using Microsoft.EntityFrameworkCore;
using TeamUp.Modules.Assembler.Domain;
using TeamUp.Modules.Assembler.Persistence;

namespace TeamUp.Modules.Assembler.Queue;

/// <summary>The Postgres-backed agent-run queue. Enqueue inserts; claim uses FOR UPDATE SKIP LOCKED
/// so multiple workers can drain concurrently without contention.</summary>
internal sealed class JobQueue(AssemblerDbContext db, TimeProvider clock)
{
    public async Task<Job> EnqueueAsync(string type, string payload, CancellationToken cancellationToken = default)
    {
        var job = new Job(type, payload, clock.GetUtcNow());
        db.Jobs.Add(job);
        await db.SaveChangesAsync(cancellationToken);
        return job;
    }

    public async Task<Job?> ClaimNextAsync(string worker, CancellationToken cancellationToken = default)
    {
        await using var transaction = await db.Database.BeginTransactionAsync(cancellationToken);

        var job = await db.Jobs
            .FromSqlRaw(
                "SELECT * FROM assembler.jobs WHERE \"Status\" = 'Pending' " +
                "ORDER BY \"CreatedAtUtc\" LIMIT 1 FOR UPDATE SKIP LOCKED")
            .FirstOrDefaultAsync(cancellationToken);

        if (job is null)
        {
            await transaction.RollbackAsync(cancellationToken);
            return null;
        }

        job.MarkProcessing(worker, clock.GetUtcNow());
        await db.SaveChangesAsync(cancellationToken);
        await transaction.CommitAsync(cancellationToken);
        return job;
    }
}