proposal-system/api/src/ProposalSystem.Infrastructure/Services/ProposalNumberGenerator.cs

using Microsoft.EntityFrameworkCore;
using ProposalSystem.Application.Interfaces;
using ProposalSystem.Infrastructure.Data;

namespace ProposalSystem.Infrastructure.Services;

public class ProposalNumberGenerator : IProposalNumberGenerator
{
    private readonly ProposalDbContext _db;

    public ProposalNumberGenerator(ProposalDbContext db)
    {
        _db = db;
    }

    public async Task<string> GenerateAsync(CancellationToken ct = default)
    {
        var year = DateTime.UtcNow.Year;
        var prefix = $"SHI-{year}-";

        // Advisory lock prevents concurrent number generation within the same transaction
        await _db.Database.ExecuteSqlRawAsync(
            "SELECT pg_advisory_xact_lock(hashtext('proposal_number_gen'))", ct);

        var lastNumber = await _db.Proposals
            .Where(p => p.ProposalNumber.StartsWith(prefix))
            .Where(p => !p.ProposalNumber.Contains("-R"))
            .OrderByDescending(p => p.ProposalNumber)
            .Select(p => p.ProposalNumber)
            .FirstOrDefaultAsync(ct);

        int nextSequence = 1;
        if (lastNumber != null)
        {
            var sequencePart = lastNumber[prefix.Length..];
            if (int.TryParse(sequencePart, out var current))
            {
                nextSequence = current + 1;
            }
        }

        return $"{prefix}{nextSequence:D4}";
    }
}