#if CSHARP_7_OR_LATER || (UNITY_2018_3_OR_NEWER && (NET_STANDARD_2_0 || NET_4_6))
#pragma warning disable CS1591 // Missing XML comment for publicly visible type or member

using System;
using System.Collections;
using System.Reflection;
using System.Runtime.ExceptionServices;
using System.Threading;
using UniRx.Async.Internal;
using UnityEngine;

namespace UniRx.Async
{
    public static class EnumeratorAsyncExtensions
    {
        public static UniTask.Awaiter GetAwaiter(this IEnumerator enumerator)
        {
            return new UniTask(EnumeratorPromise.Create(enumerator, PlayerLoopTiming.Update, CancellationToken.None, out var token), token).GetAwaiter();
        }

        public static UniTask ToUniTask(this IEnumerator enumerator)
        {
            return new UniTask(EnumeratorPromise.Create(enumerator, PlayerLoopTiming.Update, CancellationToken.None, out var token), token);
        }

        public static UniTask ConfigureAwait(this IEnumerator enumerator, PlayerLoopTiming timing = PlayerLoopTiming.Update, CancellationToken cancellationToken = default(CancellationToken))
        {
            return new UniTask(EnumeratorPromise.Create(enumerator, timing, cancellationToken, out var token), token);
        }

        class EnumeratorPromise : IUniTaskSource, IPlayerLoopItem, IPromisePoolItem
        {
            static readonly PromisePool<EnumeratorPromise> pool = new PromisePool<EnumeratorPromise>();

            IEnumerator innerEnumerator;
            CancellationToken cancellationToken;

            UniTaskCompletionSourceCore<object> core;

            EnumeratorPromise()
            {
            }

            public static IUniTaskSource Create(IEnumerator innerEnumerator, PlayerLoopTiming timing, CancellationToken cancellationToken, out short token)
            {
                if (cancellationToken.IsCancellationRequested)
                {
                    return AutoResetUniTaskCompletionSource.CreateFromCanceled(cancellationToken, out token);
                }

                var result = pool.TryRent() ?? new EnumeratorPromise();

                result.innerEnumerator = ConsumeEnumerator(innerEnumerator);
                result.cancellationToken = cancellationToken;

                TaskTracker.TrackActiveTask(result, 3);

                PlayerLoopHelper.AddAction(timing, result);

                token = result.core.Version;
                return result;
            }

            public void GetResult(short token)
            {
                try
                {
                    TaskTracker.RemoveTracking(this);
                    core.GetResult(token);
                }
                finally
                {
                    pool.TryReturn(this);
                }
            }

            public UniTaskStatus GetStatus(short token)
            {
                return core.GetStatus(token);
            }

            public UniTaskStatus UnsafeGetStatus()
            {
                return core.UnsafeGetStatus();
            }

            public void OnCompleted(Action<object> continuation, object state, short token)
            {
                core.OnCompleted(continuation, state, token);
            }

            public bool MoveNext()
            {
                if (cancellationToken.IsCancellationRequested)
                {
                    core.TrySetCanceled(cancellationToken);
                    return false;
                }

                try
                {
                    if (innerEnumerator.MoveNext())
                    {
                        return true;
                    }
                }
                catch (Exception ex)
                {
                    core.TrySetException(ex);
                    return false;
                }

                core.TrySetResult(null);
                return false;
            }

            public void Reset()
            {
                core.Reset();
                innerEnumerator = default;
                cancellationToken = default;
            }

            ~EnumeratorPromise()
            {
                if (pool.TryReturn(this))
                {
                    GC.ReRegisterForFinalize(this);
                }
            }

            // Unwrap YieldInstructions

            static IEnumerator ConsumeEnumerator(IEnumerator enumerator)
            {
                while (enumerator.MoveNext())
                {
                    var current = enumerator.Current;
                    if (current == null)
                    {
                        yield return null;
                    }
                    else if (current is CustomYieldInstruction)
                    {
                        // WWW, WaitForSecondsRealtime
                        var e2 = UnwrapWaitCustomYieldInstruction((CustomYieldInstruction)current);
                        while (e2.MoveNext())
                        {
                            yield return null;
                        }
                    }
                    else if (current is YieldInstruction)
                    {
                        IEnumerator innerCoroutine = null;
                        switch (current)
                        {
                            case AsyncOperation ao:
                                innerCoroutine = UnwrapWaitAsyncOperation(ao);
                                break;
                            case WaitForSeconds wfs:
                                innerCoroutine = UnwrapWaitForSeconds(wfs);
                                break;
                        }
                        if (innerCoroutine != null)
                        {
                            while (innerCoroutine.MoveNext())
                            {
                                yield return null;
                            }
                        }
                        else
                        {
                            yield return null;
                        }
                    }
                    else if (current is IEnumerator e3)
                    {
                        var e4 = ConsumeEnumerator(e3);
                        while (e4.MoveNext())
                        {
                            yield return null;
                        }
                    }
                    else
                    {
                        // WaitForEndOfFrame, WaitForFixedUpdate, others.
                        yield return null;
                    }
                }
            }

            // WWW and others as CustomYieldInstruction.
            static IEnumerator UnwrapWaitCustomYieldInstruction(CustomYieldInstruction yieldInstruction)
            {
                while (yieldInstruction.keepWaiting)
                {
                    yield return null;
                }
            }

            static readonly FieldInfo waitForSeconds_Seconds = typeof(WaitForSeconds).GetField("m_Seconds", BindingFlags.Instance | BindingFlags.GetField | BindingFlags.NonPublic);

            static IEnumerator UnwrapWaitForSeconds(WaitForSeconds waitForSeconds)
            {
                var second = (float)waitForSeconds_Seconds.GetValue(waitForSeconds);
                var startTime = DateTimeOffset.UtcNow;
                while (true)
                {
                    yield return null;

                    var elapsed = (DateTimeOffset.UtcNow - startTime).TotalSeconds;
                    if (elapsed >= second)
                    {
                        break;
                    }
                };
            }

            static IEnumerator UnwrapWaitAsyncOperation(AsyncOperation asyncOperation)
            {
                while (!asyncOperation.isDone)
                {
                    yield return null;
                }
            }
        }
    }
}

#endif