// 
// Copyright (c) 2004-2021 Jaroslaw Kowalski <jaak@jkowalski.net>, Kim Christensen, Julian Verdurmen
// 
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without 
// modification, are permitted provided that the following conditions 
// are met:
// 
// * Redistributions of source code must retain the above copyright notice, 
//   this list of conditions and the following disclaimer. 
// 
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution. 
// 
// * Neither the name of Jaroslaw Kowalski nor the names of its 
//   contributors may be used to endorse or promote products derived from this
//   software without specific prior written permission. 
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// THE POSSIBILITY OF SUCH DAMAGE.
// 

namespace NLog.Conditions
{
    using System;
    using NLog.Common;
    using NLog.Config;
    using NLog.Internal;

    /// <summary>
    /// Base class for representing nodes in condition expression trees.
    /// </summary>
    [NLogConfigurationItem]
    public abstract class ConditionExpression
    {
        internal static readonly object BoxedTrue = true;
        internal static readonly object BoxedFalse = false;

        /// <summary>
        /// Converts condition text to a condition expression tree.
        /// </summary>
        /// <param name="conditionExpressionText">Condition text to be converted.</param>
        /// <returns>Condition expression tree.</returns>
        public static implicit operator ConditionExpression(string conditionExpressionText)
        {
            return ConditionParser.ParseExpression(conditionExpressionText);
        }

        /// <summary>
        /// Evaluates the expression.
        /// </summary>
        /// <param name="context">Evaluation context.</param>
        /// <returns>Expression result.</returns>
        public object Evaluate(LogEventInfo context)
        {
            try
            {
                return EvaluateNode(context);
            }
            catch (Exception exception)
            {
                InternalLogger.Warn(exception, "Exception occurred when evaluating condition");

                if (exception.MustBeRethrownImmediately())
                {
                    throw;
                }

                throw new ConditionEvaluationException("Exception occurred when evaluating condition", exception);
            }
        }

        /// <summary>
        /// Returns a string representation of the expression.
        /// </summary>
        /// <returns>
        /// A <see cref="T:System.String"/> that represents the condition expression.
        /// </returns>
        public abstract override string ToString();

        /// <summary>
        /// Evaluates the expression.
        /// </summary>
        /// <param name="context">Evaluation context.</param>
        /// <returns>Expression result.</returns>
        protected abstract object EvaluateNode(LogEventInfo context);
    }
}
