using Cysharp.Threading.Tasks.Internal;
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using System;
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using System.Collections.Generic;
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using System.Threading;
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namespace Cysharp.Threading.Tasks.Linq
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{
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public static partial class UniTaskAsyncEnumerable
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{
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public static IUniTaskAsyncEnumerable<TSource> SkipLast<TSource>(this IUniTaskAsyncEnumerable<TSource> source, Int32 count)
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{
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Error.ThrowArgumentNullException(source, nameof(source));
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// non skip.
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if (count <= 0)
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{
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return source;
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}
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return new SkipLast<TSource>(source, count);
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}
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}
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internal sealed class SkipLast<TSource> : IUniTaskAsyncEnumerable<TSource>
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{
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readonly IUniTaskAsyncEnumerable<TSource> source;
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readonly int count;
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public SkipLast(IUniTaskAsyncEnumerable<TSource> source, int count)
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{
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this.source = source;
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this.count = count;
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}
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public IUniTaskAsyncEnumerator<TSource> GetAsyncEnumerator(CancellationToken cancellationToken = default)
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{
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return new _SkipLast(source, count, cancellationToken);
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}
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sealed class _SkipLast : MoveNextSource, IUniTaskAsyncEnumerator<TSource>
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{
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static readonly Action<object> MoveNextCoreDelegate = MoveNextCore;
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readonly IUniTaskAsyncEnumerable<TSource> source;
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readonly int count;
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CancellationToken cancellationToken;
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IUniTaskAsyncEnumerator<TSource> enumerator;
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UniTask<bool>.Awaiter awaiter;
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Queue<TSource> queue;
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bool continueNext;
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public _SkipLast(IUniTaskAsyncEnumerable<TSource> source, int count, CancellationToken cancellationToken)
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{
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this.source = source;
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this.count = count;
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this.cancellationToken = cancellationToken;
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TaskTracker.TrackActiveTask(this, 3);
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}
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public TSource Current { get; private set; }
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public UniTask<bool> MoveNextAsync()
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{
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cancellationToken.ThrowIfCancellationRequested();
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if (enumerator == null)
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{
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enumerator = source.GetAsyncEnumerator(cancellationToken);
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queue = new Queue<TSource>();
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}
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completionSource.Reset();
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SourceMoveNext();
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return new UniTask<bool>(this, completionSource.Version);
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}
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void SourceMoveNext()
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{
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try
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{
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LOOP:
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awaiter = enumerator.MoveNextAsync().GetAwaiter();
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if (awaiter.IsCompleted)
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{
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continueNext = true;
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MoveNextCore(this);
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if (continueNext)
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{
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continueNext = false;
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goto LOOP; // avoid recursive
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}
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}
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else
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{
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awaiter.SourceOnCompleted(MoveNextCoreDelegate, this);
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}
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}
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catch (Exception ex)
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{
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completionSource.TrySetException(ex);
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}
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}
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static void MoveNextCore(object state)
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{
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var self = (_SkipLast)state;
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if (self.TryGetResult(self.awaiter, out var result))
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{
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if (result)
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{
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if (self.queue.Count == self.count)
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{
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self.continueNext = false;
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var deq = self.queue.Dequeue();
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self.Current = deq;
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self.queue.Enqueue(self.enumerator.Current);
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self.completionSource.TrySetResult(true);
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}
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else
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{
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self.queue.Enqueue(self.enumerator.Current);
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if (!self.continueNext)
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{
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self.SourceMoveNext();
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}
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}
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}
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else
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{
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self.continueNext = false;
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self.completionSource.TrySetResult(false);
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}
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}
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else
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{
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self.continueNext = false;
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}
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}
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public UniTask DisposeAsync()
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{
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TaskTracker.RemoveTracking(this);
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if (enumerator != null)
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{
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return enumerator.DisposeAsync();
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}
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return default;
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}
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}
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}
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}
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