using System;

using System.Linq;

using System.Reactive;

using System.Reactive.Concurrency;

using System.Reactive.Linq;

using System.Reactive.Subjects;

using System.Runtime.Serialization;

using System.Windows.Input;

using Splat;

namespace ReactiveUI

{

/// <summary>

/// RoutingState manages the ViewModel Stack and allows ViewModels to

/// navigate to other ViewModels.

/// </summary>

[DataContract]

public class RoutingState : ReactiveObject

{

[DataMember] ReactiveList<IRoutableViewModel> _NavigationStack;

/// <summary>

/// Represents the current navigation stack, the last element in the

/// collection being the currently visible ViewModel.

/// </summary>

[IgnoreDataMember]

public ReactiveList<IRoutableViewModel> NavigationStack {

get { return _NavigationStack; }

protected set { _NavigationStack = value; }

}

/// <summary>

/// Navigates back to the previous element in the stack.

/// </summary>

[IgnoreDataMember]

public ReactiveCommand<Unit> NavigateBack { get; protected set; }

/// <summary>

/// Navigates to the a new element in the stack - the Execute parameter

/// must be a ViewModel that implements IRoutableViewModel.

/// </summary>

[IgnoreDataMember]

public ReactiveCommand<object> Navigate { get; protected set; }

/// <summary>

/// Navigates to a new element and resets the navigation stack (i.e. the

/// new ViewModel will now be the only element in the stack) - the

/// Execute parameter must be a ViewModel that implements

/// IRoutableViewModel.

/// </summary>

[IgnoreDataMember]

public ReactiveCommand<object> NavigateAndReset { get; protected set; }

[IgnoreDataMember]

public IObservable<IRoutableViewModel> CurrentViewModel { get; protected set; }

public RoutingState()

{

_NavigationStack = new ReactiveList<IRoutableViewModel>();

setupRx();

}

[OnDeserialized]

void setupRx(StreamingContext sc) { setupRx(); }

void setupRx()

{

NavigateBack = ReactiveCommand.Create(

NavigationStack.CountChanged.StartWith(_NavigationStack.Count).Select(x => x > 1),

_ => Observable.Return(Unit.Default));

NavigateBack.Subscribe(_ =>

NavigationStack.RemoveAt(NavigationStack.Count - 1));

Navigate = new ReactiveCommand<object>(Observable.Return(true), x => Observable.Return(x));

Navigate.Subscribe(x => {

var vm = x as IRoutableViewModel;

if (vm == null) {

throw new Exception("Navigate must be called on an IRoutableViewModel");

}

NavigationStack.Add(vm);

});

NavigateAndReset = new ReactiveCommand<object>(Observable.Return(true), x => Observable.Return(x));

NavigateAndReset.Subscribe(x => {

NavigationStack.Clear();

Navigate.ExecuteAsync(x);

});

CurrentViewModel = Observable.Concat(

Observable.Defer(() => Observable.Return(NavigationStack.LastOrDefault())),

NavigationStack.Changed.Select(_ => NavigationStack.LastOrDefault()));

}

}

public static class RoutingStateMixins

{

/// <summary>

/// Locate the first ViewModel in the stack that matches a certain Type.

/// </summary>

/// <returns>The matching ViewModel or null if none exists.</returns>

public static T FindViewModelInStack<T>(this RoutingState This)

where T : IRoutableViewModel

{

return This.NavigationStack.Reverse().OfType<T>().FirstOrDefault();

}

/// <summary>

/// Returns the currently visible ViewModel

/// </summary>

public static IRoutableViewModel GetCurrentViewModel(this RoutingState This)

{

return This.NavigationStack.LastOrDefault();

}

/// <summary>

/// Creates a ReactiveCommand which will, when invoked, navigate to the

/// type specified by the type parameter via looking it up in the

/// Dependency Resolver.

/// </summary>

public static IReactiveCommand<object> NavigateCommandFor<T>(this RoutingState This)

where T : IRoutableViewModel

{

var ret = new ReactiveCommand<object>(This.Navigate.CanExecuteObservable, x => Observable.Return(x));

ret.Select(_ => (IRoutableViewModel)Locator.Current.GetService<T>()).InvokeCommand(This.Navigate);

return ret;

}

}

}