using System.Globalization;
using System.Text.RegularExpressions;

namespace SQLInsight.Hub.Support;

/// <summary>Case numbers SUP-000001, SUP-000002 … running per customer.</summary>
public static partial class CaseNumbers
{
    public const string Prefix = "SUP-";

    /// <summary>
    /// The number after the highest SUP-&lt;digits&gt; among <paramref name="existing"/>. Other references (typed by hand,
    /// e.g. from an older system) are ignored, so they never block or reset the sequence.
    /// </summary>
    public static string Next(IEnumerable<string> existing)
    {
        ArgumentNullException.ThrowIfNull(existing);
        long highest = 0;
        foreach (var reference in existing)
        {
            var match = Number().Match(reference ?? string.Empty);
            if (match.Success && long.TryParse(match.Groups[1].Value, NumberStyles.None, CultureInfo.InvariantCulture, out var n) && n > highest)
            {
                highest = n;
            }
        }

        return Format(highest + 1);
    }

    public static string Format(long number) => Prefix + number.ToString("D6", CultureInfo.InvariantCulture);

    [GeneratedRegex(@"^\s*SUP-(\d{1,18})\s*$", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant)]
    private static partial Regex Number();
}