[ios, macos] Added offline pack context setter

Set the offline pack’s associated metadata, then replace the offline pack’s underlying offline region based on a fresh reload, without touching the master array of offline packs.

platform/darwin/src/MGLOfflinePack.h

@@ -131,9 +131,28 @@ MGL_EXPORT
 
  The context typically holds application-specific information for identifying
  the pack, such as a user-selected name.
+ 
+ To change the value of this property, use the `-setContext:completionHandler:`
+ method. If you access this property after calling that method but before its
+ completion handler is called, this property’s value may not reflect the new
+ value that you specify.
  */
 @property (nonatomic, readonly) NSData *context;
 
+/**
+ Associates arbitrary contextual data with the offline pack, replacing any
+ context that was previously associated with the offline pack.
+ 
+ Setting the context is asynchronous. The `context` property may not be updated
+ until the completion handler is called.
+ 
+ @param context The new context to associate with the offline pack.
+ @param completion The completion handler to call when the context has been
+    updated. If there is an error setting the context, the error is passed into
+    the completion handler.
+ */
+- (void)setContext:(NSData *)context completionHandler:(void (^_Nullable)(NSError * _Nullable error))completion;
+
 /**
  The pack’s current state.
 

platform/darwin/src/MGLOfflinePack.mm

@@ -10,6 +10,10 @@
 
 #import "NSValue+MGLAdditions.h"
 
+#if TARGET_OS_IPHONE || TARGET_OS_SIMULATOR
+    #import "MGLMapboxEvents.h"
+#endif
+
 #include <mbgl/map/map_options.hpp>
 #include <mbgl/storage/database_file_source.hpp>
 
@@ -111,6 +115,52 @@ private:
     return [NSData dataWithBytes:&metadata[0] length:metadata.size()];
 }
 
+- (void)setContext:(NSData *)context completionHandler:(void (^_Nullable)(NSError * _Nullable error))completion {
+    MGLAssertOfflinePackIsValid();
+    
+    mbgl::OfflineRegionMetadata metadata(context.length);
+    [context getBytes:&metadata[0] length:metadata.size()];
+    
+    [self willChangeValueForKey:@"context"];
+    __weak MGLOfflinePack *weakSelf = self;
+    _mbglDatabaseFileSource->updateOfflineMetadata(_mbglOfflineRegion->getID(), metadata, [&, completion, weakSelf](mbgl::expected<mbgl::OfflineRegionMetadata, std::exception_ptr> mbglOfflineRegionMetadata) {
+        NSError *error;
+        if (!mbglOfflineRegionMetadata) {
+            NSString *errorDescription = @(mbgl::util::toString(mbglOfflineRegionMetadata.error()).c_str());
+            error = [NSError errorWithDomain:MGLErrorDomain code:MGLErrorCodeModifyingOfflineStorageFailed userInfo:errorDescription ? @{
+                NSLocalizedDescriptionKey: errorDescription,
+            } : nil];
+#if TARGET_OS_IPHONE || TARGET_OS_SIMULATOR
+            [[MMEEventsManager sharedManager] reportError:error];
+#endif
+        }
+        dispatch_async(dispatch_get_main_queue(), [&, completion, weakSelf, error](void) {
+            [weakSelf reloadWithCompletionHandler:^(NSError * _Nullable reloadingError) {
+                MGLOfflinePack *strongSelf = weakSelf;
+                [strongSelf didChangeValueForKey:@"context"];
+                if (completion) {
+                    completion(error ?: reloadingError);
+                }
+            }];
+        });
+    });
+}
+
+- (void)reloadWithCompletionHandler:(void (^)(NSError * _Nullable error))completion {
+    auto regionID = _mbglOfflineRegion->getID();
+    MGLOfflineStorage *sharedOfflineStorage = [MGLOfflineStorage sharedOfflineStorage];
+    __weak MGLOfflinePack *weakSelf = self;
+    [sharedOfflineStorage getPacksWithCompletionHandler:^(NSArray<MGLOfflinePack *> *packs, __unused NSError * _Nullable error) {
+        for (MGLOfflinePack *pack in packs) {
+            if (pack.mbglOfflineRegion->getID() == regionID) {
+                weakSelf.mbglOfflineRegion = pack.mbglOfflineRegion;
+                break;
+            }
+        }
+        completion(error);
+    }];
+}
+
 - (void)resume {
     MGLLogInfo(@"Resuming pack download.");
     MGLAssertOfflinePackIsValid();

platform/darwin/src/MGLOfflineStorage_Private.h

@@ -31,6 +31,8 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @property (nonatomic) std::string mbglCachePath;
 
+- (void)getPacksWithCompletionHandler:(void (^)(NSArray<MGLOfflinePack *> *packs, NSError * _Nullable error))completion;
+
 @end
 
 NS_ASSUME_NONNULL_END

platform/darwin/test/MGLOfflineStorageTests.mm

@@ -139,6 +139,22 @@
     }];
     [pack requestProgress];
     [self waitForExpectationsWithTimeout:5 handler:nil];
+    
+    XCTAssertEqualObjects(pack.context, context, @"Offline pack context should match the context specified by the application.");
+    NSString *newName = @"🍑 Peach Grove";
+    NSData *newContext = [NSKeyedArchiver archivedDataWithRootObject:@{
+        nameKey: newName,
+    }];
+    
+    XCTestExpectation *contextCompletionHandlerExpectation = [self expectationWithDescription:@"set pack completion context handler"];
+    __weak MGLOfflinePack *weakPack = pack;
+    [pack setContext:newContext completionHandler:^(NSError * _Nullable error) {
+        XCTAssertNil(error);
+        XCTAssertNotNil(weakPack);
+        XCTAssertEqualObjects(weakPack.context, newContext, @"Offline pack context should match the updated context specified by the application.");
+        [contextCompletionHandlerExpectation fulfill];
+    }];
+    [self waitForExpectationsWithTimeout:5 handler:nil];
 }
 
 - (void)testAddPackForGeometry {

platform/ios/CHANGELOG.md

@@ -17,6 +17,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 
 ### Other changes
 
+* Added the `-[MGLOfflinePack setContext:completionHandler:]` method for replacing the data associated with an offline pack, such as a name. ([#288](https://github.com/mapbox/mapbox-gl-native-ios/pull/288))
 * Fixed a crash when encountering an invalid polyline. ([mapbox/mapbox-gl-native#16409](https://github.com/mapbox/mapbox-gl-native/pull/16409))
 * Fixed an issue where an `MGLMapSnapshotOptions` with an invalid `MGLMapCamera.centerCoordinate`, negative `MGLMapCamera.heading`, negative `MGLMapCamera.pitch`, and negative `MGLMapSnapshotOptions.zoomLevel` resulted in a snapshot centered on Null Island at zoom level 0 even if the style specified a different initial center coordinate or zoom level. ([#280](https://github.com/mapbox/mapbox-gl-native-ios/pull/280))
 * Fixed an error that occurred if your implementation of the `-[MGLOfflineStorageDelegate offlineStorage:URLForResourceOfKind:]` method returned a local file URL. ([mapbox/mapbox-gl-native#16428](https://github.com/mapbox/mapbox-gl-native/pull/16428)) 

platform/macos/CHANGELOG.md

@@ -15,12 +15,16 @@
 
 ### Other changes
 
-* Fixed various crashes, including crashes on launch, on macOS 10.11.0 through 10.14._x_. ([mapbox/mapbox-gl-native#16412](https://github.com/mapbox/mapbox-gl-native/pull/16412))
+* Added the `-[MGLOfflinePack setContext:completionHandler:]` method for replacing the data associated with an offline pack, such as a name. ([#288](https://github.com/mapbox/mapbox-gl-native-ios/pull/288))
 * Fixed a crash when encountering an invalid polyline. ([mapbox/mapbox-gl-native#16409](https://github.com/mapbox/mapbox-gl-native/pull/16409))
 * Fixed an issue where an `MGLMapSnapshotOptions` with an invalid `MGLMapCamera.centerCoordinate`, negative `MGLMapCamera.heading`, negative `MGLMapCamera.pitch`, and negative `MGLMapSnapshotOptions.zoomLevel` resulted in a snapshot centered on Null Island at zoom level 0 even if the style specified a different initial center coordinate or zoom level. ([#280](https://github.com/mapbox/mapbox-gl-native-ios/pull/280))
 * Fixed an error that occurred if your implementation of the `-[MGLOfflineStorageDelegate offlineStorage:URLForResourceOfKind:]` method returned a local file URL. ([mapbox/mapbox-gl-native#16428](https://github.com/mapbox/mapbox-gl-native/pull/16428)) 
 * Certain logging statements no longer run on the main thread. ([mapbox/mapbox-gl-native#16325](https://github.com/mapbox/mapbox-gl-native/pull/16325))
 
+## 0.15.1
+
+* Fixed various crashes, including crashes on launch, on macOS 10.11.0 through 10.14._x_. ([mapbox/mapbox-gl-native#16412](https://github.com/mapbox/mapbox-gl-native/pull/16412))
+
 ## 0.15.0
 
 ### Styles and rendering