lib/app: intro app.nit abstract UI API

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/lib/app/ui.nit b/lib/app/ui.nit
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+# This file is part of NIT ( http://www.nitlanguage.org ).
+#
+# 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.
+
+# Portable UI API for the _app.nit_ framework
+module ui
+
+import app_base
+
+redef class App
+       super AppComponent
+
+       # The current `Window` of this activity
+       #
+       # This attribute must be set by refinements of `App`.
+       var window: Window is writable
+
+       redef fun on_create do window.on_create
+
+       redef fun on_start do window.on_start
+
+       redef fun on_resume do window.on_resume
+
+       redef fun on_pause do window.on_pause
+
+       redef fun on_stop do window.on_stop
+
+       redef fun on_destroy do window.on_destroy
+
+       redef fun on_restore_state do window.on_restore_state
+
+       redef fun on_save_state do window.on_save_state
+end
+
+# An event created by an `AppComponent` and sent to `AppObserver`s
+interface AppEvent
+end
+
+# Observer of `AppEvent`s raised by `AppComponent`s
+interface AppObserver
+       # Notification of `event` raised by `sender`
+       #
+       # To be implemented in subclasses as needed.
+       fun on_event(event: AppEvent) do end
+end
+
+redef class AppComponent
+       super AppObserver
+
+       # All `AppObserver` notified of events raised by `self`
+       #
+       # By default, only `self` is an observer.
+       # Any other `AppObserver` can be added to this collection.
+       var observers = new HashSet[AppObserver].from([self: AppObserver])
+
+       # Propagate `event` to all `observers` by calling `AppObserver::on_event`
+       fun notify_observers(event: AppEvent)
+       do
+               for observer in observers do
+                       observer.on_event(event)
+               end
+       end
+end
+
+# A control implementing the UI
+class Control
+       super AppComponent
+
+       # Direct parent `Control` in the control tree
+       #
+       # If `null` then `self` is at the root of the tree, or not yet attached.
+       var parent: nullable CompositeControl = null is private writable(set_parent)
+
+       # Direct parent `Control` in the control tree
+       #
+       # Setting `parent` calls `remove` on the old parent and `add` on the new one.
+       fun parent=(parent: nullable CompositeControl)
+       is autoinit     do
+               var old_parent = self.parent
+               if old_parent != null and old_parent != parent then
+                       old_parent.remove self
+               end
+
+               if parent != null then parent.add self
+
+               set_parent parent
+       end
+end
+
+# A `Control` grouping other controls
+class CompositeControl
+       super Control
+
+       private var items = new HashSet[Control]
+
+       # Add `item` as a child of `self`
+       protected fun add(item: Control) do items.add item
+
+       # Remove `item` from `self`
+       protected fun remove(item: Control) do if has(item) then items.remove item
+
+       # Is `item` in `self`?
+       protected fun has(item: Control): Bool do return items.has(item)
+
+       redef fun on_create do for i in items do i.on_create
+
+       redef fun on_start do for i in items do i.on_start
+
+       redef fun on_resume do for i in items do i.on_resume
+
+       redef fun on_pause do for i in items do i.on_pause
+
+       redef fun on_stop do for i in items do i.on_stop
+
+       redef fun on_destroy do for i in items do i.on_destroy
+
+       redef fun on_restore_state do for i in items do i.on_restore_state
+
+       redef fun on_save_state do for i in items do i.on_save_state
+end
+
+# A window, root of the `Control` tree
+class Window
+       super CompositeControl
+end
+
+# A viewable `Control`
+abstract class View
+       super Control
+
+       # Is this control enabled so the user can interact with it?
+       #
+       # By default, or if set to `null`, the control is enabled.
+       var enabled: nullable Bool is writable #, abstract FIXME with #1311
+end
+
+# A control with some `text`
+abstract class TextView
+       super View
+
+       # Main `Text` of this control
+       #
+       # By default, or if set to `null`, no text is shown.
+       var text: nullable Text is writable #, abstract FIXME with #1311
+end
+
+# A control for the user to enter custom `text`
+class TextInput
+       super TextView
+end
+
+# A pushable button, raises `ButtonPressEvent`
+class Button
+       super TextView
+end
+
+# A `Button` press event
+class ButtonPressEvent
+       super AppEvent
+
+       # The `Button` that raised this event
+       var sender: Button
+end
+
+# A layout to visually organize `Control`s
+abstract class Layout
+       super View
+       super CompositeControl
+end
+
+# An horizontal linear organization
+class HorizontalLayout
+       super Layout
+end
+
+# A vertical linear organization
+class VerticalLayout
+       super Layout
+end