using Convention.RScript.Parser;
using System.Diagnostics.CodeAnalysis;

namespace Convention.RScript.Runner
{
    public class BackpointRunner : JumpRuntimePointerRunner
    {
        public override void Compile(ExpressionParser parser, RScriptSentence sentence, RScriptContext context)
        {

        }

        [return: MaybeNull]
        public override object Run(ExpressionParser parser, RScriptSentence sentence, RScriptContext context)
        {
            // 检查并跳转到上次跳转的位置
            if (parser.Evaluate<bool>(sentence.content))
            {
                if (context.GotoPointerStack.Count == 0)
                {
                    throw new RScriptRuntimeException($"No position to back.", context.CurrentRuntimePointer);
                }
                else
                {
                    DoJumpRuntimePointer(parser, context.GotoPointerStack.Pop(), context);
                }
            }
            return null;
        }
    }
}