/// <summary>

/// Ensures that the provided input string is formatted as currency based on the specified culture.

/// If the input is already in a valid currency format, it is returned unchanged. Otherwise, the string is parsed 

/// as a decimal and formatted according to the specified culture's currency format.

/// </summary>

/// <param name="input">The input string representing a monetary value to be formatted.</param>

/// <param name="culture">The culture code used to format the currency. Defaults to "en" for English if not provided.</param>

/// <returns>

/// A string formatted as currency according to the specified culture. If the input cannot be parsed as a decimal, 

/// the original input is returned unchanged.

/// </returns>

/// <example>

/// <code>

/// string formattedCurrency = EnsureCurrencyFormat("1234.56", "en-US");

/// Console.WriteLine(formattedCurrency); // Output: "$1,234.56"

/// </code>

/// </example>

internal static string EnsureCurrencyFormat(string input, string culture = "en")

{

    if (!string.IsNullOrEmpty(culture))

        culture = "en";

    var cultureName = CultureInfo.GetCultures(CultureTypes.AllCultures).First(i => i.Name == culture);

    // Check if the input is already in a valid currency format

    if (IsCurrency(input))

    {

        return input; // Return as-is if it's already in currency format

    }

​

    // Try to parse the string as a decimal and format it as currency

    if (!decimal.TryParse(input, out var amount)) return input; // Return original if it can't be parsed

    var decimalLength = "C0";

    if (!input.Contains("."))

        return amount.ToString(decimalLength,

            cultureName); // Format as currency with two decimals

    var parts = input.Split('.');

    // If there's a decimal point and something after it, return the length of the part after the decimal point

    if (parts.Length > 1)

    {

        decimalLength = "C" + parts[1].Length;

    }

​

    return amount.ToString(decimalLength, cultureName); // Format as currency with two decimals

}

​

/// <summary>

/// Determines whether the given input string is in a valid currency format.

/// The method uses a regular expression to check if the input matches a pattern similar to "$100.00" or "€100.00".

/// </summary>

/// <param name="input">The string to check for currency format.</param>

/// <returns>

/// Returns <c>true</c> if the input string matches a valid currency format (e.g., "$100.00"), 

/// otherwise returns <c>false</c>.

/// </returns>

/// <example>

/// <code>

/// bool isCurrency = IsCurrency("$100.00");

/// Console.WriteLine(isCurrency); // Output: True

/// </code>

/// </example>

private static bool IsCurrency(string input)

{

    // Regular expression to check if string matches a currency format like "$100.00"

    const string pattern = @"^[\p{Sc}]\d+(\.\d{1,2})?$";

    return Regex.IsMatch(input, pattern);

}

​

​