namespace Supermarket;

public abstract class Product
{
    public const char Separator = ';';

    public const string Invalid = "Invalid!";

    protected Product(string productName, string barcode, int quantity)
    {
        if (string.IsNullOrWhiteSpace(productName))
        {
            productName = Invalid;
        }
        ProductName = productName;
        Barcode = IsBarcodeValid(barcode) ? barcode : Invalid;
        Quantity = quantity > 0 ? quantity : 0;
    }

    public string ProductName { get; }

    public string Barcode { get; }

    public int Quantity { get; }
    
    protected virtual string[] CsvColumnNames => [nameof(Barcode), nameof(ProductName), nameof(Quantity)];
    
    protected virtual string[] CsvColumnValues => [Barcode, ProductName, Quantity.ToString()];
    
    public string GetCsvHeader()
    {
        string header = String.Empty;
        for (var i = 0; i < CsvColumnNames.Length; i++)
        {
            string columnName = CsvColumnNames[i];
            
            if(i == CsvColumnNames.Length - 1)
            {
                header += $"{columnName}";
                break;
            }
            header += $"{columnName}{Separator}";
        }

        return header;
    }
    
    public string ToCsv() => ToCsvLine(CsvColumnValues, Separator);

    protected static string ToCsvLine(string[] values, char separator)
    {
        string line = string.Empty;
        for (var i = 0; i < values.Length; i++)
        {
            string value = values[i];

            if (i == values.Length - 1)
            {
                line += $"{value}";
                break;
            }
            line += $"{value}{separator}";
        }

        return line;
    }
    
    public static bool IsBarcodeValid(string? barcode)
    {
        if (barcode == null)
        {
            return false;
        }
        
        if(barcode.Length is > 8 or < 8)
        {
            return false;
        }
        
        const int evenWeight = 3;
        const int oddWeight = 1;
        int weight = 0;

        for (int i = 0; i < barcode.Length; i++)
        {
            if (!char.IsDigit(barcode[i]))
            {
                return false;
            }

            // Skip check digit
            if (i == 7)
            {
                break;
            }

            int digit = int.Parse(barcode[i].ToString());
            weight += i % 2 == 0 ? digit * evenWeight : digit * oddWeight;
        }
        
        int calculatedCheckDigit = 10 - (weight % 10);
        if (calculatedCheckDigit == 10)
        {
            calculatedCheckDigit = 0;
        }
        
        return calculatedCheckDigit == int.Parse(barcode[^1].ToString());
    }
    
    protected static T[] AppendToArray<T>(T[] existingArray, params T[] newValues)
    {
        // we are allowed to use Lists, so why not? :)
        List<T> result = new(existingArray.Length + newValues.Length);
        result.AddRange(existingArray);
        result.AddRange(newValues);
        return result.ToArray();
    }
}