Adding DistinctUntilChanged.

AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/Operators/DistinctUntilChanged.cs

@@ -0,0 +1,182 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information. 
+
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> DistinctUntilChanged<TSource>(IAsyncObservable<TSource> source)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.DistinctUntilChanged(observer)));
+        }
+
+        public static IAsyncObservable<TSource> DistinctUntilChanged<TSource>(IAsyncObservable<TSource> source, IEqualityComparer<TSource> comparer)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.DistinctUntilChanged(observer, comparer)));
+        }
+
+        public static IAsyncObservable<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObservable<TSource> source, Func<TSource, TKey> keySelector)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.DistinctUntilChanged(observer, keySelector)));
+        }
+
+        public static IAsyncObservable<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObservable<TSource> source, Func<TSource, Task<TKey>> keySelector)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.DistinctUntilChanged(observer, keySelector)));
+        }
+
+        public static IAsyncObservable<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObservable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.DistinctUntilChanged(observer, keySelector, comparer)));
+        }
+
+        public static IAsyncObservable<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObservable<TSource> source, Func<TSource, Task<TKey>> keySelector, IEqualityComparer<TKey> comparer)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.DistinctUntilChanged(observer, keySelector, comparer)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> DistinctUntilChanged<TSource>(IAsyncObserver<TSource> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            return DistinctUntilChanged(observer, x => x, EqualityComparer<TSource>.Default);
+        }
+
+        public static IAsyncObserver<TSource> DistinctUntilChanged<TSource>(IAsyncObserver<TSource> observer, IEqualityComparer<TSource> comparer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return DistinctUntilChanged(observer, x => x, comparer);
+        }
+
+        public static IAsyncObserver<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObserver<TSource> observer, Func<TSource, TKey> keySelector)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+
+            return DistinctUntilChanged(observer, x => Task.FromResult(keySelector(x)), EqualityComparer<TKey>.Default);
+        }
+
+        public static IAsyncObserver<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObserver<TSource> observer, Func<TSource, Task<TKey>> keySelector)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+
+            return DistinctUntilChanged(observer, keySelector, EqualityComparer<TKey>.Default);
+        }
+
+        public static IAsyncObserver<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObserver<TSource> observer, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return DistinctUntilChanged(observer, x => Task.FromResult(keySelector(x)), comparer);
+        }
+
+        public static IAsyncObserver<TSource> DistinctUntilChanged<TSource, TKey>(IAsyncObserver<TSource> observer, Func<TSource, Task<TKey>> keySelector, IEqualityComparer<TKey> comparer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (keySelector == null)
+                throw new ArgumentNullException(nameof(keySelector));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            var hasCurrentKey = false;
+            var currentKey = default(TKey);
+
+            return Create<TSource>(
+                async x =>
+                {
+                    var key = default(TKey);
+
+                    try
+                    {
+                        key = await keySelector(x).ConfigureAwait(false);
+                    }
+                    catch (Exception ex)
+                    {
+                        await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                        return;
+                    }
+
+                    var equals = default(bool);
+
+                    if (hasCurrentKey)
+                    {
+                        try
+                        {
+                            equals = comparer.Equals(currentKey, key);
+                        }
+                        catch (Exception ex)
+                        {
+                            await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                            return;
+                        }
+                    }
+
+                    if (!hasCurrentKey || !equals)
+                    {
+                        hasCurrentKey = true;
+                        currentKey = key;
+
+                        await observer.OnNextAsync(x).ConfigureAwait(false);
+                    }
+                },
+                observer.OnErrorAsync,
+                observer.OnCompletedAsync
+            );
+        }
+    }
+}