namespace Supermarket;

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

    public const string Invalid = "Invalid!";

    /// <summary>
    /// The constructor of Product
    /// </summary>
    /// <param name="productName">The product name</param>
    /// <param name="barcode">The bar code</param>
    /// <param name="quantity">The quantity</param>
    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;
    }

    /// <summary>
    /// The product name
    /// </summary>
    public string ProductName { get; }

    /// <summary>
    /// The bar code of the product
    /// </summary>
    public string Barcode { get; }

    /// <summary>
    /// The quantity of the product
    /// </summary>
    public int Quantity { get; }
    
    /// <summary>
    /// The CSV column names
    /// </summary>
    protected virtual string[] CsvColumnNames => [nameof(Barcode), nameof(ProductName), nameof(Quantity)];
    
    /// <summary>
    /// The CSV column values
    /// </summary>
    protected virtual string[] CsvColumnValues => [Barcode, ProductName, Quantity.ToString()];
    
    /// <summary>
    /// The CSV header
    /// </summary>
    /// <returns>The formatted CSV header</returns>
    public string GetCsvHeader() => string.Join(Separator, CsvColumnNames);

    /// <summary>
    /// The CSV line
    /// </summary>
    /// <returns>The formatted CSV line with values</returns>
    public string ToCsv() => ToCsvLine(CsvColumnValues, Separator);

    /// <summary>
    /// The CSV line generator
    /// </summary>
    /// <param name="values">The values</param>
    /// <param name="separator">The separator</param>
    /// <returns>The formatted CSV line</returns>
    protected static string ToCsvLine(string[] values, char separator) => String.Join(separator, values);

    /// <summary>
    /// Checks if the bar code is valid
    /// </summary>
    /// <param name="barcode">The bar code to check</param>
    /// <returns>True if the bar code is valid, false otherwise</returns>
    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());
    }
    
    /// <summary>
    /// Appends new values to an existing array
    /// </summary>
    /// <param name="existingArray">The array to append to</param>
    /// <param name="newValues">The array of values to append</param>
    /// <typeparam name="T">The type</typeparam>
    /// <returns>The complete array</returns>
    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();
    }
}