// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT License.
// See the LICENSE file in the project root for more information. 

using System.Reactive.Concurrency;
using System.Threading.Tasks;

namespace System.Reactive.Linq
{
    public partial class AsyncObservable
    {
        public static IAsyncObservable<TResult> If<TResult>(Func<bool> condition, IAsyncObservable<TResult> thenSource) => If(condition, thenSource, Empty<TResult>());

        public static IAsyncObservable<TResult> If<TResult>(Func<bool> condition, IAsyncObservable<TResult> thenSource, IAsyncScheduler scheduler) => If(condition, thenSource, Empty<TResult>(scheduler));

        public static IAsyncObservable<TResult> If<TResult>(Func<bool> condition, IAsyncObservable<TResult> thenSource, IAsyncObservable<TResult> elseSource)
        {
            if (condition == null)
                throw new ArgumentNullException(nameof(condition));
            if (thenSource == null)
                throw new ArgumentNullException(nameof(thenSource));
            if (elseSource == null)
                throw new ArgumentNullException(nameof(elseSource));

            return CreateAsyncObservable<TResult>.From(
                thenSource,
                (elseSource, condition),
                static (thenSource, state, observer) =>
                {
                    var b = default(bool);

                    try
                    {
                        b = state.condition();
                    }
                    catch (Exception ex)
                    {
                        return Throw<TResult>(ex).SubscribeAsync(observer);
                    }

                    return (b ? thenSource : state.elseSource).SubscribeSafeAsync(observer);
                });
        }

        public static IAsyncObservable<TResult> If<TResult>(Func<ValueTask<bool>> condition, IAsyncObservable<TResult> thenSource) => If(condition, thenSource, Empty<TResult>());

        public static IAsyncObservable<TResult> If<TResult>(Func<ValueTask<bool>> condition, IAsyncObservable<TResult> thenSource, IAsyncScheduler scheduler) => If(condition, thenSource, Empty<TResult>(scheduler));

        public static IAsyncObservable<TResult> If<TResult>(Func<ValueTask<bool>> condition, IAsyncObservable<TResult> thenSource, IAsyncObservable<TResult> elseSource)
        {
            if (condition == null)
                throw new ArgumentNullException(nameof(condition));
            if (thenSource == null)
                throw new ArgumentNullException(nameof(thenSource));
            if (elseSource == null)
                throw new ArgumentNullException(nameof(elseSource));

            return CreateAsyncObservable<TResult>.From(
                thenSource,
                (elseSource, condition),
                static async (thenSource, state, observer) =>
                {
                    var b = default(bool);

                    try
                    {
                        b = await state.condition().ConfigureAwait(false);
                    }
                    catch (Exception ex)
                    {
                        return await Throw<TResult>(ex).SubscribeAsync(observer).ConfigureAwait(false);
                    }

                    return await (b ? thenSource : state.elseSource).SubscribeSafeAsync(observer).ConfigureAwait(false);
                });
        }
    }
}