UTB.Eshop_2021/UTB.Eshop.Web/Models/Validations/FileContentValidationAttribute.cs

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Threading.Tasks;

namespace UTB.Eshop.Web.Models.Validations
{
    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter)]
    public class FileContentValidationAttribute : ValidationAttribute, IClientModelValidator
    {
        public string ContentType { get; set; }
        public FileContentValidationAttribute(string contentType)
        {
            ContentType = contentType;
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (value == null)
            {
                return ValidationResult.Success;
            }
            else if(value is IFormFile formFile)
            {
                if (formFile.ContentType.ToLower().Contains(this.ContentType.ToLower()))
                {
                    return ValidationResult.Success;
                }
                else
                {
                    return new ValidationResult($"Content of the file ({validationContext.MemberName}) is not {ContentType}.");
                }
            }

            throw new NotImplementedException($"The attribute {nameof(FileContentValidationAttribute)} is not implemented for this type of object: {value.GetType()}");
        }

        public void AddValidation(ClientModelValidationContext context)
        {
            context.Attributes.Add("data-val", "true");
            context.Attributes.Add("data-val-filecontent", $"Content of the file is not {ContentType}.");
            context.Attributes.Add("data-val-filecontent-type", ContentType.ToLower());
        }
    }
}