using CarCareTracker.Models;

namespace CarCareTracker.Helper
{
    public interface IGasHelper
    {
        List<GasRecordViewModel> GetGasRecordViewModels(List<GasRecord> result, bool useMPG, bool useUKMPG);
        string GetAverageGasMileage(List<GasRecordViewModel> results, bool useMPG);
    }
    public class GasHelper : IGasHelper
    {
        public string GetAverageGasMileage(List<GasRecordViewModel> results, bool useMPG)
        {
            var recordsToCalculate = results.Where(x => x.IncludeInAverage);
            if (recordsToCalculate.Any())
            {
                try
                {
                    var totalMileage = recordsToCalculate.Sum(x => x.DeltaMileage);
                    var totalGallons = recordsToCalculate.Sum(x => x.Gallons);
                    var averageGasMileage = totalMileage / totalGallons;
                    if (!useMPG && averageGasMileage > 0)
                    {
                        averageGasMileage = 100 / averageGasMileage;
                    }
                    return averageGasMileage.ToString("F");
                } catch (Exception ex)
                {
                    return "0";
                }
            }
            return "0";
        }
        public List<GasRecordViewModel> GetGasRecordViewModels(List<GasRecord> result, bool useMPG, bool useUKMPG)
        {
            //need to order by to get correct results
            result = result.OrderBy(x => x.Date).ThenBy(x => x.Mileage).ToList();
            var computedResults = new List<GasRecordViewModel>();
            int previousMileage = 0;
            decimal unFactoredConsumption = 0.00M;
            int unFactoredMileage = 0;
            //perform computation.
            for (int i = 0; i < result.Count; i++)
            {
                var currentObject = result[i];
                decimal convertedConsumption;
                if (useUKMPG && useMPG)
                {
                    //if we're using UK MPG and the user wants imperial calculation insteace of l/100km
                    //if UK MPG is selected then the gas consumption are stored in liters but need to convert into UK gallons for computation.
                    convertedConsumption = currentObject.Gallons / 4.546M;
                }
                else
                {
                    convertedConsumption = currentObject.Gallons;
                }
                if (i > 0)
                {
                    var deltaMileage = currentObject.Mileage - previousMileage;
                    if (deltaMileage < 0)
                    {
                        deltaMileage = 0;
                    }
                    var gasRecordViewModel = new GasRecordViewModel()
                    {
                        Id = currentObject.Id,
                        VehicleId = currentObject.VehicleId,
                        MonthId = currentObject.Date.Month,
                        Date = currentObject.Date.ToShortDateString(),
                        Mileage = currentObject.Mileage,
                        Gallons = convertedConsumption,
                        Cost = currentObject.Cost,
                        DeltaMileage = deltaMileage,
                        CostPerGallon = convertedConsumption > 0.00M ? currentObject.Cost / convertedConsumption : 0,
                        IsFillToFull = currentObject.IsFillToFull,
                        MissedFuelUp = currentObject.MissedFuelUp,
                        Notes = currentObject.Notes,
                        Tags = currentObject.Tags,
                        ExtraFields = currentObject.ExtraFields,
                        Files = currentObject.Files
                    };
                    if (currentObject.MissedFuelUp)
                    {
                        //if they missed a fuel up, we skip MPG calculation.
                        gasRecordViewModel.MilesPerGallon = 0;
                        //reset unFactored vars for missed fuel up because the numbers wont be reliable.
                        unFactoredConsumption = 0;
                        unFactoredMileage = 0;
                    }
                    else if (currentObject.IsFillToFull && currentObject.Mileage != default)
                    {
                        //if user filled to full and an odometer is provided, otherwise we will defer calculations
                        if (convertedConsumption > 0.00M && deltaMileage > 0)
                        {
                            try
                            {
                                gasRecordViewModel.MilesPerGallon = useMPG ? (unFactoredMileage + deltaMileage) / (unFactoredConsumption + convertedConsumption) : 100 / ((unFactoredMileage + deltaMileage) / (unFactoredConsumption + convertedConsumption));
                            }
                            catch (Exception ex)
                            {
                                gasRecordViewModel.MilesPerGallon = 0;
                            }
                        }
                        //reset unFactored vars
                        unFactoredConsumption = 0;
                        unFactoredMileage = 0;
                    }
                    else
                    {
                        unFactoredConsumption += convertedConsumption;
                        unFactoredMileage += deltaMileage;
                        gasRecordViewModel.MilesPerGallon = 0;
                    }
                    computedResults.Add(gasRecordViewModel);
                }
                else
                {
                    computedResults.Add(new GasRecordViewModel()
                    {
                        Id = currentObject.Id,
                        VehicleId = currentObject.VehicleId,
                        MonthId = currentObject.Date.Month,
                        Date = currentObject.Date.ToShortDateString(),
                        Mileage = currentObject.Mileage,
                        Gallons = convertedConsumption,
                        Cost = currentObject.Cost,
                        DeltaMileage = 0,
                        MilesPerGallon = 0,
                        CostPerGallon = convertedConsumption > 0.00M ? currentObject.Cost / convertedConsumption : 0,
                        IsFillToFull = currentObject.IsFillToFull,
                        MissedFuelUp = currentObject.MissedFuelUp,
                        Notes = currentObject.Notes,
                        Tags = currentObject.Tags,
                        ExtraFields = currentObject.ExtraFields,
                        Files = currentObject.Files
                    });
                }
                if (currentObject.Mileage != default)
                {
                    previousMileage = currentObject.Mileage;
                }
            }
            return computedResults;
        }
    }
}