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--
-- All or portions of this file Copyright (c) Amazon.com, Inc. or its affiliates or
-- its licensors.
--
-- For complete copyright and license terms please see the LICENSE at the root of this
-- distribution (the "License"). All use of this software is governed by the License,
-- or, if provided, by the license below or the license accompanying this file. Do not
-- remove or modify any license notices. This file is distributed on an "AS IS" BASIS,
-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
--
--
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-- DraggableCrossCanvasElement - script for a draggable element that can be dropped on drop targets
-- on other canvases.
--
-- This makes use of some of the more advanced feature of the UiDraggableBus, such as the proxy
-- features.
--
-- Note that the element with this script on will get cloned to make a proxy draggable element.
-- So this same script runs on both the original and the proxy.
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local DraggableCrossCanvasElement = 
{
    Properties = 
    {
	},
}

function DraggableCrossCanvasElement:OnActivate()
	self.draggableHandler = UiDraggableNotificationBus.Connect(self, self.entityId)
	self.dragCanvas = EntityId()
	self.clonedElement = EntityId()
	self.originalParent = EntityId()
end

function DraggableCrossCanvasElement:OnDeactivate()
	self.draggableHandler:Disconnect()
end

function DraggableCrossCanvasElement:OnDragStart(position)

	self.isProxy = UiDraggableBus.Event.IsProxy(self.entityId)
	
	-- Since we want to support dropping on a drop target on any canvas we set this flag
	-- we want both the original and the proxy to set this flag, we turn it off on the drag end
	UiDraggableBus.Event.SetCanDropOnAnyCanvas(self.entityId, true)
	
	if (not self.isProxy) then
		-- this is the original, we need to make a new canvas in front of all the other canvases
		-- to move the proxy on
		-- If no changes have been made to canvas draw orders then the new canvas will draw in
		-- front of everything else. Otherwise, we would have to set the draw order to a high
		-- number here.
		self.dragCanvas = UiCanvasManagerBus.Broadcast.CreateCanvas()
	
		if (self.dragCanvas:IsValid()) then
			-- clone the original draggable making it a child of the root element on the new canvas
			self.clonedElement = UiCanvasBus.Event.CloneElement(self.dragCanvas, self.entityId, EntityId(), EntityId())
	
			if (self.clonedElement:IsValid()) then
				-- set the new cloned draggable element to act as a proxy for the original element
				UiDraggableBus.Event.SetAsProxy(self.clonedElement, self.entityId, position)
		
				-- hide the original element by reparenting it and disabling it so that we can drop
				-- the proxy at the original location if we want to
			    self.originalParent = UiElementBus.Event.GetParent(self.entityId)
				UiElementBus.Event.Reparent(self.entityId, EntityId(), EntityId())
				UiElementBus.Event.SetIsEnabled(self.entityId, false)
			end
		end
	else
		-- This is the proxy, it gets an OnDragStart after SetAsProxy is called, at that point we
		-- to move it to where the cursor is
    	UiTransformBus.Event.SetViewportPosition(self.entityId, position)
	end
end

function DraggableCrossCanvasElement:OnDrag(position)
	if (self.isProxy) then
		-- we do not move the original during the drag - just the proxy
	    UiTransformBus.Event.SetViewportPosition(self.entityId, position)
	end
end

function DraggableCrossCanvasElement:OnDragEnd(position)

	if (self.isProxy) then
		-- this is the proxy, it gets OnDragEnd before the original, calling
		-- ProxyDragEnd will result in OnDragEnd being called on the original
		UiDraggableBus.Event.ProxyDragEnd(self.entityId, position)
	else
		-- this is the original

		if (self.dragCanvas:IsValid()) then
			if (self.clonedElement:IsValid()) then
				-- unhide the original and put it back under its original parent
				UiElementBus.Event.SetIsEnabled(self.entityId, true)
				UiElementBus.Event.Reparent(self.entityId, self.originalParent, EntityId())
		
				-- clean up by destroying the proxy element and the temporary canvas
				UiElementBus.Event.DestroyElement(self.clonedElement)
			end

			UiCanvasManagerBus.Broadcast.UnloadCanvas(self.dragCanvas)
		end
	end

	-- turn off the "Drop on any canvas flag" just for good measure
	UiDraggableBus.Event.SetCanDropOnAnyCanvas(self.entityId, false)

end

return DraggableCrossCanvasElement