ClaudeDo/src/ClaudeDo.Worker/Queue/QueuePicker.cs

using ClaudeDo.Data;
using ClaudeDo.Data.Models;
using Microsoft.EntityFrameworkCore;

namespace ClaudeDo.Worker.Queue;

public sealed class QueuePicker : IQueuePicker
{
    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;

    public QueuePicker(IDbContextFactory<ClaudeDoDbContext> dbFactory)
        => _dbFactory = dbFactory;

    public async Task<TaskEntity?> ClaimNextAsync(DateTime now, CancellationToken ct)
    {
        // Atomic queue claim: UPDATE + RETURNING in a single statement prevents TOCTOU races.
        // Raw SQL because EF cannot express UPDATE...RETURNING.
        // Eligible task must be Queued, unblocked, and due (or unscheduled).
        // EF SQLite stores DateTime as "yyyy-MM-dd HH:mm:ss.fffffff" — same format used here for comparison.
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var nowStr = now.ToUniversalTime().ToString("yyyy-MM-dd HH:mm:ss.fffffff");
        var startedAtStr = DateTime.UtcNow.ToString("yyyy-MM-dd HH:mm:ss.fffffff");

        var rows = await ctx.Tasks.FromSqlRaw("""
            UPDATE tasks SET status = 'running', started_at = {1}
            WHERE id = (
                SELECT t.id FROM tasks t
                WHERE t.status = 'queued'
                  AND t.blocked_by_task_id IS NULL
                  AND (t.scheduled_for IS NULL OR t.scheduled_for <= {0})
                ORDER BY t.sort_order ASC, t.created_at ASC
                LIMIT 1
            )
            RETURNING *
            """, nowStr, startedAtStr).ToListAsync(ct);

        return rows.FirstOrDefault();
    }
}