WhenClause.cs

// Copyright (c) Avanade. Licensed under the MIT License. See https://github.com/Avanade/CoreEx

using System;

namespace CoreEx.Validation.Clauses
{
    /// <summary>
    /// Represents a when test clause; in that the condition must be <c>true</c> to continue.
    /// </summary>
    /// <typeparam name="TEntity">The entity <see cref="Type"/>.</typeparam>
    /// <typeparam name="TProperty">The property <see cref="Type"/>.</typeparam>
    public class WhenClause<TEntity, TProperty> : IPropertyRuleClause<TEntity, TProperty> where TEntity : class
    {
        private readonly Predicate<TEntity>? _entityPredicate;
        private readonly Predicate<TProperty>? _propertyPredicate;
        private readonly Func<bool>? _when;

        /// <summary>
        /// Initializes a new instance of the <see cref="WhenClause{TEntity, TProperty}"/> class with a <paramref name="predicate"/> being passed the <typeparamref name="TEntity"/>.
        /// </summary>
        /// <param name="predicate">The when predicate.</param>
        public WhenClause(Predicate<TEntity> predicate) => _entityPredicate = predicate.ThrowIfNull(nameof(predicate));

        /// <summary>
        /// Initializes a new instance of the <see cref="WhenClause{TEntity, TProperty}"/> class with a <paramref name="when"/> function.
        /// </summary>
        /// <param name="when">The when function.</param>
        public WhenClause(Func<bool> when) => _when = when.ThrowIfNull(nameof(when));

        /// <summary>
        /// Initializes a new instance of the <see cref="WhenClause{TEntity, TProperty}"/> class with a <paramref name="predicate"/> being passed the <typeparamref name="TProperty"/>.
        /// </summary>
        /// <param name="predicate">The when predicate.</param>
        public WhenClause(Predicate<TProperty> predicate) => _propertyPredicate = predicate.ThrowIfNull(nameof(predicate));

        /// <summary>
        /// Checks the clause.
        /// </summary>
        /// <param name="context">The <see cref="PropertyContext{TEntity, TProperty}"/>.</param>
        /// <returns><c>true</c> where validation is to continue; otherwise, <c>false</c> to stop.</returns>
        public bool Check(IPropertyContext context)
        {
            context.ThrowIfNull(nameof(context));

            return _when != null ? _when.Invoke()
                : _entityPredicate != null ? _entityPredicate.Invoke((TEntity)context.Parent.Value!)
                : _propertyPredicate!.Invoke((TProperty)context.Value!);
        }
    }
}