using Mediator;
using Microsoft.EntityFrameworkCore;
using Musify.Application.Contracts;
using Musify.Domain.ValueObjects;

namespace Musify.Application.Genres
{
    public record GetGenresQuery : IQuery<IReadOnlyList<GenreResponse>>;

    public record GenreResponse(Genre Genre, int TrackCount);

    public class GetGenresQueryHandler(IDatabase database)
        : IQueryHandler<GetGenresQuery, IReadOnlyList<GenreResponse>>
    {
        public async ValueTask<IReadOnlyList<GenreResponse>> Handle(GetGenresQuery request, CancellationToken cancellationToken)
        {
            var rows = await database.TrackTags
                .AsNoTracking()
                .Where(tag => database.UserHasTracks.Any(userTrack => userTrack.TrackId == tag.TrackId))
                .GroupBy(tag => tag.Tag)
                .Select(group => new { Genre = group.Key, TrackCount = group.Select(tag => tag.TrackId).Distinct().Count() })
                .ToListAsync(cancellationToken);

            return rows
                .OrderByDescending(row => row.TrackCount)
                .ThenBy(row => row.Genre)
                .Select(row => new GenreResponse(row.Genre, row.TrackCount))
                .ToList();
        }
    }
}