Musify/backend/Core/Musify.Application/Albums/GetAlbumsByUserId.cs

using ErrorOr;
using Mediator;
using Microsoft.EntityFrameworkCore;
using Musify.Application.Albums.Responses;
using Musify.Application.Contracts;
using Musify.Application.Shared;
using X.PagedList;
using X.PagedList.EF;

namespace Musify.Application.Albums
{
    public record GetAlbumsByUserIdQuery(long UserId, int PageNumber, int PageSize)
        : IQuery<ErrorOr<PaginatedResponse<AlbumApplicationResponse>>>;

    public class GetAlbumsByUserIdQueryHandler(IDatabase database)
        : IQueryHandler<GetAlbumsByUserIdQuery, ErrorOr<PaginatedResponse<AlbumApplicationResponse>>>
    {
        public async ValueTask<ErrorOr<PaginatedResponse<AlbumApplicationResponse>>> Handle(GetAlbumsByUserIdQuery request, CancellationToken cancellationToken)
        {
            var userExists = await database.Users
                .AsNoTracking()
                .AnyAsync(user => user.Id == request.UserId, cancellationToken);
            if (!userExists)
                return Error.NotFound(description: $"User {request.UserId} not found");

            var albumsQuery = database.Albums
                .AsNoTracking()
                .Where(album => album.OwnerUserId == request.UserId);

            var totalCount = await albumsQuery.CountAsync(cancellationToken);

            var pagedEntities = await albumsQuery
                .OrderByDescending(album => album.CreatedAt)
                .Select(album => new
                {
                    Album = album,
                    TrackCount = album.AlbumTracks.Count,
                    CoverTrackIds = album.AlbumTracks
                        .OrderBy(albumTrack => albumTrack.TrackNumber)
                        .Take(AlbumApplicationResponse.CoverTrackCount)
                        .Select(albumTrack => albumTrack.TrackId)
                        .ToList()
                })
                .ToPagedListAsync(request.PageNumber, request.PageSize, totalCount, cancellationToken);

            var pagedAlbums = new StaticPagedList<AlbumApplicationResponse>(
                pagedEntities.Select(entry => AlbumApplicationResponse.FromEntity(entry.Album, entry.TrackCount, entry.CoverTrackIds)),
                pagedEntities.PageNumber, pagedEntities.PageSize, pagedEntities.TotalItemCount);

            return PaginatedResponse<AlbumApplicationResponse>.FromPagedList(pagedAlbums);
        }
    }
}