Create FetchUnreadCountsForFeedsOperation.

Frameworks/ArticlesDatabase/Operations/FetchUnreadCountsForFeedsOperation.swift

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+//
+//  FetchUnreadCountsForFeedsOperation.swift
+//  ArticlesDatabase
+//
+//  Created by Brent Simmons on 2/1/20.
+//  Copyright © 2020 Ranchero Software. All rights reserved.
+//
+
+import Foundation
+import RSCore
+import RSDatabase
+
+/// Fetch the unread counts for a number of feeds.
+public final class FetchUnreadCountsForFeedsOperation: MainThreadOperation {
+
+	public var unreadCountDictionary: UnreadCountDictionary?
+	public let feedIDs: Set<String>
+
+	// MainThreadOperation
+	public var isCanceled = false
+	public var id: Int?
+	public weak var operationDelegate: MainThreadOperationDelegate?
+	public var name: String?
+	public var completionBlock: MainThreadOperation.MainThreadOperationCompletionBlock?
+
+	private let queue: DatabaseQueue
+	private let cutoffDate: Date
+
+	init(feedIDs: Set<String>, databaseQueue: DatabaseQueue, cutoffDate: Date) {
+		self.feedIDs = feedIDs
+		self.queue = databaseQueue
+		self.cutoffDate = cutoffDate
+	}
+
+	public func run() {
+		queue.runInDatabase { databaseResult in
+			if self.isCanceled {
+				self.informOperationDelegateOfCompletion()
+				return
+			}
+
+			switch databaseResult {
+			case .success(let database):
+				self.fetchUnreadCounts(database)
+			case .failure:
+				self.informOperationDelegateOfCompletion()
+			}
+		}
+	}
+}
+
+private extension FetchUnreadCountsForFeedsOperation {
+
+	func fetchUnreadCounts(_ database: FMDatabase) {
+		let placeholders = NSString.rs_SQLValueList(withPlaceholders: UInt(feedIDs.count))!
+		let sql = "select distinct feedID, count(*) from articles natural join statuses where feedID in \(placeholders) and read=0 and userDeleted=0 and (starred=1 or dateArrived>?) group by feedID;"
+
+		var parameters = [Any]()
+		parameters += Array(feedIDs) as [Any]
+		parameters += [cutoffDate] as [Any]
+
+		guard let resultSet = database.executeQuery(sql, withArgumentsIn: parameters) else {
+			informOperationDelegateOfCompletion()
+			return
+		}
+		if isCanceled {
+			informOperationDelegateOfCompletion()
+			return
+		}
+
+		var d = UnreadCountDictionary()
+		while resultSet.next() {
+			if isCanceled {
+				resultSet.close()
+				informOperationDelegateOfCompletion()
+				return
+			}
+			let unreadCount = resultSet.long(forColumnIndex: 1)
+			if let webFeedID = resultSet.string(forColumnIndex: 0) {
+				d[webFeedID] = unreadCount
+			}
+		}
+		resultSet.close()
+
+		unreadCountDictionary = d
+		informOperationDelegateOfCompletion()
+	}
+}