using RSG.Promises;
using System;
using System.Collections.Generic;
using System.Linq;
using RSG.Exceptions;
using UIWidgets.ui;

namespace RSG
{
    /// <summary>
    /// Implements a non-generic C# promise, this is a promise that simply resolves without delivering a value.
    /// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise
    /// </summary>
    public interface IPromise
    {
        /// <summary>
        /// ID of the promise, useful for debugging.
        /// </summary>
        int Id { get; }

        /// <summary>
        /// Set the name of the promise, useful for debugging.
        /// </summary>
        IPromise WithName(string name);

        /// <summary>
        /// Completes the promise. 
        /// onResolved is called on successful completion.
        /// onRejected is called on error.
        /// </summary>
        void Done(Action onResolved, Action<Exception> onRejected);

        /// <summary>
        /// Completes the promise. 
        /// onResolved is called on successful completion.
        /// Adds a default error handler.
        /// </summary>
        void Done(Action onResolved);

        /// <summary>
        /// Complete the promise. Adds a default error handler.
        /// </summary>
        void Done();

        /// <summary>
        /// Handle errors for the promise. 
        /// </summary>
        IPromise Catch(Action<Exception> onRejected);

        /// <summary>
        /// Add a resolved callback that chains a value promise (optionally converting to a different value type).
        /// </summary>
        IPromise<ConvertedT> Then<ConvertedT>(Func<IPromise<ConvertedT>> onResolved);

        /// <summary>
        /// Add a resolved callback that chains a non-value promise.
        /// </summary>
        IPromise Then(Func<IPromise> onResolved);

        /// <summary>
        /// Add a resolved callback.
        /// </summary>
        IPromise Then(Action onResolved);

        /// <summary>
        /// Add a resolved callback and a rejected callback.
        /// The resolved callback chains a value promise (optionally converting to a different value type).
        /// </summary>
        IPromise<ConvertedT> Then<ConvertedT>(Func<IPromise<ConvertedT>> onResolved, Func<Exception, IPromise<ConvertedT>> onRejected);

        /// <summary>
        /// Add a resolved callback and a rejected callback.
        /// The resolved callback chains a non-value promise.
        /// </summary>
        IPromise Then(Func<IPromise> onResolved, Action<Exception> onRejected);

        /// <summary>
        /// Add a resolved callback and a rejected callback.
        /// </summary>
        IPromise Then(Action onResolved, Action<Exception> onRejected);

        /// <summary>
        /// Add a resolved callback, a rejected callback and a progress callback.
        /// The resolved callback chains a value promise (optionally converting to a different value type).
        /// </summary>
        IPromise<ConvertedT> Then<ConvertedT>(Func<IPromise<ConvertedT>> onResolved, Func<Exception, IPromise<ConvertedT>> onRejected, Action<float> onProgress);

        /// <summary>
        /// Add a resolved callback, a rejected callback and a progress callback.
        /// The resolved callback chains a non-value promise.
        /// </summary>
        IPromise Then(Func<IPromise> onResolved, Action<Exception> onRejected, Action<float> onProgress);

        /// <summary>
        /// Add a resolved callback, a rejected callback and a progress callback.
        /// </summary>
        IPromise Then(Action onResolved, Action<Exception> onRejected, Action<float> onProgress);

        /// <summary>
        /// Chain an enumerable of promises, all of which must resolve.
        /// The resulting promise is resolved when all of the promises have resolved.
        /// It is rejected as soon as any of the promises have been rejected.
        /// </summary>
        IPromise ThenAll(Func<IEnumerable<IPromise>> chain);

        /// <summary>
        /// Chain an enumerable of promises, all of which must resolve.
        /// Converts to a non-value promise.
        /// The resulting promise is resolved when all of the promises have resolved.
        /// It is rejected as soon as any of the promises have been rejected.
        /// </summary>
        IPromise<IEnumerable<ConvertedT>> ThenAll<ConvertedT>(Func<IEnumerable<IPromise<ConvertedT>>> chain);

        /// <summary>
        /// Chain a sequence of operations using promises.
        /// Reutrn a collection of functions each of which starts an async operation and yields a promise.
        /// Each function will be called and each promise resolved in turn.
        /// The resulting promise is resolved after each promise is resolved in sequence.
        /// </summary>
        IPromise ThenSequence(Func<IEnumerable<Func<IPromise>>> chain);

        /// <summary>
        /// Takes a function that yields an enumerable of promises.
        /// Returns a promise that resolves when the first of the promises has resolved.
        /// </summary>
        IPromise ThenRace(Func<IEnumerable<IPromise>> chain);

        /// <summary>
        /// Takes a function that yields an enumerable of promises.
        /// Converts to a value promise.
        /// Returns a promise that resolves when the first of the promises has resolved.
        /// </summary>
        IPromise<ConvertedT> ThenRace<ConvertedT>(Func<IEnumerable<IPromise<ConvertedT>>> chain);

        /// <summary> 
        /// Add a finally callback. 
        /// Finally callbacks will always be called, even if any preceding promise is rejected, or encounters an error.
        /// The returned promise will be resolved or rejected, as per the preceding promise.
        /// </summary> 
        IPromise Finally(Action onComplete);

        /// <summary>
        /// Add a callback that chains a non-value promise.
        /// ContinueWith callbacks will always be called, even if any preceding promise is rejected, or encounters an error.
        /// The state of the returning promise will be based on the new non-value promise, not the preceding (rejected or resolved) promise.
        /// </summary>
        IPromise ContinueWith(Func<IPromise> onResolved);

        /// <summary> 
        /// Add a callback that chains a value promise (optionally converting to a different value type).
        /// ContinueWith callbacks will always be called, even if any preceding promise is rejected, or encounters an error.
        /// The state of the returning promise will be based on the new value promise, not the preceding (rejected or resolved) promise.
        /// </summary> 
        IPromise<ConvertedT> ContinueWith<ConvertedT>(Func<IPromise<ConvertedT>> onComplete);

        /// <summary>
        /// Add a progress callback.
        /// Progress callbacks will be called whenever the promise owner reports progress towards the resolution
        /// of the promise.
        /// </summary>
        IPromise Progress(Action<float> onProgress);
    }

    /// <summary>
    /// Interface for a promise that can be rejected or resolved.
    /// </summary>
    public interface IPendingPromise : IRejectable
    {
        /// <summary>
        /// ID of the promise, useful for debugging.
        /// </summary>
        int Id { get; }

        /// <summary>
        /// Resolve the promise with a particular value.
        /// </summary>
        void Resolve();

        /// <summary>
        /// Report progress in a promise.
        /// </summary>
        void ReportProgress(float progress);
    }

    /// <summary>
    /// Used to list information of pending promises.
    /// </summary>
    public interface IPromiseInfo
    {
        /// <summary>
        /// Id of the promise.
        /// </summary>
        int Id { get; }

        /// <summary>
        /// Human-readable name for the promise.
        /// </summary>
        string Name { get; }
    }

    /// <summary>
    /// Arguments to the UnhandledError event.
    /// </summary>
    public class ExceptionEventArgs : EventArgs
    {
        internal ExceptionEventArgs(Exception exception)
        {
//            Argument.NotNull(() => exception);

            this.Exception = exception;
        }

        public Exception Exception
        {
            get;
            private set;
        }
    }

    /// <summary>
    /// Represents a handler invoked when the promise is rejected.
    /// </summary>
    public struct RejectHandler
    {
        /// <summary>
        /// Callback fn.
        /// </summary>
        public Action<Exception> callback;

        /// <summary>
        /// The promise that is rejected when there is an error while invoking the handler.
        /// </summary>
        public IRejectable rejectable;
    }

    public struct ProgressHandler
    {
        /// <summary>
        /// Callback fn.
        /// </summary>
        public Action<float> callback;

        /// <summary>
        /// The promise that is rejected when there is an error while invoking the handler.
        /// </summary>
        public IRejectable rejectable;
    }

    /// <summary>
    /// Implements a non-generic C# promise, this is a promise that simply resolves without delivering a value.
    /// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise
    /// </summary>
    public class Promise : IPromise, IPendingPromise, IPromiseInfo
    {
        /// <summary>
        /// Set to true to enable tracking of promises.
        /// </summary>
        public static bool EnablePromiseTracking = false;

        /// <summary>
        /// Event raised for unhandled errors.
        /// For this to work you have to complete your promises with a call to Done().
        /// </summary>
        public static event EventHandler<ExceptionEventArgs> UnhandledException
        {
            add { unhandlerException += value; }
            remove { unhandlerException -= value; }
        }
        private static EventHandler<ExceptionEventArgs> unhandlerException;

        /// <summary>
        /// Id for the next promise that is created.
        /// </summary>
        private static int nextPromiseId;

        /// <summary>
        /// Information about pending promises.
        /// </summary>
        internal static readonly HashSet<IPromiseInfo> PendingPromises = 
            new HashSet<IPromiseInfo>();

        /// <summary>
        /// Information about pending promises, useful for debugging.
        /// This is only populated when 'EnablePromiseTracking' is set to true.
        /// </summary>
        public static IEnumerable<IPromiseInfo> GetPendingPromises()
        {
            return PendingPromises;
        }

        /// <summary>
        /// The exception when the promise is rejected.
        /// </summary>
        private Exception rejectionException;

        /// <summary>
        /// Error handlers.
        /// </summary>
        private List<RejectHandler> rejectHandlers;

        /// <summary>
        /// Represents a handler invoked when the promise is resolved.
        /// </summary>
        public struct ResolveHandler
        {
            /// <summary>
            /// Callback fn.
            /// </summary>
            public Action callback;

            /// <summary>
            /// The promise that is rejected when there is an error while invoking the handler.
            /// </summary>
            public IRejectable rejectable;
        }

        /// <summary>
        /// Completed handlers that accept no value.
        /// </summary>
        private List<ResolveHandler> resolveHandlers;

        /// <summary>
        /// Progress handlers.
        /// </summary>
        private List<ProgressHandler> progressHandlers;

        /// <summary>
        /// ID of the promise, useful for debugging.
        /// </summary>
        public int Id { get { return id; } }

        private readonly int id;

        /// <summary>
        /// Name of the promise, when set, useful for debugging.
        /// </summary>
        public string Name { get; private set; }

        /// <summary>
        /// Tracks the current state of the promise.
        /// </summary>
        public PromiseState CurState { get; private set; }

        public Promise()
        {
            this.CurState = PromiseState.Pending;
            this.id = NextId();
            if (EnablePromiseTracking)
            {
                PendingPromises.Add(this);
            }
        }

        public Promise(Action<Action, Action<Exception>> resolver)
        {
            this.CurState = PromiseState.Pending;
            this.id = NextId();
            if (EnablePromiseTracking)
            {
                PendingPromises.Add(this);
            }

            try
            {
                resolver(Resolve, Reject);
            }
            catch (Exception ex)
            {
                Reject(ex);
            }
        }

        /// <summary>
        /// Increments the ID counter and gives us the ID for the next promise.
        /// </summary>
        internal static int NextId()
        {
            return ++nextPromiseId;
        }

        /// <summary>
        /// Add a rejection handler for this promise.
        /// </summary>
        private void AddRejectHandler(Action<Exception> onRejected, IRejectable rejectable)
        {
            if (rejectHandlers == null)
            {
                rejectHandlers = new List<RejectHandler>();
            }

            rejectHandlers.Add(new RejectHandler
            {
                callback = onRejected,
                rejectable = rejectable
            });
        }

        /// <summary>
        /// Add a resolve handler for this promise.
        /// </summary>
        private void AddResolveHandler(Action onResolved, IRejectable rejectable)
        {
            if (resolveHandlers == null)
            {
                resolveHandlers = new List<ResolveHandler>();
            }

            resolveHandlers.Add(new ResolveHandler
            {
                callback = onResolved,
                rejectable = rejectable
            });
        }

        /// <summary>
        /// Add a progress handler for this promise.
        /// </summary>
        private void AddProgressHandler(Action<float> onProgress, IRejectable rejectable)
        {
            if (progressHandlers == null)
            {
                progressHandlers = new List<ProgressHandler>();
            }

            progressHandlers.Add(new ProgressHandler { callback = onProgress, rejectable = rejectable });
        }

        /// <summary>
        /// Invoke a single error handler.
        /// </summary>
        private void InvokeRejectHandler(Action<Exception> callback, IRejectable rejectable, Exception value)
        {
//            Argument.NotNull(() => callback);
//            Argument.NotNull(() => rejectable);

            try
            {
                callback(value);
            }
            catch (Exception ex)
            {
                rejectable.Reject(ex);
            }
        }

        /// <summary>
        /// Invoke a single resolve handler.
        /// </summary>
        private void InvokeResolveHandler(Action callback, IRejectable rejectable)
        {
//            Argument.NotNull(() => callback);
//            Argument.NotNull(() => rejectable);

            try
            {
                callback();
            }
            catch (Exception ex)
            {
                rejectable.Reject(ex);
            }
        }

        /// <summary>
        /// Invoke a single progress handler.
        /// </summary>
        private void InvokeProgressHandler(Action<float> callback, IRejectable rejectable, float progress)
        {
//            Argument.NotNull(() => callback);
//            Argument.NotNull(() => rejectable);

            try
            {
                callback(progress);
            }
            catch (Exception ex)
            {
                rejectable.Reject(ex);
            }
        }

        /// <summary>
        /// Helper function clear out all handlers after resolution or rejection.
        /// </summary>
        private void ClearHandlers()
        {
            rejectHandlers = null;
            resolveHandlers = null;
            progressHandlers = null;
        }

        /// <summary>
        /// Invoke all reject handlers.
        /// </summary>
        private void InvokeRejectHandlers(Exception ex)
        {
//            Argument.NotNull(() => ex);

            if (rejectHandlers != null)
            {
                rejectHandlers.Each(handler => InvokeRejectHandler(handler.callback, handler.rejectable, ex));
            }

            ClearHandlers();
        }

        /// <summary>
        /// Invoke all resolve handlers.
        /// </summary>
        private void InvokeResolveHandlers()
        {
            if (resolveHandlers != null)
            {
                resolveHandlers.Each(handler => InvokeResolveHandler(handler.callback, handler.rejectable));
            }

            ClearHandlers();
        }

        /// <summary>
        /// Invoke all progress handlers.
        /// </summary>
        private void InvokeProgressHandlers(float progress)
        {
            if (progressHandlers != null)
            {
                progressHandlers.Each(handler => InvokeProgressHandler(handler.callback, handler.rejectable, progress));
            }
        }

        /// <summary>
        /// Reject the promise with an exception.
        /// </summary>
        public void Reject(Exception ex)
        {
//            Argument.NotNull(() => ex);

            if (CurState != PromiseState.Pending)
            {
                throw new PromiseStateException(
                    "Attempt to reject a promise that is already in state: " + CurState 
                    + ", a promise can only be rejected when it is still in state: " 
                    + PromiseState.Pending
                );
            }

            rejectionException = ex;
            CurState = PromiseState.Rejected;

            if (EnablePromiseTracking)
            {
                PendingPromises.Remove(this);
            }

            Window.instance.scheduleMicrotask(() => {
                InvokeRejectHandlers(ex);
            });
        }


        /// <summary>
        /// Resolve the promise with a particular value.
        /// </summary>
        public void Resolve()
        {
            if (CurState != PromiseState.Pending)
            {
                throw new PromiseStateException(
                    "Attempt to resolve a promise that is already in state: " + CurState 
                    + ", a promise can only be resolved when it is still in state: " 
                    + PromiseState.Pending
                );
            }

            CurState = PromiseState.Resolved;

            if (EnablePromiseTracking)
            {
                PendingPromises.Remove(this);
            }

            Window.instance.scheduleMicrotask(() => {
                InvokeResolveHandlers();                
            });
        }


        /// <summary>
        /// Report progress on the promise.
        /// </summary>
        public void ReportProgress(float progress)
        {
            if (CurState != PromiseState.Pending)
            {
                throw new PromiseStateException(
                    "Attempt to report progress on a promise that is already in state: " 
                    + CurState + ", a promise can only report progress when it is still in state: " 
                    + PromiseState.Pending
                );
            }

            InvokeProgressHandlers(progress);
        }


        /// <summary>
        /// Completes the promise. 
        /// onResolved is called on successful completion.
        /// onRejected is called on error.
        /// </summary>
        public void Done(Action onResolved, Action<Exception> onRejected)
        {
            Then(onResolved, onRejected)
                .Catch(ex =>
                    PropagateUnhandledException(this, ex)
                );
        }

        /// <summary>
        /// Completes the promise. 
        /// onResolved is called on successful completion.
        /// Adds a default error handler.
        /// </summary>
        public void Done(Action onResolved)
        {
            Then(onResolved)
                .Catch(ex => 
                    PropagateUnhandledException(this, ex)
                );
        }

        /// <summary>
        /// Complete the promise. Adds a defualt error handler.
        /// </summary>
        public void Done()
        {
            Catch(ex => PropagateUnhandledException(this, ex));
        }

        /// <summary>
        /// Set the name of the promise, useful for debugging.
        /// </summary>
        public IPromise WithName(string name)
        {
            this.Name = name;
            return this;
        }

        /// <summary>
        /// Handle errors for the promise. 
        /// </summary>
        public IPromise Catch(Action<Exception> onRejected)
        {
//            Argument.NotNull(() => onRejected);

            var resultPromise = new Promise();
            resultPromise.WithName(Name);

            Action resolveHandler = () => resultPromise.Resolve();

            Action<Exception> rejectHandler = ex =>
            {
                try
                {
                    onRejected(ex);
                    resultPromise.Resolve();
                }
                catch (Exception callbackException)
                {
                    resultPromise.Reject(callbackException);
                }
            };

            ActionHandlers(resultPromise, resolveHandler, rejectHandler);
            ProgressHandlers(resultPromise, v => resultPromise.ReportProgress(v));

            return resultPromise;
        }

        /// <summary>
        /// Add a resolved callback that chains a value promise (optionally converting to a different value type).
        /// </summary>
        public IPromise<ConvertedT> Then<ConvertedT>(Func<IPromise<ConvertedT>> onResolved)
        {
            return Then(onResolved, null, null);
        }

        /// <summary>
        /// Add a resolved callback that chains a non-value promise.
        /// </summary>
        public IPromise Then(Func<IPromise> onResolved)
        {
            return Then(onResolved, null, null);
        }

        /// <summary>
        /// Add a resolved callback.
        /// </summary>
        public IPromise Then(Action onResolved)
        {
            return Then(onResolved, null, null);
        }

        /// <summary>
        /// Add a resolved callback and a rejected callback.
        /// The resolved callback chains a value promise (optionally converting to a different value type).
        /// </summary>
        public IPromise<ConvertedT> Then<ConvertedT>(Func<IPromise<ConvertedT>> onResolved, Func<Exception, IPromise<ConvertedT>> onRejected)
        {
            return Then(onResolved, onRejected, null);
        }

        /// <summary>
        /// Add a resolved callback and a rejected callback.
        /// The resolved callback chains a non-value promise.
        /// </summary>
        public IPromise Then(Func<IPromise> onResolved, Action<Exception> onRejected)
        {
            return Then(onResolved, onRejected, null);
        }

        /// <summary>
        /// Add a resolved callback and a rejected callback.
        /// </summary>
        public IPromise Then(Action onResolved, Action<Exception> onRejected)
        {
            return Then(onResolved, onRejected, null);
        }

        /// <summary>
        /// Add a resolved callback, a rejected callback and a progress callback.
        /// The resolved callback chains a value promise (optionally converting to a different value type).
        /// </summary>
        public IPromise<ConvertedT> Then<ConvertedT>(
            Func<IPromise<ConvertedT>> onResolved,
            Func<Exception, IPromise<ConvertedT>> onRejected,
            Action<float> onProgress)
        {
            // This version of the function must supply an onResolved.
            // Otherwise there is now way to get the converted value to pass to the resulting promise.
//            Argument.NotNull(() => onResolved);

            var resultPromise = new Promise<ConvertedT>();
            resultPromise.WithName(Name);

            Action resolveHandler = () =>
            {
                onResolved()
                    .Progress(progress => resultPromise.ReportProgress(progress))
                    .Then(
                        // Should not be necessary to specify the arg type on the next line, but Unity (mono) has an internal compiler error otherwise.
                        chainedValue => resultPromise.Resolve(chainedValue),
                        ex => resultPromise.Reject(ex)
                    );
            };

            Action<Exception> rejectHandler = ex =>
            {
                if (onRejected == null)
                {
                    resultPromise.Reject(ex);
                    return;
                }

                try
                {
                    onRejected(ex)
                        .Then(
                            chainedValue => resultPromise.Resolve(chainedValue),
                            callbackEx => resultPromise.Reject(callbackEx)
                        );
                }
                catch (Exception callbackEx)
                {
                    resultPromise.Reject(callbackEx);
                }
            };

            ActionHandlers(resultPromise, resolveHandler, rejectHandler);
            if (onProgress != null)
            {
                ProgressHandlers(this, onProgress);
            }

            return resultPromise;
        }

        /// <summary>
        /// Add a resolved callback, a rejected callback and a progress callback.
        /// The resolved callback chains a non-value promise.
        /// </summary>
        public IPromise Then(Func<IPromise> onResolved, Action<Exception> onRejected, Action<float> onProgress)
        {
            var resultPromise = new Promise();
            resultPromise.WithName(Name);

            Action resolveHandler = () =>
            {
                if (onResolved != null)
                {
                    onResolved()
                        .Progress(progress => resultPromise.ReportProgress(progress))
                        .Then(
                            () => resultPromise.Resolve(),
                            ex => resultPromise.Reject(ex)
                        );
                }
                else
                {
                    resultPromise.Resolve();
                }
            };

            Action<Exception> rejectHandler = ex =>
            {
                if (onRejected != null)
                {
                    onRejected(ex);
                }

                resultPromise.Reject(ex);
            };

            ActionHandlers(resultPromise, resolveHandler, rejectHandler);
            if (onProgress != null)
            {
                ProgressHandlers(this, onProgress);
            }

            return resultPromise;
        }

        /// <summary>
        /// Add a resolved callback, a rejected callback and a progress callback.
        /// </summary>
        public IPromise Then(Action onResolved, Action<Exception> onRejected, Action<float> onProgress)
        {
            var resultPromise = new Promise();
            resultPromise.WithName(Name);

            Action resolveHandler = () =>
            {
                if (onResolved != null)
                {
                    onResolved();
                }

                resultPromise.Resolve();
            };

            Action<Exception> rejectHandler = ex =>
            {
                if (onRejected != null)
                {
                    onRejected(ex);
                    resultPromise.Resolve();
                    return;
                }

                resultPromise.Reject(ex);
            };

            ActionHandlers(resultPromise, resolveHandler, rejectHandler);
            if (onProgress != null)
            {
                ProgressHandlers(this, onProgress);
            }

            return resultPromise;
        }

        /// <summary>
        /// Helper function to invoke or register resolve/reject handlers.
        /// </summary>
        private void ActionHandlers(IRejectable resultPromise, Action resolveHandler, Action<Exception> rejectHandler)
        {
            if (CurState == PromiseState.Resolved)
            {
                InvokeResolveHandler(resolveHandler, resultPromise);
            }
            else if (CurState == PromiseState.Rejected)
            {
                InvokeRejectHandler(rejectHandler, resultPromise, rejectionException);
            }
            else
            {
                AddResolveHandler(resolveHandler, resultPromise);
                AddRejectHandler(rejectHandler, resultPromise);
            }
        }

        /// <summary>
        /// Helper function to invoke or register progress handlers.
        /// </summary>
        private void ProgressHandlers(IRejectable resultPromise, Action<float> progressHandler)
        {
            if (CurState == PromiseState.Pending)
            {
                AddProgressHandler(progressHandler, resultPromise);
            }
        }

        /// <summary>
        /// Chain an enumerable of promises, all of which must resolve.
        /// The resulting promise is resolved when all of the promises have resolved.
        /// It is rejected as soon as any of the promises have been rejected.
        /// </summary>
        public IPromise ThenAll(Func<IEnumerable<IPromise>> chain)
        {
            return Then(() => All(chain()));
        }

        /// <summary>
        /// Chain an enumerable of promises, all of which must resolve.
        /// Converts to a non-value promise.
        /// The resulting promise is resolved when all of the promises have resolved.
        /// It is rejected as soon as any of the promises have been rejected.
        /// </summary>
        public IPromise<IEnumerable<ConvertedT>> ThenAll<ConvertedT>(Func<IEnumerable<IPromise<ConvertedT>>> chain)
        {
            return Then(() => Promise<ConvertedT>.All(chain()));
        }

        /// <summary>
        /// Returns a promise that resolves when all of the promises in the enumerable argument have resolved.
        /// Returns a promise of a collection of the resolved results.
        /// </summary>
        public static IPromise All(params IPromise[] promises)
        {
            return All((IEnumerable<IPromise>)promises); // Cast is required to force use of the other All function.
        }

        /// <summary>
        /// Returns a promise that resolves when all of the promises in the enumerable argument have resolved.
        /// Returns a promise of a collection of the resolved results.
        /// </summary>
        public static IPromise All(IEnumerable<IPromise> promises)
        {
            var promisesArray = promises.ToArray();
            if (promisesArray.Length == 0)
            {
                return Resolved();
            }

            var remainingCount = promisesArray.Length;
            var resultPromise = new Promise();
            resultPromise.WithName("All");
            var progress = new float[remainingCount];

            promisesArray.Each((promise, index) =>
            {
                promise
                    .Progress(v =>
                    {
                        progress[index] = v;
                        if (resultPromise.CurState == PromiseState.Pending)
                        {
                            resultPromise.ReportProgress(progress.Average());
                        }
                    })
                    .Then(() =>
                    {
                        progress[index] = 1f;

                        --remainingCount;
                        if (remainingCount <= 0 && resultPromise.CurState == PromiseState.Pending)
                        {
                            // This will never happen if any of the promises errorred.
                            resultPromise.Resolve();
                        }
                    })
                    .Catch(ex =>
                    {
                        if (resultPromise.CurState == PromiseState.Pending)
                        {
                            // If a promise errorred and the result promise is still pending, reject it.
                            resultPromise.Reject(ex);
                        }
                    })
                    .Done();
            });

            return resultPromise;
        }

        /// <summary>
        /// Chain a sequence of operations using promises.
        /// Reutrn a collection of functions each of which starts an async operation and yields a promise.
        /// Each function will be called and each promise resolved in turn.
        /// The resulting promise is resolved after each promise is resolved in sequence.
        /// </summary>
        public IPromise ThenSequence(Func<IEnumerable<Func<IPromise>>> chain)
        {
            return Then(() => Sequence(chain()));
        }

        /// <summary>
        /// Chain a number of operations using promises.
        /// Takes a number of functions each of which starts an async operation and yields a promise.
        /// </summary>
        public static IPromise Sequence(params Func<IPromise>[] fns)
        {
            return Sequence((IEnumerable<Func<IPromise>>)fns);
        }

        /// <summary>
        /// Chain a sequence of operations using promises.
        /// Takes a collection of functions each of which starts an async operation and yields a promise.
        /// </summary>
        public static IPromise Sequence(IEnumerable<Func<IPromise>> fns)
        {
            var promise = new Promise();

            int count = 0;

            fns.Aggregate(
                Resolved(),
                (prevPromise, fn) =>
                {
                    int itemSequence = count;
                    ++count;

                    return prevPromise
                            .Then(() =>
                            {
                                var sliceLength = 1f / count;
                                promise.ReportProgress(sliceLength * itemSequence);
                                return fn();
                            })
                            .Progress(v =>
                            {
                                var sliceLength = 1f / count;
                                promise.ReportProgress(sliceLength * (v + itemSequence));
                            })
                    ;
                }
            )
            .Then(() => promise.Resolve())
            .Catch(promise.Reject);

            return promise;
        }

        /// <summary>
        /// Takes a function that yields an enumerable of promises.
        /// Returns a promise that resolves when the first of the promises has resolved.
        /// </summary>
        public IPromise ThenRace(Func<IEnumerable<IPromise>> chain)
        {
            return Then(() => Race(chain()));
        }

        /// <summary>
        /// Takes a function that yields an enumerable of promises.
        /// Converts to a value promise.
        /// Returns a promise that resolves when the first of the promises has resolved.
        /// </summary>
        public IPromise<ConvertedT> ThenRace<ConvertedT>(Func<IEnumerable<IPromise<ConvertedT>>> chain)
        {
            return Then(() => Promise<ConvertedT>.Race(chain()));
        }

        /// <summary>
        /// Returns a promise that resolves when the first of the promises in the enumerable argument have resolved.
        /// Returns the value from the first promise that has resolved.
        /// </summary>
        public static IPromise Race(params IPromise[] promises)
        {
            return Race((IEnumerable<IPromise>)promises); // Cast is required to force use of the other function.
        }

        /// <summary>
        /// Returns a promise that resolves when the first of the promises in the enumerable argument have resolved.
        /// Returns the value from the first promise that has resolved.
        /// </summary>
        public static IPromise Race(IEnumerable<IPromise> promises)
        {
            var promisesArray = promises.ToArray();
            if (promisesArray.Length == 0)
            {
                throw new InvalidOperationException("At least 1 input promise must be provided for Race");
            }

            var resultPromise = new Promise();
            resultPromise.WithName("Race");

            var progress = new float[promisesArray.Length];

            promisesArray.Each((promise, index) =>
            {
                promise
                    .Progress(v =>
                    {
                        progress[index] = v;
                        resultPromise.ReportProgress(progress.Max());
                    })
                    .Catch(ex =>
                    {
                        if (resultPromise.CurState == PromiseState.Pending)
                        {
                            // If a promise errorred and the result promise is still pending, reject it.
                            resultPromise.Reject(ex);
                        }
                    })
                    .Then(() =>
                    {
                        if (resultPromise.CurState == PromiseState.Pending)
                        {
                            resultPromise.Resolve();
                        }
                    })
                    .Done();
            });

            return resultPromise;
        }

        /// <summary>
        /// Convert a simple value directly into a resolved promise.
        /// </summary>
        public static IPromise Resolved()
        {
            var promise = new Promise();
            promise.Resolve();
            return promise;
        }

        /// <summary>
        /// Convert an exception directly into a rejected promise.
        /// </summary>
        public static IPromise Rejected(Exception ex)
        {
//            Argument.NotNull(() => ex);

            var promise = new Promise();
            promise.Reject(ex);
            return promise;
        }

        public IPromise Finally(Action onComplete)
        {
            var promise = new Promise();
            promise.WithName(Name);

            this.Then(() => promise.Resolve());
            this.Catch(e => {
                try {
                    onComplete();
                    promise.Reject(e);
                } catch (Exception ne) {
                    promise.Reject(ne);
                }
            });

            return promise.Then(onComplete);
        }

        public IPromise ContinueWith(Func<IPromise> onComplete)
        {
            var promise = new Promise();
            promise.WithName(Name);

            this.Then(() => promise.Resolve());
            this.Catch(e => promise.Resolve());

            return promise.Then(onComplete);
        }

        public IPromise<ConvertedT> ContinueWith<ConvertedT>(Func<IPromise<ConvertedT>> onComplete)
        {
            var promise = new Promise();
            promise.WithName(Name);

            this.Then(() => promise.Resolve());
            this.Catch(e => promise.Resolve());

            return promise.Then(onComplete);
        }

        public IPromise Progress(Action<float> onProgress)
        {
            if (onProgress != null)
            {
                ProgressHandlers(this, onProgress);
            }
            return this;
        }

        /// <summary>
        /// Raises the UnhandledException event.
        /// </summary>
        internal static void PropagateUnhandledException(object sender, Exception ex)
        {
            if (unhandlerException != null)
            {
                unhandlerException(sender, new ExceptionEventArgs(ex));
            }
        }
    }
}