/*

* Copyright 2016 Square Inc.

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

package flow;

import android.support.annotation.NonNull;

public interface Dispatcher {

/**

* Called when the history is about to change. Note that Flow does not consider the

* Traversal to be finished, and will not actually update the history, until the callback is

* triggered. Traversals cannot be canceled.

* <p>

* Also called immediately after {@link Flow#setDispatcher}, to update the new dispatcher

* to Flow's current state. Such bootstrap Traversals have a null {@link Traversal#origin},

* and {@link Direction#REPLACE} as their direction. It should be noted that the dispatcher

* is set and unset each time the app pauses and resumes, meaning the dispatcher will receive

* a bootstrap call each time the app is activated.

* <p>

* Dispatchers are required to be idempotent. They should check whether the app is already in

* the correct state for the incoming key before performing any redundant work. (This probably

* includes comparing the {@link Flow#getKey(android.view.View) key of the currently visible

* view(s)} to that in {@link Traversal#destination} before doing any unnecessary inflation

* and rendering). If no update is needed, short circuit

* by firing the callback immediately and returning.

*

* @param callback Must be called to indicate completion of the traversal.

*/

void dispatch(@NonNull Traversal traversal, @NonNull TraversalCallback callback);

}