laatzen/LaaProductionWeb/LaaProduction.Personalization/ComponentModel.DataAnnotations/DateTimeAttribute.cs

namespace LaaProduction.Personalization.ComponentModel.DataAnnotations
{
    using System;
    using System.ComponentModel.DataAnnotations;
    using System.Reflection;

    public class DateTimeAttribute : ValidationAttribute
    {
        private readonly DateTimeOptions option;
        private readonly String otherProperty;

        public DateTimeAttribute(DateTimeOptions option, String otherProperty)
        {
            this.option = option;
            this.otherProperty = $"{otherProperty}";
        }

        protected override ValidationResult IsValid(Object value, ValidationContext validationContext)
        {
            var validationMessage = default(String);

            if (value is DateTime currentDate)
            {
                var property = validationContext
                    ?.ObjectType
                    ?.GetProperty(this.otherProperty, BindingFlags.Public | BindingFlags.Instance);

                if (property is null)
                {
                    validationMessage = $"The '{this.otherProperty}' is invalid.";
                }
                else
                {
                    var otherValue = property
                        .GetValue(validationContext?.ObjectInstance);
                    var otherDisplayName = property
                        .GetCustomAttribute<DisplayAttribute>()
                        ?.GetName() ?? this.otherProperty;

                    if (otherValue is DateTime otherDate)
                    {
                        if (this.option == DateTimeOptions.GreaterThan && currentDate <= otherDate)
                        {
                            validationMessage = $"The '{validationContext.DisplayName}' should be greater than '{otherDisplayName}'";
                        }
                        else if (this.option == DateTimeOptions.SmallerThan && currentDate >= otherDate)
                        {
                            validationMessage = $"The '{validationContext.DisplayName}' should be smaller than '{otherDisplayName}'";
                        }
                    }
                    else
                    {
                        validationMessage = $"The '{otherDisplayName}' is invalid.";
                    }
                }
            }
            else
            {
                validationMessage = $"The '{validationContext?.DisplayName}' is invalid.";
            }

            if (String.IsNullOrWhiteSpace(validationMessage))
            {
                return ValidationResult.Success;
            }

            return new ValidationResult(validationMessage);
        }
    }

    public enum DateTimeOptions
    {
        GreaterThan,
        SmallerThan,
    }
}