fetch items in background task

apple/OmnivoreKit/Sources/App/Services.swift

@@ -27,7 +27,7 @@ extension Services {
       if let task = task as? BGAppRefreshTask {
         EventTracker.trackForDebugging("executing app.omnivore.fetchLinkedItems bg task")
         logger.debug("in background task register closure")
-        startBackgroundFetch(task: task)
+        performBackgroundFetch(task: task)
       }
     }
   }
@@ -45,7 +45,8 @@ extension Services {
     }
   }
 
-  static func startBackgroundFetch(task: BGAppRefreshTask) {
+  static func performBackgroundFetch(task: BGAppRefreshTask) {
+    Services.logger.debug("starting background fetch")
     scheduleBackgroundFetch()
     let services = Services()
 
@@ -54,22 +55,25 @@ extension Services {
       logger.debug("handling background fetch expiration")
     }
 
-    services.peformBackgroundFetch()
-    EventTracker.trackForDebugging("background fetch task completed successfully")
-    task.setTaskCompleted(success: true)
-  }
-
-  func peformBackgroundFetch() {
-    Services.logger.debug("starting background fetch")
-
-    guard authenticator.hasValidAuthToken else {
-      EventTracker.trackForDebugging("background fetch failed: user does not habe a valid auth token")
+    guard services.authenticator.hasValidAuthToken else {
+      EventTracker.trackForDebugging("background fetch failed: user does not have a valid auth token")
       Services.logger.debug("background fetch failed: user does not habe a valid auth token")
+      task.setTaskCompleted(success: false)
       return
     }
 
-    Services.logger.debug("ayo this is a background task!")
-    // TODO: perform tasks using data service
+    Task {
+      do {
+        try await services.dataService.fetchLinkedItemsBackgroundTask()
+        logger.debug("fetch complete")
+        EventTracker.trackForDebugging("background fetch task completed successfully")
+        task.setTaskCompleted(success: true)
+      } catch {
+        logger.debug("fetch failed")
+        EventTracker.trackForDebugging("background fetch task failed")
+        task.setTaskCompleted(success: false)
+      }
+    }
   }
 }
 

apple/OmnivoreKit/Sources/App/Views/Home/HomeFeedViewModel.swift

@@ -98,7 +98,9 @@ import Views
       isLoading = false
       receivedIdx = thisSearchIdx
       cursor = queryResult.cursor
-      await dataService.prefetchPages(itemIDs: newItems.map(\.unwrappedID))
+      if let username = dataService.currentViewer?.username {
+        await dataService.prefetchPages(itemIDs: newItems.map(\.unwrappedID), username: username)
+      }
     } else {
       updateFetchController(dataService: dataService)
     }

apple/OmnivoreKit/Sources/Services/DataService/FetchLinkedItemsBackgroundTask.swift

@@ -0,0 +1,57 @@
+import CoreData
+import Foundation
+import Models
+import SwiftGraphQL
+
+extension DataService {
+  public func fetchLinkedItemsBackgroundTask() async throws {
+    // Query the server for item IDs and compare against CoreData
+    // to see what we're missing
+    let missingItemIds = try await fetchMissingItemIDs()
+    guard !missingItemIds.isEmpty else { return }
+
+    let username: String? = await backgroundContext.perform(schedule: .immediate) {
+      let fetchRequest: NSFetchRequest<Models.Viewer> = Viewer.fetchRequest()
+      fetchRequest.fetchLimit = 1 // we should only have one viewer saved
+      return try? self.backgroundContext.fetch(fetchRequest).first?.username
+    }
+
+    guard let username = username else {
+      throw BasicError.message(messageText: "could not retrieve username from core data")
+    }
+
+    // Fetch the items
+    for itemID in missingItemIds { // TOOD: run these in parallel
+      logger.debug("fetching item with ID: \(itemID)")
+      _ = try await articleContent(username: username, itemID: itemID, useCache: false)
+      logger.debug("done fetching item with ID: \(itemID)")
+    }
+  }
+
+  func fetchMissingItemIDs(previouslyFetchedIDs: [String] = [], cursor: String? = nil) async throws -> [String] {
+    logger.debug("fetching more IDS: \(cursor ?? "no cursor")")
+    let maxItemCount = 30
+    let fetchResult = try await fetchLinkedItemIDs(limit: 10, cursor: cursor)
+    let newItemsToFetch = await itemsNotInStore(from: fetchResult.itemIDs)
+    let itemsToFetch = previouslyFetchedIDs + newItemsToFetch
+
+    if newItemsToFetch.isEmpty || itemsToFetch.count > maxItemCount || fetchResult.cursor == nil {
+      return itemsToFetch
+    } else {
+      return try await fetchMissingItemIDs(previouslyFetchedIDs: itemsToFetch, cursor: fetchResult.cursor)
+    }
+  }
+
+  func itemsNotInStore(from itemIDs: [String]) async -> [String] {
+    let fetchRequest: NSFetchRequest<Models.LinkedItem> = LinkedItem.fetchRequest()
+    fetchRequest.predicate = NSPredicate(format: "id IN %@", itemIDs)
+
+    return await backgroundContext.perform(schedule: .immediate) {
+      if let foundIDs = (try? self.backgroundContext.fetch(fetchRequest).map(\.unwrappedID)) {
+        return itemIDs.filter { !foundIDs.contains($0) }
+      } else {
+        return []
+      }
+    }
+  }
+}

apple/OmnivoreKit/Sources/Services/DataService/Queries/ArticleContentQuery.swift

@@ -9,9 +9,9 @@ extension DataService {
     let retryCount: Int
   }
 
-  public func prefetchPages(itemIDs: [String]) async {
-    guard let username = currentViewer?.username else { return }
-
+  public func prefetchPages(itemIDs: [String], username: String) async {
+    // TODO: make this concurrent
+    // TODO: make a non-pending page option for BG tasks
     for itemID in itemIDs {
       await prefetchPage(pendingLink: PendingLink(itemID: itemID, retryCount: 1), username: username)
     }
@@ -183,9 +183,8 @@ extension DataService {
       let fetchRequest: NSFetchRequest<Models.LinkedItem> = LinkedItem.fetchRequest()
       fetchRequest.predicate = NSPredicate(format: "id == %@", item.id)
 
-      let linkedItem = try? self.backgroundContext.fetch(fetchRequest).first
-
-      guard let linkedItem = linkedItem else { return }
+      let existingItem = try? self.backgroundContext.fetch(fetchRequest).first
+      let linkedItem = existingItem ?? LinkedItem(entity: LinkedItem.entity(), insertInto: self.backgroundContext)
 
       let highlightObjects = highlights.map {
         $0.asManagedObject(context: self.backgroundContext)

apple/OmnivoreKit/Sources/Services/DataService/Queries/LinkedItemIDsQuery.swift

@@ -0,0 +1,67 @@
+import Foundation
+import Models
+import SwiftGraphQL
+
+extension DataService {
+  struct LinkedItemIDFetchResult {
+    let itemIDs: [String]
+    let cursor: String?
+  }
+
+  func fetchLinkedItemIDs(limit: Int, cursor: String?) async throws -> LinkedItemIDFetchResult {
+    enum QueryResult {
+      case success(result: LinkedItemIDFetchResult)
+      case error(error: String)
+    }
+
+    let articleIDSelection = Selection.SearchItemEdge {
+      try $0.node(selection: Selection.SearchItem { try $0.id() })
+    }
+
+    let selection = Selection<QueryResult, Unions.SearchResult> {
+      try $0.on(
+        searchError: .init {
+          QueryResult.error(error: try $0.errorCodes().description)
+        },
+        searchSuccess: .init {
+          QueryResult.success(
+            result: LinkedItemIDFetchResult(
+              itemIDs: try $0.edges(selection: articleIDSelection.list),
+              cursor: try $0.pageInfo(selection: Selection.PageInfo {
+                try $0.endCursor()
+              })
+            )
+          )
+        }
+      )
+    }
+
+    let query = Selection.Query {
+      try $0.search(
+        after: OptionalArgument(cursor),
+        first: OptionalArgument(limit),
+        query: OptionalArgument(nil),
+        selection: selection
+      )
+    }
+
+    let path = appEnvironment.graphqlPath
+    let headers = networker.defaultHeaders
+
+    return try await withCheckedThrowingContinuation { continuation in
+      send(query, to: path, headers: headers) { queryResult in
+        guard let payload = try? queryResult.get() else {
+          continuation.resume(throwing: BasicError.message(messageText: "network error"))
+          return
+        }
+
+        switch payload.data {
+        case let .success(result: result):
+          continuation.resume(returning: result)
+        case .error:
+          continuation.resume(throwing: BasicError.message(messageText: "LinkedItem fetch error"))
+        }
+      }
+    }
+  }
+}

apple/OmnivoreKit/Sources/Services/InternalModels/InternalLinkedItem.swift

@@ -54,7 +54,6 @@ struct InternalLinkedItem {
 }
 
 extension Sequence where Element == InternalLinkedItem {
-  // TODO: -optimization use batch update?
   func persist(context: NSManagedObjectContext) -> [LinkedItem]? {
     var linkedItems: [LinkedItem]?
     context.performAndWait {