterService.IntegerStack.Pop();
            var loopBody = interpreterService.ExecStack.Pop();

            if (destinationIndex == currentIndex)
            {
                interpreterService.IntegerStack.Push(currentIndex);
                interpreterService.ExecStack.Push(loopBody);
            }
            else
            {
                var nextIndex = destinationIndex < currentIndex
                    ? currentIndex - 1
                    : currentIndex + 1;

                interpreterService.IntegerStack.Push(currentIndex);
                interpreterService.IntegerStack.Push(nextIndex);
                interpreterService.IntegerStack.Push(destinationIndex);

                var expression = new ExecDoRangeExpression();
                interpreterService.ExecStack.Push(loopBody);
                interpreterService.ExecStack.Push(loopBody);
                interpreterService.ExecStack.Push(expression);
            }
        }
    }
}