using System;
using System.Threading.Tasks;
using Compliance.DTOs;
using Compliance.Domain.Models;

namespace Compliance.Services.ValidationRules
{
    public class ReadingPeriodValidationRule : IValidationRule
    {
        private const string RULE_NAME = "Reading Period Validation";
        private const int MIN_READING_DAYS = 27;
        private const int MAX_READING_DAYS = 33;
        private const string PERIOD_ERROR_FORMAT = 
            "Reading period of {0} days is outside allowed range ({1}-{2} days)";

        public int Priority => 1;

        public Task<ValidationResult> ValidateAsync(
            BillComplianceRequest request,
            DistributorInformation distributorInfo,
            Client clientInfo)
        {
            var readingPeriod = CalculateReadingPeriod(request);
            var isValid = IsValidReadingPeriod(readingPeriod);
            
            return Task.FromResult(isValid 
                ? ValidationResult.Success(RULE_NAME)
                : ValidationResult.Failure(RULE_NAME, 
                    FormatErrorMessage(readingPeriod)));
        }

        private static int CalculateReadingPeriod(BillComplianceRequest request) =>
            (request.CurrentReadingDate - request.PreviousReadingDate).Days;

        private static bool IsValidReadingPeriod(int days) =>
            days >= MIN_READING_DAYS && days <= MAX_READING_DAYS;

        private static string FormatErrorMessage(int days) =>
            string.Format(PERIOD_ERROR_FORMAT, days, MIN_READING_DAYS, MAX_READING_DAYS);
    }
}