using System.Text.RegularExpressions;

namespace PowderCoating.Web.Helpers;

/// <summary>
/// Parses payment terms strings (e.g., "Net 30", "2/10 Net 30", "Due on Receipt")
/// to compute due dates and extract early-payment discount terms.
/// </summary>
public static class PaymentTermsParser
{
    private static readonly Regex NetDaysRegex  = new(@"\bnet\s+(\d+)", RegexOptions.IgnoreCase | RegexOptions.Compiled);
    private static readonly Regex EarlyDiscountRegex = new(@"(\d+(?:\.\d+)?)/(\d+)\s+net", RegexOptions.IgnoreCase | RegexOptions.Compiled);

    /// <summary>
    /// Returns the due date calculated from <paramref name="invoiceDate"/> and the supplied terms.
    /// Returns null when the terms string cannot be parsed.
    /// </summary>
    public static DateTime? CalculateDueDate(string? terms, DateTime invoiceDate)
    {
        if (string.IsNullOrWhiteSpace(terms)) return null;

        var normalized = terms.Trim().ToLowerInvariant();
        if (Regex.IsMatch(normalized, @"\b(receipt|due\s*now|cod|immediate)\b"))
            return invoiceDate;

        var match = NetDaysRegex.Match(terms);
        if (match.Success && int.TryParse(match.Groups[1].Value, out var days))
            return invoiceDate.AddDays(days);

        return null;
    }

    /// <summary>
    /// Extracts early-payment discount terms from a string like "2/10 Net 30".
    /// Returns (percent: 2, days: 10) for that example, or (0, 0) if not present.
    /// </summary>
    public static (decimal Percent, int Days) ParseEarlyPaymentDiscount(string? terms)
    {
        if (string.IsNullOrWhiteSpace(terms)) return (0, 0);

        var match = EarlyDiscountRegex.Match(terms);
        if (match.Success
            && decimal.TryParse(match.Groups[1].Value, out var percent)
            && int.TryParse(match.Groups[2].Value, out var days))
            return (percent, days);

        return (0, 0);
    }
}