NetNewsWire/Frameworks/Account/Feedly/Operations/FeedlyMirrorCollectionsAsFoldersOperation.swift

//
//  FeedlyMirrorCollectionsAsFoldersOperation.swift
//  Account
//
//  Created by Kiel Gillard on 20/9/19.
//  Copyright © 2019 Ranchero Software, LLC. All rights reserved.
//

import Foundation
import os.log

protocol FeedlyFeedsAndFoldersProviding {
	var feedsAndFolders: [([FeedlyFeed], Folder)] { get }
}

/// Reflect Collections from Feedly as Folders.
final class FeedlyMirrorCollectionsAsFoldersOperation: FeedlyOperation, FeedlyFeedsAndFoldersProviding {
	
	let account: Account
	let collectionsProvider: FeedlyCollectionProviding
	let log: OSLog
	
	private(set) var feedsAndFolders = [([FeedlyFeed], Folder)]()

	init(account: Account, collectionsProvider: FeedlyCollectionProviding, log: OSLog) {
		self.collectionsProvider = collectionsProvider
		self.account = account
		self.log = log
	}
	
	override func run() {
		defer {
			didFinish()
		}
		
		let localFolders = account.folders ?? Set()
		let collections = collectionsProvider.collections
		
		feedsAndFolders = collections.compactMap { collection -> ([FeedlyFeed], Folder)? in
			let parser = FeedlyCollectionParser(collection: collection)
			guard let folder = account.ensureFolder(with: parser.folderName) else {
				assertionFailure("Why wasn't a folder created?")
				return nil
			}
			folder.externalID = parser.externalID
			return (collection.feeds, folder)
		}
		
		os_log(.debug, log: log, "Ensured %i folders for %i collections.", feedsAndFolders.count, collections.count)
		
		// Remove folders without a corresponding collection
		let collectionFolders = Set(feedsAndFolders.map { $0.1 })
		let foldersWithoutCollections = localFolders.subtracting(collectionFolders)
		
		if !foldersWithoutCollections.isEmpty {
			for unmatched in foldersWithoutCollections {
				account.removeFolder(unmatched)
			}
			
			os_log(.debug, log: log, "Removed %i folders: %@", foldersWithoutCollections.count, foldersWithoutCollections.map { $0.externalID ?? $0.nameForDisplay })
		}
	}
}