TabBarCollectionView.swift

//
//  TabBarCollectionView.swift
//
//  Copyright © 2020 DuckDuckGo. All rights reserved.
//
//  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.
//

import Cocoa
import os.log

final class TabBarCollectionView: NSCollectionView {

    override var acceptsFirstResponder: Bool {
        return false
    }
    
    override func awakeFromNib() {
        super.awakeFromNib()
        
        let nib = NSNib(nibNamed: "TabBarViewItem", bundle: nil)
        register(nib, forItemWithIdentifier: TabBarViewItem.identifier)

        // Register for the dropped object types we can accept.
        registerForDraggedTypes([.URL])
        // Enable dragging items from our CollectionView to other applications.
        setDraggingSourceOperationMask([.private], forLocal: false)
        // Enable dragging items within and into our CollectionView.
        setDraggingSourceOperationMask([.private], forLocal: true)
    }

    override func selectItems(at indexPaths: Set<IndexPath>, scrollPosition: NSCollectionView.ScrollPosition) {
        super.selectItems(at: indexPaths, scrollPosition: scrollPosition)

        updateItemsLeftToSelectedItems(indexPaths)
    }

    func clearSelection(animated: Bool = false) {
        if animated {
            animator().deselectItems(at: selectionIndexPaths)
        } else {
            deselectItems(at: selectionIndexPaths)
        }
    }
    
    func scrollToSelected() {
        guard selectionIndexPaths.count == 1, let indexPath = selectionIndexPaths.first else {
            os_log("TabBarCollectionView: More than 1 item or no item highlighted", type: .error)
            return
        }

        let rect = frameForItem(at: indexPath.item)
        animator().performBatchUpdates({
            animator().scrollToVisible(rect)
        }, completionHandler: nil)
    }
    
    func scrollToEnd(completionHandler: ((Bool) -> Void)? = nil) {
        animator().performBatchUpdates({
            animator().scroll(CGPoint(x: self.bounds.size.width, y: 0))
        }, completionHandler: completionHandler)
    }

    func scrollToBeginning(completionHandler: ((Bool) -> Void)? = nil) {
        animator().performBatchUpdates({
            animator().scroll(CGPoint(x: 0, y: 0))
        }, completionHandler: completionHandler)
    }

    func invalidateLayout() {
        NSAnimationContext.current.duration = 1/3
        collectionViewLayout?.invalidateLayout()
    }

    private func updateItemsLeftToSelectedItems(_ selectionIndexPaths: Set<IndexPath>) {
        visibleItems().forEach {
            ($0 as? TabBarViewItem)?.isLeftToSelected = false
        }

        for indexPath in selectionIndexPaths where indexPath.item > 0 {
            let leftToSelectionIndexPath = IndexPath(item: indexPath.item - 1)
            (item(at: leftToSelectionIndexPath) as? TabBarViewItem)?.isLeftToSelected = true
        }
    }
}

extension NSCollectionView {

    var clipView: NSClipView? {
        return enclosingScrollView?.contentView
    }

    var isAtEndScrollPosition: Bool {
        guard let clipView = clipView else {
            os_log("TabBarCollectionView: Clip view is nil", type: .error)
            return false
        }

        return clipView.bounds.origin.x + clipView.bounds.size.width >= bounds.size.width
    }

    var isAtStartScrollPosition: Bool {
        guard let clipView = clipView else {
            os_log("TabBarCollectionView: Clip view is nil", type: .error)
            return false
        }

        return clipView.bounds.origin.x <= 0
    }

}