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using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Query;
namespace HyperBooru.Services;
public enum FeedSortOrder {
Ascending,
Descending
}
public enum FeedSortType {
Chronological,
Rating
}
public record FeedOptions {
public FeedSortType SortType { get; set; }
public FeedSortOrder SortOrder { get; set; }
public bool RandomPosition { get; set; }
public Func<IQueryable<Media>, IQueryable<Media>>? IncludeProperties { get; set; }
}
public interface IFeedService {
public IEnumerable<Media> Feed { get; }
public void InitializeFeed(FeedOptions feedOptions);
public Media[] Next(int count);
}
public class FeedService : IFeedService {
private const int FeedChunkSize = 50;
private FeedOptions? feedOptions;
private Media? last;
private IDbContextFactory<HBContext> dbFactory;
public FeedService(IDbContextFactory<HBContext> dbFactory) =>
this.dbFactory = dbFactory;
public void InitializeFeed(FeedOptions feedOptions) {
this.feedOptions = feedOptions;
last = null;
}
public IEnumerable<Media> Feed {
get {
last = null;
while(true) {
var media = Next(FeedChunkSize);
if(media.Count() == 0)
break;
foreach(var m in media)
yield return m;
}
}
}
public Media[] Next(int count) =>
NextDbChunk(Math.Abs(count), count < 0);
private Media[] NextDbChunk(int chunkSize, bool reverse = false) {
if(feedOptions is null)
throw new InvalidOperationException("Feed must be initialized first");
while(true) {
var db = dbFactory.CreateDbContext();
IQueryable<Media> media = db.Media;
if(feedOptions.IncludeProperties is not null)
media = feedOptions.IncludeProperties(media);
var sortOrder = feedOptions.SortOrder;
if(reverse)
sortOrder = sortOrder == FeedSortOrder.Ascending
? FeedSortOrder.Descending
: FeedSortOrder.Ascending;
if(last is not null) {
switch(feedOptions.SortType) {
case FeedSortType.Chronological:
if(sortOrder == FeedSortOrder.Descending)
media = media.Where(m => m.ObjectId < last.ObjectId);
else
media = media.Where(m => m.ObjectId > last.ObjectId);
break;
}
media = media.Where(m => m.ObjectId != last.ObjectId);
}
switch(feedOptions.SortType) {
case FeedSortType.Chronological:
if(sortOrder == FeedSortOrder.Descending)
media = media.OrderByDescending(m => m.ObjectId);
else
media = media.OrderBy(m => m.ObjectId);
break;
}
Media[] mediaArray = media
.Take(chunkSize)
.ToArray();
if(mediaArray.Count() != 0)
last = mediaArray.Last();
}
}
}
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