Prefer task api

apollo-ios-pagination/Sources/ApolloPagination/AnyGraphQLPager.swift

@@ -1,7 +1,6 @@
 import Apollo
 import ApolloAPI
 import Combine
-import Dispatch
 
 /// Type-erases a query pager, transforming data from a generic type to a specific type, often a view model or array of view models.
 public class AnyGraphQLQueryPager<Model> {
@@ -87,46 +86,34 @@ public class AnyGraphQLQueryPager<Model> {
   /// Load the next page, if available.
   /// - Parameters:
   ///   - cachePolicy: The Apollo `CachePolicy` to use. Defaults to `returnCacheDataAndFetch`.
-  ///   - callbackQueue: The `DispatchQueue` that the `completion` fires on. Defaults to `main`.
   ///   - completion: A completion block that will always trigger after the execution of this operation. Passes an optional error, of type `PaginationError`, if there was an internal error related to pagination. Does not surface network errors. Defaults to `nil`.
   public func loadNext(
     cachePolicy: CachePolicy = .returnCacheDataAndFetch,
-    callbackQueue: DispatchQueue = .main,
     completion: ((PaginationError?) -> Void)? = nil
   ) {
-    pager.loadNext(cachePolicy: cachePolicy, callbackQueue: callbackQueue, completion: { error in
-      callbackQueue.async { completion?(error) }
-    })
+    pager.loadNext(cachePolicy: cachePolicy, completion: completion)
   }
 
   /// Load the previous page, if available.
   /// - Parameters:
   ///   - cachePolicy: The Apollo `CachePolicy` to use. Defaults to `returnCacheDataAndFetch`.
-  ///   - callbackQueue: The `DispatchQueue` that the `completion` fires on. Defaults to `main`.
   ///   - completion: A completion block that will always trigger after the execution of this operation. Passes an optional error, of type `PaginationError`, if there was an internal error related to pagination. Does not surface network errors. Defaults to `nil`.
   public func loadPrevious(
     cachePolicy: CachePolicy = .returnCacheDataAndFetch,
-    callbackQueue: DispatchQueue = .main,
     completion: ((PaginationError?) -> Void)? = nil
   ) {
-    pager.loadPrevious(cachePolicy: cachePolicy, callbackQueue: callbackQueue, completion: { error in
-      callbackQueue.async { completion?(error) }
-    })
+    pager.loadPrevious(cachePolicy: cachePolicy, completion: completion)
   }
 
   /// Loads all pages.
   /// - Parameters:
   ///   - fetchFromInitialPage: Pass true to begin loading from the initial page; otherwise pass false.  Defaults to `true`.  **NOTE**: Loading all pages with this value set to `false` requires that the initial page has already been loaded previously.
-  ///   - callbackQueue: The `DispatchQueue` that the `completion` fires on. Defaults to `main`.
   ///   - completion: A completion block that will always trigger after the execution of this operation. Passes an optional error, of type `PaginationError`, if there was an internal error related to pagination. Does not surface network errors. Defaults to `nil`.
   public func loadAll(
     fetchFromInitialPage: Bool = true,
-    callbackQueue: DispatchQueue = .main,
     completion: ((PaginationError?) -> Void)? = nil
   ) {
-    pager.loadAll(fetchFromInitialPage: fetchFromInitialPage, callbackQueue: callbackQueue, completion: { error in
-      callbackQueue.async { completion?(error) }
-    })
+    pager.loadAll(fetchFromInitialPage: fetchFromInitialPage, completion: completion)
   }
 
   /// Discards pagination state and fetches the first page from scratch.

apollo-ios-pagination/Sources/ApolloPagination/GraphQLQueryPager.swift

@@ -12,17 +12,14 @@ public protocol PagerType {
   func cancel()
   func loadPrevious(
     cachePolicy: CachePolicy,
-    callbackQueue: DispatchQueue,
     completion: ((PaginationError?) -> Void)?
   )
   func loadNext(
     cachePolicy: CachePolicy,
-    callbackQueue: DispatchQueue,
     completion: ((PaginationError?) -> Void)?
   )
   func loadAll(
     fetchFromInitialPage: Bool,
-    callbackQueue: DispatchQueue,
     completion: ((PaginationError?) -> Void)?
   )
   func refetch(cachePolicy: CachePolicy)
@@ -34,6 +31,7 @@ public class GraphQLQueryPager<InitialQuery: GraphQLQuery, PaginatedQuery: Graph
   let pager: AsyncGraphQLQueryPager<InitialQuery, PaginatedQuery>
   private var subscriptions = Subscriptions()
   private var completionManager = CompletionManager()
+  private let callbackPriority: CallbackPriority
 
   public var publisher: AnyPublisher<Result<PaginationOutput<InitialQuery, PaginatedQuery>, Error>, Never> {
     get async { await pager.$currentValue.compactMap { $0 }.eraseToAnyPublisher() }
@@ -43,9 +41,11 @@ public class GraphQLQueryPager<InitialQuery: GraphQLQuery, PaginatedQuery: Graph
     client: ApolloClientProtocol,
     initialQuery: InitialQuery,
     watcherDispatchQueue: DispatchQueue = .main,
+    callbackPriority: CallbackPriority = .main,
     extractPageInfo: @escaping (PageExtractionData<InitialQuery, PaginatedQuery>) -> P,
     pageResolver: ((P, PaginationDirection) -> PaginatedQuery?)?
   ) {
+    self.callbackPriority = callbackPriority
     pager = .init(
       client: client,
       initialQuery: initialQuery,
@@ -74,8 +74,9 @@ public class GraphQLQueryPager<InitialQuery: GraphQLQuery, PaginatedQuery: Graph
 
   /// Convenience initializer
   /// - Parameter pager: An `AsyncGraphQLQueryPager`.
-  public init(pager: AsyncGraphQLQueryPager<InitialQuery, PaginatedQuery>) {
+  public init(pager: AsyncGraphQLQueryPager<InitialQuery, PaginatedQuery>, callbackPriority: CallbackPriority = .main) {
     self.pager = pager
+    self.callbackPriority = callbackPriority
   }
 
   /// Allows the caller to subscribe to new pagination results.
@@ -108,11 +109,9 @@ public class GraphQLQueryPager<InitialQuery: GraphQLQuery, PaginatedQuery: Graph
   /// Loads the previous page, if we can.
   /// - Parameters:
   ///   - cachePolicy: The Apollo `CachePolicy` to use. Defaults to `fetchIgnoringCacheData`.
-  ///   - callbackQueue: The `DispatchQueue` that the `completion` fires on. Defaults to `main`.
   ///   - completion: A completion block that will always trigger after the execution of this operation. Passes an optional error, of type `PaginationError`, if there was an internal error related to pagination. Does not surface network errors. Defaults to `nil`.
   public func loadPrevious(
     cachePolicy: CachePolicy = .fetchIgnoringCacheData,
-    callbackQueue: DispatchQueue = .main,
     completion: ((PaginationError?) -> Void)? = nil
   ) {
     execute(completion: completion) { [weak self] in
@@ -123,11 +122,9 @@ public class GraphQLQueryPager<InitialQuery: GraphQLQuery, PaginatedQuery: Graph
   /// Loads the next page, if we can.
   /// - Parameters:
   ///   - cachePolicy: The Apollo `CachePolicy` to use. Defaults to `fetchIgnoringCacheData`.
-  ///   - callbackQueue: The `DispatchQueue` that the `completion` fires on. Defaults to `main`.
   ///   - completion: A completion block that will always trigger after the execution of this operation. Passes an optional error, of type `PaginationError`, if there was an internal error related to pagination. Does not surface network errors. Defaults to `nil`.
   public func loadNext(
     cachePolicy: CachePolicy = .fetchIgnoringCacheData,
-    callbackQueue: DispatchQueue = .main,
     completion: ((PaginationError?) -> Void)? = nil
   ) {
     execute(completion: completion) { [weak self] in
@@ -138,11 +135,9 @@ public class GraphQLQueryPager<InitialQuery: GraphQLQuery, PaginatedQuery: Graph
   /// Loads all pages.
   /// - Parameters:
   ///   - fetchFromInitialPage: Pass true to begin loading from the initial page; otherwise pass false.  Defaults to `true`.  **NOTE**: Loading all pages with this value set to `false` requires that the initial page has already been loaded previously.
-  ///   - callbackQueue: The `DispatchQueue` that the `completion` fires on. Defaults to `main`.
   ///   - completion: A completion block that will always trigger after the execution of this operation. Passes an optional error, of type `PaginationError`, if there was an internal error related to pagination. Does not surface network errors. Defaults to `nil`.
   public func loadAll(
     fetchFromInitialPage: Bool = true,
-    callbackQueue: DispatchQueue = .main,
     completion: ((PaginationError?) -> Void)? = nil
   ) {
     execute(completion: completion) { [weak self] in
@@ -170,13 +165,47 @@ public class GraphQLQueryPager<InitialQuery: GraphQLQuery, PaginatedQuery: Graph
 
   private func execute(completion: ((PaginationError?) -> Void)?, operation: @escaping () async throws -> Void) {
     Task<_, Never> { [weak self] in
-      let completionHandler = Completion(completion: completion)
-      await self?.completionManager.append(completion: completionHandler)
+      guard let self else { return }
+      let completionHandler = Completion(priority: callbackPriority, completion: completion)
+      await self.completionManager.append(completion: completionHandler)
       do {
         try await operation()
-        await self?.completionManager.execute(completion: completionHandler, with: nil)
+        await self.completionManager.execute(completion: completionHandler, with: nil)
       } catch {
-        await self?.completionManager.execute(completion: completionHandler, with: error as? PaginationError ?? .unknown(error))
+        await self.completionManager.execute(completion: completionHandler, with: error as? PaginationError ?? .unknown(error))
+      }
+    }
+  }
+}
+
+public enum CallbackPriority {
+  case main, high, medium, low, userInitiated, utility, background
+
+  var taskPriority: TaskPriority? {
+    switch self {
+    case .main:
+      return nil
+    case .background:
+      return .background
+    case .high:
+      return .high
+    case .medium:
+      return .medium
+    case .low:
+      return .low
+    case .userInitiated:
+      return .userInitiated
+    case .utility:
+      return .utility
+    }
+  }
+
+  func perform(_ body: @Sendable @escaping () throws -> Void) async rethrows {
+    if self == .main {
+      try await MainActor.run(body: body)
+    } else {
+      Task.detached(priority: taskPriority) {
+        try body()
       }
     }
   }
@@ -192,14 +221,18 @@ private actor Subscriptions {
 
 private class Completion {
   var completion: ((PaginationError?) -> Void)?
+  var priority: CallbackPriority
 
-  init(completion: ((PaginationError?) -> Void)?) {
+  init(priority: CallbackPriority, completion: ((PaginationError?) -> Void)?) {
+    self.priority = priority
     self.completion = completion
   }
 
   func execute(error: PaginationError?) async {
-    completion?(error)
-    completion = nil
+    await priority.perform { [weak self] in
+      self?.completion?(error)
+      self?.completion = nil
+    }
   }
 }