Services/FeedService.cs


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using Microsoft.EntityFrameworkCore;
using System.Data.Common;

namespace HyperBooru.Services;

public enum FeedOrder {
    Chronological,
    Rating
}

public interface IFeedService {
    public IEnumerable<Media> Feed { get; }

    public void InitializeFeed(
        FeedOrder order = FeedOrder.Chronological,
        bool descending = true,
        bool randomPosition = false);
}

public class FeedService : IFeedService {
    private FeedConfiguration? feedConfig;

    private IDbContextFactory<HBContext> dbFactory;

    public FeedService(IDbContextFactory<HBContext> dbFactory) =>
        this.dbFactory = dbFactory;

    public void InitializeFeed(
        FeedOrder order,
        bool descending,
        bool randomPosition) {

        feedConfig = new() {
            Order          = order,
            Descending     = descending,
            RandomPosition = randomPosition
        };
    }

    public IEnumerable<Media> Feed {
        get {
            if(feedConfig is null)
                throw new InvalidOperationException("Feed must be initialized first");

            while(true) {
                var db = dbFactory.CreateDbContext();

                IOrderedQueryable<Media> media;

                switch(feedConfig.Order) {
                    default:
                    case FeedOrder.Chronological:
                        if(feedConfig.Descending)
                            media = db.Media.OrderByDescending(m => m.ObjectId);
                        else
                            media = db.Media.OrderBy(m => m.ObjectId);
                        break;
                }

                Media[] mediaArray = media.Take(50).ToArray();

                db.Dispose();

                if(mediaArray.Count() == 0)
                    break;

                foreach(var m in mediaArray)
                    yield return m;
            }
        }
    }

    private record FeedConfiguration {
        public FeedOrder Order          { get; set; }
        public bool      Descending     { get; set; }
        public bool      RandomPosition { get; set; }
    }
}