fix(image-loader): queue stucks processing same url more than concurr…

…ency

When loading the same url more than the allowed by 'concurrency', the
queue may gets stuck, because the logic to prevent same image from loading
at same time doesn't release the 'processing' counter , which is
incremented always, even when processing a url that is already being
processed.

src/providers/image-loader.ts

@@ -248,29 +248,31 @@ export class ImageLoader {
 
     // take the first item from queue
     const currentItem: QueueItem = this.queue.splice(0, 1)[0];
+
+    // function to call when done processing this item
+    // this will reduce the processing number
+    // then will execute this function again to process any remaining items
+    const done = () => {
+      this.processing--;
+      this.processQueue();
+
+      // only delete if it's the last/unique occurrence in the queue
+      if (this.currentlyProcessing[currentItem.imageUrl] !== undefined && !this.currentlyInQueue(currentItem.imageUrl)) {
+        delete this.currentlyProcessing[currentItem.imageUrl];
+      }
+    };
+
+    const error = (e) => {
+      currentItem.reject();
+      this.throwError(e);
+      done();
+    };
+
     if (this.currentlyProcessing[currentItem.imageUrl] === undefined) {
       this.currentlyProcessing[currentItem.imageUrl] = new Promise((resolve, reject) => {
         // process more items concurrently if we can
         if (this.canProcess) this.processQueue();
 
-        // function to call when done processing this item
-        // this will reduce the processing number
-        // then will execute this function again to process any remaining items
-        const done = () => {
-          this.processing--;
-          this.processQueue();
-
-          if (this.currentlyProcessing[currentItem.imageUrl] !== undefined) {
-            delete this.currentlyProcessing[currentItem.imageUrl];
-          }
-        };
-
-        const error = (e) => {
-          currentItem.reject();
-          this.throwError(e);
-          done();
-        };
-
         const localDir = this.file.cacheDirectory + this.config.cacheDirectoryName + '/';
         const fileName = this.createFileName(currentItem.imageUrl);
 
@@ -294,11 +296,13 @@ export class ImageLoader {
             }).catch((e) => {
               //Could not write image
               error(e);
+              reject(e);
             });
           },
           (e) => {
             //Could not get image via httpClient
             error(e);
+            reject(e);
           }
         );
       });
@@ -307,11 +311,24 @@ export class ImageLoader {
       this.currentlyProcessing[currentItem.imageUrl].then(() => {
         this.getCachedImagePath(currentItem.imageUrl).then((localUrl) => {
           currentItem.resolve(localUrl);
-        })
+        });
+        done();
+      },
+      (e) => {
+        error(e);
       });
     }
   }
 
+  /**
+   * Search if the url is currently in the queue
+   * @param imageUrl {string} Image url to search
+   * @returns {boolean}
+   */
+  private currentlyInQueue(imageUrl: string) {
+    return this.queue.some(item => item.imageUrl === imageUrl);
+  }
+
   /**
    * Initialize the cache service
    * @param replace {boolean} Whether to replace the cache directory if it already exists