using System;
using System.Threading.Tasks;
using System.Text;
using Compliance.Domain.Models;
using Compliance.DTOs;
using Compliance.Infrastructure.Repositories;

namespace Compliance.Services.ValidationRules
{
    public class FlagTariffValidationRule(IDistributorRepository distributorRepository) : IValidationRule
    {
        private readonly IDistributorRepository _distributorRepository = distributorRepository;
        private const string RULE_NAME = "Flag Tariff Validation";
        private const string FLAG_ERROR = "Flag tariff amount doesn't match the expected value for the current flag color";
        private const string EXEMPT_ERROR = "Flag tariff charged to exempt consumer";
        private const string COLOR_ERROR = "Invalid flag color applied";
        private const decimal TOLERANCE = 0.01m;
        private const decimal KWH_BLOCK = 100m;  // Flag tariff is applied per 100 kWh
        public int Priority => 4;  // Run after tariff component validation

        public async Task<ValidationResult> ValidateAsync(
            BillComplianceRequest request,
            DistributorInformation distributorInfo,
            Client clientInfo)
        {
            var flagInfo = await _distributorRepository.GetFlagTariffInformationAsync(
                request.DistributorName,
                request.Month) ?? throw new InvalidOperationException("Flag tariff information not found");

            var isValid = true;
            var message = new StringBuilder();

            // Check if consumer is exempt
            if (flagInfo.ExemptGroups.Contains(request.ConsumerGroup.ToLower()))
            {
                if (request.FlagAmount != 0)
                {
                    isValid = false;
                    message.AppendLine(EXEMPT_ERROR);
                }
                return new ValidationResult
                {
                    IsValid = isValid,
                    RuleName = RULE_NAME,
                    Message = message.ToString().TrimEnd()
                };
            }

            // Validate flag color
            if (!IsValidFlagColor(request.AppliedFlag))
            {
                isValid = false;
                message.AppendLine($"{COLOR_ERROR}. Found: {request.AppliedFlag}");
            }

            // Calculate expected flag amount
            var expectedFlagAmount = CalculateFlagAmount(
                request.ConsumptionAmount,
                flagInfo.FlagColor,
                flagInfo.FlagValue,
                request.BillingDays,
                flagInfo.ApplyPartialMonth,
                flagInfo.ValidFromDay);

            if (Math.Abs(request.FlagAmount - expectedFlagAmount) > TOLERANCE)
            {
                isValid = false;
                message.AppendLine($"{FLAG_ERROR}. Expected: {expectedFlagAmount:F2}, Found: {request.FlagAmount:F2}");
            }

            return new ValidationResult
            {
                IsValid = isValid,
                RuleName = RULE_NAME,
                Message = message.ToString().TrimEnd()
            };
        }

        private static bool IsValidFlagColor(string flagColor)
        {
            return flagColor.ToUpper() switch
            {
                "GREEN" => true,
                "YELLOW" => true,
                "RED1" => true,
                "RED2" => true,
                _ => false
            };
        }

        private static decimal CalculateFlagAmount(
            decimal consumption,
            string flagColor,
            decimal flagValue,
            int billingDays,
            bool applyPartialMonth,
            int validFromDay)
        {
            if (flagColor.Equals("GREEN", StringComparison.CurrentCultureIgnoreCase)) return 0;

            // Calculate number of 100 kWh blocks
            var blocks = Math.Ceiling(consumption / KWH_BLOCK);

            // If partial month application is enabled, prorate the flag value
            if (applyPartialMonth)
            {
                var applicableDays = billingDays - (validFromDay - 1);
                if (applicableDays < billingDays)
                {
                    return blocks * flagValue * (applicableDays / (decimal)billingDays);
                }
            }

            return blocks * flagValue;
        }
    }
}