add ImageFetchStrategy to either pull from Firebase to memory or to a file

Author: rsnider19

lib/firebase_image.dart

@@ -2,3 +2,4 @@ library firebase_image;
 
 export 'src/firebase_image.dart';
 export 'src/cache_refresh_strategy.dart';
+export 'src/image_fetch_strategy.dart';

lib/src/cache_manager.dart

@@ -6,10 +6,13 @@ import 'package:firebase_image/src/firebase_image.dart';
 import 'package:firebase_image/src/image_object.dart';
 import 'package:firebase_core/firebase_core.dart';
 import 'package:firebase_storage/firebase_storage.dart';
+import 'package:flutter/cupertino.dart';
 import 'package:sqflite/sqflite.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:path/path.dart';
 
+import 'image_fetch_strategy.dart';
+
 class FirebaseImageCacheManager {
   static const String key = 'firebase_image';
 
@@ -19,10 +22,12 @@ class FirebaseImageCacheManager {
   String basePath;
 
   final CacheRefreshStrategy cacheRefreshStrategy;
+  final ImageFetchStrategy imageFetchStrategy;
 
-  FirebaseImageCacheManager(
-    this.cacheRefreshStrategy,
-  );
+  FirebaseImageCacheManager({
+    @required this.cacheRefreshStrategy,
+    this.imageFetchStrategy = ImageFetchStrategy.FETCH_TO_MEMORY,
+  }) : assert(cacheRefreshStrategy != null);
 
   Future<void> open() async {
     db = await openDatabase(
@@ -139,11 +144,30 @@ class FirebaseImageCacheManager {
     return null;
   }
 
-  Future<Uint8List> remoteFileBytes(
-      FirebaseImageObject object, int maxSizeBytes) {
+  Future<Uint8List> _fetchToMemory(FirebaseImageObject object, int maxSizeBytes) {
     return object.reference.getData(maxSizeBytes);
   }
 
+  Future<Uint8List> _fetchToFile(FirebaseImageObject object) async {
+    Directory dir = await getApplicationSupportDirectory();
+    File file = File('${dir.path}/${object.remotePath}');
+    file.createSync(recursive: true);
+    StorageFileDownloadTask task = object.reference.writeToFile(file);
+    await task.future;
+    return file.readAsBytesSync();
+  }
+
+  Future<Uint8List> remoteFileBytes(FirebaseImageObject object, int maxSizeBytes) {
+    if (imageFetchStrategy == ImageFetchStrategy.FETCH_TO_FILE) {
+      return _fetchToFile(object);
+    }
+    else if (imageFetchStrategy == ImageFetchStrategy.FETCH_TO_MEMORY) {
+      return _fetchToMemory(object, maxSizeBytes);
+    }
+
+    throw(Exception("ImageFetchStrategy missing"));
+  }
+
   Future<Uint8List> upsertRemoteFileToCache(
       FirebaseImageObject object, int maxSizeBytes) async {
     if (CacheRefreshStrategy.BY_METADATA_DATE == this.cacheRefreshStrategy) {

lib/src/firebase_image.dart

@@ -9,6 +9,8 @@ import 'package:firebase_storage/firebase_storage.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
+import 'image_fetch_strategy.dart';
+
 class FirebaseImage extends ImageProvider<FirebaseImage> {
   // Default: True. Specified whether or not an image should be cached (optional)
   final bool shouldCache;
@@ -28,6 +30,9 @@ class FirebaseImage extends ImageProvider<FirebaseImage> {
   /// The model for the image object
   final FirebaseImageObject _imageObject;
 
+  /// Default: FETCH_TO_MEMORY. Specifies the strategy in which to fetch the image from Firebase (optional)
+  final ImageFetchStrategy imageFetchStrategy;
+
   /// Fetches, saves and returns an ImageProvider for any image in a readable Firebase Cloud Storeage bucket.
   ///
   /// [location] The URI of the image, in the bucket, to be displayed
@@ -43,6 +48,7 @@ class FirebaseImage extends ImageProvider<FirebaseImage> {
     this.maxSizeBytes = 2500 * 1000, // 2.5MB
     this.cacheRefreshStrategy = CacheRefreshStrategy.BY_METADATA_DATE,
     this.firebaseApp,
+    this.imageFetchStrategy = ImageFetchStrategy.FETCH_TO_MEMORY,
   }) : _imageObject = FirebaseImageObject(
           bucket: _getBucket(location),
           remotePath: _getImagePath(location),
@@ -74,7 +80,8 @@ class FirebaseImage extends ImageProvider<FirebaseImage> {
   Future<Uint8List> _fetchImage() async {
     Uint8List bytes;
     FirebaseImageCacheManager cacheManager = FirebaseImageCacheManager(
-      cacheRefreshStrategy,
+      cacheRefreshStrategy: cacheRefreshStrategy,
+      imageFetchStrategy: imageFetchStrategy,
     );
 
     if (shouldCache) {

lib/src/image_fetch_strategy.dart

@@ -0,0 +1,7 @@
+enum ImageFetchStrategy {
+  // Asynchronously downloads the object at the StorageReference to a list in memory.
+  // A list of the provided max size will be allocated.
+  FETCH_TO_MEMORY,
+  // Asynchronously downloads the object to a specified system file.
+  FETCH_TO_FILE,
+}