using Microsoft.EntityFrameworkCore;


/// <summary>
/// Provides filtered, sorted work queue views for each workflow stage.
/// All queues sort by UpdatedAt ASC to enforce FIFO processing — the oldest
/// pending item is always at the top of the queue.
/// </summary>
public class WorkQueueService : IWorkQueueService
{
    private readonly AppDbContext _db;

    public WorkQueueService(AppDbContext db)
    {
        _db = db;
    }

    public async Task<WorkQueueResponse> GetVerificationQueueAsync(int page, int pageSize)
    {
        var query = _db.DigitizationBatches
            .Where(b => b.Status == BatchStatus.PendingVerification)
            .OrderBy(b => b.UpdatedAt);

        return await BuildQueueResponseAsync("verification", query, page, pageSize);
    }

    public async Task<WorkQueueResponse> GetEntryQueueAsync(int page, int pageSize)
    {
        var entryStatuses = new[]
        {
            BatchStatus.Uploaded,
            BatchStatus.InEntry,
            BatchStatus.Rejected
        };

        var query = _db.DigitizationBatches
            .Where(b => entryStatuses.Contains(b.Status))
            .OrderBy(b => b.UpdatedAt);

        return await BuildQueueResponseAsync("entry", query, page, pageSize);
    }

    public async Task<WorkQueueResponse> GetClinicalApprovalQueueAsync(int page, int pageSize)
    {
        var query = _db.DigitizationBatches
            .Where(b => b.Status == BatchStatus.AwaitingClinicalApproval)
            .OrderBy(b => b.UpdatedAt);

        return await BuildQueueResponseAsync("clinical-approval", query, page, pageSize);
    }

    private async Task<WorkQueueResponse> BuildQueueResponseAsync(
        string queueName,
        IOrderedQueryable<DigitizationBatch> query,
        int page,
        int pageSize)
    {
        var totalCount = await query.CountAsync();
        var totalPages = (int)Math.Ceiling((double)totalCount / pageSize);

        var items = await query
            .Include(b => b.EnteredByUser)
            .Include(b => b.Events)
            .Skip((page - 1) * pageSize)
            .Take(pageSize)
            .Select(b => new WorkQueueItemResponse(
                b.Id,
                b.Status.ToDbString(),
                b.BatchType.ToDbString(),
                b.Track.ToDbString(),
                b.PatientId,
                b.EnteredByUserId,
                b.EnteredByUser != null ? b.EnteredByUser.FullName : null,
                b.RejectionReason,
                b.CreatedAt,
                b.UpdatedAt,
                b.Events.Count
            ))
            .ToListAsync();

        return new WorkQueueResponse(queueName, items, page, pageSize, totalCount, totalPages);
    }
}