using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace QuantEngine.Infrastructure.Data
{
    /// <summary>
    /// Orders DbUp migration scripts by their numeric V{n} version instead of plain ordinal
    /// string order. Without this, "V10__Name.sql" sorts before "V2__Name.sql" (and, as
    /// happened on 2026-07-24, zero-padded "V003_Name.sql" sorts before unpadded
    /// "V1__Name.sql") because ordinal comparison looks at characters, not numeric value.
    /// That mismatch let a migration with an unmet table dependency run first and silently
    /// no-op, and another one run first and hard-fail, blocking every migration after it on a
    /// fresh database. This comparer makes the "V{n}" scheme collision-proof regardless of
    /// digit count or padding, so it can never happen again.
    /// </summary>
    public class MigrationScriptNameComparer : IComparer<string>
    {
        private static readonly Regex VersionPattern = new(@"V(\d+)", RegexOptions.Compiled);

        public int Compare(string? x, string? y)
        {
            if (x == null || y == null)
            {
                return string.CompareOrdinal(x, y);
            }

            var matchX = VersionPattern.Match(x);
            var matchY = VersionPattern.Match(y);

            if (matchX.Success && matchY.Success)
            {
                var versionX = long.Parse(matchX.Groups[1].Value);
                var versionY = long.Parse(matchY.Groups[1].Value);
                if (versionX != versionY)
                {
                    return versionX.CompareTo(versionY);
                }
            }

            return string.CompareOrdinal(x, y);
        }
    }
}