// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import SwiftUI
/// Class to handle destination drag interactions in the overflow menu
/// customization flow.
class DestinationDragHandler: ObservableObject {
/// Collection of data for the current drag interaction.
struct CurrentDragData {
var item: OverflowMenuDestination
var initialIndex: Int
var initialDestinationUsageEnabled: Bool
}
/// The destination customization model underlying the session.
@ObservedObject var destinationModel: DestinationCustomizationModel
/// The data for the current drag session. `nil` if nothing is being dragged.
@Published private(set) var currentDrag: CurrentDragData? = nil
/// Whether the drag is currently over the destinations row. This is necessary
/// because the drag system doesn't currently offer a way to tell in general
/// when a drag ends, so the state needs to be correct for whenever the drag
/// happens to end.
@Published var dragOnDestinations = false
/// Stores all currently existing item providers weakly.
var providers: [WeakItemProviderContainer] = []
init(destinationModel: DestinationCustomizationModel) {
self.destinationModel = destinationModel
}
/// Begin a new drag of the given `destination`.
func startDrag(from item: OverflowMenuDestination) {
// End any existing drag in case it wasn't able to be ended before.
endDrag()
guard let index = destinationModel.shownDestinations.firstIndex(of: item) else {
return
}
currentDrag = CurrentDragData(
item: item, initialIndex: index,
initialDestinationUsageEnabled: destinationModel.destinationUsageEnabled)
}
/// Ends the current drag state.
func endDrag() {
currentDrag = nil
dragOnDestinations = false
}
/// Returns a new drop delegate for drop actions on the provided
/// `destination`.
func newDropDelegate(forDestination destination: OverflowMenuDestination)
-> DestinationDropDelegate
{
return DestinationDropDelegate(handler: self, destination: destination)
}
/// Returns a new drop delegate for the entire destination list.
func newDestinationListDropDelegate() -> DestinationListDropDelegate {
return DestinationListDropDelegate(handler: self)
}
/// Returns a new item provider for the drag interaction.
func newItemProvider(forDestination destination: OverflowMenuDestination) -> NSItemProvider {
let itemProvider = DidEndItemProvider(object: destination.name as NSString)
itemProvider.delegate = self
// When VoiceOver is enabled, sometimes the system requests 2 providers
// before deallocating one, so storing all existing providers is required
// to know when all providers have been destroyed.
providers.append(WeakItemProviderContainer(provider: itemProvider))
return itemProvider
}
/// Performs a drop into a list. Should be passed to `List`'s `.onInsert`
/// method.
func performListDrop(index: Int, providers: [NSItemProvider]) {
currentDrag?.item.shown = false
}
/// Drop delegate for an individual destination. This is used for drop actions
/// when the user's finger is over the given destination.
struct DestinationDropDelegate: DropDelegate {
let handler: DestinationDragHandler
let destination: OverflowMenuDestination
func dropUpdated(info: DropInfo) -> DropProposal? {
return DropProposal(operation: .move)
}
/// Ends the current drag.
func performDrop(info: DropInfo) -> Bool {
// Any necessary state has already been updated, so just stop the current
// drag.
handler.endDrag()
return true
}
/// Updates the state when the user's finger enters the given destination.
func dropEntered(info: DropInfo) {
// Moves the dragged destination to the position where the user's finger
// is and updates the `destinationUsageEnabled` property if the order has
// changed.
guard let currentDrag = handler.currentDrag else {
return
}
handler.dragOnDestinations = true
guard
let fromIndex = handler.destinationModel.shownDestinations.firstIndex(
of: currentDrag.item)
else {
return
}
handler.destinationModel.destinationUsageEnabled =
currentDrag.initialDestinationUsageEnabled && fromIndex == currentDrag.initialIndex
guard let toIndex = handler.destinationModel.shownDestinations.firstIndex(of: destination)
else {
return
}
if fromIndex != toIndex {
withAnimation {
self.handler.destinationModel.shownDestinations.move(
fromOffsets: IndexSet(integer: fromIndex),
toOffset: toIndex > fromIndex ? toIndex + 1 : toIndex)
}
}
}
}
/// Drop delegate for the entire destination list. This allow making changes
/// for if the user drags the destination out of the list.
struct DestinationListDropDelegate: DropDelegate {
let handler: DestinationDragHandler
func dropUpdated(info: DropInfo) -> DropProposal? {
return DropProposal(operation: .cancel)
}
/// Ends the current drag. Any necessary state has already been updated.
func performDrop(info: DropInfo) -> Bool {
handler.endDrag()
return true
}
/// Updates the drag state for when the user's finger leaves the row.
func dropExited(info: DropInfo) {
// As the system does not notify the app when the drag directly ends, any
// preparation for a drag ending in random space must be set up here.
handler.dragOnDestinations = false
}
/// Updates the drag state for when the user's finger enters the row.
func dropEntered(info: DropInfo) {
// Set up the correct state for if a drag re-enters the destinations list.
handler.dragOnDestinations = true
}
}
}
extension DestinationDragHandler: DidEndItemProviderDelegate {
func didEndItemProviderDidEnd(_ provider: DidEndItemProvider) {
providers = providers.filter { container in
container.provider != nil && container.provider != provider
}
if providers.isEmpty {
endDrag()
}
}
}
protocol DidEndItemProviderDelegate: AnyObject {
/// Alerts the delegate when the item provider is being deinitialized.
func didEndItemProviderDidEnd(_ provider: DidEndItemProvider)
}
/// A custom item provider class that alerts its delegate when it is about to
/// be de-initialized.
class DidEndItemProvider: NSItemProvider {
weak var delegate: DidEndItemProviderDelegate?
deinit {
delegate?.didEndItemProviderDidEnd(self)
}
}
/// Container class that holds a weak `DidEndItemProvider`, allowing for
/// collections to hold this weakly.
class WeakItemProviderContainer {
weak var provider: DidEndItemProvider?
init(provider: DidEndItemProvider?) {
self.provider = provider
}
}
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