// Licensed to the .NET Foundation under one or more agreements.

// The .NET Foundation licenses this file to you under the MS-PL license.

// See the LICENSE file in the project root for more information.

using System;

using System.Linq;

using System.Reactive;

using System.Reactive.Concurrency;

using System.Reactive.Linq;

using System.Runtime.Serialization;

namespace ReactiveUI

{

/// <summary>

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

/// navigate to other ViewModels.

/// </summary>

[DataContract]

public class RoutingState : ReactiveObject

{

static RoutingState()

{

RxApp.EnsureInitialized();

}

[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; }

}

[IgnoreDataMember]

IScheduler scheduler;

/// <summary>

/// The scheduler used for commands. Defaults to <c>RxApp.MainThreadScheduler</c>.

/// </summary>

[IgnoreDataMember]

public IScheduler Scheduler {

get { return this.scheduler; }

set {

if (this.scheduler != value) {

this.scheduler = value;

this.setupRx();

}

}

}

/// <summary>

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

/// </summary>

[IgnoreDataMember]

public ReactiveCommand<Unit, 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<IRoutableViewModel, IRoutableViewModel> 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<IRoutableViewModel, IRoutableViewModel> 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()

{

var scheduler = this.scheduler ?? RxApp.MainThreadScheduler;

var countAsBehavior = Observable.Concat(

Observable.Defer(() => Observable.Return(_NavigationStack.Count)),

NavigationStack.CountChanged);

NavigateBack =

ReactiveCommand.CreateFromObservable(() => {

NavigationStack.RemoveAt(NavigationStack.Count - 1);

return Observables.Unit;

},

countAsBehavior.Select(x => x > 1),

scheduler);

Navigate = ReactiveCommand.CreateFromObservable<IRoutableViewModel, IRoutableViewModel>(x => {

var vm = x as IRoutableViewModel;

if (vm == null) {

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

}

NavigationStack.Add(vm);

return Observable.Return(x);

},

outputScheduler: scheduler);

NavigateAndReset = ReactiveCommand.CreateFromObservable<IRoutableViewModel, IRoutableViewModel>(x => {

NavigationStack.Clear();

return Navigate.Execute(x);

},

outputScheduler: scheduler);

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();

}

}

}