Add transaction support to Database Reference.

Author: FrankSalad

ios/Firestack/FirestackDatabase.h

@@ -18,6 +18,7 @@
 }
 
 @property NSMutableDictionary *dbReferences;
+@property NSMutableDictionary *transactions;
 
 @end
 

ios/Firestack/FirestackDatabase.m

@@ -364,6 +364,7 @@ - (id) init
     self = [super init];
     if (self != nil) {
         _dbReferences = [[NSMutableDictionary alloc] init];
+        _transactions = [[NSMutableDictionary alloc] init];
     }
     return self;
 }
@@ -455,7 +456,58 @@ - (id) init
     }
 }
 
+RCT_EXPORT_METHOD(beginTransaction:(NSString *) path
+                  withIdentifier:(NSString *) identifier
+                  applyLocally:(BOOL) applyLocally
+                  onComplete:(RCTResponseSenderBlock) onComplete)
+{
+    NSMutableDictionary *transactionState = [NSMutableDictionary new];
+    [_transactions setValue:transactionState forKey:identifier];
+    dispatch_semaphore_t sema = dispatch_semaphore_create(0);
+    [transactionState setObject:sema forKey:@"semaphore"];
+    
+    FIRDatabaseReference *ref = [self getPathRef:path];
+    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+        [ref runTransactionBlock:^FIRTransactionResult * _Nonnull(FIRMutableData * _Nonnull currentData) {
+            [self sendEventWithName:DATABASE_TRANSACTION_EVENT
+                               body:@{
+                                      @"id": identifier,
+                                      @"originalValue": currentData.value
+                                      }];
+            // Wait for the event handler to call tryCommitTransaction
+            dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
+            BOOL abort = [transactionState valueForKey:@"abort"];
+            id value = [transactionState valueForKey:@"value"];
+            [_transactions removeObjectForKey:identifier];
+            if (abort) {
+                return [FIRTransactionResult abort];
+            } else {
+                currentData.value = value;
+                return [FIRTransactionResult successWithValue:currentData];
+            }
+        } andCompletionBlock:^(NSError * _Nullable error, BOOL committed, FIRDataSnapshot * _Nullable snapshot) {
+            [self handleCallback:@"transaction" callback:onComplete databaseError:error];
+        } withLocalEvents:applyLocally];
+    });
+}
 
+RCT_EXPORT_METHOD(tryCommitTransaction:(NSString *) identifier
+                  withData:(NSDictionary *) data
+                  orAbort:(BOOL) abort)
+{
+    NSMutableDictionary *transactionState = [_transactions valueForKey:identifier];
+    if (!transactionState) {
+        NSLog(@"tryCommitTransaction for unknown ID %@", identifier);
+    }
+    dispatch_semaphore_t sema = [transactionState valueForKey:@"semaphore"];
+    if (abort) {
+        [transactionState setValue:@true forKey:@"abort"];
+    } else {
+        id newValue = [data valueForKey:@"value"];
+        [transactionState setValue:newValue forKey:@"value"];
+    }
+    dispatch_semaphore_signal(sema);
+}
 
 RCT_EXPORT_METHOD(on:(NSString *) path
                   modifiersString:(NSString *) modifiersString
@@ -610,7 +662,7 @@ - (NSString *) getDBListenerKey:(NSString *) path
 
 // Not sure how to get away from this... yet
 - (NSArray<NSString *> *)supportedEvents {
-    return @[DATABASE_DATA_EVENT, DATABASE_ERROR_EVENT];
+    return @[DATABASE_DATA_EVENT, DATABASE_ERROR_EVENT, DATABASE_TRANSACTION_EVENT];
 }
 
 

ios/Firestack/FirestackEvents.h

@@ -29,6 +29,7 @@ static NSString *const DEBUG_EVENT = @"debug";
 // Database
 static NSString *const DATABASE_DATA_EVENT = @"database_event";
 static NSString *const DATABASE_ERROR_EVENT = @"database_error";
+static NSString *const DATABASE_TRANSACTION_EVENT = @"database_transaction_update";
 
 static NSString *const DATABASE_VALUE_EVENT = @"value";
 static NSString *const DATABASE_CHILD_ADDED_EVENT = @"child_added";

lib/modules/database/index.js

@@ -19,6 +19,7 @@ export default class Database extends Base {
   constructor(firestack: Object, options: Object = {}) {
     super(firestack, options);
     this.subscriptions = {};
+    this.transactions = {};
     this.serverTimeOffset = 0;
     this.persistenceEnabled = false;
     this.namespace = 'firestack:database';
@@ -33,6 +34,11 @@ export default class Database extends Base {
       err => this._handleDatabaseError(err)
     );
 
+    this.transactionListener = FirestackDatabaseEvt.addListener(
+      'database_transaction_update',
+      event => this._handleDatabaseTransaction(event)
+    );
+
     this.offsetRef = this.ref('.info/serverTimeOffset');
     this.offsetRef.on('value', (snapshot) => {
       this.serverTimeOffset = snapshot.val() || this.serverTimeOffset;
@@ -153,6 +159,37 @@ export default class Database extends Base {
     FirestackDatabase.goOffline();
   }
 
+  addTransaction(path, updateCallback, applyLocally, onComplete) {
+    let id = this._generateTransactionID();
+    this.transactions[id] = updateCallback;
+    return new Promise((resolve, reject) => {
+      FirestackDatabase.beginTransaction(path, id, applyLocally || false, (error, result) => {
+        onComplete && onComplete(error);
+        if (error)
+          reject(error);
+        else
+          resolve();
+        delete this.transactions[id];
+      });  
+    });
+  }
+
+  _generateTransactionID() {
+    // 10 char random alphanumeric
+    return Math.random().toString(36).substr(2, 10);
+  }
+
+  _handleDatabaseTransaction(event) {
+    const {id, originalValue} = event;
+    const updateCallback = this.transactions[id];
+    const newValue = updateCallback(originalValue);
+    let abort = false;
+    if (newValue === undefined) {
+      abort = true;
+    }
+    FirestackDatabase.tryCommitTransaction(id, {value: newValue}, abort);
+  }
+
   /**
    *  INTERNALS
    */

lib/modules/database/reference.js

@@ -123,6 +123,11 @@ export default class Reference extends ReferenceBase {
     return this.db.off(path, modifiersString, eventName, origCB);
   }
 
+  transaction(transactionUpdate, onComplete, applyLocally) {
+    const path = this._dbPath();
+    return this.db.addTransaction(path, transactionUpdate, applyLocally, onComplete);
+  }
+
   /**
    * MODIFIERS
    */