Musify/backend/Core/Musify.Application/Users/GetUserProfile.cs

using System.Text.Json.Serialization;
using ErrorOr;
using Mediator;
using Microsoft.EntityFrameworkCore;
using Musify.Application.Contracts;
using Musify.Application.Serialization;

namespace Musify.Application.Users
{
    public record GetUserProfileQuery(long UserId, long? ViewerId = null) : IQuery<ErrorOr<UserProfileResponse>>;

    public record UserProfileResponse(
        [property: JsonConverter(typeof(LongAsStringConverter))] long Id,
        string Name,
        string? FirstName,
        string? SecondName,
        string? ProfilePictureUrl,
        DateTime CreatedAt,
        int FollowersCount,
        int FollowingCount,
        bool IsFollowing,
        bool CanViewFollowers);

    public class GetUserProfileQueryHandler(IDatabase database)
        : IQueryHandler<GetUserProfileQuery, ErrorOr<UserProfileResponse>>
    {
        public async ValueTask<ErrorOr<UserProfileResponse>> Handle(GetUserProfileQuery request, CancellationToken cancellationToken)
        {
            var user = await database.Users
                .AsNoTracking()
                .Where(u => u.Id == request.UserId)
                .Select(u => new
                {
                    u.Id,
                    u.Name,
                    u.FirstName,
                    u.SecondName,
                    u.ProfilePictureUrl,
                    u.CreatedAt
                })
                .SingleOrDefaultAsync(cancellationToken);

            if (user == null)
                return Error.NotFound();

            var followersCount = await database.UserFollows
                .AsNoTracking()
                .CountAsync(f => f.FollowedId == request.UserId, cancellationToken);

            var followingCount = await database.UserFollows
                .AsNoTracking()
                .CountAsync(f => f.FollowerId == request.UserId, cancellationToken);

            var isFollowing = request.ViewerId is { } viewerId && viewerId != request.UserId &&
                await database.UserFollows
                    .AsNoTracking()
                    .AnyAsync(f => f.FollowerId == viewerId && f.FollowedId == request.UserId, cancellationToken);

            var canViewFollowers = await FollowVisibility.CanViewFollowersAsync(
                database, request.ViewerId, request.UserId, cancellationToken);

            return new UserProfileResponse(
                user.Id,
                user.Name,
                user.FirstName,
                user.SecondName,
                user.ProfilePictureUrl,
                user.CreatedAt,
                followersCount,
                followingCount,
                isFollowing,
                canViewFollowers);
        }
    }
}