using CarCareTracker.Models;

namespace CarCareTracker.Helper
{
    public interface IGasHelper
    {
        List<GasRecordViewModel> GetGasRecordViewModels(List<GasRecord> result, bool useMPG, bool useUKMPG);
    }
    public class GasHelper : IGasHelper
    {
        public List<GasRecordViewModel> GetGasRecordViewModels(List<GasRecord> result, bool useMPG, bool useUKMPG)
        {
            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;
                    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 = currentObject.Cost / convertedConsumption,
                        IsFillToFull = currentObject.IsFillToFull,
                        MissedFuelUp = currentObject.MissedFuelUp
                    };
                    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)
                    {
                        //if user filled to full.
                        gasRecordViewModel.MilesPerGallon = useMPG ? (unFactoredMileage + deltaMileage) / (unFactoredConsumption + convertedConsumption) : 100 / ((unFactoredMileage + deltaMileage) / (unFactoredConsumption + convertedConsumption));
                        //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 = currentObject.Cost / convertedConsumption,
                        IsFillToFull = currentObject.IsFillToFull,
                        MissedFuelUp = currentObject.MissedFuelUp
                    });
                }
                previousMileage = currentObject.Mileage;
            }
            return computedResults;
        }
    }
}