using System;
using System.Linq.Expressions;

namespace Abp.Specifications
{
    /// <summary>
    /// Represents the specification which indicates the semantics opposite to the given specification.
    /// </summary>
    /// <typeparam name="T">The type of the object to which the specification is applied.</typeparam>
    public class NotSpecification<T> : Specification<T>
    {
        private readonly ISpecification<T> _specification;

        /// <summary>
        /// Initializes a new instance of <see cref="NotSpecification{T}"/> class.
        /// </summary>
        /// <param name="specification">The specification to be reversed.</param>
        public NotSpecification(ISpecification<T> specification)
        {
            _specification = specification;
        }

        /// <summary>
        /// Gets the LINQ expression which represents the current specification.
        /// </summary>
        /// <returns>The LINQ expression.</returns>
        public override Expression<Func<T, bool>> ToExpression()
        {
            var expression = _specification.ToExpression();
            return Expression.Lambda<Func<T, bool>>(
                Expression.Not(expression.Body),
                expression.Parameters
            );
        }
    }
}