Firestore project: Import of API interfaces. (#1337)

- 198063502 Address comment upstream. by zxu <zxu>
  - 197942352 Fix style upstream and fix destination depot in copybara. by zxu <zxu>
  - 197925542 Fix headers with change from GitHub, see the current diff... by zxu <zxu>
  - 197922012 Implement ListenerRegistration::Remove(). by zxu <zxu>
  - 197713382 Implement more on listener class and implement ListenerRe... by zxu <zxu>
  - 196551381 Implement more on listener class and implement the Docume... by zxu <zxu>
  - 196276752 Implement the SnapshotMetadata with inline methods and (n... by zxu <zxu>
  - 195841793 Implement the wrapper class for callback (EventListener). by zxu <zxu>
  - 194112388 Add Android-Wrapper for DocumentReference's non-callback ... by zxu <zxu>
  - 192445183 Add Android-Wrapper for Firestore's remaining methods. by zxu <zxu>
  - 190986604 Manually import the public portion of by mcg <mcg>
  - 189013767 Add Android-Wrapper for Firestore's method that does not ... by zxu <zxu>
  - 188809445 Import of firebase-ios-sdk from Github. by mcg <mcg>
  - 187049498 Import of firebase-ios-sdk from Github. by mcg <mcg>
  - 184568931 Import of firebase-ios-sdk from Github. by mcg <mcg>

ORIGINAL_AUTHOR=Firebase <firebase-noreply>
PiperOrigin-RevId: 198063502

18 files changed, 650 insertions, 77 deletions

diff --git a/Firestore/core/include/firebase/firestore/CMakeLists.txt b/Firestore/core/include/firebase/firestore/CMakeLists.txt
index e4e7acd..0c7fd48 100644
--- a/Firestore/core/include/firebase/firestore/CMakeLists.txt
+++ b/Firestore/core/include/firebase/firestore/CMakeLists.txt
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Hack to make the headers show up in IDEs
+# Workaround to make the headers show up in IDEs
 # (see https://stackoverflow.com/questions/27039019/ and open issue on CMake
 # issue tracker: https://gitlab.kitware.com/cmake/cmake/issues/15234)
 add_custom_target(firebase_firestore_types_ide SOURCES
diff --git a/Firestore/core/include/firebase/firestore/collection_reference.h b/Firestore/core/include/firebase/firestore/collection_reference.h
new file mode 100644
index 0000000..4d47248
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/collection_reference.h
@@ -0,0 +1,98 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_COLLECTION_REFERENCE_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_COLLECTION_REFERENCE_H_
+
+namespace firebase {
+namespace firestore {
+
+class CollectionReferenceInternal;
+class FirestoreInternal;
+
+/**
+ * A CollectionReference refers to a collection of documents location in a
+ * Firestore database and can be used for adding documents, getting document
+ * references, and querying for documents.
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class CollectionReference {
+ public:
+  /**
+   * @brief Default constructor. This creates an invalid CollectionReference.
+   * Attempting to perform any operations on this reference will fail unless a
+   * valid CollectionReference has been assigned to it.
+   */
+  CollectionReference();
+
+  /**
+   * @brief Copy constructor. It's totally okay (and efficient) to copy
+   * CollectionReference instances, as they simply point to the same location in
+   * the database.
+   *
+   * @param[in] reference CollectionReference to copy from.
+   */
+  CollectionReference(const CollectionReference& reference);
+
+  /**
+   * @brief Move constructor. Moving is an efficient operation for
+   * CollectionReference instances.
+   *
+   * @param[in] reference CollectionReference to move data from.
+   */
+  CollectionReference(CollectionReference&& reference);
+
+  /** @brief Required virtual destructor. */
+  virtual ~CollectionReference();
+
+  /**
+   * @brief Copy assignment operator. It's totally okay (and efficient) to copy
+   * CollectionReference instances, as they simply point to the same location in
+   * the database.
+   *
+   * @param[in] reference CollectionReference to copy from.
+   *
+   * @returns Reference to the destination CollectionReference.
+   */
+  CollectionReference& operator=(const CollectionReference& reference);
+
+  /**
+   * @brief Move assignment operator. Moving is an efficient operation for
+   * CollectionReference instances.
+   *
+   * @param[in] reference CollectionReference to move data from.
+   *
+   * @returns Reference to the destination CollectionReference.
+   */
+  CollectionReference& operator=(CollectionReference&& reference);
+
+ protected:
+  explicit CollectionReference(CollectionReferenceInternal* internal);
+
+ private:
+  friend class DocumentReference;
+  friend class DocumentReferenceInternal;
+  friend class FirestoreInternal;
+
+  // TODO(zxu123): investigate possibility to use std::unique_ptr or
+  // firebase::UniquePtr.
+  CollectionReferenceInternal* internal_ = nullptr;
+};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_COLLECTION_REFERENCE_H_
diff --git a/Firestore/core/include/firebase/firestore/document_change.h b/Firestore/core/include/firebase/firestore/document_change.h
new file mode 100644
index 0000000..4812290
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/document_change.h
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_DOCUMENT_CHANGE_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_DOCUMENT_CHANGE_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * A DocumentChange represents a change to the documents matching a query. It
+ * contains the document affected and the type of change that occurred (added,
+ * modified, or removed).
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class DocumentChange {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_DOCUMENT_CHANGE_H_
diff --git a/Firestore/core/include/firebase/firestore/document_reference.h b/Firestore/core/include/firebase/firestore/document_reference.h
index d295188..9385ed3 100644
--- a/Firestore/core/include/firebase/firestore/document_reference.h
+++ b/Firestore/core/include/firebase/firestore/document_reference.h
@@ -29,6 +29,17 @@
 #include <functional>
 #endif
 
+#include "firebase/app.h"
+#include "firebase/firestore/collection_reference.h"
+#include "firebase/firestore/document_snapshot.h"
+#include "firebase/firestore/event_listener.h"
+#include "firebase/firestore/field_value.h"
+#include "firebase/firestore/firestore.h"
+#include "firebase/firestore/firestore_errors.h"
+#include "firebase/firestore/listener_registration.h"
+#include "firebase/firestore/set_options.h"
+#include "firebase/future.h"
+
 // TODO(rsgowman): Note that RTDB uses:
 //   #if defined(FIREBASE_USE_MOVE_OPERATORS) || defined(DOXYGEN
 // to protect move operators from older compilers. But all our supported
@@ -36,34 +47,12 @@
 // here so we don't forget to mention this during the API review, and should be
 // removed once this note has migrated to the API review doc.
 
-// TODO(rsgowman): replace these forward decls with appropriate includes (once
-// they exist)
-namespace firebase {
-class App;
-template <typename T>
-class Future;
-}  // namespace firebase
-
 namespace firebase {
 namespace firestore {
 
-// TODO(rsgowman): replace these forward decls with appropriate includes (once
-// they exist)
-class FieldValue;
-class DocumentSnapshot;
+class DocumentReferenceInternal;
 class Firestore;
-class Error;
-template <typename T>
-class EventListener;
-class ListenerRegistration;
-class CollectionReference;
-class DocumentListenOptions;
-// TODO(rsgowman): not quite a forward decl, but required to make the default
-// parameter to Set() "compile".
-class SetOptions {
- public:
-  SetOptions();
-};
+class FirestoreInternal;
 
 // TODO(rsgowman): move this into the FieldValue header
 #ifdef STLPORT
@@ -80,12 +69,19 @@ using MapFieldValue = std::unordered_map<std::string, FieldValue>;
  *
  * Create a DocumentReference via Firebase::Document(const string& path).
  *
+ * NOT thread-safe: an instance should not be used from multiple threads
+ *
  * Subclassing Note: Firestore classes are not meant to be subclassed except for
  * use in test mocks. Subclassing is not supported in production code and new
  * SDK releases may break code that does so.
  */
 class DocumentReference {
  public:
+  enum class MetadataChanges {
+    kExclude,
+    kInclude,
+  };
+
   /**
    * @brief Default constructor. This creates an invalid DocumentReference.
    * Attempting to perform any operations on this reference will fail (and cause
@@ -269,28 +265,15 @@ class DocumentReference {
    * this DocumentReference. (Ownership is not transferred; you are responsible
    * for making sure that listener is valid as long as this DocumentReference is
    * valid and the listener is registered.)
+   * @param[in] metadata_changes Indicates whether metadata-only changes (i.e.
+   * only DocumentSnapshot.getMetadata() changed) should trigger snapshot
+   * events.
    *
    * @return A registration object that can be used to remove the listener.
    */
   virtual ListenerRegistration AddSnapshotListener(
-      EventListener<DocumentSnapshot>* listener);
-
-  /**
-   * @brief Starts listening to the document referenced by this
-   * DocumentReference.
-   *
-   * @param[in] options The options to use for this listen.
-   * @param[in] listener The event listener that will be called with the
-   * snapshots, which must remain in memory until you remove the listener from
-   * this DocumentReference. (Ownership is not transferred; you are responsible
-   * for making sure that listener is valid as long as this DocumentReference is
-   * valid and the listener is registered.)
-   *
-   * @return A registration object that can be used to remove the listener.
-   */
-  virtual ListenerRegistration AddSnapshotListener(
-      const DocumentListenOptions& options,
-      EventListener<DocumentSnapshot>* listener);
+      EventListener<DocumentSnapshot>* listener,
+      MetadataChanges metadata_changes = MetadataChanges::kExclude);
 
 #if defined(FIREBASE_USE_STD_FUNCTION) || defined(DOXYGEN)
   /**
@@ -299,6 +282,9 @@ class DocumentReference {
    *
    * @param[in] callback function or lambda to call. When this function is
    * called, exactly one of the parameters will be non-null.
+   * @param[in] metadata_changes Indicates whether metadata-only changes (i.e.
+   * only DocumentSnapshot.getMetadata() changed) should trigger snapshot
+   * events.
    *
    * @return A registration object that can be used to remove the listener.
    *
@@ -306,28 +292,21 @@ class DocumentReference {
    * std::function is not supported on STLPort.
    */
   virtual ListenerRegistration AddSnapshotListener(
-      std::function<void(const DocumentSnapshot*, const Error*)> callback);
-
-  /**
-   * @brief Starts listening to the document referenced by this
-   * DocumentReference.
-   *
-   * @param[in] options The options to use for this listen.
-   * @param[in] callback function or lambda to call. When this function is
-   * called, exactly one of the parameters will be non-null.
-   *
-   * @return A registration object that can be used to remove the listener.
-   *
-   * @note This method is not available when using STLPort on Android, as
-   * std::function is not supported on STLPort.
-   */
-  virtual ListenerRegistration AddSnapshotListener(
-      const DocumentListenOptions& options,
-      std::function<void(const DocumentSnapshot*, const Error*)> callback);
+      std::function<void(const DocumentSnapshot*, const Error*)> callback,
+      MetadataChanges metadata_changes = MetadataChanges::kExclude);
 #endif  // defined(FIREBASE_USE_STD_FUNCTION) || defined(DOXYGEN)
+
+ protected:
+  explicit DocumentReference(DocumentReferenceInternal* internal);
+
+ private:
+  friend class FirestoreInternal;
+
+  // TODO(zxu123): investigate possibility to use std::unique_ptr or
+  // firebase::UniquePtr.
+  DocumentReferenceInternal* internal_ = nullptr;
 };
 
-// TODO(rsgowman): probably define and inline here.
 bool operator==(const DocumentReference& lhs, const DocumentReference& rhs);
 
 inline bool operator!=(const DocumentReference& lhs,
diff --git a/Firestore/core/include/firebase/firestore/document_snapshot.h b/Firestore/core/include/firebase/firestore/document_snapshot.h
new file mode 100644
index 0000000..3be72b5
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/document_snapshot.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_DOCUMENT_SNAPSHOT_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_DOCUMENT_SNAPSHOT_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * A DocumentSnapshot contains data read from a document in your Firestore
+ * database. The data can be extracted with the data() method or by using
+ * FooValue() to access a specific field, where Foo is the type of that field.
+ *
+ * For a DocumentSnapshot that points to a non-existing document, any data
+ * access will cause a failed assertion. You can use the exists() method to
+ * explicitly verify a documents existence.
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class DocumentSnapshot {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_DOCUMENT_SNAPSHOT_H_
diff --git a/Firestore/core/include/firebase/firestore/event_listener.h b/Firestore/core/include/firebase/firestore/event_listener.h
index 6c94428..cbe8a28 100644
--- a/Firestore/core/include/firebase/firestore/event_listener.h
+++ b/Firestore/core/include/firebase/firestore/event_listener.h
@@ -22,19 +22,19 @@
 #ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_EVENT_LISTENER_H_
 #define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_EVENT_LISTENER_H_
 
+#include "firebase/firestore/firestore_errors.h"
+
 namespace firebase {
 namespace firestore {
 
-// TODO(rsgowman): replace these forward decl's with appropriate includes (once
-// they exist)
-class Error;
-
 /**
  * @brief An interface for event listeners.
  */
 template <typename T>
 class EventListener {
  public:
+  virtual ~EventListener() {
+  }
   /**
    * @brief OnEvent will be called with the new value or the error if an error
    * occurred.
@@ -44,7 +44,7 @@ class EventListener {
    * @param value The value of the event. null if there was an error.
    * @param error The error if there was error. null otherwise.
    */
-  void OnEvent(const T* value, const Error* error);
+  virtual void OnEvent(const T* value, const Error* error) = 0;
 };
 
 }  // namespace firestore
diff --git a/Firestore/core/include/firebase/firestore/field_path.h b/Firestore/core/include/firebase/firestore/field_path.h
new file mode 100644
index 0000000..29e1dea
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/field_path.h
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIELD_PATH_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIELD_PATH_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * A FieldPath refers to a field in a document. The path may consist of a single
+ * field name (referring to a top level field in the document), or a list of
+ * field names (referring to a nested field in the document).
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class FieldPath {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIELD_PATH_H_
diff --git a/Firestore/core/include/firebase/firestore/field_value.h b/Firestore/core/include/firebase/firestore/field_value.h
new file mode 100644
index 0000000..d919de4
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/field_value.h
@@ -0,0 +1,33 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIELD_VALUE_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIELD_VALUE_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * Sentinel values that can be used when writing document fields with setData()
+ * or updateData().
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class FieldValue {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIELD_VALUE_H_
diff --git a/Firestore/core/include/firebase/firestore/firestore.h b/Firestore/core/include/firebase/firestore/firestore.h
index 793fdd0..6591a72 100644
--- a/Firestore/core/include/firebase/firestore/firestore.h
+++ b/Firestore/core/include/firebase/firestore/firestore.h
@@ -22,23 +22,19 @@
 #ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIRESTORE_H_
 #define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_FIRESTORE_H_
 
+#include <memory>
 #include <string>
 
-// TODO(rsgowman): replace these forward decl's with appropriate includes (once
-// they exist)
-namespace firebase {
-class App;
-class InitResult;
-}  // namespace firebase
+#include "firebase/app.h"
+#include "firebase/firestore/collection_reference.h"
+#include "firebase/firestore/document_reference.h"
+#include "firebase/firestore/settings.h"
 
 namespace firebase {
 namespace firestore {
 
-// TODO(rsgowman): replace these forward decl's with appropriate includes (once
-// they exist)
 class DocumentReference;
-class CollectionReference;
-class Settings;
+class FirestoreInternal;
 
 /**
  * @brief Entry point for the Firebase Firestore C++ SDK.
@@ -152,6 +148,16 @@ class Firestore {
 
   /** Globally enables / disables Firestore logging for the SDK. */
   static void set_logging_enabled(bool logging_enabled);
+
+  Firestore(const Firestore& src) = delete;
+  Firestore& operator=(const Firestore& src) = delete;
+
+ private:
+  explicit Firestore(::firebase::App* app);
+
+  // TODO(zxu123): investigate possibility to use std::unique_ptr or
+  // firebase::UniquePtr.
+  FirestoreInternal* internal_ = nullptr;
 };
 
 }  // namespace firestore
diff --git a/Firestore/core/include/firebase/firestore/firestore_errors.h b/Firestore/core/include/firebase/firestore/firestore_errors.h
index 7a0ff7c..92c0c92 100644
--- a/Firestore/core/include/firebase/firestore/firestore_errors.h
+++ b/Firestore/core/include/firebase/firestore/firestore_errors.h
@@ -109,6 +109,10 @@ enum FirestoreErrorCode {
   Unauthenticated = 16
 };
 
+// TODO(zxu123): decide whether we actually want an Error class or just use
+// enum.
+using Error = FirestoreErrorCode;
+
 }  // namespace firestore
 }  // namespace firebase
 
diff --git a/Firestore/core/include/firebase/firestore/listener_registration.h b/Firestore/core/include/firebase/firestore/listener_registration.h
new file mode 100644
index 0000000..a37c2aa
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/listener_registration.h
@@ -0,0 +1,92 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_LISTENER_REGISTRATION_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_LISTENER_REGISTRATION_H_
+
+namespace firebase {
+namespace firestore {
+
+class FirestoreInternal;
+class ListenerRegistrationInternal;
+
+/** Represents a listener that can be removed by calling remove. */
+class ListenerRegistration {
+ public:
+  /**
+   * @brief Default constructor. This creates a no-op instance.
+   */
+  ListenerRegistration();
+
+  /**
+   * @brief Copy constructor. It's totally okay to copy ListenerRegistration
+   * instances.
+   *
+   * @param[in] registration ListenerRegistration to copy from.
+   */
+  ListenerRegistration(const ListenerRegistration& registration);
+
+  /**
+   * @brief Move constructor. Moving is an efficient operation for
+   * ListenerRegistration instances.
+   *
+   * @param[in] registration ListenerRegistration to move data from.
+   */
+  ListenerRegistration(ListenerRegistration&& registration);
+
+  ~ListenerRegistration();
+
+  /**
+   * @brief Copy assignment operator. It's totally okay to copy
+   * ListenerRegistration instances.
+   *
+   * @param[in] registration ListenerRegistration to copy from.
+   *
+   * @returns Reference to the destination ListenerRegistration.
+   */
+  ListenerRegistration& operator=(const ListenerRegistration& registration);
+
+  /**
+   * @brief Move assignment operator. Moving is an efficient operation for
+   * ListenerRegistration instances.
+   *
+   * @param[in] registration ListenerRegistration to move data from.
+   *
+   * @returns Reference to the destination ListenerRegistration.
+   */
+  ListenerRegistration& operator=(ListenerRegistration&& registration);
+
+  /**
+   * Removes the listener being tracked by this ListenerRegistration. After the
+   * initial call, subsequent calls have no effect.
+   */
+  void Remove();
+
+ private:
+  friend class DocumentReferenceInternal;
+  friend class ListenerRegistrationInternal;
+  friend class FirestoreInternal;
+
+  explicit ListenerRegistration(ListenerRegistrationInternal* internal);
+
+  FirestoreInternal* firestore_ = nullptr;
+  ListenerRegistrationInternal* internal_ = nullptr;
+};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_LISTENER_REGISTRATION_H_
diff --git a/Firestore/core/include/firebase/firestore/query.h b/Firestore/core/include/firebase/firestore/query.h
new file mode 100644
index 0000000..da6dfdd
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/query.h
@@ -0,0 +1,33 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_QUERY_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_QUERY_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * A Query which you can read or listen to. You can also construct refined
+ * Query objects by adding filters and ordering.
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class Query {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_QUERY_H_
diff --git a/Firestore/core/include/firebase/firestore/query_snapshot.h b/Firestore/core/include/firebase/firestore/query_snapshot.h
new file mode 100644
index 0000000..ffa2bd6
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/query_snapshot.h
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_QUERY_SNAPSHOT_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_QUERY_SNAPSHOT_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * A QuerySnapshot contains zero or more DocumentSnapshot objects. It can be
+ * iterated using a range-based for loop and its size can be inspected with
+ * empty() and count().
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class QuerySnapshot {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_QUERY_SNAPSHOT_H_
diff --git a/Firestore/core/include/firebase/firestore/set_options.h b/Firestore/core/include/firebase/firestore/set_options.h
new file mode 100644
index 0000000..802f3b5
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/set_options.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SET_OPTIONS_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SET_OPTIONS_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * An options object that configures the behavior of Set() calls. By providing
+ * the SetOptions objects returned by Merge(), the Set() methods in
+ * DocumentReference, WriteBatch and Transaction can be configured to perform
+ * granular merges instead of overwriting the target documents in their
+ * entirety.
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class SetOptions {
+ public:
+  SetOptions();
+};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SET_OPTIONS_H_
diff --git a/Firestore/core/include/firebase/firestore/settings.h b/Firestore/core/include/firebase/firestore/settings.h
new file mode 100644
index 0000000..9356b26
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/settings.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SETTINGS_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SETTINGS_H_
+
+namespace firebase {
+namespace firestore {
+
+class SettingsInternal;
+
+/** Settings used to configure a Firestore instance. */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class Settings {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SETTINGS_H_
diff --git a/Firestore/core/include/firebase/firestore/snapshot_metadata.h b/Firestore/core/include/firebase/firestore/snapshot_metadata.h
new file mode 100644
index 0000000..9bcc54c
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/snapshot_metadata.h
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SNAPSHOT_METADATA_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SNAPSHOT_METADATA_H_
+
+namespace firebase {
+namespace firestore {
+
+/** Metadata about a snapshot, describing the state of the snapshot. */
+class SnapshotMetadata {
+ public:
+  SnapshotMetadata(bool has_pending_writes, bool is_from_cache)
+      : has_pending_writes_(has_pending_writes), is_from_cache_(is_from_cache) {
+  }
+
+  bool has_pending_writes() const {
+    return has_pending_writes_;
+  }
+
+  bool is_from_cache() const {
+    return is_from_cache_;
+  }
+
+ private:
+  const bool has_pending_writes_;
+  const bool is_from_cache_;
+};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_SNAPSHOT_METADATA_H_
diff --git a/Firestore/core/include/firebase/firestore/transaction.h b/Firestore/core/include/firebase/firestore/transaction.h
new file mode 100644
index 0000000..be043b8
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/transaction.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_TRANSACTION_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_TRANSACTION_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * Transaction provides methods to read and write data within a transaction.
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class Transaction {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_TRANSACTION_H_
diff --git a/Firestore/core/include/firebase/firestore/write_batch.h b/Firestore/core/include/firebase/firestore/write_batch.h
new file mode 100644
index 0000000..bd2c12f
--- /dev/null
+++ b/Firestore/core/include/firebase/firestore/write_batch.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_WRITE_BATCH_H_
+#define FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_WRITE_BATCH_H_
+
+namespace firebase {
+namespace firestore {
+
+/**
+ * A write batch is used to perform multiple writes as a single atomic unit.
+ *
+ * A WriteBatch object provides methods for adding writes to the write batch.
+ * None of the writes will be committed (or visible locally) until commit() is
+ * called.
+ *
+ * Unlike transactions, write batches are persisted offline and therefore are
+ * preferable when you don't need to condition your writes on read data.
+ */
+// TODO(zxu123): add more methods to complete the class and make it useful.
+class WriteBatch {};
+
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_INCLUDE_FIREBASE_FIRESTORE_WRITE_BATCH_H_