using System;

using System.Collections.Generic;

using System.Linq;

using System.Reactive.Concurrency;

using System.Text;

namespace ReactiveUI

{

/// <summary>

/// This scheduler attempts to deal with some of the brain-dead defaults

/// on certain Microsoft platforms that make it difficult to access the

/// Dispatcher during startup. This class wraps a scheduler and if it

/// isn't available yet, it simply runs the scheduled item immediately.

/// </summary>

public class WaitForDispatcherScheduler : IScheduler

{

IScheduler _innerScheduler;

readonly Func<IScheduler> _schedulerFactory;

public WaitForDispatcherScheduler(Func<IScheduler> schedulerFactory)

{

_schedulerFactory = schedulerFactory;

// NB: Creating a scheduler will fail on WinRT if we attempt to do

// so on a non-UI thread, even if the underlying Dispatcher exists.

// We assume (hope?) that WaitForDispatcherScheduler will be created

// early enough that this won't be the case.

attemptToCreateScheduler();

}

public IDisposable Schedule<TState>(TState state, Func<IScheduler, TState, IDisposable> action)

{

return attemptToCreateScheduler().Schedule(state, action);

}

public IDisposable Schedule<TState>(TState state, TimeSpan dueTime, Func<IScheduler, TState, IDisposable> action)

{

return attemptToCreateScheduler().Schedule(state, dueTime, action);

}

public IDisposable Schedule<TState>(TState state, DateTimeOffset dueTime, Func<IScheduler, TState, IDisposable> action)

{

return attemptToCreateScheduler().Schedule(state, dueTime, action);

}

public DateTimeOffset Now {

get { return attemptToCreateScheduler().Now; }

}

IScheduler attemptToCreateScheduler()

{

if (_innerScheduler != null) return _innerScheduler;

try {

_innerScheduler = _schedulerFactory();

return _innerScheduler;

} catch (InvalidOperationException) {

// NB: Dispatcher's not ready yet. Keep using CurrentThread

return CurrentThreadScheduler.Instance;

}

}

}

}