request cancellation

2025-08-06 23:57:33 -04:00
parent cb51300356
commit 86ee4ff822
14 changed files with 558 additions and 180 deletions
@@ -3,6 +3,13 @@ import Flutter
 import MobileCoreServices
 import Photos

+struct Request {
+  var managerId: Int32?
+  var workItem: DispatchWorkItem?
+  var isCancelled = false
+  let callback: (Result<[String: Int64], any Error>) -> Void
+}
+
 class ThumbnailApiImpl: ThumbnailApi {
  private static let cacheManager = PHImageManager.default()
  private static let fetchOptions = {
@@ -22,29 +29,45 @@ class ThumbnailApiImpl: ThumbnailApi {
  private static let processingQueue = DispatchQueue(label: "thumbnail.processing", qos: .userInteractive, attributes: .concurrent)
  private static let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
  private static let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue).rawValue
+  private static var requests = [Int64: Request]()
+  private static let cancelledResult = Result<[String: Int64], any Error>.success([:])
  
-  func getThumbnailBuffer(assetId: String, width: Int64, height: Int64, completion: @escaping (Result<[String: Int64], any Error>) -> Void) {
-    Self.processingQueue.async {
+  func requestImage(assetId: String, requestId: Int64, width: Int64, height: Int64, completion: @escaping (Result<[String: Int64], any Error>) -> Void) {
+    var request = Request(callback: completion)
+    let item = DispatchWorkItem {
      guard let asset = PHAsset.fetchAssets(withLocalIdentifiers: [assetId], options: Self.fetchOptions).firstObject
-      else { completion(.failure(PigeonError(code: "", message: "Could not get asset data for \(assetId)", details: nil))); return }
+      else {
+        Self.requests[requestId] = nil
+        completion(.failure(PigeonError(code: "", message: "Could not get asset data for \(assetId)", details: nil)))
+        return
+      }
      
-      Self.cacheManager.requestImage(
+      request.managerId = Self.cacheManager.requestImage(
        for: asset,
        targetSize: CGSize(width: Double(width), height: Double(height)),
        contentMode: .aspectFit,
        options: Self.requestOptions,
        resultHandler: { (image, info) -> Void in
+          defer { Self.requests[requestId] = nil }
          guard let image = image,
                let cgImage = image.cgImage else {
-            completion(.failure(PigeonError(code: "", message: "Could not get pixel data for \(assetId)", details: nil)))
-            return
+            return completion(.failure(PigeonError(code: "", message: "Could not get pixel data for \(assetId)", details: nil)))
          }
-
+          
+          if request.isCancelled {
+            return completion(Self.cancelledResult)
+          }
+          
          let pointer = UnsafeMutableRawPointer.allocate(
            byteCount: Int(cgImage.width) * Int(cgImage.height) * 4,
            alignment: MemoryLayout<UInt8>.alignment
          )
          
+          if request.isCancelled {
+            pointer.deallocate()
+            return completion(Self.cancelledResult)
+          }
+          
          guard let context = CGContext(
            data: pointer,
            width: cgImage.width,
@@ -55,14 +78,41 @@ class ThumbnailApiImpl: ThumbnailApi {
            bitmapInfo: Self.bitmapInfo
          ) else {
            pointer.deallocate()
-            completion(.failure(PigeonError(code: "", message: "Could not create context for \(assetId)", details: nil)))
-            return
+            return completion(.failure(PigeonError(code: "", message: "Could not create context for \(assetId)", details: nil)))
          }
+          
+          if request.isCancelled {
+            pointer.deallocate()
+            return completion(Self.cancelledResult)
+          }
+          
          context.interpolationQuality = .none
          context.draw(cgImage, in: CGRect(x: 0, y: 0, width: cgImage.width, height: cgImage.height))
+          
+          if request.isCancelled {
+            pointer.deallocate()
+            return completion(Self.cancelledResult)
+          }
+          
          completion(.success(["pointer": Int64(Int(bitPattern: pointer)), "width": Int64(cgImage.width), "height": Int64(cgImage.height)]))
        }
      )
    }
+    
+    request.workItem = item
+    Self.requests[requestId] = request
+    Self.processingQueue.async(execute: item)
+  }
+  
+  func cancelImageRequest(requestId: Int64) {
+    guard var request = Self.requests.removeValue(forKey: requestId) else { return }
+    request.isCancelled = true
+    guard let item = request.workItem else { return }
+    item.cancel()
+    if item.isCancelled {
+      request.callback(Self.cancelledResult)
+    } else if let managerId = request.managerId {
+      Self.cacheManager.cancelImageRequest(managerId)
+    }
  }
 }