TransactionRequestValidator.cs

using FluentValidation;
using FluentValidation.Results;
using Vanquis.Digital.Services.WebAPI.Requests;
using Microsoft.Extensions.Options;
using Vanquis.Digital.Services.WebAPI.Helper;

namespace Vanquis.Digital.Services.WebAPI.ModelValidators
{
    public class TransactionRequestValidator : AbstractValidator<TransactionsRequest>
    {
        public int MaxTransactionRangeInDays;

        public TransactionRequestValidator(IOptions<AppSettings> appSettings)
        {
            MaxTransactionRangeInDays = appSettings.Value.MaxTransactionRangeInDays;

            RuleFor(x => x.To).NotNull();
            RuleFor(x => x.From).NotNull();
            Custom(ValidDateRange);
        }

        public ValidationFailure ValidDateRange(TransactionsRequest request)
        {
            if (!request.To.HasValue || !request.From.HasValue) return null;

            if (request.To.Value < request.From.Value) return new ValidationFailure("To", "To should be greater then From.");        

            var exceedRequestRange = (request.To.Value - request.From.Value).Days > MaxTransactionRangeInDays;

            if (exceedRequestRange) return new ValidationFailure("To", $"Range requested exceeds limit. ({MaxTransactionRangeInDays} days)");
            
            return null;
        }
    }

    
}