namespace Deltares.Standard.Specifications
{
    /// <summary>
    /// With this class a value of an object bound to a property can be tested against the specification.
    /// This is a variant of the ParameterizedSpecification
    /// </summary>
    /// <typeparam name="TCandidate">The candidate type</typeparam>
    /// <typeparam name="TValue">The candidate property type</typeparam>
    public abstract class ValueBoundSpecification<TCandidate, TValue> : SpecificationBase<TCandidate>
    {
        private readonly string attributeName;
        private readonly TValue attributeValue;
        private TValue candidateValue;

        protected ValueBoundSpecification(string attributeName, TValue attributeValue)
        {
            this.attributeName = attributeName;
            this.attributeValue = attributeValue;
        }

        /// <summary>
        /// Gets the attribute value.
        /// </summary>
        public TValue AttributeValue
        {
            get { return attributeValue; }
        }

        /// <summary>
        /// Gets the candidate value.
        /// </summary>
        public TValue CandidateValue
        {
            get { return candidateValue; }
        }

        /// <summary>
        /// Gets the candidate string value.
        /// </summary>
        /// <param name="candidate">The candidate.</param>
        /// <returns></returns>
        protected string GetCandidateStringValue(TCandidate candidate)
        {
            return GetCandidateObjectValue(candidate).ToString();
        }

        /// <summary>
        /// Gets the candidate T value.
        /// </summary>
        /// <param name="candidate">The candidate.</param>
        /// <returns></returns>
        protected TValue GetCandidateTValue(TCandidate candidate)
        {
            if (candidateValue.Equals(default(TValue)))
                candidateValue = (TValue) GetCandidateObjectValue(candidate);

            return candidateValue;
        }

        /// <summary>
        /// Gets the candidate object value.
        /// </summary>
        /// <param name="candidate">The candidate.</param>
        /// <returns></returns>
        private object GetCandidateObjectValue(TCandidate candidate)
        {
            return candidate.GetType().GetProperty(attributeName).GetValue(candidate, null);
        }
    }
}