Newtonsoft.Json/Linq/JsonPath/PathFilter.cs

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using System.Collections.Generic;
using System.Globalization;
using Newtonsoft.Json.Utilities;

namespace Newtonsoft.Json.Linq.JsonPath
{
    internal abstract class PathFilter
    {
        public abstract IEnumerable<JToken> ExecuteFilter(IEnumerable<JToken> current, bool errorWhenNoMatch);

        protected static JToken GetTokenIndex(JToken t, bool errorWhenNoMatch, int index)
        {
            JArray a = t as JArray;
            JConstructor c = t as JConstructor;

            if (a != null)
            {
                if (a.Count <= index)
                {
                    if (errorWhenNoMatch)
                        throw new JsonException("Index {0} outside the bounds of JArray.".FormatWith(CultureInfo.InvariantCulture, index));

                    return null;
                }

                return a[index];
            }
            else if (c != null)
            {
                if (c.Count <= index)
                {
                    if (errorWhenNoMatch)
                        throw new JsonException("Index {0} outside the bounds of JConstructor.".FormatWith(CultureInfo.InvariantCulture, index));

                    return null;
                }

                return c[index];
            }
            else
            {
                if (errorWhenNoMatch)
                    throw new JsonException("Index {0} not valid on {1}.".FormatWith(CultureInfo.InvariantCulture, index, t.GetType().Name));

                return null;
            }
        }
    }
}